Purification, crystallization and preliminary X-ray analysis of an aminoacylhistidine dipeptidase (PepD) from Vibrio alginolyticus

The aminoacylhistidine dipeptidase (PepD) protein encoded by Vibrio algino­lyticus pepD was successfully overexpressed and characterized and the putative active-site residues responsible for metal binding and catalysis were identified. The purified enzyme contained two zinc ions per monomer. The recombinant dipeptidase enzyme, which was identified as a homodimer in solution, exhibited broad substrate specificity for Xaa-His dipeptides, with highest activity towards the His-His dipeptide. The purified protein was crystallized using the hanging-drop vapour-diffusion method. Preliminary crystallographic analysis showed that the crystal belonged to space group P6₁ or P6₅, with unit-cell parameters a = b = 80.42, c = 303.11 Å. The crystal contained two molecules per asymmetric unit and the predicted solvent content was 53.4%.