Identification of Porphyromonas gingivalis components that mediate its interactions with fibronectin

Porphyromonas (Bacteroides) gingivalis W12 binds and degrades human plasma fibronectin. In the presence of the protease inhibitor N-alpha-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 Kd for the reaction was estimated to be on the order of 100 nM, and there was an average of 3.5 x 10(3) fibronectin binding sites per cell. Unlabeled fibronectin inhibited the binding of 125I-fibronectin to bacteria; however, fibrinogen was an even more efficient inhibitor of 125I-fibronectin binding. Unrelated proteins were without effect on fibronectin binding. A fibronectin-binding component (Mr, 150,000) was identified in sodium dodecyl sulfate-solubilized P. gingivalis. Fibronectin was degraded into discrete peptides by P. gingivalis W12. The degradation of fibronectin was inhibited by N-alpha-p-tosyl-L-lysyl chloromethyl ketone. Two P. gingivalis components (Mrs, 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 (Mr, 150,000 immobilized on a nitrocellulose membrane.