This domain is found in a group of proteins from Gammaproteobacteria, including Invasin from Yersinia pseudotuberculosis, a protein that allows this enteric bacteria to penetrate cultured mammalian cells by binding several beta-1 chain integrins. This domain adopts the folding topology of the C1 set of IgSF domains with two additional beta-strands [1].

1: Crystal structure of invasin: a bacterial integrin-binding protein. Hamburger ZA, Brown MS, Isberg RR, Bjorkman PJ; Science. 1999;286:291-295. PMID:10514372