Pilus chaperones represent a new type of protein-folding catalyst

Abstract

Adhesive type 1 pili from uropathogenic Escherichia coli strains have a crucial role during infection by mediating the attachment to and potentially the invasion of host tissue. These filamentous, highly oligomeric protein complexes are assembled by the 'chaperone-usher' pathway, in which the individual pilus subunits fold in the bacterial periplasm and form stoichiometric complexes with a periplasmic chaperone molecule that is essential for pilus assembly. The chaperone subsequently delivers the subunits to an assembly platform (usher) in the outer membrane, which mediates subunit assembly and translocation to the cell surface. Here we show that the periplasmic type 1 pilus chaperone FimC binds non-native pilus subunits and accelerates folding of the subunit FimG by 100-fold. Moreover, we find that the FimC-FimG complex is formed quantitatively and very rapidly when folding of FimG is initiated in the presence of both FimC and the assembly-competent subunit FimF, even though the FimC-FimG complex is thermodynamically less stable than the FimF-FimG complex. FimC thus represents a previously unknown type of protein-folding catalyst, and simultaneously acts as a kinetic trap preventing spontaneous subunit assembly in the periplasm.

Quality control of disulfide bond formation in pilus subunits by the chaperone FimC

“…Our results, together with previous reports 13,23,24,48 , suggest a straightforward model for the FimC-catalyzed subunit folding of FimA and other pilus subunits. As the FimA fold has a high topological complexity (contact order) 28 , this might be the dominant factor determining the high kinetic barrier of spontaneous FimA folding.…”

“…Recently, we reported the NMR structure of a designed, selfcomplemented FimA variant (FimAa) 28 , in which FimA is artificially extended at its C terminus by a hexaglycine linker followed by the FimA donor strand segment (residues [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20]. FimAa has the same slow, spontaneous folding rate as wild-type FimA (1.6-h folding half-life) and adopts a conformation in which the C-terminal copy of the donor strand is incorporated into the tertiary structure in an antiparallel orientation relative to the FimA F strand, which corres ponds to the expected donor strand insertion pattern in the quaternary structure of the pilus rod 28 .…”

“…The pilus subunits enter the periplasm in an unfolded conformation and are recognized by the chaperone FimC, which catalyzes their folding 13 . FimC also provides a β-strand that complements the fold of the bound subunits and is inserted in a parallel orientation relative to the last (F) strand of the subunit (Fig.…”

Rationally designed small compounds inhibit pilus biogenesis in uropathogenic bacteria

“…PapD is the prototypic periplasmic chaperone and is required for P pilus assembly. PapD-like chaperones act by binding to and catalyzing folding of pilus subunits newly translocated into the periplasm (7,8). The chaperone-subunit complexes are then targeted to an outer membrane assembly site called the usher.…”

Molecular mechanism of bacterial type 1 and P pili assembly

“…type 1 and P pili, respectively-is embedded into the OM via the β-barrel assembly machinery (BAM complex) [9,10]. The periplasmic chaperones FimC and PapD promote subunit/pilin folding as they are released by the Sec translocon and target pilus subunits to their respective usher [11,12].…”