INVOLVEMENT OF ARGININE-SPECIFIC CYSTEINE PROTEINASE (ARG-GINGIPAIN) IN FIMBRIATION OF PORPHYROMONAS-GINGIVALIS

Arginine-specific cysteine proteinase (Arg-gingipain [RGP]), a major p roteinase secreted from the oral anaerobic bacterium Porphyromonas gin givalis, is encoded by two separate genes (rgpA and rgpB) on the P. gi ngivalis chromosome and widely implicated as an important virulence fa ctor in the pathogenesis of periodontal disease (K. Nakayama, T. Kadow aki, K. Okamoto, and K. Yamamoto, J. Biol. Chem. 270:23619-23626, 1995 ). In this study, we investigated the role of RGP in the formation of P. gingivalis fimbriae which are thought to mediate adhesion of the or ganism to the oral surface by use of the rgp mutants. Electron microsc opic observation revealed that the rgpA rgpB double (RGP-null) mutant possessed very few fimbriae on the cell surface, whereas the number of fimbriae of the rgpA or rgpB mutant was similar to that of the wild-t ype parent strain, The rgpB(+) revertants that were isolated from the double mutant and recovered 20 to 40% of RGP activity of the wild-type parent possessed as many fimbriae as the wild-type parent, indicating that RGP significantly contributes to the fimbriation of P. gingivali s as well as to the degradation of various host proteins, disturbance of host defense mechanisms, and hemagglutination, Immunoblot analysis of cell extracts of these mutants with antifimbrilin antiserum reveale d that the rgpA rgpB double mutant produced small amounts of two immun oreactive proteins with molecular masses of 45 and 43 kDa, correspondi ng to those of the precursor and mature forms of fimbrilin, respective ly, The result suggests that RGP may function as a processing proteina se for fimbrilin maturation, In addition, a precursor form of the 75-k Da protein, one of the major outer membrane proteins of P. gingivalis, was accumulated in the rgpA rgpB double mutant but not in the single mutants and the revertants, suggesting an extensive role for RGP in th e maturation of some of the cell surface proteins.