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Ushers are a family of integral outer membrane proteins participating in the chaperone (usher) secretion pathway, a terminal branch of the General Secretion Pathway (GSP) dedicated to the biogenesis of adhesive surface structures associated with pathogenesis. As the name of the pathway implies, these proteins work in conjunction with a periplasmic chaperone in order to assemble and secrete more than 30 different surface molecules in a broad range of Gram-negative bacteria. The most studied example of the chaperone (usher) pathway is the assembly and biogenesis of the type 1 and P pili, expressed by the uropathogenic Escherichia coli. Members of the Usher family (like PapC, FasD, FaeD and FimD), display properties of ß-barrel proteins and form channels consisting of 24 beta-strands, as shown in the crystal structure of PapC. It has been proposed that Ushers form twin dimeric pores in the outer membrane and the C-terminal parts of the sequences are responsible for the dimerization. In addition, the N-terminal 100-120 amino acids are believed to be involved in the recognition of the periplasmic chaperone.
Topology of the outer membrane usher PapC determined by site-directed fluorescence labeling
J Biol Chem. 2004 Dec 17;279(51):53747-54. doi: 10.1074/jbc.M409192200. Epub 2004 Oct 12.
The outer membrane usher forms a twin-pore secretion complex
J Mol Biol. 2004 Dec 10;344(5):1397-407. doi: 10.1016/j.jmb.2004.10.008.
Ushers and secretins: channels for the secretion of folded proteins across the bacterial outer membrane
J Mol Microbiol Biotechnol. 2002 Jan;4(1):11-20.
The usher N terminus is the initial targeting site for chaperone-subunit complexes and participates in subsequent pilus biogenesis events
J Bacteriol. 2004 Aug;186(16):5321-31. doi: 10.1128/JB.186.16.5321-5331.2004.
Fiber formation across the bacterial outer membrane by the chaperone/usher pathway
Cell. 2008 May 16;133(4):640-52. doi: 10.1016/j.cell.2008.03.033.
|Proteins in this family with 3D-structure|