The bacterial immunoglobulin-like (Ig) domain 1 or Big-1 domain is a domain of ~95 amino acids present in bacterial adhesion molecules of the intimin/invasin family, involved in pathogenicity. The domain is named after the 3D structure of the domain in enteropathogenic Escherichia coli intimin and in Yersinia pseudotuberculosis invasin, which are both adhesins with a tandem repeat of the Big-1 domain. The 3D structure of the Big-1 domain is a β-sheet sandwich (see <PDB:1CWV>) with a topology similar to eukaryotic members of the immunoglobulin superfamily (see <PDOC50835>). In most intimin/invasin proteins the Big-1 domain occurs in a tandem, N-terminal to a different Ig-like domain, followed by a C-terminal C-type lectin-like domain. Big-1 can also occur in combination with the lysM domain or in a tandem repeat of several copies. Big-1 proteins are surface-expressed proteins that mediate mammalian host cell invasion or attachment. The tandem of Ig-like domains appears to form a rod to link the bacterial outer membrane anchor to the C-terminal lectin-like domain to interact with their receptors in the host cell membrane [1,2,3].

Some proteins known to contain a Big-1 (Bacterial Ig-like domain 1) domain:

• Escherichia coli O127:H6/EPEC and O157:H7/EHEC intimin or attaching and effacing protein, present on the surface of diarrheagenic enteric bacteria and involved in adhesion to mammalian epithelial cells in the gut. Intimin binds to the bacterial Tir protein, which is secreted and inserted into the host membrane.
• Yersinia pseudotuberculosis and Y. enterocolitica invasin, an outer membrane protein that mediates entry into eukaryotic cells by binding to β-1 integrins.
• Escherichia coli yeeJ, a hypothetical protein.

The profile we developed covers the entire Big-1 (Bacterial Ig-like domain 1) domain.