ARG-GINGIPAIN ACTS AS A MAJOR PROCESSING ENZYME FOR VARIOUS CELL-SURFACE PROTEINS IN PORPHYROMONAS-GINGIVALIS

Arg-gingipain (RGP) is an Arg-X-specific cysteine proteinase produced by the Gram-negative anaerobe Porphyromonas gingivalis and has been sh own to be a potent virulence factor in progressive periodontal disease (Nakayama, K., Kadowaki, T,, Okamoto, K,, and Yamamoto, K, (1995) J, Biol, Chem, 270, 23619-23626), In this study, we provide evidence that RGP acts as a major processing enzyme for various cell surface and se cretory proteins in P, gingivalis. Fimbrilin, a major component of fim briae, remained in the precursor form in the RGP-null mutant. Prefimbr ilin expressed in Escherichia coil was converted to the mature fimbril in in vitro when incubated with purified RGP, but its conversion was s uppressed by potent RGP inhibitors. The results were consistent with t he electron microscopic observation indicating little or no fimbriatio n in the RGP-null mutant. The immunogenic 75-kDa cell surface protein was also shown to retain its preform in the RGP-null mutant. In additi on, Lys-gingipain (KGP) was found to be abnormally processed in the RG P-null mutant, In contrast, both prefimbrilin and the 75-kDa protein p recursor were processed to their respective mature forms in the KG;P-n ull mutant, suggesting that KGP is not involved in the normal processi ng mechanisms of these proteins. These results suggest that RGP not on ly acts as a direct virulence factor but also makes a significant cont ribution as a major processing enzyme to the virulence of P. gingivali s,