NMR Structure of the Escherichia coli Type 1 Pilus Subunit FimF and Its Interactions with Other Pilus Subunits

Structure, Folding and Stability of FimA, the Main Structural Subunit of Type 1 Pili from Uropathogenic Escherichia coli Strains

“…In addition, a oneturn α-helix (residues 25-28) and two other one-turn 3 10 helices (39-41 and 80-82) could be identified in the structure. The disordered N-terminal segment of FimAa (1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19), which is supposed to act as a donor strand for a preceding subunit in the assembled pilus, shows no observable interaction with the rest of the protein (Fig. 5a) as was also observed before for the N-terminal segment of the subunit FimF.…”

“…5a) as was also observed before for the N-terminal segment of the subunit FimF. 14 The hexaglycine linker (161-166), inserted between the natural FimA C-terminus and the C-terminal FimA donor strand segment, appears to be unstructured and dynamic, indicating that the chosen (Gly) 6 linker is long enough and does not impose any strain on the insertion of the additional, selfcomplementing donor strand G (167-182). All unstructured regions in FimAa (see high local r.m.…”

“…FimAa adopts the expected Ig-like fold, which has been observed for all other structures of pilus subunits from chaperone-usher systems determined so far. 4,[13][14][15][16][17][18][19][20]35 The artificial C-terminal extension (G-strand in the solved NMR structure) complements the Ig-fold in a canonical manner (i.e., runs antiparallel with the F-strand). The fold is mainly determined by two β-sheets, the first being composed of strand A (29)(30)(31)(32)(33)(34)(35)(36)(37)(38), the donor strand G (167-182), strand F (146-159) and strand C (67-75), and the second being composed of strands B′ (45)(46)(47)(48)(49), B″ (52-62), E (127-141), D′ (99-105) and D″ (122-124), that are packed against each other in a wound fashion (Fig.…”

“…The N-terminal donor strand (residues 1-20) is indicated in red, and the FimA pilin domain, in blue. (Middle) FimAa: wild-type FimA extended at the C-terminus by a hexaglycine linker (gray) and its own donor strand segment (residues [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20]. (Bottom) FimAt, N-terminally truncated FimA.…”

“…However, it inserts its donor strand segment in a parallel orientation relative to the C-terminal F-strand of the subunits, while donor strand insertion in the opposite, "antiparallel" orientation is observed in subunit-subunit interactions. 4,[13][14][15][16][17][18][19][20] In addition, FimC catalyzes pilus subunit folding 21,22 and prevents the premature assembly of the subunits in the periplasm. FimC-bound subunits are then transferred to the assembly platform FimD, which recognizes chaperone-subunit complexes and catalyzes subunit assembly and translocation through the outer membrane and release of free FimC to the periplasm (Fig.…”