Structural Basis for Mechanical Force Regulation of the Adhesin FimH via Finger Trap-like β Sheet Twisting

Abstract

Summary The Escherichia coli fimbrial adhesive protein, FimH, mediates shear-dependent binding to mannosylated surfaces via force-enhanced allosteric catch bonds, but the underlying structural mechanism was previously unknown. Here we present the crystal structure of FimH incorporated into the multi-protein fimbrial tip, where the anchoring (pilin) domain of FimH interacts with the mannose-binding (lectin) domain and causes a twist in the β-sandwich fold of the latter. This loosens the mannose-binding pocket on the opposite end of lectin domain, resulting in an inactive low-affinity state of the adhesin. The autoinhibition effect of the pilin domain is removed by application of tensile force across the bond, which separates the domains and causes the lectin domain to untwist and clamp tightly around ligand like a finger trap toy. Thus, β-sandwich domains, which are common in multidomain proteins exposed to tensile force in vivo, can undergo drastic allosteric changes and be subjected to mechanical regulation.

Mechanism of allosteric propagation across a β‐sheet structure investigated by molecular dynamics simulations

“…7(a)] 10. In particular, transition to low affinity upon docking of the pilin domain involves the tilting of β 17‐22 which is part of the clamp segment and is located at the edge of the large β sheet (the nomenclature “ β xx‐yy” indicates a β strand from residue xx to residue yy).…”

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

“…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 .…”

“…Type 1 pili are composed of two different subassemblies: a 1-to 2-μm-long and 7-nm-thick helical, rod-like structure containing up to 3,000 copies of the main structural subunit FimA and a flexible tip fibrillum containing one or several copies of the minor subunits FimG and FimF and a single copy of FimH at the tip of the pilus [2][3][4][5] (Fig. 1a).…”

Ideal, catch, and slip bonds in cadherin adhesion

“…Slip bonds are the most commonly observed interactions in biology. Catch bonds, which provide a way for molecules to grip tightly and stabilize their attachments in the presence of mechanical stress, have been observed with motor proteins like myosin (19) and kinetochores (20) and with adhesive proteins like selectins (21)(22)(23), FimH (24,25), and integrins (26), but not with cadherins. The third type of biomolecular interaction, ideal bonds, have also been proposed to play a role in permitting adhesive proteins to withstand mechanical stress (17).…”