The FCT and equivalent region genes of Streptococcus pyogenes and other related bacteria encode surface proteins that include fibronectin- and collagen-binding proteins and the serological markers known as T antigens. Some of these proteins give rise to pilus-like appendages [1]. The FctA family is found in many Firmicutes and related bacteria. In S. pyogenes, the pili have a role in bacterial adherence and colonisation of human tissues [2]. Members of this family have a conserved N-terminal lysine and C-terminal asparagine that can form a covalent isopeptide bond [3].

1: Role of streptococcal T antigens in superficial skin infection. Lizano S, Luo F, Bessen DE; J Bacteriol. 2007;189:1426-1434. PMID:17012387

2: Streptococcus pyogenes pili promote pharyngeal cell adhesion and biofilm formation. Manetti AG, Zingaretti C, Falugi F, Capo S, Bombaci M, Bagnoli F, Gambellini G, Bensi G, Mora M, Edwards AM, Musser JM, Graviss EA, Telford JL, Grandi G, Margarit I; Mol Microbiol. 2007;64:968-983. PMID:17501921

3: Stabilizing isopeptide bonds revealed in gram-positive bacterial pilus structure. Kang HJ, Coulibaly F, Clow F, Proft T, Baker EN; Science. 2007;318:1625-1628. PMID:18063798