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Introduction: Resident mesenchymal stem cells (MSCs) in the tumor microenvironment play an important role in tumor progression. Up to now, the mechanism of resident MSCs promoting gastric cancer cell migration remains unclear. Methods: We tested the migration ability of gastric cancer cells by transwell assays in this study. The inflammatory factors secreted by MSCs were detected by Luminex and ELISA. The activation of NF-κB signaling was detected by western blot. The exosomes derived from MSCs were isolated and identified by transmission electron microscope, nano-sight and western blot. The expression of miR-374a-5p was confirmed by qRT-PCR and its downstream target HAPLN1 by luciferase reporter assay. The expression of adhesion molecules of gastric cancer cells was detected by flow cytometry. Results: MiR-374a-5p could regulate the expression of inflammatory factors by activating NF-κB signaling. The increase of MCP-1 and the decrease of IFN-γ promoted the migration of gastric cancer cells. The miR-374a-5p in MSCs could be encapsulated and delivered to gastric cancer cells by exosomes derived from MSCs. Exogenous miR-374a-5p up-regulated the expression of adhesion molecules in gastric cancer cells by targeting HAPLN1. And miR-374a-5p-enriched exosomes also promoted the migration of gastric cancer cells. Conclusion: MiR-374a-5p promoted gastric cancer metastasis, and resident MSCs in the gastric cancer microenvironment played a major role in the regulation of gastric cancer metastasis. The study will provide new ideas and potential targets for the prevention and treatment of gastric cancer metastasis.

Acid-sensing ion channels (ASICs) are proton-gated cation channels critical for neuronal functions. Studies of ASIC1, a major ASIC isoform and proton sensor, have identified acidic pocket, an extracellular region enriched in acidic residues, as a key participant in channel gating. While binding to this region by the venom peptide psalmotoxin modulates channel gating, molecular and structural mechanisms of ASIC gating modulation by small molecules are poorly understood. Here, combining functional, crystallographic, computational and mutational approaches, we show that two structurally distinct small molecules potently and allosterically inhibit channel activation and desensitization by binding at the acidic pocket and stabilizing the closed state of rat/chicken ASIC1. Our work identifies a previously unidentified binding site, elucidates a molecular mechanism of small molecule modulation of ASIC gating, and demonstrates directly the structural basis of such modulation, providing mechanistic and structural insight into ASIC gating, modulation and therapeutic targeting., Liu et al study the molecular and structural mechanism of the modulation of ASIC1 channel gating using functional, crystallographic, computational and mutational approaches. They identify small molecules that allosterically stabilize the closed state by binding at the acidic pocket of the channel.

A meta-analysis was performed to evaluate the prognostic impact of diabetes on the clinical outcome for patients with pancreatic cancer following the adjuvant chemotherapy. To identify all researches and studies relevant to the prognostic impact of diabetes on the clinical outcome for patients with pancreatic cancer following the adjuvant chemotherapy, a comprehensive literature search was performed until January 30, 2018, by searching PubMed, EMBASE, and the Cochrane Library. The relevant data were extracted from included studies by two reviewers independently. HR and its 95% confidence interval (CI) were synthesized using STATA 12.0 software. All of six studies consisting of 4241 pancreatic cancer patients (1034 patients with DM and 3207 patients without DM) were eligible and included in this meta-analysis. The result of meta-analysis under a fixed model showed that there are significant differences in overall survival (HR 1.16, 95% CI 1.08–1.25, P = 0.000) and T stage (OR 1.30, 95% CI 1.08–2.17, P = 0.005) between PC patients with DM following chemotherapy and PC patients without DM following chemotherapy. There was no significant difference in gender (OR 1.23, 95% CI 1.00–1.50, P = 0.051), tumor locations (OR 1.13, 95% CI 0.81–1.56, P = 0.476), cancer extent (OR 0.85, 95% CI 0.48–1.50, P = 0.569), N stage (OR 1.01, 95% CI 0.58–1.74, P = 0.973), and M stage (OR 0.64, 95% CI 0.21–1.99, P = 0.441) between diabetic PC patients and non-diabetic patients. Diabetes mellitus patients who undergo chemotherapy for pancreatic cancer present with a reduced survival and lager tumor. Pancreatic cancer patients with DM also have a higher risk of death after chemotherapy.

