Identification and Characterization of Prokaryotic Dipeptidyl-Peptidase 5 from Porphyromonas gingivalis

Porphyromonas gingivalis, a Gram-negative asaccharolytic anaerobe, is one of the major causative organisms of chronic periodontitis. The bacterium utilizes amino acids as energy and carbon sources, and incorporates them mainly as dipeptides. Therefore, a wide variety of dipeptide production processes mediated by dipeptidyl-peptidases (DPPs) should be beneficial for the organism. In the present study, we identified the fourth P. gingivalis enzyme, DPP5. A DPP7-like activity still remained in a dpp4-7-11 disrupted P. gingivalis ATCC 33277. PGN_0756, currently annotated as a prolyl oligopeptidase, possessed an activity indistinguishable from that of the triple dpp gene-disrupted strain, and was identified as a bacterial orthologue of fungal DPP5, because of its substrate specificity and 28.5% amino acid sequence identity with an Aspergillus fumigatus entity. P. gingivalis DPP5 was composed of 684 amino acids with an apparent molecular weight of 66 kDa, while it preferred Ala and hydrophobic residues, had no activity toward Pro at the P1 position, and no preference for hydrophobic P2 residues, showed an optimal pH of 6.7 in the presence of NaCl, demonstrated kcat/Km values for Gly-Phe-MCA and Lys-Ala-MCA of 13.01 and 11.02 μM-1 s-1, respectively, and was localized in the periplasm. DPP5 elaborately complemented DPP7 in liberation of dipeptides with hydrophobic P1 residues. Examinations of dpp- and gingipain gene-disrupted mutants indicated that DPP4, DPP5, DPP7, and DPP11 together with Arg- and Lys-gingipains cooperatively liberate most dipeptides from nutrient oligopeptides. This is the first study to report that DPP5 is expressed not only in eukaryotes, but also distributed in prokaryotes