User:John S. de Banzie/CarboxypeptidaseA

Carboxypeptidase A with Substrate

spinqualitylabelsall models Carboxypeptidase A with the dipeptide Gly-Tyr in the active site, 3cpa Show:Asymmetric Unit Biological Assembly Drag the structure with the mouse to rotate   Export Animated Image   Print3D Carboxypeptidase A catalyses the release of the C-terminal amino acid from a polypeptide chain. The initial image shows carboxypeptidase with a dipeptide (green) in the active site. Natural substrates would usually be longer. The enzyme has mixed secondary structure. A zinc ion (violet) is present. The ion is involved in binding and catalysis. Substrate binding involves three interactions between the substrate and the active site. 1. Between the carbonyl group of the penultimate residue in the substrate (in this case, Gly) and the zinc ion and an arginyl residue in the enzyme. 2. Between the C-terminal carboxyl group and asparaginyl, arginyl, and tyrosyl residues in the enzyme. 3. Between the C-terminal R group and a hydrophobic pocket in the enzyme. Catalysis involves electron withdrawal from the carbonyl of the penultimate residue (in this case, Gly) by the zinc ion and an arginyl residue, and acid-base catalysis by a glutamyl residue of a nucleophilic attack on that same group. (X-ray crystallography with intact substrate was possible because Gly-Tyr is hydrolyzed very slowly and because X-ray crystallography was carried out at -9°C.)

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John S. de Banzie