Objective. To evaluate the prognostic value of lncRNA PVT1 for patients with gastric cancer. Methods. A comprehensive literature searching was performed in PubMed, Cochrane Library, Web of Science, Embase, CNKI, CBM, and Wanfang Database to identify published studies on the expression level of lncRNA PVT1 in human gastric cancer. STATA 12.0 was conducted to perform the meta-analysis. Clinical outcomes including patients’ age, genders, TNM stage, OS, and DFS were assessed in the study. Results. A total of 8 studies involving 747 patients were included in this meta-analysis. The results of meta-analysis showed that higher expression level of lncRNA PVT1 was associated with GC patients’ gender (for male: OR = 2.27 , 95% CI: 1.67~3.07, P = 0.000 ), invasion depth (for T3~4: OR = 3.98 , 95% CI: 2.85~5.56, P = 0.000 ), poorer OS ( HR = 1.68 , 95% CI: 1.43~1.97, P = 0.000 ), and DFS ( HR = 1.74 , 95% CI: 1.44~2.08, P = 0.000 ). Conclusion. Higher expression level of lncRNA PVT1 is significantly associated with GC patients’ gender, invasion depth, poorer OS, and worse DFS. lncRNA PVT1 might act as a novel predictive biomarker of poor prognosis and clinicopathological characteristics for gastric cancer.

Claudin 18.2 (CLDN 18.2) is a major component of the tight junctions and is highly expressed in several cancers including gastric (80%), esophageal (80%), pancreatic (60%) and lung cancers, but only expressed at very low levels in healthy tissues. The chimeric IgG1 CLDN 18.2 antibody zolbetuximab significantly improved PFS and OS in gastric cancer patients in a CLDN 18.2-dependent manner on the background of EOX. This research aimed to produce humanized anti-claudin18.2 antibodies with enhanced activities and improved pharmaceutical characteristics compared to known CLDN 18.2 antibodies. We used several immunization methods to produce mouse anti-CLDN18.2 antibodies with high affinity and excellent selectivity against CLDN 18.1. Humanization of a selected clone led to a humanized anti-CLDN18.2 antibody (h533o) with significantly improved binding affinity and cellular activity in ADCC and CDC assays compared to zolbetuximab. The binding affinity of h533o was relatively insensitive to elevated temperatures or acidity, suggesting the robustness of target engaging ability in tumor microenvironment. Maturation and selection by the off-rate approach, using phage libraries that systematically modified the CDR regions, identified multiple antibodies with comparable affinity and selectivity. Mutational scan of the Fc region in h533o identified SPX-101 with reduced ADA effect in mice while retaining other favorable properties. SPX-101 suppressed tumor growth in several xenograft mouse models including NUGC4 and HEK293 cells that stably expressed CLDN18.2. In summary, SPX-101 represents a humanized anti-CLDN18.2 antibody with high affinity and specificity, high effector cell-mediated cytotoxicity, low immunogenicity, and in vivo tumor control efficacy in xenograft rodent models. Citation Format: Guidong Zhu, Jichun Ma, Jingdong Ye, Jingdong Qin, Yi Cai. Discovery and preclinical characterizations of a humanized anti-claudin 18.2 antibody SPX-101 [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 3361.

This research aimed to produce anti-claudin18.2 (CLDN 18.2)/anti-PD-L1 bispecific antibodies to enhance the therapeutic index and expand the responsive population of the parent anti-CLDN 18.2 and anti-PD-L1 antibodies through the mechanisms of tumor-specific distribution and synergistic tumor killing. CLDN 18.2 is highly expressed in several tumors but is minimally expressed in normal tissues and a chimeric IgG1 CLDN 18.2 antibody zolbetuximab significantly improved PFS and OS in gastric cancer patients in a CLDN 18.2-dependent manner on the background of EOX. However, the response rate was moderate (~10%), leaving room for further improvement. Anti-PD-L1 antibodies showed remarkable efficacy in lung cancer and melanoma but in various settings of gastric cancer they showed weaker benefits, which warrant optimization. We designed anti-claudin18.2/anti-PD-L1 bispecific antibodies in the SMARTOPTM format, where a single-chain diabody containing optimized CLDN 18.2 and PD-L1 binding variable domains is connected to the Fc domain by linkers that can be optimized by phage display libraries. The bispecific antibodies were selected by affinity at low pH values and slow off-rate to improve the therapeutic window by enhancing tumor retention and preserving or improving binding affinity in the low pH tumor microenvironment. Immunogenicity was optimized by mutating the surface residues and disulfide bonds were inserted to improve stability. A representative bispecific antibody SPX-301 showed comparable binding affinity to the CLDN 18.2 and PD-L1 antigens to the parent antibodies (SPX-101 and durvalumab, respectively). SPX-301 represents a novel anti-claudin18.2/anti-PD-L1 bispecific antibody in the SMARTOPTM format. The format demonstrated excellence retention of antigen binding affinity, high expression levels, minimal aggregation, and straightforward purification. The preclinical characterizations of SPX-301 will also be presented. Citation Format: Guidong Zhu, Jingdong Ye, Jichun Ma, Jingdong Qin, Yi Cai. Discovery of an anti-claudin18.2/anti-PD-L1 bispecific antibody SPX-301 in the SMARTOPTM format [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 534.

