Peptidase M14-like domain of carboxypeptidase (CP) T (CPT), CPT belongs to the M14 family of metallocarboxypeptidases (MCPs). The M14 family are zinc-binding CPs which hydrolyze single, C-terminal amino acids from polypeptide chains, and have a recognition site for the free C-terminal carboxyl group, which is a key determinant of specificity. CPT has moderate similarity to CPA and CPB, and exhibits dual-substrate specificity by cleaving C-terminal hydrophobic amino acid residues like CPA and C-terminal positively charged residues like CPB. CPA and CPB are M14 family peptidases but do not belong to this CPT group. The substrate specificity difference between CPT and CPA and CPB is ascribed to a few amino acid substitutions at the substrate-binding pocket while the spatial organization of the binding site remains the same as in all Zn-CPs. CPT has increased thermal stability in presence of Ca2+ ions, and two disulfide bridges which give an additional stabilization factor.
Comment:Metallocarboxypeptidases share the zinc binding motif HXXE...H, where the zinc ion is penta-coordinated to ND1 atoms of the histidines, OE1 and OE2 atoms of the glutamic acid, and to a water molecule in a slightly distorted tetrahedral manner.
Structure:1OBR: Thermoactinomyces vulgaris Carboxypeptidase T; contacts at 3.5A
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