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Human telomerase reverse transcriptase (hTERT), the catalytic subunit of human telomerase, is responsible for the synthesis and maintenance of the telomeric repeats at the distal ends of human chromosomes. Telomerase expression is repressed in normal human cells and is activated in immortal cells and during tumorigenesis, but the mechanism by which telomerase expression is regulated is not fully understood. Previous studies have shown that c-Myc stimulates hTERT transcription through the binding sites located on the hTERT promoter. In this study, we sought to determine whether BRCA1 inhibits hTERT transcription through its direct interaction with c-Myc. In ovarian cancer cells, c-Myc increased hTERT expression by threefold and BRCA1 completely abrogated this activity. A mutation in the c-Myc-binding site (E-box) of the hTERT promoter resulted in the loss of activation by c-Myc and in the loss of inhibition by BRCA1. Deletion of the c-Myc-binding domain in BRCA1 resulted in the loss of BRCA1’s ability to inhibit transcription of the hTERT promoter. In addition, BRCA1 associates with c-Myc and inhibits the binding activity of c-Myc to the hTERT promoter. Our data indicate that BRCA1 is involved in regulating cellular immortalization through the modulation of c-Myc on the hTERT promoter. [Copyright &y& Elsevier]

ω-transaminase has attracted growing attention for chiral amine synthesis, although it commonly suffers from severe by-product inhibition. ω-transaminase CrmG is critical for the biosynthesis of Caerulomycin A, a natural product that possesses broad bioactivity, including immunosuppressive and anti-cancer. Compared to L-Arg, amino donor L-Glu, L-Gln or L-Ala is more preferred by CrmG. In this study, we determined the crystal structure of CrmG in complex with amino donor L-Arg, unveiling the detailed binding mode. Specifically, L-Arg exhibits an extensive contact with aromatic residues F207 and W223 on the roof of CrmG active site via cation-π network. This interaction may render the deamination by-product of L-Arg to be an inhibitor against PMP-bound CrmG by stabilizing its flexible roof, thus reducing the reactivity of L-Arg as an amino donor for CrmG. These data provide further evidence to support our previous proposal that CrmG can overcome inhibition from those by-products that are not able to stabilize the flexible roof of active site in PMP-bound CrmG. Thus, our result can not only facilitate the biosynthesis of CRM A but also be beneficial for the rational design of ω-transaminase to bypass by-product inhibition. • Crystal structure of CrmG in complex with amino donor L-Arg is reported. • L-Arg interacts with the roof of CrmG active site via unique cation-π network. • The interaction with the roof impairs reactive efficiency of L-Arg as CrmG amino donor. [ABSTRACT FROM AUTHOR]

The estrogen-related receptor (ERR) family members are reported to bind DNA elements as either monomer or dimer. However, to date, only one solution NMR structure of ERRβ in complex with a half-site DNA element has been reported. To better understand the DNA regulation mechanism, we determined the crystal structure of ERRγ-DBD bound to a natural DR1 element in Pla2g12b promoter to 2.2 Å resolution. Combined with biochemical assays, we show that ERRγ acts as a dimer and the C-terminal extension region undergoes conformational rearrangement when binding to the downstream DR1 element. In addition, the T-box region on the dimerization interface exhibits unique main-chain conformation. Thus, our structure presents a novel dimer interface for NR binding on DR1 DNA and provides a molecular basis for understanding the homodimer organization of ERR on DR1 elements. • We determined the first dimeric structure of ERRγ-DBD in complex with a DR1 element. • The CTE tail of ERRγ-DBD undergoes conformational rearrangement when binding to the downstream DR1 element. • The T-box conformation of ERRγ-DBD is unique on the dimer interface when binding to DR1. [ABSTRACT FROM AUTHOR]

IDO1 (indoleamine 2, 3-dioxygenase 1), a well characterized immunosuppressive enzyme, has attracted growing attention as a potential target for cancer immunotherapy. Hydroxylamidine compounds INCB024360 and INCB14943 (INCB024360 analogue) are highly effective IDO1 inhibitors. INCB024360 is undergoing clinical trials for treatment of various types of human cancer. Here, we determined the co-crystal structure of IDO1 and INCB14943, and elucidate the detailed binding mode. INCB14943 binds to heme iron in IDO1 protein through the oxime nitrogen. Further analysis also reveals that a halogen bonding interaction between the chlorine atom (3-Cl) of INCB14943 and the sulphur atom of C129 significantly improves the inhibition activity against IDO1. Comparing with the other reported inhibitors, the oxime nitrogen and halogen bond interaction are identified as the unique features of INCB14943 among the IDO1 inhibitors. Thus, our study provides novel insights into the interaction between a small molecule inhibitor INCB14943 and IDO1 protein. The structural information will facilitate future IDO1 inhibitor design. [ABSTRACT FROM AUTHOR]

