This is a family of bacterial protein modules thought to function in various roles including cell adhesion, cell lysis and carbohydrate binding [1]. A tandem repeat of these modules (either two or three repeats) constitute the haemagglutinin/adhesin (HA) regions of the gingipains, RgpA, Swiss:Q51816 and Kgp, Swiss:P72194 and Swiss:P72197 [3] expressed by Porphyromonas gingivalis (Bacteroides gingivalis) [2]. They form components of the major extracellular virulence complex RgpA-Kgp - a mixture of proteinases and adhesin domains [4]. The adhesin domains in this complex are found in proteinase-cleaved forms when isolated from the cell surface [5]. Haemagglutinin genes of P. gingivalis [6] (hagA1 HAGA1_PORGI - Swiss:P59915 - and hagA2 HAGA2_PORGI - Swiss:Q51845) suggest that such proteins are composed of eight to ten tandem repeats of these adhesin modules [1]. Genomic data predicts that homologous protein modules are also expressed by a number of other bacteria and form part of putative multi-domain proteins, eg. Swiss:Q26BR9 and Swiss:B0VGL6. These domains may be acting in concert with other adhesion modules thought to be part of these multi-domain proteins such as fibronectin type III, Pfam:PF00041, and Meprin, A5, mu (MAM), Pfam:PF00629, domains.

1: STRUCTURE DETERMINATION AND ANALYSIS OF A HEMOLYTIC GINGIPAIN ADHESIN DOMAIN FROM PORPHYROMONAS GINGIVALIS. Li N, Yun P, Nadkarni MA, Ghadikolaee NB, Nguyen KA, Lee M, Hunter N, Collyer CA; Mol Microbiol. 2010; [Epub ahead of print] PMID:20233299

2: Molecular cloning and structural characterization of the Arg-gingipain proteinase of Porphyromonas gingivalis. Biosynthesis as a proteinase-adhesin polyprotein. Pavloff N, Potempa J, Pike RN, Prochazka V, Kiefer MC, Travis J, Barr PJ; J Biol Chem. 1995;270:1007-1010. PMID:7836351

3: Molecular cloning and characterization of Porphyromonas gingivalis lysine-specific gingipain. A new member of an emerging family of pathogenic bacterial cysteine proteinases. Pavloff N, Pemberton PA, Potempa J, Chen WC, Pike RN, Prochazka V, Kiefer MC, Travis J, Barr PJ; J Biol Chem. 1997;272:1595-1600. PMID:8999833

4: A cell-associated protein complex of Porphyromonas gingivalis W50 composed of Arg- and Lys-specific cysteine proteinases and adhesins. Bhogal PS, Slakeski N, Reynolds EC; Microbiology 1997;143:2485-2495. PMID:9245829

5: Major outer membrane proteins and proteolytic processing of RgpA and Kgp of Porphyromonas gingivalis W50. Veith PD, Talbo GH, Slakeski N, Dashper SG, Moore C, Paolini RA, Reynolds EC; Biochem J. 2002;363:105-115. PMID:11903053

6: The hemagglutinin gene A (hagA) of Porphyromonas gingivalis 381 contains four large, contiguous, direct repeats. Han N, Whitlock J, Progulske-Fox A; Infect Immun. 1996;64:4000-4007. PMID:8926061