Porphyromonas gingivalis, a major periodontal pathogen, must acquire nutrients from host derived substrates, overcome oxidative stress and subvert the immune system. These activities can be coordinated via the gingipains which represent the most significant virulence factor produced by this organism. In the context of our contribution to this field, we will review the current understanding of gingipain biogenesis, glycosylation, and regulation, as well as discuss their role in oxidative stress resistance and apoptosis. We can postulate a model, in which gingipains may be part of the mechanism for P. gingivalis virulence. KeywordsPorphyromonas gingivalis; gingipains; apoptosis; caspase-independent apoptosis; oxidative stress; VimA; anoikis; N-cadherin; VE-cadherin; integrin β1; VimA; VimE; VimF; DNA repair; glycosylation; virulence; host cell survival; HRgpA; RgpB; Kgp; Review INTRODUCTIONP. gingivalis, a black-pigmented, Gram-negative anaerobe, is an important etiological agent of periodontal disease and is also linked to cardiovascular disease and other systemic diseases [reviewed in (43,103)]. The inflammatory nature of periodontal disease implies that innate host defense mechanisms play a vital role in limiting bacterial growth. During active infection including tissue invasion, toxic reactive oxygen metabolites (e.g. superoxides, hydrogen peroxide and hydroxyl radicals) are mostly generated by polymorphonuclear leukocytes and macrophages (27,29). In order to survive in the inflammatory environment of the periodontal pocket, the bacterium must not only obtain nutrients for growth, but also overcome oxidative stress and subvert the immune defense system. Coordinated regulation of these activities would be beneficial to the bacterium. While there is documented evidence of the response of P. gingivalis to environmental stimulus (56,117,126), one possible mechanism for coordination may occur via the gingipains produced by this bacterium. The presence of P. gingivalis in the periodontal pocket and the high levels of gingipain activity detected in gingival crevicular fluid could implicate a role for gingipains in the destruction of the highly vascular periodontal tissue. Protease-associated degradation of cell-cell adhesion proteins on epithelial and endothelial cells resulting in cell death will compromise tissue integrity and facilitate spreading of the bacterium. Furthermore, degradation of the immune response components will facilitate the survival of the organism. Together, these activities may also satisfy the nutritional requirements of the organism. Gingipain-dependent heme accumulation on the bacterium cell surface may also act as an "oxidative sink", thus, leading to protection against oxidative stress (191,193). We will discuss the role of the gingipains in the survival/pathogenicity of P. gingivalis and the unique vim (virulence modulating) locus that is involved in regulation of the gingipains. We will highlight some of our observations that are consistent with the hypothesis that the gingipain...