Capnocytophaga gingivalis aminopeptidase: a potential virulence factor

The production and properties of an aminopeptidase from Capnocytophaga gingivalis were studied. C. gingivalis was grown in continuous culture over a range of dilution rates and the cell-bound and extracellular levels of aminopeptidase and trypsin-like protease (TLPase) measured. At high growth rates (0.6 mu rel) TLPase specific activity was low and found exclusively as cell-bound activity; at low growth rates (0.0375 mu rel), specific activity was high and 26% was found as extracellular activity. In contrast, aminopeptidase specific activity was highest at 0.3 mu rel and the ratio of cell-bound to extracellular activity was relatively constant at all growth rates. Only about 5% of the total activity was extracellular. The aminopeptidase, which has a wide specificity towards artificial substrates, was purified to homogeneity, as judged by SDS-PAGE, from the supernatant fluid of cells grown in continuous culture in a tryptone/glucose/thiamine medium. The enzyme has a molecular mass of 61 kDa, a pl of 6.3, a pH optimum close to 7.5 and showed a requirement for magnesium or calcium ions. The N-terminal sequence of the first 10 amino acids (Asp-Val-Asn-Met-Leu-Trp-Tyr-Val-x-Arg...) showed no similarity to any published sequence. This enzyme in its cell-bound or extracellular form may be important in the nutrition and pathogenesis of C. gingivalis in the human oral cavity.