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Donor strand exchange and conformational changes during E. coli fimbrial formation.

ABSTRACT: Fimbriae and pili are macromolecular structures on the surface of Gram negative bacteria that are important for cellular adhesion. A 2.7Å resolution crystal structure of a complex of Escherichia coli fimbrial proteins containing FimH, FimG, FimF, and FimC provides the most complete model to date for the arrangement of subunits assembled in the native structure. The first three proteins form the tip of the fimbriae while FimC is the chaperone protein involved in the usher/chaperone assembly process. The subunits interact through donor strand complementation where a ?-strand from a subunit completes the ?-sandwich structure of the neighboring subunit or domain closer to the tip of the fimbria. The function of FimC is to provide a surrogate donor strand before delivery of each subunit to the FimD usher and the growing fimbria. Comparison of the subunits in this structure and their chaperone-bound complexes show that the two FimH domains change their relative orientation and position in forming the tip structure. Also, the non-chaperone subunits undergo a conformational change in their first ?-strand when the chaperone is replaced by the native donor strand. Some residues move as much as 14Å in the process. This structural shift has not been noted in structural studies of other bacterial adhesion sub-structures assembled via donor strand complementation. The domains undergo a significant structural change in the donor strand binding groove during fimbrial assembly, and this likely plays a role in determining the specificity of subunit-subunit interactions among the fimbrial proteins.

SUBMITTER: Le Trong I

PROVIDER: S-EPMC2964381 | biostudies-literature | 2010 Dec

REPOSITORIES: biostudies-literature

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Donor strand exchange and conformational changes during E. coli fimbrial formation.

Le Trong Isolde I Aprikian Pavel P Kidd Brian A BA Thomas Wendy E WE Sokurenko Evgeni V EV Stenkamp Ronald E RE

Journal of structural biology 20100604 3

Fimbriae and pili are macromolecular structures on the surface of Gram negative bacteria that are important for cellular adhesion. A 2.7Å resolution crystal structure of a complex of Escherichia coli fimbrial proteins containing FimH, FimG, FimF, and FimC provides the most complete model to date for the arrangement of subunits assembled in the native structure. The first three proteins form the tip of the fimbriae while FimC is the chaperone protein involved in the usher/chaperone assembly proce ...[more]

PMID: 20570733

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Project description:Membrane attack complex/perforin-like (MACPF) proteins comprise the largest superfamily of pore-forming proteins, playing crucial roles in immunity and pathogenesis. Soluble monomers assemble into large transmembrane pores via conformational transitions that remain to be structurally and mechanistically characterised. Here we present an 11 Å resolution cryo-electron microscopy (cryo-EM) structure of the two-part, fungal toxin Pleurotolysin (Ply), together with crystal structures of both components (the lipid binding PlyA protein and the pore-forming MACPF component PlyB). These data reveal a 13-fold pore 80 Å in diameter and 100 Å in height, with each subunit comprised of a PlyB molecule atop a membrane bound dimer of PlyA. The resolution of the EM map, together with biophysical and computational experiments, allowed confident assignment of subdomains in a MACPF pore assembly. The major conformational changes in PlyB are a ∼70° opening of the bent and distorted central β-sheet of the MACPF domain, accompanied by extrusion and refolding of two α-helical regions into transmembrane β-hairpins (TMH1 and TMH2). We determined the structures of three different disulphide bond-trapped prepore intermediates. Analysis of these data by molecular modelling and flexible fitting allows us to generate a potential trajectory of β-sheet unbending. The results suggest that MACPF conformational change is triggered through disruption of the interface between a conserved helix-turn-helix motif and the top of TMH2. Following their release we propose that the transmembrane regions assemble into β-hairpins via top down zippering of backbone hydrogen bonds to form the membrane-inserted β-barrel. The intermediate structures of the MACPF domain during refolding into the β-barrel pore establish a structural paradigm for the transition from soluble monomer to pore, which may be conserved across the whole superfamily. The TMH2 region is critical for the release of both TMH clusters, suggesting why this region is targeted by endogenous inhibitors of MACPF function.

Dataset Information

Donor strand exchange and conformational changes during E. coli fimbrial formation.

Publications

Donor strand exchange and conformational changes during E. coli fimbrial formation.

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