106 results on '"Hanqiao Feng"'
Search Results
2. Development of a substrate-based cyclic phosphopeptide inhibitor of protein phosphatase 2C(delta), Wip1
- Author
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Yamaguchi, Hiroshi, Durell, Stewart R., Hanqiao Feng, Yawen Bai, Anderson, Carl W., and Appella, Ettore
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Phosphatases -- Chemical properties ,Cellular signal transduction -- Research ,Oncogenes -- Research ,Biological sciences ,Chemistry - Abstract
Phosphopeptide inhibitors for WipI were designed on the basis of its optimal substrate sequence. It was found that phosphoserine-containing diphosphorylated peptides with the sequence pSXpY inhibited Wip1 phosphatase activity, whereas phosphothreonine-containing peptides with the sequence pTXpY were physiological substrates.
- Published
- 2006
3. Design and folding of a multidomain protein
- Author
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Zheng Zhou, Hanqiao Feng, Hongyi Zhou, and Bai, Yawen
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Cytochromes -- Chemical properties ,Proteins -- Chemical properties ,Protein folding -- Research ,Biological sciences ,Chemistry - Abstract
Two well-studied small alpha-helical proteins, the B-domain of protein A and Rd-apocytochrome b562 were coupled by fusing the C-terminal helix of the B-domain of protein A with the N-terminal helix of Rd-apocyt b562 without changing their hydrophobic core residues. The results suggest that the two domains have weakenergetic coupling.
- Published
- 2005
4. A Small Number of Residues Can Determine if Linker Histones Are Bound On or Off Dyad in the Chromatosome
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Charles D. Schwieters, Rodolfo Ghirlando, Shipeng Li, Yawen Bai, Bing-Rui Zhou, and Hanqiao Feng
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0301 basic medicine ,MTSL ,Biology ,Article ,Histones ,03 medical and health sciences ,chemistry.chemical_compound ,Structural Biology ,Animals ,Humans ,Nucleosome ,Molecular Biology ,Nucleosome binding ,030102 biochemistry & molecular biology ,Linker DNA ,Molecular biology ,Nucleosomes ,Chromatin ,030104 developmental biology ,Histone ,Amino Acid Substitution ,chemistry ,Chromatosome ,biology.protein ,Biophysics ,Mutant Proteins ,Chickens ,Linker ,Protein Binding - Abstract
Linker histones bind to the nucleosome and regulate the structure and function of chromatin. We have previously shown that the globular domains of chicken H5 and Drosophila H1 linker histones bind to the nucleosome with on- or off-dyad modes, respectively. To explore the determinant for the distinct binding modes, we investigated the binding of a mutant globular domain of H5 to the nucleosome. This mutant, termed GH5_pMut, includes substitutions of five globular domain residues of H5 with the corresponding residues in the globular domain of Drosophila H1. The residues at these five positions play important roles in nucleosome binding by either H5 or Drosophila H1. NMR and spin-labeling experiments showed that GH5_pMut bound to the nucleosome off the dyad. We further found that the nucleosome array condensed by either the GH5_pMut or the globular domain of Drosophila H1 displayed a similar sedimentation coefficient, whereas the same nucleosome array condensed by the wild-type globular domain of H5 showed a much larger sedimentation coefficient. Moreover, NMR and spin-labeling results from the study of the nucleosome in complex with the full-length human linker histone H1.0, whose globular domain shares high sequence conservation with the corresponding globular domain of H5, are consistent with an on-dyad binding mode. Taken together, our results suggest that a small number of residues in the globular domain of a linker histone can control its binding location on the nucleosome and higher-order chromatin structure.
- Published
- 2016
5. Binding Affinity and Function of the Extremely Disordered Protein Complex Containing Human Linker Histone H1.0 and Its Chaperone ProTα
- Author
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Bing-Rui Zhou, Yawen Bai, and Hanqiao Feng
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0301 basic medicine ,Plasma protein binding ,Calorimetry ,Biochemistry ,Article ,Histones ,03 medical and health sciences ,Histone H1 ,Fluorescence Resonance Energy Transfer ,Nucleosome ,Humans ,Amino Acid Sequence ,Protein Precursors ,030102 biochemistry & molecular biology ,biology ,Chemistry ,Isothermal titration calorimetry ,Chromatin ,Nucleosomes ,Dissociation constant ,Intrinsically Disordered Proteins ,Thymosin ,Kinetics ,030104 developmental biology ,Chaperone (protein) ,Multiprotein Complexes ,biology.protein ,Biophysics ,Linker ,Molecular Chaperones ,Protein Binding - Abstract
It was recently reported that human linker histone H1.0 and its chaperone prothymosin-α (ProTα) form an extremely disordered 1:1 complex with an ultrahigh affinity (equilibrium dissociation constant K(D) of ∼2 × 10(−12) M) measured using a single-molecule Förster resonance energy transfer method. It was hypothesized that the ultrahigh affinity and extreme disorder may be required for the chaperone function of ProTα, in which it displaces the linker histone from condensed chromatin. Here, we measure the binding affinity for the ProTα–H1.0 complex using isothermal titration calorimetry and report a K(D) value of (4.6 ± 0.5) × 10(−7) M. In addition, we show that ProTα facilitates the formation of the H1.0–nucleosome complex in vitro. The results of our study contrast with those of the previous report and provide new insights into the chaperone function of ProTα. Possible causes for the observed discrepancy in binding affinity are discussed.
- Published
- 2018
6. Distinct Structures and Dynamics of Chromatosomes with Different Human Linker Histone Isoforms
- Author
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Tara Fox, Bing-Rui Zhou, Natalia de Val, Seyit Kale, Rodolfo Ghirlando, Yawen Bai, Htet Khant, Hanqiao Feng, and Anna R. Panchenko
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Gene isoform ,Biology ,Article ,Histones ,03 medical and health sciences ,chemistry.chemical_compound ,0302 clinical medicine ,Histone H2A ,Humans ,Protein Isoforms ,Nucleosome ,Molecular Biology ,030304 developmental biology ,0303 health sciences ,Cryoelectron Microscopy ,DNA ,Cell Biology ,Nucleosomes ,Chromatin ,Histone ,chemistry ,Chromatosome ,Biophysics ,biology.protein ,Linker ,030217 neurology & neurosurgery - Abstract
Summary The repeating structural unit of metazoan chromatin is the chromatosome, a nucleosome bound to a linker histone, H1. There are 11 human H1 isoforms with diverse cellular functions, but how they interact with the nucleosome remains elusive. Here, we determined the cryoelectron microscopy (cryo-EM) structures of chromatosomes containing 197 bp DNA and three different human H1 isoforms, respectively. The globular domains of all three H1 isoforms bound to the nucleosome dyad. However, the flanking/linker DNAs displayed substantial distinct dynamic conformations. Nuclear magnetic resonance (NMR) and H1 tail-swapping cryo-EM experiments revealed that the C-terminal tails of the H1 isoforms mainly controlled the flanking DNA orientations. We also observed partial ordering of the core histone H2A C-terminal and H3 N-terminal tails in the chromatosomes. Our results provide insights into the structures and dynamics of the chromatosomes and have implications for the structure and function of chromatin.
- Published
- 2021
7. Structural basis of H2A.Z recognition by SRCAP chromatin-remodeling subunit YL1
- Author
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Jizhong Lou, Zhuqiang Zhang, Zheng Zhou, Guohong Li, Debbie Wei, Hanqiao Feng, Carl Wu, Anand Ranjan, Jicheng Zhao, Xiaoping Liang, Feng Wang, Yingzi Huang, Xuehui Liu, Lu Pan, Qiang Zhong, Li Huang, and Shan Shan
- Subjects
Models, Molecular ,0301 basic medicine ,animal structures ,Protein subunit ,Molecular Sequence Data ,Mineralogy ,Crystallography, X-Ray ,Chromatin remodeling ,Histones ,03 medical and health sciences ,0302 clinical medicine ,Protein structure ,Structural Biology ,Animals ,Drosophila Proteins ,Nucleosome ,Histone Chaperones ,Amino Acid Sequence ,Enhancer ,Molecular Biology ,Binding Sites ,biology ,Chromatin Assembly and Disassembly ,Protein Structure, Tertiary ,Chromatin ,Cell biology ,Protein Subunits ,Drosophila melanogaster ,030104 developmental biology ,Histone ,030220 oncology & carcinogenesis ,Chaperone (protein) ,embryonic structures ,biology.protein ,Protein Multimerization ,Sequence Alignment ,Protein Binding - Abstract
Histone variant H2A.Z, a universal mark of dynamic nucleosomes flanking gene promoters and enhancers, is incorporated into chromatin by SRCAP (SWR1), an ATP-dependent, multicomponent chromatin-remodeling complex. The YL1 (Swc2) subunit of SRCAP (SWR1) plays an essential role in H2A.Z recognition, but how it achieves this has been unclear. Here, we report the crystal structure of the H2A.Z-binding domain of Drosophila melanogaster YL1 (dYL1-Z) in complex with an H2A.Z-H2B dimer at 1.9-Å resolution. The dYL1-Z domain adopts a new whip-like structure that wraps over H2A.Z-H2B, and preferential recognition is largely conferred by three residues in loop 2, the hyperacidic patch and the extended αC helix of H2A.Z. Importantly, this domain is essential for deposition of budding yeast H2A.Z in vivo and SRCAP (SWR1)-catalyzed histone H2A.Z replacement in vitro. Our studies distinguish YL1-Z from known H2A.Z chaperones and suggest a hierarchical mechanism based on increasing binding affinity facilitating H2A.Z transfer from SRCAP (SWR1) to the nucleosome.