Background: Although several researches have investigated the association between development and metastasis of gastric cancer (GC) and the expression level of MT1JP, there are no consensuses about whether its expression is associated with overall survival (OS) and clinical feature for GC patients. Methods: The databases including PubMed, EMBase databases, and the Cochrane Library were searched from inception to January 30, 2016, to identify the eligible studies. The quality of included studies was assessed according to reporting recommendations for tumor marker prognostic studies (REMARK). The association between expression level of LncRNA HOTAIR with OS for GC patients was assessed by calculating the pooled hazard ratio (HR) and 95% confidence interval (95% CI) using STATA version 12.0. Heterogeneity among studies will be assessed using the I2 statistic. Results: Randomized controlled trials (RCTs), prospective cohort studies, and case–control studies will be used for the qualitative and quantitative synthesis of the meta-analysis to explore the association between MT1JP expression levels with OS for gastric cancer patients. Conclusion: We aim to draw an objective conclusion of the association between MT1JP expression levels with OS for gastric cancer patients.

Background: Pancreatic cancer (PC) is a devastating malignant tumor. Although surgical resection may offer a good prognosis and prolong survival, approximately 80% patients with PC are always diagnosed as unresectable tumor. National Comprehensive Cancer Network's (NCCN) recommended gemcitabine-based chemotherapy as efficient treatment. While, according to recent studies, targeted agents might be a better available option for advanced or metastatic pancreatic cancer patients. The aim of this systematic review and network meta-analysis will be to examine the differences of different targeted interventions for advanced/metastatic PC patients. Methods: We will conduct this systematic review and network meta-analysis using Bayesian method and according to Preferred Reporting Items for Systematic review and Meta-Analysis Protocols (PRISMA-P) statement. To identify relevant studies, 6 electronic databases including PubMed, EMBASE, the Cochrane Central Register of Controlled Trials (CENTRAL), Web of science, CNKI (Chinese National Knowledge Infrastructure), and CBM (Chinese Biological Medical Database) will be searched. The risk of bias in included randomized controlled trials (RCTs) will be assessed using the Cochrane Handbook version 5.1.0. And we will use GRADE approach to assess the quality of evidence from network meta-analysis. Data will be analyzed using R 3.4.1 software. Results and conclusion: To the best of our knowledge, this systematic review and network meta-analysis will firstly use both direct and indirect evidence to compare the differences of different targeted agents and targeted agents plus chemotherapy for advanced/metastatic pancreatic cancer patients. This is a protocol of systematic review and meta-analysis, so the ethical approval and patient consent are not required. We will disseminate the results of this review by submitting to a peer-reviewed journal.

Human mucin 1 (MUC1) is a target for immunotherapy. The major problem associated with MUC1‑based cancer vaccines is the weakness of the immunogenicity of MUC1. The present study aimed to develop an efficient cancer vaccine through generating a recombinant fusion protein consisting of MUC1 and maltose‑binding protein (MBP) by inserting seven tandem repeats encoding the human MUC1 gene into the pMAL‑c2 expression vector. Bacillus Calmette‑Guerin (BCG) was used as an adjuvant. MUC1 was found to predominantly induce T helper type 2 (Th2) cell responses. MUC1/BCG and MUC1‑MBP were found to generate T helper (Th) type 1 and 2 responses, while MUC1‑MBP/BCG induced a Th1 immune profile and stimulated MUC1‑specific cytotoxic T lymphocyte killing activity. MUC1‑MBP, as well as MBP and BCG alone were found to induce natural killer (NK) cell activity, with MUC1‑MBP/BCG observed to synergistically induce NK cell activity. Furthermore, MUC1‑MBP/BCG significantly inhibited MUC1+ B16 cell growth in mice. These findings show that MBP augments the immunogenicity of MUC1 and that BCG enhances the efficacy of the MUC1‑MBP vaccine. Thus, MUC1‑MBP/BCG may have potential as a cancer vaccine for clinical application.

