Gingipains, the Major Cysteine Proteinases and Virulence Factors of Porphyromonas gingivalis: Structure, Function and Assembly of Multidomain Protein Complexes

Abstract

Gingipains, extracellular cysteine proteinases of Porphyromonas gingivalis, constitute the major virulence factor of this periodontopathogenic bacterium. They are the product of three genes, two coding for an Arg-specific (RgpA and RgpB) and one for a Lys-specific proteinase (Kgp). Proteinase domains of RgpA and RgpB are virtually identical; however, the gene encoding the former enzyme is missing a large segment coding for hemaglutinin / adhesin (HA) domains. The latter domains are present also in Kgp. The tertiary structure of RgpB revealed that the proteinase domain of gingipains has a protein fold referred to as the caspase-hemoglobinase fold. On this basis, they are also evolutionary related to other highly specific proteinases including clostripain, caspases, legumains and separase (clan CD of cysteine peptidases). Gingipains are produced as large preproproteins and are subject to elaborate, not yet fully understood, secretion, glycosylation, activation, and maturation processes. How they traverse the outer membrane is unknown, although it can be hypothesized that they use an autotransporter pathway. Apparently during transport through the periplasm the LPS-like glycan moiety is added at the conserved C-terminal portion of progingipains. At the cell surface pro-gingipains fold into partially active, single-chain zymogens and undergo autocatalytic, intermolecular processing. Two sequential cleavages within the profragment domain enhance zymogen activity and in the case of RgpA and Kgp are followed by excision of the individual HA domains. These domains are further truncated at the C-terminus by concerted action of Kgp and carboxypeptidase and form a non-covalent multidomain, multifunctional complex anchored into the outer membrane by the glycated, C-terminal HA domain. This hypothetical scenario is a reasonable explanation for the occurrence of many forms of gingipains.

Characterization of the Porphyromonas gingivalis Type IX Secretion Trans-envelope PorKLMNP Core Complex

“…These data therefore suggest that either additional T9SS subunits are present in the Ͼ1. 4 MDa complex or that this complex results from the multimerization of the minimal PorK 2 L 3 M 2 N 2 complex. These two hypotheses are likely, as most secretion apparatuses form large channels to accommodate folded effectors (35), multimerization has been reported for the T6SS TssJLM membrane complex that comprises five copies of dimers of TssJLM heterotrimers (32), and additional components have been identified recently to interact with the PorKN complex (29).…”

“…Recently, a number of proteins responsible for the active release of these proteins at the bacterial cell surface, named Por, have been identified (10 -15). Although there is little evidence that these proteins assemble a secretion machine, they were collectively grouped under the name Porphyromonas secretion system and, more recently, type IX secretion system (T9SS) 4 (10,16). In addition to the gingipains, this secretion apparatus transports the Hbp35 heme-binding protein peptidylarginine deiminase, a toxin responsible for host protein, the citrullination and rheumatoid arthritis, and Maf5, a subunit of the extracellular Maf fimbriae (17)(18)(19).…”

Structure of the streptococcal endopeptidase IdeS, a cysteine proteinase with strict specificity for IgG

“…Extracellular bacterial cysteine proteinases have also been characterized from other pathogenic bacteria such as Clostridium histolyticum, Porphyromonas gingivalis, and Staphylococcus aureus (2). These cysteine proteinases exhibit broad substrate specificity and are consequently expressed as proenzymes, requiring proteolytic processing to convert into their mature forms (7)(8)(9)(10)(11)(12)(13)(14).…”

Possible Roles of IL-33 in Periodontal Diseases: Porphyromonas gingivalis Induced IL-33 in Human Gingival Epithelial Cells

“…mRNA Expression in Human Gingival Epithelial Cells by P. gingivalis P. gingivalis produces two types of arginine-specific cysteine proteinases (Arg-gingipains, RgpA and RgpB) and a lysine-specific cysteine proteinase (Lys-gingipain, Kgp) [18]. Gingipains are localized to a cell-associated form, a soluble form, and released as outer membrane blebs [18].…”

“…Gingipains are localized to a cell-associated form, a soluble form, and released as outer membrane blebs [18]. We next examined whether enzymatic activities of gingipains are involved in the IL-33-inducing capacity in Ca9-22 cells and primary oral epithelial cells.…”