- Published
- 2016
8. cryo-EM Structures of Chromatosomes Containing Human Linker Histone Variants
- Author
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Natalia de Val, Bing-Rui Zhou, Hanqiao Feng, and Yawen Bai
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Cryo-electron microscopy ,Chemistry ,Biophysics ,Linker ,Histone variants - Published
- 2020
9. Synthesis of poly(glycolide-CO-2-hydro-2-oxo-1,3,2-dioxaphosphorinane)
- Author
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Changlie, Fan, Ying, Mei, Zhenhua, Liu, Renxi, Zhuo, and Hanqiao, Feng
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- 1997
- Full Text
- View/download PDF
10. Revisit of reconstituted 30-nm nucleosome arrays reveals an ensemble of dynamic structures
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Ping Zhang, Victor B. Zhurkin, Jiansheng Jiang, K.N. Sathish Yadav, Hanqiao Feng, Bing-Rui Zhou, Davood Norouzi, Yawen Bai, Rodolfo Ghirlando, and Rui Wang
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0301 basic medicine ,Models, Molecular ,Materials science ,Molecular Conformation ,Crystallography, X-Ray ,Article ,03 medical and health sciences ,Structure-Activity Relationship ,0302 clinical medicine ,Structural Biology ,Histone H5 ,Nucleosome ,Disulfides ,A fibers ,Molecular Biology ,Chromatin Fiber ,Conclusive evidence ,Chromatin ,Structure and function ,Nucleosomes ,Solutions ,030104 developmental biology ,Biophysics ,Linker ,030217 neurology & neurosurgery - Abstract
It has long been suggested that chromatin may form a fiber with a diameter of ~30 nm that suppresses transcription. Despite nearly four decades of study, the structural nature of the 30-nm chromatin fiber and conclusive evidence of its existence in vivo remain elusive. The key support for the existence of specific 30 nm chromatin fiber structures is based on the determination of the structures of reconstituted nucleosome arrays using X-ray crystallography and single particle cryo-electron microscopy coupled with glutaraldehyde chemical cross-linking. Here we report the characterization of these nucleosome arrays in solution using analytical ultracentrifugation, nuclear magnetic resonance, and small angle X-ray scattering. We found that the physical properties of these nucleosome arrays in solution are not consistent with formation of just a few discrete structures of nucleosome arrays. In addition, we obtained a crystal of the nucleosome in complex with the globular domain of linker histone H5 that shows a new form of nucleosome packing and suggests a plausible alternative compact conformation for nucleosome arrays. Taken together, our results challenge the key evidence for the existence of a limited number of structures of reconstituted nucleosome arrays in solution by revealing that the reconstituted nucleosome arrays are actually best described as an ensemble of various conformations with a zigzagged arrangement of nucleosomes. Our finding has implications for understanding the structure and function of chromatin in vivo.
- Published
- 2018
11. Structural mechanisms of centromeric nucleosome recognition by the kinetochore protein CENP-N
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Sagar Chittori, Sriram Subramaniam, Hayden Saunders, Yawen Bai, Alexander E. Kelly, Jingjun Hong, Hanqiao Feng, and Rodolfo Ghirlando
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0301 basic medicine ,Chromosomal Proteins, Non-Histone ,Xenopus ,Kinetochore assembly ,Centromere ,DNA Mutational Analysis ,macromolecular substances ,Article ,Protein Structure, Secondary ,Chromosome segregation ,03 medical and health sciences ,Histone H3 ,Protein structure ,Nucleosome ,Animals ,Humans ,Amino Acid Sequence ,Kinetochores ,Multidisciplinary ,Chemistry ,Kinetochore ,Cryoelectron Microscopy ,Cell biology ,Chromatin ,Nucleosomes ,030104 developmental biology ,Centromere Protein A - Abstract
Recognizing centromere by kinetochore The kinetochore proteins CENP-N and CENP-C recognize the histone H3 variant CENP-A in the centromeric nucleosome. This ensures proper kinetochore assembly and accurate segregation of chromosomes. Chittori et al. describe the cryo-electron microscopy structure of the human CENP-A nucleosome-CENP-N complex. The interaction of CENP-N with CENP-A and the nucleosomal DNA together ensure specific and stable centromeric nucleosome recognition. Mutational analyses using both human and Xenopus CENP-A and CENP-N proteins suggest that the proteins have coevolved to preserve the interacting surfaces. Science , this issue p. 339
- Published
- 2017
12. Structural Mechanisms of Nucleosome Recognition by Linker Histones
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Jiansheng Jiang, T. Sam Xiao, Hanqiao Feng, Bing-Rui Zhou, Yawen Bai, and Rodolfo Ghirlando
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Models, Molecular ,Histone-modifying enzymes ,Molecular Sequence Data ,Solenoid (DNA) ,Crystallography, X-Ray ,Article ,Histones ,Histone code ,Nucleosome ,Animals ,Drosophila Proteins ,Amino Acid Sequence ,Molecular Biology ,Genetics ,Binding Sites ,biology ,Cell Biology ,Linker DNA ,Chromatin ,Nucleosomes ,Histone ,Drosophila melanogaster ,Chromatosome ,Biophysics ,biology.protein ,Protein Binding - Abstract
Linker histones bind to the nucleosome and regulate the structure of chromatin and gene expression. Despite more than three decades of effort, the structural basis of nucleosome recognition by linker histones remains elusive. Here, we report the crystal structure of the globular domain of chicken linker histone H5 in complex with the nucleosome at 3.5 A resolution, which is validated using nuclear magnetic resonance spectroscopy. The globular domain sits on the dyad of the nucleosome and interacts with both DNA linkers. Our structure integrates results from mutation analyses and previous cross-linking and fluorescence recovery after photobleach experiments, and it helps resolve the long debate on structural mechanisms of nucleosome recognition by linker histones. The on-dyad binding mode of the H5 globular domain is different from the recently reported off-dyad binding mode of Drosophila linker histone H1. We demonstrate that linker histones with different binding modes could fold chromatin to form distinct higher-order structures.
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- 2015
- Full Text
- View/download PDF
13. The Catalytic Subunit of the SWR1 Remodeler Is a Histone Chaperone for the H2A.Z-H2B Dimer
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Hanqiao Feng, T. Sam Xiao, Carl Wu, Jiansheng Jiang, Jingjun Hong, Rodolfo Ghirlando, Yawen Bai, Jianhong Chen, Anand Ranjan, and Feng Wang
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Models, Molecular ,Enzyme complex ,Saccharomyces cerevisiae Proteins ,animal structures ,Molecular Sequence Data ,Saccharomyces cerevisiae ,Crystallography, X-Ray ,Article ,Histones ,X-Ray Diffraction ,Histone H1 ,Histone H2A ,Histone methylation ,Histone code ,Nucleosome ,Amino Acid Sequence ,Cloning, Molecular ,Molecular Biology ,Adenosine Triphosphatases ,biology ,Cell Biology ,Chromatin Assembly and Disassembly ,Protein Structure, Tertiary ,Cell biology ,Protein Subunits ,Histone ,Biochemistry ,Chaperone (protein) ,embryonic structures ,biology.protein ,Dimerization - Abstract
Histone variant H2A.Z-containing nucleosomes exist at most eukaryotic promoters and play important roles in gene transcription and genome stability. The multisubunit nucleosome-remodeling enzyme complex SWR1, conserved from yeast to mammals, catalyzes the ATP-dependent replacement of histone H2A in canonical nucleosomes with H2A.Z. How SWR1 catalyzes the replacement reaction is largely unknown. Here, we determined the crystal structure of the N-terminal region (599-627) of the catalytic subunit Swr1, termed Swr1-Z domain, in complex with the H2A.Z-H2B dimer at 1.78 Å resolution. The Swr1-Z domain forms a 310 helix and an irregular chain. A conserved LxxLF motif in the Swr1-Z 310 helix specifically recognizes the αC helix of H2A.Z. Our results show that the Swr1-Z domain can deliver the H2A.Z-H2B dimer to the DNA-(H3-H4)2 tetrasome to form the nucleosome by a histone chaperone mechanism.
