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Articles by Kaixian Chen
Total Records ( 2 ) for Kaixian Chen
  Shuai Chen , Tiancen Hu , Jian Zhang , Jing Chen , Kaixian Chen , Jianping Ding , Hualiang Jiang and Xu Shen
  SARS-CoV 3C-like protease (3CLpro) is an attractive target foranti-severe acute respiratory syndrome (SARS) drug discovery,and its dimerization has been extensively proved to be indispensablefor enzymatic activity. However, the reason why the dissociatedmonomer is inactive still remains unclear due to the absenceof the monomer structure. In this study, we showed that mutationof the dimer-interface residue Gly-11 to alanine entirely abolishedthe activity of SARS-CoV 3CLpro. Subsequently, we determinedthe crystal structure of this mutant and discovered a completecrystallographic dimer dissociation of SARS-CoV 3CLpro. Themutation might shorten the α-helix A` of domain I and cause amis-oriented N-terminal finger that could not correctly squeezeinto the pocket of another monomer during dimerization, thusdestabilizing the dimer structure. Several structural featuresessential for catalysis and substrate recognition are severelyimpaired in the G11A monomer. Moreover, domain III rotates dramaticallyagainst the chymotrypsin fold compared with the dimer, fromwhich we proposed a putative dimerization model for SARS-CoV3CLpro. As the first reported monomer structure for SARS-CoV3CLpro, the crystal structure of G11A mutant might provide insightinto the dimerization mechanism of the protease and supply directstructural evidence for the incompetence of the dissociatedmonomer.
  Liang Zhang , Weizhi Liu , Tiancen Hu , Li Du , Cheng Luo , Kaixian Chen , Xu Shen and Hualiang Jiang
  β-Hydroxyacyl-acyl carrier protein dehydratase (FabZ) is an important enzyme for the elongation cycles of both saturated and unsaturated fatty acids biosyntheses in the type II fatty acid biosynthesis system (FAS II) pathway. FabZ has been an essential target for the discovery of compounds effective against pathogenic microbes. In this work, to characterize the catalytic and inhibitory mechanisms of FabZ, the crystal structures of the FabZ of Helicobacter pylori (HpFabZ) and its complexes with two newly discovered inhibitors have been solved. Different from the structures of other bacterial FabZs, HpFabZ contains an extra short two-turn α-helix (α4) between α3 and β3, which plays an important role in shaping the substrate-binding tunnel. Residue Tyr-100 at the entrance of the tunnel adopts either an open or closed conformation in the crystal structure. The crystal structural characterization, the binding affinity determination, and the enzymatic activity assay of the HpFabZ mutant (Y100A) confirm the importance of Tyr-100 in catalytic activity and substrate binding. Residue Phe-83 at the exit tunnel was also refined in two alternative conformations, leading the tunnel to form an L-shape and U-shape. All these data thus contributed much to understanding the catalytic mechanism of HpFabZ. In addition, the co-crystal structures of HpFabZ with its inhibitors have suggested that the enzymatic activity of HpFabZ could be inhibited either by occupying the entrance of the tunnel or plugging the tunnel to prevent the substrate from accessing the active site. Our study has provided some insights into the catalytic and inhibitory mechanisms of FabZ, thus facilitating antibacterial agent development.
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