The structural basis for catalysis and specificity of the X-prolyl dipeptidyl aminopeptidase from Lactococcus lactis.

The X-prolyl dipeptidyl aminopeptidase (X-PDAP) from Lactococcus lactis is a dimeric enzyme catalyzing the removal of Xaa-Pro dipeptides from the N terminus of peptides. The structure of the enzyme was solved at 2.2 A resolution and provides a model for the peptidase family S15. Each monomer is composed of four domains. The larger one presents an alpha/beta hydrolase fold and comprises the active site serine. The specificity pocket is mainly built by residues from a small helical domain which is, together with the N-terminal domain, essential for dimerization. A C-terminal moiety probably plays a role in the tropism of X-PDAP toward the cellular membrane. These results give new insights for further exploration of the role of the enzymes of the SC clan.