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- 2014
14. Structural insights into the histone H1-nucleosome complex
- Author
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Yuedong Yang, Yaoqi Zhou, Hidenori Kato, Hanqiao Feng, Yawen Bai, Liang Dai, and Bing-Rui Zhou
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Models, Molecular ,Magnetic Resonance Spectroscopy ,Macromolecular Substances ,Molecular Sequence Data ,Molecular Conformation ,Calorimetry ,Histones ,chemistry.chemical_compound ,Histone H1 ,Nucleosome ,Amino Acid Sequence ,Genetics ,Multidisciplinary ,biology ,Biological Sciences ,Linker DNA ,Nucleosomes ,Chromatin ,Histone ,chemistry ,Chromatosome ,Mutagenesis, Site-Directed ,biology.protein ,Biophysics ,Linker ,DNA ,Protein Binding - Abstract
Linker H1 histones facilitate formation of higher-order chromatin structures and play important roles in various cell functions. Despite several decades of effort, the structural basis of how H1 interacts with the nucleosome remains elusive. Here, we investigated Drosophila H1 in complex with the nucleosome, using solution nuclear magnetic resonance spectroscopy and other biophysical methods. We found that the globular domain of H1 bridges the nucleosome core and one 10-base pair linker DNA asymmetrically, with its α3 helix facing the nucleosomal DNA near the dyad axis. Two short regions in the C-terminal tail of H1 and the C-terminal tail of one of the two H2A histones are also involved in the formation of the H1-nucleosome complex. Our results lead to a residue-specific structural model for the globular domain of the Drosophila H1 in complex with the nucleosome, which is different from all previous experiment-based models and has implications for chromatin dynamics in vivo.
- Published
- 2013
15. Identification of Functionally Conserved Regions in the Structure of the Chaperone/CenH3/H4 Complex
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Yawen Bai, Rodolfo Ghirlando, Zheng Zhou, Hanqiao Feng, and Jingjun Hong
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Models, Molecular ,Magnetic Resonance Spectroscopy ,DNA Mutational Analysis ,Saccharomyces cerevisiae ,Plasma protein binding ,Article ,Histones ,Kluyveromyces ,Histone H3 ,Structural Biology ,Protein Interaction Mapping ,Centromere ,Humans ,Histone Chaperones ,Molecular Biology ,Genetics ,Kluyveromyces lactis ,biology ,food and beverages ,biology.organism_classification ,Cell biology ,Histone ,CDC37 ,Chaperone (protein) ,Mutagenesis, Site-Directed ,biology.protein ,Protein Binding - Abstract
In eukaryotes, a variant of conventional histone H3 termed CenH3 epigenetically marks the centromere. The conserved CenH3 chaperone specifically recognizes CenH3 and is required for CenH3 deposition at the centromere. Recently, the structures of the chaperone/CenH3/H4 complexes have been determined for Homo sapiens (Hs) and the budding yeasts Saccharomyces cerevisiae (Sc) and Kluyveromyces lactis (Kl). Surprisingly, the three structures are very different, leading to different proposed structural bases for chaperone function. The question of which structural region of CenH3 provides the specificity determinant for the chaperone recognition is not fully answered. Here, we investigated these issues using solution NMR and site-directed mutagenesis. We discovered that, in contrast to previous findings, the structures of the Kl and Sc chaperone/CenH3/H4 complexes are actually very similar. This new finding reveals that both budding yeast and human chaperones use a similar structural region to block DNA from binding to the histones. Our mutational analyses further indicate that the N-terminal region of the CenH3 α2 helix is sufficient for specific recognition by the chaperone for both budding yeast and human. Thus, our studies have identified conserved structural bases of how the chaperones recognize CenH3 and perform the chaperone function.
- Published
- 2013
16. The Folding Pathway of T4 Lysozyme: The High-resolution Structure and Folding of a Hidden Intermediate
- Author
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Yawen Bai, Hidenori Kato, and Hanqiao Feng
- Subjects
Protein Folding ,Protein domain ,Phi value analysis ,Protein Structure, Secondary ,Article ,Evolution, Molecular ,Protein structure ,Structural Biology ,Bacteriophage T4 ,Amino Acid Sequence ,Nuclear Magnetic Resonance, Biomolecular ,Molecular Biology ,Chemistry ,Temperature ,Protein engineering ,Hydrogen-Ion Concentration ,Protein Structure, Tertiary ,Folding (chemistry) ,Crystallography ,Thermodynamics ,Muramidase ,Mutant Proteins ,Protein folding ,Downhill folding ,Heteronuclear single quantum coherence spectroscopy ,Hydrogen - Abstract
Folding intermediates have been detected and characterized for many proteins. However, their structures at atomic resolution have only been determined for two small single domain proteins: Rd-apocytochrome b(562) and engrailed homeo domain. T4 lysozyme has two easily distinguishable but energetically coupled domains: the N and C-terminal domains. An early native-state hydrogen exchange experiment identified an intermediate with the C-terminal domain folded and the N-terminal domain unfolded. We have used a native-state hydrogen exchange-directed protein engineering approach to populate this intermediate and demonstrated that it is on the folding pathway and exists after the rate-limiting step. Here, we determined its high-resolution structure and the backbone dynamics by multi-dimensional NMR methods. We also characterized the folding behavior of the intermediate using stopped-flow fluorescence, protein engineering, and native-state hydrogen exchange. Unlike the folding intermediates of the two single-domain proteins, which have many non-native side-chain interactions, the structure of the hidden folding intermediate of T4 lysozyme is largely native-like. It folds like many small single domain proteins. These results have implications for understanding the folding mechanism and evolution of multi-domain proteins.
- Published
- 2007
17. Characterization of the p300 Taz2-p53 TAD2 complex and comparison with the p300 Taz2-p53 TAD1 complex
- Author
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Ettore Appella, Sharlyn J. Mazur, Lisa M. Miller Jenkins, Yawen Bai, Hanqiao Feng, Harichandra D. Tagad, Stewart R. Durell, and Joseph E. Tropea
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Models, Molecular ,Protein Conformation ,Plasma protein binding ,Biology ,Molecular Dynamics Simulation ,Biochemistry ,Article ,Protein–protein interaction ,Transactivation ,Mediator ,Humans ,Protein Interaction Domains and Motifs ,Protein Structure, Quaternary ,Transcription factor ,Nuclear Magnetic Resonance, Biomolecular ,Histone Acetyltransferases ,Histone Acetyltransferase p300 ,Calorimetry, Differential Scanning ,Protein Stability ,Isothermal titration calorimetry ,Hydrogen Bonding ,Hydrogen-Ion Concentration ,Peptide Fragments ,Recombinant Proteins ,Chromatin ,Crystallography ,Kinetics ,Amino Acid Substitution ,Biophysics ,Mutagenesis, Site-Directed ,Mutant Proteins ,Tumor Suppressor Protein p53 ,E1A-Associated p300 Protein - Abstract
The p53 tumor suppressor is a critical mediator of the cellular response to stress. The N-terminal transactivation domain of p53 makes protein interactions that promote its function as a transcription factor. Among those cofactors is the histone acetyltransferase p300, which both stabilizes p53 and promotes local chromatin unwinding. Here, we report the nuclear magnetic resonance solution structure of the Taz2 domain of p300 bound to the second transactivation subdomain of p53. In the complex, p53 forms an α-helix between residues 47 and 55 that interacts with the α1–α2–α3 face of Taz2. Mutational analysis indicated several residues in both p53 and Taz2 that are critical for stabilizing the interaction. Finally, further characterization of the complex by isothermal titration calorimetry revealed that complex formation is pH-dependent and releases a bound chloride ion. This study highlights differences in the structures of complexes formed by the two transactivation subdomains of p53 that may be broadly observed and play critical roles in p53 transcriptional activity.
- Published
- 2015
18. Detection of a hidden folding intermediate in the focal adhesion target domain: Implications for its function and folding
- Author
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Zheng Zhou, Hanqiao Feng, and Yawen Bai
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Models, Molecular ,Protein Denaturation ,Protein Folding ,Phi value analysis ,Plasma protein binding ,Biochemistry ,Domain (software engineering) ,Focal adhesion ,Protein structure ,Structural Biology ,Protein Structure, Quaternary ,Molecular Biology ,Focal Adhesions ,Chemistry ,Circular Dichroism ,Temperature ,Folding (chemistry) ,Kinetics ,Crystallography ,Focal Adhesion Protein-Tyrosine Kinases ,Mutation ,Helix ,Biophysics ,Thermodynamics ,Protein folding ,Hydrogen ,Protein Binding - Abstract
The focal adhesion target (FAT) domain of focal adhesion kinase has a four-helix bundle structure. Based on a hydrogen exchange-constrained computer simulation study and some indirect experimental results, it has been suggested that a partially unfolded state of the FAT domain with the N-terminal helix unfolded plays an important role in its biological function. Here, using a native-state hydrogen exchange method, we directly detected an intermediate with the N-terminal helix unfolded in a mutant (Y925E) of the FAT domain. In addition, kinetic folding studies on the FAT domain suggest that this intermediate exists on the native side of the rate-limiting transition state for folding. These results provide more direct evidence of the existence of the proposed intermediate and help to understand the folding mechanism of small single domain proteins.