Mesothelin is a tumor differentiation antigen that is highly expressed in many epithelial cancers, with limited expression in normal human tissues. Binding of mesothelin on normal mesothelial cells lining the pleura or peritoneum to the tumor-associated cancer antigen 125 (CA-125) can lead to heterotypic cell adhesion and tumor metastasis within the pleural and peritoneal cavities. This binding can be prevented by MORAb-009, a humanized monoclonal antibody against mesothelin currently under clinical trials. We show here that MORAb-009 recognizes a non-linear epitope that is contained in the first 64-residue fragment of the mesothelin. We further demonstrate that the recognition is independent of glycosylation state of the protein but sensitive to the loss of a disulfide bond linking residues Cys-7 and Cys-31. The crystal structure of the complex between the mesothelin N-terminal fragment and Fab of MORAb-009 at 2.6 Å resolution reveals an epitope encompassing multiple secondary structural elements of the mesothelin, including residues from helix α1, the loops linking helices α1 and α2, and between helices α4 and α5. The mesothelin fragment has a compact, right-handed superhelix structure consisting of five short helices and connecting loops. A residue essential for complex formation has been identified as Phe-22, which projects its side chain into a hydrophobic niche formed on the antibody recognition surface upon antigen-antibody contact. The overlapping binding footprints of both the monoclonal antibody and the cancer antigen CA-125 explains the therapeutic effect and provides a basis for further antibody improvement.

Crystallization has long been one of the bottlenecks in obtaining structural information at atomic resolution for membrane proteins. This is largely due to difficulties in obtaining high-quality protein samples. One frequently used indicator of protein quality for successful crystallization is the monodispersity of proteins in solution, which is conventionally obtained by size exclusion chromatography (SEC) or by dynamic light scattering (DLS). Although useful in evaluating the quality of soluble proteins, these methods are not always applicable to membrane proteins either because of the interference from detergent micelles or because of the requirement for large sample quantities. Here, the use of blue native polyacrylamide gel electrophoresis (BN–PAGE) to assess aggregation states of membrane protein samples is reported. A strong correlation is demonstrated between the monodispersity measured by BN–PAGE and the propensity for crystallization of a number of soluble and membrane protein complexes. Moreover, it is shown that there is a direct correspondence between the oligomeric states of proteins as measured by BN–PAGE and those obtained from their crystalline forms. When applied to a membrane protein with unknown structure, BN–PAGE was found to be useful and efficient for selecting well behaved proteins from various constructs and in screening detergents. Comparisons of BN–PAGE with DLS and SEC are provided.

The mitochondrial outer membrane-anchored monoamine oxidase (MAO) is a biochemically important flavoenzyme that catalyzes the deamination of biogenic and xenobiotic amines. Its two subtypes, MAOA and MAOB, are linked to several psychiatric disorders and therefore are interesting targets for drug design. To understand the relationship between structure and function of this enzyme, we extended our previous low-resolution rat MAOA structure to the high-resolution wild-type and G110A mutant human MAOA structures at 2.2 and 2.17 Å, respectively. The high-resolution MAOA structures are similar to those of rat MAOA and human MAOB, but different from the known structure of human MAOA [De Colibus L, et al. (2005) Proc Natl Acad Sci USA 102:12684–12689], specifically regarding residues 108–118 and 210–216, which surround the substrate/inhibitor cavity. The results confirm that the inhibitor selectivity of MAOA and MAOB is caused by the structural differences arising from Ile-335 in MAOA vs. Tyr-326 in MAOB. The structures exhibit a C-terminal transmembrane helix with clear electron density, as is also seen in rat MAOA. Mutations on one residue of loop 108–118, G110, which is far from the active center but close to the membrane surface, cause the solubilized enzyme to undergo a dramatic drop in activity, but have less effect when the enzyme is anchored in the membrane. These results suggest that the flexibility of loop 108–118, facilitated by anchoring the enzyme into the membrane, is essential for controlling substrate access to the active site. We report on the observation of the structure–function relationship between a transmembrane helical anchor and an extra-membrane domain.

