Outer-membrane PapC molecular usher discriminately recognizes periplasmic chaperone-pilus subunit complexes.

Abstract

P pili are highly ordered composite structures consisting of thin fibrillar tips joined end-to-end to rigid helical rods. The production of these virulence-associated structures requires a periplasmic chaperone (PapD) and an outer membrane protein (PapC) that is the prototype member of a newly recognized class of proteins that we have named "molecular ushers." Two in vitro assays showed that the preassembly complexes that PapD forms with the three most distal tip fibrillar proteins (PapG, PapF, and PapE) bound to PapC. The relative afimity of each complex for PapC was found to

Rationally designed small compounds inhibit pilus biogenesis in uropathogenic bacteria

“…Protein production was induced by the addition of isopropyl-␤-D-thiogalactopyranoside (IPTG) to a final concentration of 0.1 mM and continuing growth for 60 min. Periplasmic extracts were prepared by the sucrose͞ lysozyme method as described (9). Outer membranes were purified by using ultracentrifugation and solubilized in 1% elugent and 20 mM Hepes (pH 7.5) (35).…”

“…The chaperone-subunit complexes are then targeted to an outer membrane assembly site called the usher. The usher forms a pore that selectively discriminates among the chaperone-subunit complexes, a process that facilitates the ordered assembly of pili (9,10).…”

Crystallization and preliminary X-ray diffraction studies of the FimC–FimH chaperone–adhesin complex from Escherichia coli

“…These highly conserved assembly systems consist of periplasmic immunoglobulin-like chaperones (Holmgren, Kuehn, Br~ind6n & Hultgren, 1992;Hultgren et al, 1993;Hung, Knight, Woods, Pinkner & Hultgren, 1996) and outer membrane associated ushers (Dodson, Jacob-Dubuisson, Striker & Hultgren, 1993). The usher molecules are large proteins that are involved in export of organelle subunits and may also function as platforms for organelle assembly.…”

Molecular mechanism of bacterial type 1 and P pili assembly

“…Previously, only chaperone-subunit complexes were found to bind to the usher, not the free chaperone [48,49]. Because the usher almost exclusively interacts with the chaperone of the chaperone-subunit complex [45,50], recruitment of solely a chaperone without its subunit cargo is avoided by a so-called proline lock within the usher binding surface (UBS) of the chaperone: the structure of a chaperone without cargo shows a pair of conserved proline residues at the beginning of the subunit-binding F 1 G 1 loop that occlude the usher-binding surface and prevent the usher from binding.…”