- Published
- 2006
19. A protein folding pathway with multiple folding intermediates at atomic resolution
- Author
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Yawen Bai, Hanqiao Feng, and Zheng Zhou
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Models, Molecular ,Protein Folding ,Multidisciplinary ,Nitrogen Isotopes ,Nitrogen ,Chemistry ,Biophysics ,Phi value analysis ,Protein engineering ,Biological Sciences ,Protein Engineering ,Biophysical Phenomena ,Protein Structure, Tertiary ,Folding (chemistry) ,Crystallography ,Cytochromes b5 ,Atomic resolution ,Lattice protein ,Helix ,Protein folding ,Nuclear Magnetic Resonance, Biomolecular ,Topology (chemistry) ,Hydrogen - Abstract
Using native-state hydrogen-exchange-directed protein engineering and multidimensional NMR, we determined the high-resolution structure (rms deviation, 1.1 Å) for an intermediate of the four-helix bundle protein: Rd-apocytochrome b 562 . The intermediate has the N-terminal helix and a part of the C-terminal helix unfolded. In earlier studies, we also solved the structures of two other folding intermediates for the same protein: one with the N-terminal helix alone unfolded and the other with a reorganized hydrophobic core. Together, these structures provide a description of a protein folding pathway with multiple intermediates at atomic resolution. The two general features for the intermediates are ( i ) native-like backbone topology and ( ii ) nonnative side-chain interactions. These results have implications for important issues in protein folding studies, including large-scale conformation search, φ-value analysis, and computer simulations.
- Published
- 2005
20. Repacking of hydrophobic residues in a stable mutant of apocytochrome b562 selected by phage-display and proteolysis
- Author
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Yawen Bai and Hanqiao Feng
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Models, Molecular ,Protein Folding ,Phage display ,Stereochemistry ,Proteolysis ,Mutant ,Protein design ,Protein Engineering ,Biochemistry ,Protein Structure, Secondary ,Protein structure ,Peptide Library ,Structural Biology ,Consensus Sequence ,Lattice protein ,medicine ,Consensus sequence ,Computer Simulation ,Hydrophobic collapse ,Nuclear Magnetic Resonance, Biomolecular ,Molecular Biology ,medicine.diagnostic_test ,Chemistry ,Hydrolysis ,Hydrogen Bonding ,Cytochrome b Group ,Protein Structure, Tertiary ,Crystallography ,Mutagenesis, Site-Directed ,Hydrophobic and Hydrophilic Interactions - Abstract
To test a hydrophobic core-directed protein design approach, we previously have used phage-display and proteolysis to select stably folded proteins from a library of mutants of apocytochrome b562. The consensus sequence of the selected mutants has hydrophilic residues at two of the three positions that are designed to form a hydrophobic core. To understand this unexpected result, we determined the high-resolution structure of one of the selected mutants using multi-dimensional nuclear magnetic resonance (NMR). The structure shows that the two hydrophilic residues in the consensus sequence were on the surface of the structure. Instead, two of their neighboring hydrophobic residues reorganized their side-chain conformations and formed the hydrophobic core. This result suggests that the hydrophobic core-directed protein design by phage-display and proteolysis is a valid method in general but alternative hydrophobic packing needs to be considered in the initial design. The unexpected repacking of the hydrophobic residues also highlights the plastic nature of protein structures. Proteins 2004. © 2004 Wiley-Liss, Inc.
- Published
- 2004
21. The Folding Pathway of Barnase: The Rate-Limiting Transition State and a Hidden Intermediate under Native Conditions
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Ngoc-Diep Vu, Hanqiao Feng, and Yawen Bai
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Protein Denaturation ,Protein Folding ,Protein Conformation ,Glycine ,Bacillus ,Phi value analysis ,Biochemistry ,Protein Structure, Secondary ,Ribonucleases ,Bacterial Proteins ,Side chain ,Nuclear Magnetic Resonance, Biomolecular ,Protein secondary structure ,Guanidine ,Barnase ,Alanine ,biology ,Transition (genetics) ,Chemistry ,Deuterium Exchange Measurement ,Limiting ,State (functional analysis) ,Hydrogen-Ion Concentration ,Folding (chemistry) ,Kinetics ,Crystallography ,Amino Acid Substitution ,Models, Chemical ,Nonlinear Dynamics ,biology.protein ,Protons ,Signal Transduction - Abstract
The nature of the rate-limiting transition state at zero denaturant (TS(1)) and whether there are hidden intermediates are the two major unsolved problems in defining the folding pathway of barnase. In earlier studies, it was shown that TS(1) has small phi values throughout the structure of the protein, suggesting that the transition state has either a defined partially folded secondary structure with all side chains significantly exposed or numerous different partially unfolded structures with similar stability. To distinguish the two possibilities, we studied the effect of Gly mutations on the folding rate of barnase to investigate the secondary structure formation in the transition state. Two mutations in the same region of a beta-strand decreased the folding rate by 20- and 50-fold, respectively, suggesting that the secondary structures in this region are dominantly formed in the rate-limiting transition state. We also performed native-state hydrogen exchange experiments on barnase at pD 5.0 and 25 degrees C and identified a partially unfolded state. The structure of the intermediate was investigated using protein engineering and NMR. The results suggest that the intermediate has an omega loop unfolded. This intermediate is more folded than the rate-limiting transition state previously characterized at high denaturant concentrations (TS(2)). Therefore, it exists after TS(2) in folding. Consistent with this conclusion, the intermediate folds with the same rate and denaturant dependence as the wild-type protein, but unfolds faster with less dependence on the denaturant concentration. These and other results in the literature suggest that barnase folds through partially unfolded intermediates that exist after the rate-limiting step. Such folding behavior is similar to those of cytochrome c and Rd-apocyt b(562). Together, we suggest that other small apparently two-state proteins may also fold through hidden intermediates.
- Published
- 2004
22. Specific Non-Native Hydrophobic Interactions in a Hidden Folding Intermediate: Implications for Protein Folding
- Author
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Rebecca S. Lipsitz, Hanqiao Feng, Jiro Takei, Yawen Bai, and Nico Tjandra
- Subjects
Models, Molecular ,Protein Folding ,Chemistry ,Phi value analysis ,Protein engineering ,Contact order ,Biochemistry ,Folding (chemistry) ,Kinetics ,Crystallography ,Lattice protein ,Biophysics ,Protein folding ,Downhill folding ,Folding funnel ,Nuclear Magnetic Resonance, Biomolecular - Abstract
Structures of intermediates and transition states in protein folding are usually characterized by amide hydrogen exchange and protein engineering methods and interpreted on the basis of the assumption that they have native-like conformations. We were able to stabilize and determine the high-resolution structure of a partially unfolded intermediate that exists after the rate-limiting step of a four-helix bundle protein, Rd-apocyt b(562), by multidimensional NMR methods. The intermediate has partial native-like secondary structure and backbone topology, consistent with our earlier native state hydrogen exchange results. However, non-native hydrophobic interactions exist throughout the structure. These and other results in the literature suggest that non-native hydrophobic interactions may occur generally in partially folded states. This can alter the interpretation of mutational protein engineering results in terms of native-like side chain interactions. In addition, since the intermediate exists after the rate-limiting step and Rd-apocyt b(562) folds very rapidly (k(f) approximately 10(4) s(-1)), these results suggest that non-native hydrophobic interactions, in the absence of topological misfolding, are repaired too rapidly to slow folding and cause the accumulation of folding intermediates. More generally, these results illustrate an approach for determining the high-resolution structure of folding intermediates.
- Published
- 2003
23. Role of polyethylene glycol in formation and structure of regenerated cellulose microporous membrane
- Author
-
Guang Yang, Lina Zhang, and Hanqiao Feng
- Subjects
technology, industry, and agriculture ,Regenerated cellulose ,Filtration and Separation ,Polyethylene glycol ,Microporous material ,Biochemistry ,Miscibility ,chemistry.chemical_compound ,Crystallinity ,Membrane ,chemistry ,Chemical engineering ,PEG ratio ,Polymer chemistry ,General Materials Science ,Physical and Theoretical Chemistry ,Cellulose - Abstract
Porous formation and supermolecular structure of regenerated cellulose (RC) microporous membranes prepared by coagulating mixture solution of cellulose cuoxam and polyethylene glycol (PEG400, PEG2000, PEG6000 and PEG20000) were investigated. SEM showed that the cellulose cuoxam/PEG mixture solution formed a homogeneous blend, and the miscibility between cellulose and PEG decreased with increasing molecular weight (M-w) of PEG. The mixture solutions exhibited homogeneous particles in aqueous 10 wt.% NaOH solution, and a smooth surface of RC membrane was observed after immersing in 5 wt.% H2SO4, suggesting that a new molecular architecture of cellulose is formed during the H2SO4 coagulation process. With an increase in M-w of PEG, crystallinity chi(c) slightly decreased, while (1 (1) over bar 0) plane orientation parameter f(//)(1 (1) over bar 0) of the membranes increased. The C-13 CP/MAS NMR spectra indicated that the PEG molecules as pore former were completely removed from the membranes mixed with PEG400, while only 4 wt.% PEG remained in the membranes mixed with PEG2000, PEG6000 and PEG20000. The results of a spin-lattice relaxation suggested that intramolecular hydrogen bonds of cellulose molecules in the membranes decreased, and inter-molecular hydrogen bonds increased, when M-w of PEG increased. M-w of PEG plays an important role in the morphology, structure and the pore size of the microporous cellulose membranes. (C) 1999 Elsevier Science B.V. All rights reserved.
