Identification of Porphyromonas gingivalis components that mediate its interactions with fibronectin

Porphyromonas (Bacteriodes) gingivalis W12 binds and degrades human plasma fibronectin. In the presence of the protease inhibitor N-α-p-tosyl-L-lysyl chloromethyl ketone, P gingivalis cells accumulated substantial amounts of ¹²⁵I-fibronectin as a function of incubation time. Fibronectin binding was specific, reversible, and saturable. The K(d) for the reaction was estimated to be on the order of 100 nM, and there was an average of 3.5 x 10³ fibronectin binding sites per cell. Unlabled fibronectin inhibited the binding of ¹²⁵I-fibronectin to proteins were without effect on fibronectin binding. A fibronectin-binding component (M(r), 150,000) was identified in sodium dodecyl sulfate-solubilized P. gingivalis. Fibronectin was degraded into discrete peptides by P. ginvialis W12. The degradation of fibronectin was inhibited by N-α-p-tosyl-L-lysyl chloromethyl ketone. Two P. gingivalis components (M(r)S, 120,000 and 150,000) degraded fibronectin in substrate-containing gels following sodium dodecyl sulfate-polyacrylamide gel electrophoresis. In a previous study (M. S. Lantz, R. D. Allen, T. A. Vail, L. M. Switalski, and M. Hook, J. Bacteriol. 173:495-504, 1991), we found that the same strain of P. gingivalis bound and subsequently degraded human fibrinogen via apparently distinct cell surface components of molecular sizes similar to those of components now implicated in the binding and degradation of fibronectin. These results raise the possibility that the two ligands are recognized and modified by the same components on P. gingivalis W12. In support of this hypothesis, unlabeled fibrinogen effectively inhibited the binding of ¹²⁵I-fibronectin to bacteria and blocked ¹²⁵I-fibronectin binding to a P. gingivalis ligand-binding component (M(r), 150,000) immobilized on a nitrocellulose membrane.