The three-dimensional structure of human procarboxypeptidase A2. Deciphering the basis of the inhibition, activation and intrinsic activity of the zymogen.
The three-dimensional structure of human procarboxypeptidase A2 has been determined using X-ray crystallography at 1.8 A resolution. This is the first detailed structural report of a human pancreatic carboxypeptidase and of its zymogen. Human procarboxypeptidase A2 is formed by a pro-segment of 96 residues, which inhibits the enzyme, and a carboxypeptidase moiety of 305 residues. The pro-enzyme maintains the general fold when compared with other non-human counterparts. The globular part of the pro-segment docks into the enzyme moiety and shields the S2-S4 substrate binding sites, promoting inhibition. Interestingly, important differences are found in the pro-segment which allow the identification of the structural determinants of the diverse activation behaviours of procarboxypeptidases A1, B and A2, particularly of the latter. The benzylsuccinic inhibitor is able to diffuse into the active site of procarboxypeptidase A2 in the crystals. The structure of the zymogen-inhibitor complex has been solved at 2.2 A resolution. The inhibitor enters the active site through a channel formed at the interface between the pro-segment and the enzyme regions and interacts with important elements of the active site. The derived structural features explain the intrinsic activity of A1/A2 pro-enzymes for small substrates.
García-Sáez
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Departament de Biologia Molecular i Cel.lular, Centre d'Investigació i Desenvolupament-CSIC, Jordi Girona 18-26, 08034 Barcelona, Spain.
Reverter
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Vendrell
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Avilés
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FX
Coll
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D001665:Binding Sites; D002268:Carboxypeptidases / Q000037:antagonists & inhibitors / Q000737:chemistry*; D043422:Carboxypeptidases A; D018360:Crystallography, X-Ray; D004789:Enzyme Activation; D004792:Enzyme Precursors / Q000037:antagonists & inhibitors / Q000737:chemistry*; D006801:Humans; D008024:Ligands; D008958:Models, Molecular; D011487:Protein Conformation; D017510:Protein Folding; D013386:Succinates / Q000494:pharmacology
D004792:Enzyme Precursors; D008024:Ligands; D013386:Succinates; C000249:benzylsuccinic acid; D002268:Carboxypeptidases; D043422:Carboxypeptidases A