- Published
- 1999
24. Introduction of a Triazole Amino Acid into a Peptoid Oligomer Induces Turn Formation in Aqueous Solution
- Author
-
Jonathan K. Pokorski, Lisa M. Miller Jenkins, and Yawen Bai, Daniel H. Appella, Stewart R. Durell, and Hanqiao Feng
- Subjects
Models, Molecular ,chemistry.chemical_classification ,Aqueous solution ,Molecular Structure ,Organic Chemistry ,Triazole ,Water ,Stereoisomerism ,Peptoid ,Triazoles ,Biochemistry ,Combinatorial chemistry ,Oligomer ,Protein Structure, Secondary ,Amino acid ,Solutions ,Turn (biochemistry) ,Folding (chemistry) ,Peptoids ,chemistry.chemical_compound ,chemistry ,Glycine ,Physical and Theoretical Chemistry - Abstract
Peptoids are a non-natural class of oligomers that are composed of repeating N-substituted glycine units and are capable of folding into helices that mimic peptide structure and function. In this letter, we report the concise synthesis of a 1,5-substituted triazole amino acid (Tzl) and its subsequent incorporation into a short peptoid. The Tzl amino acid was shown to induce turn formation in aqueous solution, thus expanding the structural repertoire available to peptoid chemists.
- Published
- 2007
25. 5 Structural mechanisms of nucleosome recognition by linker histones
- Author
-
Jiansheng Jiang, T. Sam Xiao, Rui Wang, Bing-Rui Zhou, Hanqiao Feng, Yawen Bai, and Rodolfo Ghirlando
- Subjects
Histone ,biology ,Structural Biology ,Chemistry ,Chromatosome ,Biophysics ,biology.protein ,Nucleosome ,General Medicine ,Molecular Biology ,Linker DNA ,Linker - Published
- 2015
26. Miscibility and specific interactions in poly(β-hydroxybutyrate-co-β-hydroxyvalerate) and poly(p-vinylphenol) blends
- Author
-
Lisong Dong, Zhiliu Feng, Peixiang Xing, and Hanqiao Feng
- Subjects
Materials science ,Polymers and Plastics ,Hydrogen bond ,Organic Chemistry ,General Physics and Astronomy ,Miscibility ,Crystallography ,symbols.namesake ,chemistry.chemical_compound ,Differential scanning calorimetry ,Fourier transform ,chemistry ,Polymer chemistry ,Materials Chemistry ,symbols ,Phenol ,Polymer blend ,Spectroscopy ,Glass transition - Abstract
The blends of poly(beta-hydroxybutyrate-co-beta-hydroxyvalerate) (P(HB-co-HV)/poly(p-vinylphenol)(PVPh) were investigated by differential scanning calorimetry (DSC), Fourier transform IR (FT-IR) spectroscopy and high-resolution solid-state C-13 NMR techniques. Single glass transition temperatures existing in the whole composition range indicates that these blends are miscible. The presence of hydrogen bonding between the hydroxyl of PVPh and carbonyl of P(HB-co-HV), shown by FT-IR spectra, is the origin of the miscibility. Furthermore, results obtained by high-resolution solid-state C-13 NMR give more information about the structure of the blends. (C) 1998 Elsevier Science Ltd. All rights reserved.
- Published
- 1998
27. Compatibilization effect of graft copolymer on immiscible polymer blends: 1. LLDPE/SBS/LLDPE-g-PS systems
- Author
-
Jun Tian, Hanqiao Feng, Chaohui Ye, Zhiliu Feng, and Baotong Huang
- Subjects
Materials science ,Polymers and Plastics ,Organic Chemistry ,Concentration effect ,Compatibilization ,Grafting ,Amorphous solid ,Linear low-density polyethylene ,chemistry.chemical_compound ,chemistry ,Solubilization ,Materials Chemistry ,Copolymer ,Polymer blend ,Composite material - Abstract
The compatibilizing effect of graft copolymer, linear low density polyethylene-g-polystyrene (LLDPE- g -PS), on immiscible blends of LLDPE with styrene-butadiene-styrene triblock copolymer (SBS) has been investigated by means of 13 C CPMAS n.m.r. and d.s.c. techniques. The results indicate that LLDPE- g -PS is an effective compatibilizer for LLDPE/SBS blends. It was found that LLDPE- g -PS chains connect two immiscible components, LLDPE and SBS, through solubilization of chemically identical segments of LLDPE- g -PS into the amorphous region of LLDPE and PS block domain of SBS, respectively. It was also found that LLDPE- g -PS chains connect the crystalline region of LLDPE by isomorphism, with serious effects on the supermolecular structure of LLDPE. The effect of LLDPE- g -PS on the supermolecular structure of LLDPE in the LLDPE/SBS blends obviously depends on the composition of the blends, but has little dependence on the PS grafting yields of LLDPE- g -PS.
- Published
- 1998
28. High resolution solid-state NMR and DSC study of poly(ethylene glycol)-silicate hybrid materials via sol-gel process
- Author
-
Dayong He, Hanqiao Feng, Weibin Chen, and Chaohui Ye
- Subjects
Materials science ,Polymers and Plastics ,technology, industry, and agriculture ,Concentration effect ,macromolecular substances ,General Chemistry ,Microstructure ,Surfaces, Coatings and Films ,law.invention ,chemistry.chemical_compound ,chemistry ,Chemical engineering ,law ,Polymer chemistry ,PEG ratio ,Materials Chemistry ,Crystallization ,Glass transition ,Hybrid material ,Ethylene glycol ,Sol-gel - Abstract
Hybrid materials incorporating poly(ethylene glycol) (PEG) with tetraethoxysilane (TEOS) via a sol-gel process were studied for a wide range of compositions of PEG by DSC and high resolution solid-state C-13- and Si-29-NMR spectroscopy. The results indicate that the microstructure of the hybrid materials and the crystallization behavior of PEG in hybrids strongly depend on the relative content of PEG. With an increasing content of PEG, the microstructure of hybrid materials changes a lot, from intimate mixing to macrophase separation. It is found that the glass transition temperatures (T-g) (around 373 K) of PEG homogeneously embedded in a silica network are much higher than that (about 223 K) of pure PEG and also much higher in melting temperatures T-m (around 323 K) than PEG crystallites in heterogeneous hybrids. Meanwhile, the lower the PEG content, the more perfect the silica network, and the higher the T-g of PEG embedded in hybrids. An extended-chain structure of PEG was supposed to be responsible for the unusually high T-g of PEG. Homogeneous PEG-TEOS hybrids on a molecular level can be obtained provided that the PEG. content in the hybrids is less than 30% by weight. (C) 1998 John Wiley & Sons, Inc.
- Published
- 1998
29. Synthesis and Characterization of Styrene-Butadiene Block Copolymer/Silicate Hybrid Materials via the Sol-Gel Process I. Four-Arm Star Styrene-Butadiene Block Copolymer/Silica Hybrids
- Author
-
Chaohui Ye, Weibin Chen, and Hanqiao Feng
- Subjects
Styrene-butadiene ,Materials science ,Polymers and Plastics ,Dynamic mechanical analysis ,Thermogravimetry ,chemistry.chemical_compound ,chemistry ,Polymer chemistry ,Materials Chemistry ,Copolymer ,Thermal stability ,Polystyrene ,Hybrid material ,Sol-gel - Abstract
Novel hybrid materials incorporating four-arm star styrene-butadiene block copolymer (SB-4A) with tetraethoxysilane (TEOS) have been successfully prepared by a sol-gel process. The properties, microstructure, and dynamics of the hybrid materials were investigated in detail by means of dynamic mechanical analysis (DMA), thermogravimetry (TG), and NMR techniques. The results indicate that the properties of the hybrids strongly depend on the TOES content and the silica networks prefer to form in the polystyrene (PS) domains. There exists an optimum range of TEOS content, in this work 30–50% by weight, within which the properties of the hybrids obtained were well improved: storage modulus increases, thermal stability raises, and the high-temperature Tg shifts to higher temperature. 29Si NMR spectrum shows that in the hybrids with well improved properties silica networks formed with Q4 in the greatest abundance.
