title: Crystal structure of carboxypeptidase A complexed with an inactivator in two crystal forms.
abstract: Two different crystal forms of carboxypeptidase A (CPA) complexed with an inactivator were obtained by the method of hanging drop vapor diffusion. The inactivator, 2-benzyl-3-iodo-propanoic acid (BIPA), binds covalently to an active site residue Glu270 of CPA. The complexes were crystallized in the space group P2(1) (CPA-I) and P2(1)2(1)2(1) (CPA-II), respectively. The structures of both crystal forms were determined by molecular replacement using the native CPA crystal structure as the search model. The final crystallographic residuals are 0.163 for CPA-I and 0.152 for CPA-II. Except for the modification of Glu270, the inactivator exhibits normal binding mode compared with other ligand complexes of CPA. In the final electron density difference maps (2Fo-Fc, Fo-Fc), the density of the iodo ion could not be found in both crystal forms while the conserved water molecule remains coordinated to Zn2+ as in the native CPA. Comparisons of the complexes of CPA-BIPA with the native CPA and the CPA-D-Phe complex are presented. The mechanism of the inactivation of CPA and its implication for catalytic mechanism were discussed.
authors.affiliation: Institute of Biophysics, Chinese Academy of Sciences, Beijing.
authors.forename: J J
authors.initials: JJ
authors.lastname: Chai
authors.forename: C
authors.initials: C
authors.lastname: He
authors.forename: M
authors.initials: M
authors.lastname: Li
authors.forename: L
authors.initials: L
authors.lastname: Tang
authors.forename: M
authors.initials: M
authors.lastname: Luo
mesh_terms: D000818:Animals; D001555:Benzene Derivatives; D001665:Binding Sites; D002268:Carboxypeptidases / Q000037:antagonists & inhibitors / Q000737:chemistry* / Q000378:metabolism; D043422:Carboxypeptidases A; D002417:Cattle; D003460:Crystallization; D018360:Crystallography, X-Ray; D004583:Electrons; D018698:Glutamic Acid / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D008024:Ligands; D008956:Models, Chemical; D010179:Pancreas; D011422:Propionates / Q000378:metabolism*; D011487:Protein Conformation; D013696:Temperature; D014867:Water / Q000378:metabolism; D015032:Zinc / Q000378:metabolism
chemical_list: C117375:2-benzyl-3-iodo-propanoic acid; D001555:Benzene Derivatives; D008024:Ligands; D011422:Propionates; D014867:Water; D018698:Glutamic Acid; D002268:Carboxypeptidases; D043422:Carboxypeptidases A; D015032:Zinc