Regulation of Protease Expression in Porphyromonas gingivalis

Although the strong protease activity of Porphyromonas gingivalis appears to be an important virulence property of these organisms, little information is currently available regarding the regulation of expression of the multiple protease genes. Utilizing the lacZ reporter gene strategy, the environmental factors which regulate the expression of the Arg-gingipain gene rgpA and the prtT protease gene were investigated. These two genes are reciprocally regulated since factors which retarded growth (iron depletion and nutrient limitation) appeared to upregulate rgpA expression while down-regulating prtT expression. However, inactivation of the major rgpA gene resulted in increased transcription of the prtT and tpr protease genes while decreasing expression of the Lys-gingipain kgp gene as detected by Northern blot analysis. By contrast, inactivation of the prtT gene did not significantly affect kgp expression but moderately decreased rgpA mRNA levels. These results indicate that the protease genes of P. gingivalis are not coordinately regulated and suggest that some of these enzymes play specific roles in the physiology and/or virulence of these organisms.