Biomaterial Database

Comparison of the structures of three carboxypeptidase A-phosphonate complexes determined by X-ray crystallography. 1991

H Kim, and W N Lipscomb

Gibbs Chemical Laboratory, Harvard University, Cambridge, Massachusetts 02138.

The structures of the complexes of carboxypeptidase A (CPA) with two tight-binding phosphonate inhibitors have been determined by X-ray crystallography. The inhibitors, Cbz-Phe-ValP-(O)-Phe[ZFVP(O)F] and Cbz-Ala-GlyP-(O)-Phe[ZAGP(O)F], bind noncovalently to CPA with dissociation constants (Ki's) of 11 fM and 710 pM, respectively. The CPA-ZFVP(O)F complex crystallizes in the space group P2(1)2(1)2(1) with unit cell parameters a = 65.3 A, b = 63.4 A, and c = 76.0 A, and the CPA-ZAGP(O)F complex crystallizes in the space group P2(1)2(1)2(1) with unit cell parameters a = 63.4 A, b = 65.9 A, and c = 74.4 A. Both structures were determined by molecular replacement to a resolution of 2.0 A. The final crystallographic residuals are 0.189 for the CPA-ZFVP(O)F complex and 0.191 for the CPA-ZAGP(O)F complex. The CPA-ZFVP(O)F complex exhibits the lowest Ki yet determined for an enzyme-inhibitor interaction. Comparison of the CPA-ZFVP(O)F structure with that of the CPA-ZAAP(O)F complex [Kim, H., & Lipscomb, W.N. (1990) Biochemistry 29, 5546-5555] indicates the likely important contributions of hydrophobic and weakly polar enzyme-inhibitor interactions to the exceptional stability of the CPA-ZFVP(O)F complex. Among these interactions is a network of four aromatic rings of CPA and ZFVP(O)F in a configuration that allows stabilizing aromatic-aromatic edge-to-face interactions from one ring to the next. A comparison of the structures of the CPA-ZFVP(O)F, CPA-ZAAP(O)F and CPA-ZAGP(O)F complexes shows that all three phosphonates assume a similar binding mode in the active-site binding groove of CPA. For ZAGP(O)F, the glycyl P1 residue does not lead to an anomalous or a partially disordered binding mode as seen in some previous complexes of CPA involving dipeptide analogue inhibitors with glycyl P1 residues. The additional enzyme-inhibitor interactions for these tripeptide phosphonates secure a binding mode in which a Pi portion of the inhibitor is clearly bound by the corresponding Si binding subsite. These three phosphonates have been implicated as transition-state analogues of the CPA-catalyzed reaction. The phosphinyl groups of these phosphonates coordinate to the active-site zinc in a manner that has been proposed as a characteristic feature of the general-base (Zn-hydroxyl or Zn-water) mechanism for the CPA-catalyzed reaction. Further mechanistic proposals are made for Arg-127, whose probable role in binding substrates is apparent in these CPA-phosphonate complexes.

UI	MeSH Term	Description	Entries
D007700	Kinetics	The rate dynamics in chemical or physical systems.
D008958	Models, Molecular	Models used experimentally or theoretically to study molecular shape, electronic properties, or interactions; includes analogous molecules, computer-generated graphics, and mechanical structures.	Molecular Models,Model, Molecular,Molecular Model
D008969	Molecular Sequence Data	Descriptions of specific amino acid, carbohydrate, or nucleotide sequences which have appeared in the published literature and/or are deposited in and maintained by databanks such as GENBANK, European Molecular Biology Laboratory (EMBL), National Biomedical Research Foundation (NBRF), or other sequence repositories.	Sequence Data, Molecular,Molecular Sequencing Data,Data, Molecular Sequence,Data, Molecular Sequencing,Sequencing Data, Molecular
D011487	Protein Conformation	The characteristic 3-dimensional shape of a protein, including the secondary, supersecondary (motifs), tertiary (domains) and quaternary structure of the peptide chain. PROTEIN STRUCTURE, QUATERNARY describes the conformation assumed by multimeric proteins (aggregates of more than one polypeptide chain).	Conformation, Protein,Conformations, Protein,Protein Conformations
D002268	Carboxypeptidases	Enzymes that act at a free C-terminus of a polypeptide to liberate a single amino acid residue.	Carboxypeptidase
D002384	Catalysis	The facilitation of a chemical reaction by material (catalyst) that is not consumed by the reaction.	Catalyses
D000595	Amino Acid Sequence	The order of amino acids as they occur in a polypeptide chain. This is referred to as the primary structure of proteins. It is of fundamental importance in determining PROTEIN CONFORMATION.	Protein Structure, Primary,Amino Acid Sequences,Sequence, Amino Acid,Sequences, Amino Acid,Primary Protein Structure,Primary Protein Structures,Protein Structures, Primary,Structure, Primary Protein,Structures, Primary Protein
D001665	Binding Sites	The parts of a macromolecule that directly participate in its specific combination with another molecule.	Combining Site,Binding Site,Combining Sites,Site, Binding,Site, Combining,Sites, Binding,Sites, Combining
D013237	Stereoisomerism	The phenomenon whereby compounds whose molecules have the same number and kind of atoms and the same atomic arrangement, but differ in their spatial relationships. (From McGraw-Hill Dictionary of Scientific and Technical Terms, 5th ed)	Molecular Stereochemistry,Stereoisomers,Stereochemistry, Molecular,Stereoisomer
D013379	Substrate Specificity	A characteristic feature of enzyme activity in relation to the kind of substrate on which the enzyme or catalytic molecule reacts.	Specificities, Substrate,Specificity, Substrate,Substrate Specificities