Chapter 21 : Porphyromonas gingivalis

Abstract:

Porphyromonas gingivalis, the etiological agent of periodontal disease, is an anaerobe that requires iron in the form of heme for growth. This chapter discusses the roles of specific outer membrane proteins and gingipains in heme accumulation by P.gingivalis. The binding and accumulation of hemoglobin by P.gingivalis is currently the focus of investigations being conducted in several independent laboratories. Recent investigations have indicated a significant role for the P.gingivalis gingipain proteases in the acquisition of heme from hemoglobin. The gingipains of P.gingivalis specifically cleave substrates behind either arginine or lysine residues. In addition to gingipains, hemagglutinins may aid in iron-heme utilization in P.gingivalis. Due to the obligate requirement for iron by P.gingivalis the expression of specific iron uptake systems is an important survival mechanism. The development of effective control strategies for P.gingivalis infection requires an understanding of the iron transport systems required for in vivo growth of this organism. P.gingivalis does not produce siderophores as do many other pathogens. Recent investigations of the acquisition of heme by P.gingivalis have led to the identification of several outer membrane receptors. While the function of many of these putative receptors remains to be determined by mutational analysis, the initial analyses have provided the primary insight into how P.gingivalis acquires heme. The involvement of the gingipains, particularly Kgp, indicates that in addition to specific outer membrane proteins, P.gingivalis may use a hemophorelike delivery system.