7cpa
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(New page: 200px<br /><applet load="7cpa" size="450" color="white" frame="true" align="right" spinBox="true" caption="7cpa, resolution 2.0Å" /> '''COMPARISON OF THE STR...)
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COMPARISON OF THE STRUCTURES OF THREE CARBOXYPEPTIDASE A-PHOSPHONATE COMPLEXES DETERMINED BY X-RAY CRYSTALLOGRAPHY
Overview
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.
About this Structure
7CPA is a Single protein structure of sequence from Bos taurus with ZN and FVF as ligands. Active as Carboxypeptidase A, with EC number 3.4.17.1 Full crystallographic information is available from OCA.
Reference
Comparison of the structures of three carboxypeptidase A-phosphonate complexes determined by X-ray crystallography., Kim H, Lipscomb WN, Biochemistry. 1991 Aug 20;30(33):8171-80. PMID:1868092
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