Metallopeptidase family M49 is characterized by five conserved sequence regions and the unique motif HEXXGH with two histidines - ligands of the active-site zinc ion. The crystal structure of the yeast ortholog represents a prototype for the whole family.
To investigate the role of two invariant amino acid residues, a Glu(461) of the zinc-binding motif, and a Tyr(327), 21 angstrom from the catalytic zinc center, mutational analysis of the yeast enzyme was performed.
The substitution of Glu(461) to glutamine decreased k(cat) for the substrate hydrolysis almost by 10 000-fold. The replacement of Tyr(327) by Phe or Ala reduced the catalytic efficiency (k(cat)/K-m) by two orders of magnitude. The affinity for the heptapeptide valorphin was siginificantly lowered in all mutants, indicating the contribution of both Glu(461) and Tyr(327) in substrate binding. Taken together, the effect of mutating Glu(461) is consistent with this residue being essential in M49 peptidase catalysis
