Human Dipeptidyl Peptidase III: the Role of Asn406 in Ligand Binding and Hydrolysis

Human dipeptidyl peptidase III (DPP III) is a member of the zinc-metallopeptidase family M49 with a role in intracellular protein catabolism. Ligand-free crystal structure of yeast and human orthologues provided insight into the enzyme's active center and enabled some assumptions about the enzyme - substrate interactions. The molecular modeling performed for human and yeast DPP III indicated involvement of Asn406 and Asn415, respectively in ligand binding. To investigate further the role of this asparagine residue, conserved in all eukaryotic M49 peptidases, a site-directed mutagenesis of human DPP III was carried out. Replacement of Asn406 with Gln, but not with Ser, resulted in a large decrease in the enzyme's binding affinity for competitive peptide inhibitor and in catalytic efficiency. Molecular dynamics simulations performed for enzyme-substrate complexes, revealed changed coordination of the active-site zinc ion and the orientation of the catalytically important His568, in N406Q, but not in the N406S complexes.(doi: 10.5562/cca1808)