The three-dimensional structure of the bifunctional tryptophan synthase alpha(2)beta(2) complex from Pyrococcus furiosus was determined by crystallographic analysis. This crystal structure, with the structures of an alpha subunit monomer and a beta(2) subunit dimer that have already been reported, is the first structural set in which changes in structure that occur upon the association of the individual tryptophan synthase subunits were observed. To elucidate the structural basis of the stimulation of the enzymatic activity of each of the alpha and beta(2) subunits upon alpha(2)beta(2) complex formation, the conformational changes due to complex formation were analyzed in detail compared with the structures of the alpha monomer and beta(2) subunit dimer. The major conformational changes due to complex formation occurred in the region correlated with the catalytic function of the enzyme as follows. (1) Structural changes in the beta subunit were greater than those in the alpha subunit. (2) Large movements of A46 and L165 in the alpha subunit due to complex formation caused a more open conformation favoring the entry of the substrate at the alpha active site. (3) The major changes in the beta subunit were the broadening of a long tunnel through which the alpha subunit product (indole) is transferred to the beta active site and the opening of an entrance at the beta active site. (4) The changes in the conformations of both the alpha and beta subunits due to complex formation contributed to the stabilization of the subunit association, which is critical for the stimulation of the enzymatic activities.

The structure of the tryptophan synthase β2 subunit (Pfβ2) from the hyperthermophile, Pyrococcus furiosus, was determined by X-ray crystallographic analysis at 2.2 A resolution, and its stability was examined by DSC. This is the first report of the X-ray structure of the tryptophan synthase β2 subunit alone, although the structure of the tryptophan synthase α2β2 complex from Salmonella typhimurium has already been reported. The structure of Pfβ2 was essentially similar to that of the β2 subunit (Stβ2) in the α2β2 complex from S. typhimurium. The sequence alignment with secondary structures of Pfβ and Stβ in monomeric form showed that six residues in the N-terminal region and three residues in the C-terminal region were deleted in Pfβ, and one residue at Pro366 of Stβ and at Ile63 of Pfβ was inserted. The denaturation temperature of Pfβ2 was higher by 35 °C than the reported values from mesophiles at ≈ pH 8. On the basis of structural information on both proteins, the analyses of the contributions of each stabilization factor indicate that: (a) the higher stability of Pfβ2 is not caused by either a hydrophobic interaction or an increase in ion pairs; (b) the number of hydrogen bonds involved in the main chains of Pfβ is greater by about 10% than that of Stβ, indicating that the secondary structures of Pfβ are more stabilized than those of Stβ and (c) the sequence of Pfβ seems to be better fitted to an ideally stable structure than that of Stβ, as assessed from X-ray structure data.

Monoamine oxidase is a flavin-containing enzyme located at the mitochondrial outer membrane that catalyzes the oxidative deamination of amines. To investigate the role of tyrosine residues near the FAD-binding site, Cys-406, of monoamine oxidase A, the tyrosine residues at posiyions 402, 407, and 410 were indurdually replaced with alanine or phenylalanine and the effects of the mutations on catalytic activity, FAD binding, and enzyme structure were examined. Half or fewer of the mutant proteins incorporated FAD. The mutation of Tyr-407 to alanine led to an almost completely loss of catalytic activity for serotonin, PEA, tyramine, and tryptamine. A substantial decrease in the catalytic activity was also observed with the enzymes mutated at Tyr-402 and Tyr-410 to alanine, although the effect of the latter mutation was much less. All these mutants were sensitive to trypsin treatment of the purified enzyme, while the wild type enzyme was resistant to treatment. On the other hand, substitution of Tyr-402 or Tyr-407 with phenylalanine had little effect on these properties. Taken together, we conclude that tyrosine residues near Cys-406 may be form a pocket to facilitates FAD incorporation, the catalytic center, and a stable conformation, probably through interactions among the aromatic rings of the tyrosine residues and FAD.

