Enzymatic properties of dipeptidyl aminopeptidase IV produced by the periodontal pathogen Porphyromonas gingivalis and its participation in virulence

Porphyromonas gingivalis is a major pathogen associated with adult periodon titis. We cloned and sequenced the gene (npp) coding for dipeptidyl aminope ptidase TV (DPPIV) from P. gingivalis W83, based on the amino acid sequence s of peptide fragments derived from purified DPPIV. An Escherichia coli str ain overproducing P. gingivalis DPPIV was constructed. The enzymatic proper ties of recombinant DPPIV purified from the overproducer were similar to th ose of DPPIV isolated from P. gingivalis. The three amino acid residues Ser , Asp, and His, which are thought to form a catalytic triad in the C-termin al catalytic domain of eukaryotic DPPIV, are conserved in P. gingivalis DPP IV. When each of the corresponding residues of the enzyme was substituted w ith Ala by site-directed mutagenesis, DPPIV activity significantly decrease d, suggesting that these three residues of P. gingivalis DPPIV are involved in the catalytic reaction. DPPIV-deficient mutants of P. gingivalis were c onstructed and subjected to animal experiments. Mice injected with the wild -type strain developed abscesses to a greater extent and died more frequent ly than those challenged with mutant strains. Mice injected with the mutant s exhibited faster recovery from the infection, as assessed by weight gain and the rate of lesion healing. This decreased virulence of mutants compare d with the parent strain suggests that DPPIV is a potential virulence facto r of P. gingivalis and may play important roles in the pathogenesis of adul t periodontitis induced by the organism.