- Published
- 1997
30. Interfacial structure and properties of polyurethane/poly(methylacrylate-co-styrene) coating to regenerated cellulose film
- Author
-
Haiqing Liu, Lina Zhang, Hanqiao Feng, Shanhong Yan, and Guang Yang
- Subjects
Materials science ,Polymers and Plastics ,Regenerated cellulose ,engineering.material ,Condensed Matter Physics ,Styrene ,chemistry.chemical_compound ,chemistry ,Coating ,Transmission electron microscopy ,Differential thermal analysis ,Ultimate tensile strength ,Materials Chemistry ,engineering ,Physical and Theoretical Chemistry ,Cellulose ,Composite material ,Polyurethane - Abstract
A semiinterpenetrating polymer network (IPN) containing 72 wt % polyurethane (PU) and 6 wt % poly(methylacrylate-co-styrene) [P(MA-St)] was coated onto surfaces of regenerated cellulose (RC) film, which was prepared by coagulating a cellulose cuoxam from bagasse pulp. The interfacial structures, bonding manner, and the strength of the coated film were studied by infrared (IR),13C nuclear magnetic resonance (NMR), differential thermal analysis (DTA), transmission electron microscopy (TEM), and electron probe microscopy analysis (EPMA). It was shown that the RC film coated with PU/P(MA-St) has strong interfacial interactions, where covalent and hydrogen bonds are formed across the interface between cellulose and the PU/P(MA-St) coating. The interfacial structure of the coated film is regarded as a shared PU network crosslinked simultaneously with P(MA-St) and cellulose film. The tensile strength, water resistivity, and optical transmission of the coated films were considerably higher than that of the uncoated films. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35: 2495–2501, 1997
- Published
- 1997
31. N.m.r. investigation of phase separation in poly(N-isopropyl acrylamide)/water solutions
- Author
-
Fang Zeng, Zhen Tong, and Hanqiao Feng
- Subjects
Aqueous solution ,Polymers and Plastics ,Proton ,Hydrogen bond ,Organic Chemistry ,Analytical chemistry ,Backbone chain ,Lower critical solution temperature ,Hydrophobic effect ,chemistry.chemical_compound ,chemistry ,Polymer chemistry ,Materials Chemistry ,Side chain ,Isopropyl - Abstract
1H and 13C n.m.r. spectra of poly(N-isopropyl acrylamide) (PNIPA) in D2O and CDCl3 were measured at several temperatures encompassing the lower critical solution temperature (LCST) about 32°C of the PNIPA/water solution, using a high resolution n.m.r. spectrometer (500 MHz for proton). The PNIPA/CDCl3 is homogeneous in the temperature ranging from 16 to 36°C and the hydrogen bonds of the amide groups are weakened by the solvation of CDCl3 and broken by heating. In the PNIPA/D2O solution, the proton and 13C spectra are well resolved below the LCST. Whereas at temperatures above the LCST, all the resonance peaks except that for water proton became broad and the spectra lost their fine structure. The integral intensity of the water proton relative to that of the lone proton in the isopropyl group increases with increasing temperature, suggesting that some water molecules appear to be released out of the hydrated shells around the polymer chains. When the solution was heated from 22 to 35°C, the spin-lattice relaxation time T1 for the proton of the methyl group in the isopropyl residue increased, while that for the protons of the methylene and methyne groups of the backbone chain decreased. This indicates that during heating the relaxation of the isopropyl side chain slows down and that of the main chain speeds up. The phase separation was qualitatively interpreted with the Nemethy-Scheraga model for the hydrophobic bonding.
- Published
- 1997
32. The miscibility of homopolymer/random copolymer blends—3. Blends of SAA with polymethacrylates and polyesters
- Author
-
Hanqiao Feng, Chaohui Ye, and Zhiliu Feng
- Subjects
Materials science ,Polymers and Plastics ,Organic Chemistry ,General Physics and Astronomy ,Methacrylate ,Miscibility ,Polyester ,chemistry.chemical_compound ,chemistry ,visual_art ,Polymer chemistry ,Materials Chemistry ,Copolymer ,visual_art.visual_art_medium ,Polymer blend ,Polystyrene ,Polycarbonate ,Methyl methacrylate - Abstract
The miscibility of blends of poly(styrene-co-allyl alcohol) (SAA) with poly(methyl methacrylate) (PMMA), poly(ethyl methacrylate) (PEMA), poly(n-butyl methacrylate) (PnBMA), poly-epsilon-caprolactone (PCL) or polycarbonate (PC) has been studied by means of NMR, FT-IR and DSC techniques. It was found that SAA and PMMA, PEMA or PCL form miscible blends and SAA is only partially miscible with PC or PnBMA. Both phenyl groups and hydroxyl groups in SAA are involved in the intermolecular interactions between SAA and PMMA, PEMA or PCL. Also the hydroxyl-carbonyl hydrogen bonds existing in all the miscible blends studied are formed partially at the expense of the disruption of self-association of hydroxyl groups in pure SAA. (C) 1997 Elsevier Science Ltd. All rights reserved.
- Published
- 1997
33. The aggregation state of polyimide
- Author
-
Zhiliu Feng, Hao Tang, Lisong Dong, Hanqiao Feng, and Haobin Luo
- Subjects
Polymers and Plastics ,Chemistry ,Organic Chemistry ,Relaxation (NMR) ,Analytical chemistry ,General Physics and Astronomy ,Concentration effect ,Modulus ,Miscibility ,Fluorescence ,Spectral line ,Materials Chemistry ,Organic chemistry ,Glass transition ,Polyimide - Abstract
The aggregation slate of polyimide in solution and in the solid state were studied using the NMR and fluorescence techniques. The experiment results show that the decay of spin-spin relaxation of polyimides with concentration can be described as a single exponential, biexponential, triexponential, biexponential profile. Meanwhile, the intensities of fluorencence spectra increase rapidly with the concentration, and some peaks have a red-shift. Based upon these experiment results, it can be concluded that polyimide in solution is very flexible, and there are several critical concentrations at which polyimide has distinctly different aggregation states. The existence of intermolecular charge transfer interaction between polyimide chains has been proved, and the interaction has a profound effect on the glass transition temperature, T-g, and the dynamic mechanical modulus of polyimide. (C) 1997 Elsevier Science Ltd.
- Published
- 1997
34. NMR relaxation and micro-imaging study of polystyrene in concentrated cyclohexane solution
- Author
-
Guangliang Ding, Hanzhen Yuan, Hanqiao Feng, Shizhen Mao, and You-Ru Du
- Subjects
chemistry.chemical_classification ,Cyclohexane ,General Mathematics ,Polymer ,Solvent ,chemistry.chemical_compound ,Nuclear magnetic resonance ,chemistry ,medicine ,Physical chemistry ,Polystyrene ,Swelling ,medicine.symptom ,Pendant group ,Dispersion (chemistry) ,Dissolution ,Mathematics - Abstract
13C-relaxation times of polystyrene (PS) in its θ solvent, cyclohexane, are measured at different temperatures. A two-step model for the dissolution is proposed. Swelling of the polymer below the θ temperature is eventually the dispersion of the side group phenyl rings only. While above the θ temperature, complete dissolution is the dispersion of the main chain at a molecular level. The results of T1(C) are confirmed by1H-NMR imaging. NMR and its imaging are powerful twls to study the dynamic behavior of dissolution process of polymers in their θ solvents.
- Published
- 1997
35. A conserved mechanism for centromeric nucleosome recognition by centromere protein CENP-C
- Author
-
Jiansheng Jiang, Aaron F. Straight, Yawen Bai, Bing-Rui Zhou, Hanqiao Feng, T. Sam Xiao, Rodolfo Ghirlando, Hidenori Kato, and Marieke Rozendaal
- Subjects
Chromosomal Proteins, Non-Histone ,Kinetochore assembly ,Amino Acid Motifs ,Centromere ,Molecular Sequence Data ,macromolecular substances ,Biology ,Editorials: Cell Cycle Features ,Autoantigens ,Article ,Protein Structure, Secondary ,Histones ,Histone H1 ,Histone H2A ,Histone code ,Nucleosome ,Animals ,Humans ,Histone octamer ,Amino Acid Sequence ,Conserved Sequence ,Genetics ,Multidisciplinary ,Binding Sites ,Cell biology ,Nucleosomes ,Chromatosome ,Drosophila ,Hydrophobic and Hydrophilic Interactions ,Centromere Protein A - Abstract
Kinetochore Targeting Chromosomes must be segregated accurately during cell division. This is facilitated by the attachment of mitotic spindle microtubules to the kinetochore at the chromosomal centromere. The centromere is marked with the histone H3 variant CenH3 (CENP-A in human), and CENP-C forms part of the inner kinetochore. Kato et al. (p. 1110 ) used structural biology, biochemistry, and mutagenesis to show that CENP-C recognizes CENP-A chromatin via several different interactions. The CENP-C "central domain" makes close contact with the acidic patch of histones H2A/H2B, and the highly conserved "CENP-C motif" senses both the acidic patch and recognizes the hydrophobicity of the otherwise nonconserved CenH3 tail, supporting a conserved mechanism of centromere targeting by the kinetochore.