To detect high density lipoprotein binding proteins, a new ligand blotting method that uses apolipoprotein AI-dinitrophenol as a ligand was established. Apolipoprotein AI-dinitrophenol was prepared by incubating the mixture of apolipoprotein AI and 2,4-dinitrobenzene sulfonic acid sodium salt at pH 8.5. Four to six dinitrophenol groups were found to be conjugated w,ith an apolipoprotein AI molecule without any obvious impairment of its binding activity to the binding proteins. By this detection procedure, we detected two apolipoprotein AI binding proteins in plasma membrane fractions from bovine liver and adrenal cortex with molecular masses of 120 kDa and 95 kDa. Since this new ligand blotting method is simple and time-saving, it is expected to become a useful tool in the studies on high density lipoprotein binding proteins.

The mesothelin-specific monoclonal antibody MORAb-009 is capable of blocking the binding of mesothelin to CA-125 and displays promising anticancer potential. It is currently undergoing clinical trials. In order to understand the basis of the interaction between MORAb-009 and mesothelin at atomic resolution, both the Fab fragment of MORAb-009 and the complex between the Fab and an N-terminal fragment of mesothelin (residues 7-64) were crystallized. The crystals of the Fab diffracted X-rays to 1.75 Å resolution and had the symmetry of space group P4(1)2(1)2, with unit-cell parameters a = b = 140.6, c = 282.0 Å. The crystals of the mesothelin-Fab complex diffracted to 2.6 Å resolution and belonged to the hexagonal space group P6(4), with unit-cell parameters a = b = 146.2, c = 80.9 Å. Structural analyses of these molecules are in progress.

Mesothelin is a tumor differentiation antigen that is highly expressed in many epithelial cancers, with limited expression in normal human tissues. Binding of mesothelin on normal mesothelial cells lining the pleura or peritoneum to the tumor-associated cancer antigen 125 (CA-125) can lead to heterotypic cell adhesion and tumor metastasis within the pleural and peritoneal cavities. This binding can be prevented by MORAb-009, a humanized monoclonal antibody against mesothelin currently under clinical trials. We show here that MORAb-009 recognizes a non-linear epitope that is contained in the first 64-residue fragment of the mesothelin. We further demonstrate that the recognition is independent of glycosylation state of the protein but sensitive to the loss of a disulfide bond linking residues Cys-7 and Cys-31. The crystal structure of the complex between the mesothelin N-terminal fragment and Fab of MORAb-009 at 2.6 Å resolution reveals an epitope encompassing multiple secondary structural elements of the mesothelin, including residues from helix α1, the loops linking helices α1 and α2, and between helices α4 and α5. The mesothelin fragment has a compact, right-handed superhelix structure consisting of five short helices and connecting loops. A residue essential for complex formation has been identified as Phe-22, which projects its side chain into a hydrophobic niche formed on the antibody recognition surface upon antigen-antibody contact. The overlapping binding footprints of both the monoclonal antibody and the cancer antigen CA-125 explains the therapeutic effect and provides a basis for further antibody improvement.

Development of cisplatin resistance in cancer cells appears to be a consequence of multiple epigenetic alterations in genes involved in DNA damage repair, proto-oncogenes, apoptosis, transporters, transcription factors, etc. In this study, we found that expression of the hypothetical transmembrane protein TMEM205 (previously known as MBC3205) is associated with cisplatin resistance. TMEM205 was first detected by functional cloning from a retroviral cDNA library made from human cisplatin-resistant (CP-r) cells. TMEM205 is predicted to be a transmembrane protein, but its expression, localization, and function have not previously been investigated. A polyclonal antibody directed to the TMEM205 protein was raised in our laboratory. Using this antibody, it was demonstrated that this protein is located at the cell surface. Its expression is increased in our cisplatin-selected CP-r cell lines, as demonstrated by immunoblotting, confocal examination, and immuno-electron microscopy. Stable transfection of the TMEM205 gene confers resistance to cisplatin by approximately 2.5-fold. Uptake assays with Alexa Fluor-cisplatin showed reduced accumulation in CP-r KB-CP.3 and KB-CP.5 cells, and in TMEM205-transfected cells. Analysis of TMEM205 expression profiles in normal human tissues indicates a differential expression pattern with higher expression levels in the liver, pancreas, and adrenal glands. These results indicate that a novel mechanism for cisplatin resistance is mediated by TMEM205, and also suggest that overexpression of TMEM205 in CP-r cells may be valuable as a biomarker or target in cancer chemotherapy.

