This entry represents BIg21(Bacterial Immunoglobulin-like 21) found in InvasinE (InvE). Invasins are members of the inverse autotransporter (IAT) family also referred to as type Ve secretion system. In general, they consist of an N-terminal beta-barrel-like domain, which is responsible for attachment of invasin to the outer membrane region of bacteria, repetitive Immunoglobuli-like (Ig) domains, which vary significantly in number among all the invasins, and the C-terminal domain/adhesion domain (AD) Pfam:PF05689, which provides invasins with the specificity to bind to its host target molecules. The overall structure of InvE shows that it comprises of three domain architecture in which the domains BIg20 (Bacterial Immunoglobulin-like 20) and BIg21 adopt two layer beta-sandwich fold resembling eukaryotic members of Immunoglobulin-superfamily (IgSF), while the AD is a globular, alpha/beta-domain. The structure of BIg21 belongs to the I2 set of IgSF with a unique modification in the C-E interstrand loop, important for its interaction with AD. BIg21 and AD form a functional super-domain as well, necessary to target the host receptor [1].

1: Structure of the Y. pseudotuberculosis adhesin InvasinE. Sadana P, Monnich M, Unverzagt C, Scrima A; Protein Sci. 2017;26:1182-1195. PMID:28370712