- Published
- 2013
36. Structural mechanisms of centromeric nucleosome recognition by the kinetochore protein CENP-N.
- Author
-
Chittori, Sagar, Jingjun Hong, Saunders, Hayden, Hanqiao Feng, Ghirlando, Rodolfo, Kelly, Alexander E., Yawen Bai, and Subramaniam, Sriram
- Published
- 2018
- Full Text
- View/download PDF
37. Compatibilization effect of graft copolymer on immiscible polymer blends. II. LLDPE/PS/LLDPE-g-PS systems
- Author
-
Hanqiao Feng, Chaohui Ye, and Jun Tian
- Subjects
Polypropylene ,Materials science ,Polymers and Plastics ,General Chemistry ,Compatibilization ,Polyethylene ,Surfaces, Coatings and Films ,Amorphous solid ,Linear low-density polyethylene ,chemistry.chemical_compound ,chemistry ,Materials Chemistry ,Copolymer ,Polystyrene ,Polymer blend ,Composite material - Abstract
compatibilizing effect of graft copolymer, linear low density polyethylene-g-polystyrene (LLDPE-g-PS), on immiscible blends of LLDPE with styrene-butadiene-styrene triblock copolymer (SBS) has been investigated by means of C-13 CPMAS n.m.r. and d.s.c. techniques. The results indicate that LLDPE-g-PS is an effective compatibilizer for LLDPE/SBS blends. It was found that LLDPE-g-PS chains connect two immiscible components, LLDPE and SBS, through solubilization of chemically identical segments of LLDPE-g-PS into the amorphous region of LLDPE acid PS block domain of SBS, respectively. It was also found that LLDPE-g-PS chains connect the crystalline region of LLDPE by isomorphism, with serious effects on the supermolecular structure of LLDPE. The effect of LLDPE-g-PS on the supermolecular structure of LLDPE in the LLDPE/SBS blends obviously depends on the composition of the blends, but has little dependence on the PS grafting yields of LLDPE-g-PS. (C) 1998 Elsevier Science Ltd. All rights reserved.
- Published
- 1996
38. The Miscibility of Homopolymer/Random Copolymer Blends IV. Poly(vinylidene chloride-co-acrylonitrile)/Poly(methyl methacrylate) Blends
- Author
-
Chaohui Ye, Hanqiao Feng, and Zhiliu Feng
- Subjects
Materials science ,Polymers and Plastics ,Hydrogen ,Hydrogen bond ,chemistry.chemical_element ,Poly(methyl methacrylate) ,Chloride ,Miscibility ,chemistry.chemical_compound ,chemistry ,visual_art ,Polymer chemistry ,Materials Chemistry ,visual_art.visual_art_medium ,medicine ,Copolymer ,Methyl methacrylate ,Acrylonitrile ,medicine.drug - Abstract
The miscibility of blends of poly(vinylidene chloride-co-acrylonitrile) (VDC-AN) and poly(methyl methacrylate) (PMMA) has been studied with DSC, FT-IR, and NMR methods. The results indicate that the VDC-AN/PMMA blends are miscibile on a molecular level, and the dipole-dipole interactions between C=O and C-Cl-2 and/or interpolymer hydrogen bondings between COOCH3 and CN and CCl groups play the role on the miscibility of the blends. It is found that the -CCl2- groups have two different chemical environments in the pure VDC-AN copolymer, which may result from the different configurations of the copolymer, such as -CCl2- groups in the ''alternating'' segments and -CCl2- groups in the ''blocky'' segments as proposed. It is the -CCl2- group in the ''alternating'' segment that takes part in the dipole-dipole interaction with C=O group in PMMA.
- Published
- 1996
39. The Miscibility of Homopolymer/Random Copolymer Blends I. Poly(styrene-co-acrylonitrile)/Poly(ethyl methacrylate) and Poly(styrene-co-acrylonitrile)/Poly(methyl methacrylate) Blends
- Author
-
Chaohui Ye, Zhiliu Feng, and Hanqiao Feng
- Subjects
Materials science ,Polymers and Plastics ,technology, industry, and agriculture ,macromolecular substances ,equipment and supplies ,Methacrylate ,Poly(methyl methacrylate) ,Miscibility ,Styrene ,body regions ,chemistry.chemical_compound ,chemistry ,visual_art ,Polymer chemistry ,Materials Chemistry ,visual_art.visual_art_medium ,Copolymer ,Polystyrene ,Methyl methacrylate ,Acrylonitrile - Abstract
The miscibility of blends of poly(styrene-co-acrylonitrile) (SAN) with poly(methyl methacrylate) (PMMA) or poly(ethyl methacrylate) (PEMA) has been investigated by means of NMR and DSC techniques. It is found that there are intermolecular interactions between the phenyl groups in SAN and carbonyl groups in PMMA or PEMA, and the strength of this intermolecular interaction strongly depends on the properties of ester side groups in PEMA or PMMA, composition of the blends and a certain composition of the copolymer. It is this specific interaction instead of the intramolecular repulsion force within the copolymer that plays a key role for the miscibility of SAN/PMMA and SAN/PEMA blends.
- Published
- 1996
40. High resolution 1H spectra of powdered solids observed by Hahn echo pulse sequence with magic-angle spinning
- Author
-
Hanqiao Feng, Nianhua Yang, Jinyuan Zhou, Chaohui Ye, Feng Deng, Jian Zhi Hu, and Liyun Li
- Subjects
Nuclear and High Energy Physics ,Hot Temperature ,Magnetic Resonance Spectroscopy ,Chemical Phenomena ,Analytical chemistry ,Spectral line ,Fumarates ,Magic angle spinning ,Molecule ,Instrumentation ,Spinning ,Crystallography ,Radiation ,Molecular Structure ,Chemistry, Physical ,Chemistry ,Chemical shift ,Temperature ,Water ,Pulse sequence ,General Chemistry ,Malonates ,Melting point ,Spin echo ,Protons ,Crystallization ,Hydrogen - Abstract
The 1H magic-angle spinning (MAS) spectrum for a typical powdered solid is composed of a high resolution component and a broadline component. The high resolution component can be well isolated from the broadline component by the Hahn echo sequence with a long echo time. Compared with the CRAMPS experiment, which measures the proton system as a whole, the high resolution echo-MAS method measures only a fraction of the solid, which is usually small at room temperature and quite different from the majority of the solid in both molecular motion and chemical environment. It is shown that for a sample of fumaric acid monoethyl ester, the chemical shifts of the high resolution component are apparently distinguishable from the isotropic chemical shifts of the broadline component in the CRAMPS spectrum as the temperature approaches the melting point. In addition, for a sample of malonic acid, the echo-MAS spectrum is sensitive to moisture and temperature, while its corresponding CRAMPS spectrum is not. It is suggested that the molecules which produce the high resolution component are related to the lattice defects in a solid, including the surface disorder of the polycrystallites, while the molecules that generate the broadline component are located on the rigid lattice of the solid.
- Published
- 1996
41. Biodegradability of Regenerated Cellulose Films in Soil
- Author
-
Lianshuang Zheng, Haiqing Liu, Jiayao Zhang, Yumin Du, Lina Zhang, and Hanqiao Feng
- Subjects
Scanning electron microscope ,General Chemical Engineering ,Regenerated cellulose ,General Chemistry ,Biodegradation ,Industrial and Manufacturing Engineering ,chemistry.chemical_compound ,chemistry ,Chemical engineering ,Ultimate tensile strength ,Degradation (geology) ,Organic chemistry ,Hemicellulose ,Cellulose ,Kraft paper - Abstract
Regenerated cellulose films and a water-resistant film coated with thin Tung oil were prepared by using a cellulose cuoxam solution from pulps of cotton linter, cotton stalk, and wheat straw. They were buried in the soil to test biodegradability. The results showed that viscosity average molecular weight Mη, tensile strength σb, and the weight of the degraded films decreased sharply with the progress of degradation time, and the kinetics of decay were discussed. The degradation half-lives t1/2 of the films in soil at 10−20 °C were given to be 30−42 days, and after 2 months the films were decomposed into CO2 and water. The α-cellulose in soil was more readily biodegraded than hemicellulose, and regenerated cellulose film was more readily biodegraded than kraft paper. Nuclear magnetic resonance and scanning electron micrographs indicated that the biodegradation process of the films was performed through random breakdown of bonds of cellulose macromolecules resulting from the microorganism cleavage.