Pleotropic drug resistant protein 5 (Pdr5p) is a plasma membrane ATP-binding cassette (ABC) transporter and the major drug efflux pump in Saccharomyces cerevisiae. The Pdr5p family of fungal transporters possesses a number of structural features significantly different from other modeled or crystallized ABC transporters, which include a reverse topology, an atypical ATP-binding site, a very low sequence similarity in the transmembrane section and long linkers between domains. These features present a considerable hurdle in molecular modeling studies of these important transporters. Here, we report the creation of an atomic model of Pdr5p based on a combination of homology modeling and ab initio methods, incorporating information from consensus transmembrane segment prediction, residue lipophilicity, and sequence entropy. Reported mutations in the transmembrane substrate-binding pocket that altered drug-resistance were used to validate the model, and one mutation that changed the communication pattern between transmembrane and nucleotide-binding domains was used in model improvement. The predictive power of the model was demonstrated experimentally by the increased sensitivity of yeast mutants to clotrimazole having alanine substitutions for Thr1213 and Gln1253, which are predicted to be in the substrate-binding pocket, without reducing the amount of Pdr5p in the plasma membrane. The quality and reliability of our model are discussed in the context of various approaches used for modeling different parts of the structure.

The structure of the tryptophan synthase beta2 subunit (Pfbeta2) from the hyperthermophile, Pyrococcus furiosus, was determined by X-ray crystallographic analysis at 2.2 A resolution, and its stability was examined by DSC. This is the first report of the X-ray structure of the tryptophan synthase beta2 subunit alone, although the structure of the tryptophan synthase alpha2beta2 complex from Salmonella typhimurium has already been reported. The structure of Pfbeta2 was essentially similar to that of the beta2 subunit (Stbeta2) in the alpha2beta2 complex from S. typhimurium. The sequence alignment with secondary structures of Pfbeta and Stbeta in monomeric form showed that six residues in the N-terminal region and three residues in the C-terminal region were deleted in Pfbeta, and one residue at Pro366 of Stbeta and at Ile63 of Pfbeta was inserted. The denaturation temperature of Pfbeta2 was higher by 35 degrees C than the reported values from mesophiles at approximately pH 8. On the basis of structural information on both proteins, the analyses of the contributions of each stabilization factor indicate that: (a) the higher stability of Pfbeta2 is not caused by either a hydrophobic interaction or an increase in ion pairs; (b) the number of hydrogen bonds involved in the main chains of Pfbeta is greater by about 10% than that of Stbeta, indicating that the secondary structures of Pfbeta are more stabilized than those of Stbeta and (c) the sequence of Pfbeta seems to be better fitted to an ideally stable structure than that of Stbeta, as assessed from X-ray structure data.

Monoamine oxidase (MAO), a mitochondrial outer membrane enzyme, catalyzes the degradation of neurotransmitters in the central nervous system and is the target for anti-depression drug design. Two subtypes of MAO, MAOA and MAOB, are similar in primary sequences but have unique substrate and inhibitor specificities. The structures of human MAOB complexed with various inhibitors were reported early. To understand the mechanisms of specific substrate and inhibitor recognitions of MAOA and MAOB, we have determined the crystal structure of rat MAOA complexed with the specific inhibitor, clorgyline, at 3.2A resolution. The comparison of the structures between MAOA and MAOB clearly explains the specificity of clorgyline for MAOA inhibition. The fitting of serotonin into the binding pockets of MAOs demonstrates that MAOB Tyr326 would block access of the 5-hydroxy group of serotonin into the enzyme. These results will lead to further understanding of the MAOA function and to new anti-depression drug design. This study also presents that MAOA has a transmembrane helix at the C-terminal region. This is the first crystal structure of membrane protein with an isolated transmembrane helix.

Monoamine oxidase (MAO) is an FAD-containing mitochondrial outer-membrane protein which catalyzes the degradation of several neurotransmitters in the central nervous system. The two subtypes of MAO, MAOA and MAOB, have similar primary sequences but different substrate and inhibitor specificities. The structure of human MAOB has recently been determined, but the structure of MAOA remains unknown. To clarify the mechanisms underlying their unique substrate and inhibitor recognition and thereby facilitate the development of new specific inhibitors to treat MAO-related neurological disorders, rat MAOA was crystallized in a complex with the specific inhibitor clorgyline. Diffraction data were collected to 3.2 A resolution. The crystal belongs to the space group P4(3)2(1)2, with unit-cell parameters a = b = 158.2, c = 258.4 A.