Figure 1: FimH·DsG resembles fimbrial tip FimH.

(a) Preparation of the FimH·DsG complex by DSE. Left: reaction scheme of the DSE reaction, in which DsG displaces the FimC chaperone from the FimH pilin domain. Right: kinetics of the FimH·DsG complex formation at 37 °C, monitored by analytical gel filtration. DSE was initiated by mixing the FimC·FimH complex (15 μM) with excess DsG peptide (50 μM). Samples were removed after different incubation times, rapidly cooled on ice and immediately subjected to gel filtration. The reaction can be followed by the decrease in the FimC·FimH complex concentration and the simultaneous increase in the concentrations of FimH·DsG and free FimC (FimC and FimH·DsG coelute as a single peak at ∼12 ml). The chromatogram at the bottom shows that the FimC·FimH complex is stable against dissociation/aggregation under the chosen conditions. The rate constant of DSE estimated from these data is ∼0.5 M⁻¹ s⁻¹. (b) Structure of FimH^F18·DsG (lectin domain FimH_L, red; pilin domain FimH_P, yellow; DsG, blue; circle and square indicate N- and C termini, respectively). (c) FimH from the fimbrial tip structure (left, PDB ID: 3JWN (ref. 17); FimG, blue; FimF, green) is superposed onto FimH^F18·DsG based on their pilin domains (aa. 160–279), in the superposition (right) fimbrial FimH is shown in grey. (d) Close-up on the DsG peptide (stick representation) bound to FimH^F18·DsG with 2F_o–F_c electron density map. Backbone hydrogen bonds of the DsG peptide and β-strands 2 (β2) and 9 (β9) of FimH_P are indicated.