Asp- and Glu-specific novel dipeptidyl peptidase 11 of porphyromonas gingivalis ensures utilization of Proteinaceous energy sources

Abstract

Porphyromonas gingivalis and Porphyromonas endodontalis, asaccharolytic black-pigmented anaerobes, are predominant pathogens of human chronic and periapical periodontitis, respectively. They incorporate di- and tripeptides from the environment as carbon and energy sources. In the present study we cloned a novel dipeptidyl peptidase (DPP) gene of P. endodontalis ATCC 35406, designated as DPP11. The DPP11 gene encoded 717 amino acids with a molecular mass of 81,090 Da and was present as a 75-kDa form with an N terminus of Asp 22.A homology search revealed the presence of a P. gingivalis orthologue, PGN0607, that has been categorized as an isoform of authentic DPP7. P. gingivalis DPP11 was exclusively cell-associated as a truncated 60-kDa form, and the gene ablation retarded cell growth. DPP11 specifically removed dipeptides from oligopeptides with the penultimate N-terminal Asp and Glu and has a P2-position preference to hydrophobic residues. Optimum pH was 7.0, and the k cat/K m value was higher for Asp than Glu. Those activities were lost by substitution of Ser 652 in P. endodontalis and Ser 655 in P. gingivalis DPP11 to Ala, and they were consistently decreased with increasing NaCl concentration. Arg 670 is a unique amino acid completely conserved in all DPP11 members distributed in the genera Porphyromonas, Bacteroides, and Parabacteroides, whereas this residue is converted to Gly in all authentic DPP7 members. Substitution analysis suggested that Arg 670 interacts with an acidic residue of the substrate. Considered to preferentially utilize acidic amino acids, DPP11 ensures efficient degradation of oligopeptide substrates in these Gram-negative anaerobic rods. © 2011 by The American Society for Biochemistry and Molecular Biology, Inc.