Outer membrane usher protein (IPR000015)

Short name: Fimb_usher

Overlapping homologous superfamilies


Family relationships



In Gram-negative bacteria the biogenesis of fimbriae (or pili) requires a two- component assembly and transport system which is composed of a periplasmic chaperone and an outer membrane protein which has been termed a molecular 'usher' [PMID: 7909802, PMID: 7906265, PMID: 7906046].

The usher protein is rather large (from 86 to 100 kDa) and seems to be mainly composed of membrane-spanning beta-sheets, a structure reminiscent of porins. Although the degree of sequence similarity of these proteins is not very high, they share a number of characteristics. One of these is the presence of two pairs of cysteines, the first one located in the N-terminal part and the second at the C-terminal extremity that are probably involved in disulphide bonds. The best conserved region is located in the central part of these proteins [PMID: 19380723, PMID: 18485872].

GO terms

Biological Process

GO:0009297 pilus assembly

Molecular Function

GO:0015473 fimbrial usher porin activity

Cellular Component

GO:0016020 membrane

Contributing signatures

Signatures from InterPro member databases are used to construct an entry.