- Published
- 1996
42. NMR study of miscibility and morphology of polyimide/polyimide blends
- Author
-
Hanqiao Feng, Zhiliu Feng, Chaochui Ye, Ping Zhang, and Zhenhua Sun
- Subjects
Morphology (linguistics) ,Materials science ,Polymers and Plastics ,Organic Chemistry ,Intermolecular force ,Resonance ,Condensed Matter Physics ,Miscibility ,Spectral line ,Molecular aggregation ,Molecular level ,Polymer chemistry ,Materials Chemistry ,Physical and Theoretical Chemistry ,Polyimide - Abstract
The miscibility and morphology of polyimide/polyimide blends, PEI-E/PTI-E(a)) and PBPI-E/IPTI-E(a)), have been studied by means of C-13 CPMAS NMR technique. The results indicate that PEI-E/PTI-E blends are miscible on a molecular level, but molecular aggregation exists in pure PBPI-E specimen as well as PBPI-E/PTI-E blends with high content of PBPI-E, which vanishes in the blends with high content of PTI-E. When the content of PBPI-E is higher than that of PTI-E, the addition of PTI-E to PBPI-E has almost no effect on the size of the PBPI-E rigid domains, but has a large effect on the populations of the PBPI-E rigid domains. It is the intermolecular charge-transfer interaction that plays a critical role in the miscibility of PEI-E/PTI-E and PBPI-E/PTI-E blends.
- Published
- 1995
43. NMR Study on the Relationship between Miscibility and Anti-Aging Performance of Blends Containing Block Copolymers
- Author
-
Chaohui Ye, Hanqiao Feng, and Zhiliu Feng
- Subjects
chemistry.chemical_classification ,Materials science ,Polymers and Plastics ,Double bond ,Miscibility ,chemistry.chemical_compound ,Polybutadiene ,chemistry ,Chemical engineering ,Solubilization ,Polymer chemistry ,Materials Chemistry ,Copolymer ,Molecule ,Polystyrene - Abstract
The anti-aging performance of blends of polystyrene (PS), styrene-butadiene triblock copolymers (SBS), and PS/styrene-butadiene (SB)-4A (Carm star SE block copolymer) has been studied by means of C-13 NMR techniques. It is found that the anti-aging performance of these kinds of blends largely depends on their miscibility with PS of different molecular weight M(PS). The larger the quantities of PS solubilized in polybutadiene (PBD) domains, the better the anti-aging performance of the blends. It is also found that the anti-aging performance of these blends has dependence on molecular architectures of the SE block copolymers. For the aged blends, the double bonds of PBD were broken, meanwhile serious cross-linking networks formed in the blends. The proposed anti-aging mechanism is that the PS solubilized in PBD domains can efficiently prevent oxygen molecules from diffusing into PBD domains, therefore, successfully stop the oxidative process of PBD.
- Published
- 1995
44. Miscibility of homopolymer/random copolymer blends—2. SMA/PMMA blend
- Author
-
Hanqiao Feng, Lianfang Shen, and Zhiliu Feng
- Subjects
Materials science ,Polymers and Plastics ,education ,Organic Chemistry ,Intermolecular force ,technology, industry, and agriculture ,General Physics and Astronomy ,macromolecular substances ,equipment and supplies ,Methacrylate ,SMA ,Miscibility ,body regions ,Molecular level ,Intramolecular force ,Materials Chemistry ,Copolymer ,Composite material ,Fourier transform infrared spectroscopy - Abstract
The miscibility of blends of PMMA with SMA (50 wt% MA) has been investigated by means of NMR, FTIR and DSC techniques. The results indicate that the SMA/PMMA blends are miscible on a molecular level, and there are strong intermolecular interactions between the phenyl groups in SMA and carbonyl groups in PMMA. It is the intermolecular interactions instead of the intramolecular repulsion forces within the SMA copolymer that make the SMA/PMMA blends miscible. It is also found that the strength of the intermolecular interactions to some degree depends on the compositions of the blends.
- Published
- 1995
45. Problems: 10202-10210
- Author
-
Vidav, Ivan, Ramos, Edgar A., West, Douglas B., Sinkhorn, Richard, Bloom, David M., Freden, Eric, Golomb, Solomon, Hanqiao, Feng, Ng, Siu-Ah, and Fremlin, D. H.
- Published
- 1992
- Full Text
- View/download PDF
46. 10209
- Author
-
Hanqiao, Feng, Ng, Siu-Ah, and Martin, Reiner
- Published
- 1993
- Full Text
- View/download PDF
47. Histone H4 K16Q mutation, an acetylation mimic, causes structural disorder of its N-terminal basic patch in the nucleosome
- Author
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Hidenori Kato, James M. Gruschus, Yawen Bai, Hanqiao Feng, Rodolfo Ghirlando, and Bing-Rui Zhou
- Subjects
Models, Molecular ,Protein Folding ,Protein Conformation ,Molecular Sequence Data ,Biology ,Article ,Histone H4 ,Histones ,Histone H1 ,Structural Biology ,Nucleosome ,Histone code ,Animals ,Drosophila Proteins ,Histone octamer ,Amino Acid Sequence ,Molecular Biology ,Nuclear Magnetic Resonance, Biomolecular ,Lysine ,Acetylation ,Chromatin Assembly and Disassembly ,Linker DNA ,Chromatin ,Recombinant Proteins ,Nucleosomes ,Histone ,Biochemistry ,Chromatosome ,Mutation ,biology.protein ,Biophysics - Abstract
Histone tails and their posttranslational modifications play important roles in regulating the structure and dynamics of chromatin. For histone H4, the basic patch K(16)R(17)H(18)R(19) in the N-terminal tail modulates chromatin compaction and nucleosome sliding catalyzed by ATP-dependent ISWI chromatin remodeling enzymes while acetylation of H4 K16 affects both functions. The structural basis for the effects of this acetylation is unknown. Here, we investigated the conformation of histone tails in the nucleosome by solution NMR. We found that backbone amides of the N-terminal tails of histones H2A, H2B, and H3 are largely observable due to their conformational disorder. However, only residues 1-15 in H4 can be detected, indicating that residues 16-22 in the tails of both H4 histones fold onto the nucleosome core. Surprisingly, we found that K16Q mutation in H4, a mimic of K16 acetylation, leads to a structural disorder of the basic patch. Thus, our study suggests that the folded structure of the H4 basic patch in the nucleosome is important for chromatin compaction and nucleosome remodeling by ISWI enzymes while K16 acetylation affects both functions by causing structural disorder of the basic patch K(16)R(17)H(18)R(19).
- Published
- 2012
48. Miscibility, Microstructure, and Dynamics of Blends Containing Block Copolymer. 1. Miscibility of Blends of Homopolystyrene with Styrene-Butadiene Block Copolymers
- Author
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Hanzhen Yuan, Hanqiao Feng, Zhiliu Feng, and Lianfang Shen
- Subjects
chemistry.chemical_classification ,Materials science ,Styrene-butadiene ,Morphology (linguistics) ,Polymers and Plastics ,Organic Chemistry ,Polymer ,Microstructure ,Miscibility ,Inorganic Chemistry ,chemistry.chemical_compound ,chemistry ,Chemical engineering ,Polymer chemistry ,Materials Chemistry ,Copolymer - Abstract
The microstructures of styrene-butadiene triblock (SBS) and styrene-butadiene four-arm star block (SB-4A) copolymers and their blends with homopolystyrene (PS) of different molecular weights, MPS, have been investigated by means of small-angle X-ray scatt
- Published
- 1994
49. Miscibility, Microstructure, and Dynamics of Blends Containing Block Copolymer. 2. Microstructure of Blends of Homopolystyrene with Styrene-Butadiene Block Copolymers
- Author
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Hanqiao Feng, Zhiliu Feng, and Lianfang Shen
- Subjects
Inorganic Chemistry ,Polymers and Plastics ,Organic Chemistry ,Materials Chemistry - Published
- 1994
50. Structure of the budding yeast Saccharomyces cerevisiae centromeric histones Cse4-H4 complexed with the chaperone Scm3
- Author
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Bing-Rui Zhou, Hanqiao Feng, Zheng Zhou, and Yawen Bai
- Subjects
Kluyveromyces lactis ,Fungal protein ,Multidisciplinary ,biology ,medicine.diagnostic_test ,Proteolysis ,Saccharomyces cerevisiae ,biology.organism_classification ,Histone ,Biochemistry ,Chaperone (protein) ,Kluyveromyces ,Centromere ,biology.protein ,medicine - Abstract
Based on the crystal structure of the budding yeast Kluyveromyces lactis (Kl) Scm3–Cse4–H4 complex and the proteolysis results of the budding yeast Saccharomyces cerevisiae (Sc) Scm3–Cse4–H4 complex, Cho and Harrison (1) questioned our NMR structure of the Sc Scm3–Cse4–H4 complex (2), stating that “The construct deleted helix I of H4, however, and this deletion, together with omission of about 20 residues in the N-terminal part of the conserved region of Scm3, appears to have generated severe distortions in about half the structure, leading to incorrect conclusions about histone conformational differences and about a number of the Scm3-Cse4 contacts.”
- Published
- 2011
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