Abstract: BRCA1 plays an important role in maintaining genomic stability through its involvement in DNA repair. Although it is known that BRCA1 and RAD51 form distinct DNA repair subnuclear complexes, or foci, following environmental insults to the DNA, the role of BRCA1 in this process remains to be characterized. The purpose of the study was therefore to determine the role of BRCA1 in the formation of RAD51 foci following treatment with cisplatin and ionizing radiation. We found that although a functional BRCA1 is required for the subnuclear assembly of BRCA1 foci following treatment with either ionizing radiation or cisplatin, a functional BRCA1 is required for RAD51 foci to form following treatment with cisplatin but not with ionizing radiation. Similar results were obtained in SKOV-3 cells when the level of BRCA1 expression was knocked down by stable expression of a retrovirus-mediated small-interfering RNA against BRCA1. We also found that the carboxyl-terminal of BRCA1 contains uncharacterized phosphorylation sites that are responsive to cisplatin. The functional BRCA1 is also required for breast and ovarian cancer cells to mount resistance to cisplatin. These results suggest that the carboxyl-terminal of BRCA1 is required for the cisplatin-induced recruitment of RAD51 to the DNA-damage site, which may contribute to cisplatin resistance. [Copyright &y& Elsevier]

Aflatoxin-oxidase (AFO), a newly discovered oxidase isolated from Armillariella tabescens , was reported to perform aflatoxin B1 (AFB1) detoxification through breaking the bisfuran ring of AFB1. However, based on sequence alignment, we found that AFO shares high sequence identities with dipeptidyl peptidase III (DPP III) family members. To understand the functions of AFO, we determined its crystal structures in the absence and presence of zinc, copper ion, and employed HPLC to test if AFO could cleave the substrates of DPP III. Our structures reveal that AFO contains the classic DPP III activity center and the HPLC results further confirm that AFO possesses the dipeptidyl peptidase activity. Therefore, AFO should belong to DPP III family. Interestingly, unlike reported classic DPP III structure that has a large domain movement upon substrate binding, the AFO structures all adopt the closed conformation, independent of substrate binding. This conformation characteristic of AFO may be related to its enzyme activities. Taken together, our results demonstrate that AFO is a dual activity enzyme with both aflatoxin-oxidase and dipeptidyl peptidase activities and its unique conformation feature expands our understanding on the mode of reaction for this enzyme family. [ABSTRACT FROM AUTHOR]

Lipases play an important role in physiological metabolism and diseases, and also have multiple industrial applications. Rational modification of lipase specificity may increase the commercial utility of this group of enzymes, but is hindered by insufficient mechanistic understanding. Here, we report the 2.0 Å resolution crystal structure of a mono- and di-acylglycerols lipase from Malassezia globosa ( Mg MDL2). Interestingly, residues Phe278 and Glu282 were found to involve in substrate recognition because mutation on each residue led to convert Mg MDL2 to a triacylglycerol (TAG) lipase. The Phe278Ala and Glu282Ala mutants also acquired ability to synthesize TAGs by esterification of glycerol and fatty acids. By in silicon analysis, steric hindrance of these residues seemed to be key factors for the altered substrate specificity. Our work may shed light on understanding the unique substrate selectivity mechanism of mono- and di-acylglycerols lipases, and provide a new insight for engineering biocatalysts with desired catalytic behaviors for biotechnological application. [ABSTRACT FROM AUTHOR]

The dengue virus NS2B-NS3 protease (NS2B-NS3p), an important antiviral target for drug development, has been reported to adopt an open or closed conformation in crystal structures with different NS2B C-terminus (NS2Bc) positioning. In solution, nevertheless, NS2B-NS3p forms a mixture of open, closed and maybe other intermediate conformations, which is difficult to characterize using conventional biophysical and biochemical techniques. In this study, we developed a new strategy to analyze these conformational changes using 19 F NMR spectroscopy. Low pH or bovine pancreatic trypsin inhibitor (BPTI) binding promote the conformation change from open to closed, showing the importance of charge forces in the interaction between NS2Bc and NS3p. The mutation H51A impairs the charge interaction and the pH dependence of the conformational changes. It stabilizes the open conformation, while the addition of BPTI still converts NS2B-NS3p from open to closed conformation. [ABSTRACT FROM AUTHOR]

Abstract: A novel gene designated as fragile site-associated (FSA) gene was recently identified by positional cloning from the CHO 1q31 fragile site which plays an important role in regulating amplification of multidrug resistance (mdr1) gene in multidrug-resistant cells. FSA produces a message of ∼16kb which encodes an open-reading frame of 5005 amino acids. FSA shares sequence similarity with that in Caenorhabditis elegans lpd-3, a lipid storage gene. Using immunohistochemical staining and RNA in situ hybridization we report here that expression of FSA is associated with developmental programs of spermatogenesis and mammary gland in mice. Real-time RT-PCR results also support the upregulation of FSA expression in mammary gland development. Expression of FSA in many tissues including colon, skin, ovary, prostate, and bladder is mainly in the postmitotic, well-differentiated compartments. Moreover, levels of FSA expression are downregulated in tumors of these tissue origins. These results suggest that FSA also plays important roles in regulating mammalian epithelial growth and differentiation and tumor development. [Copyright &y& Elsevier]