title: The crystal structure of Escherichia coli group 4 capsule protein GfcC reveals a domain organization resembling that of Wza.
abstract: We report the 1.9 Å resolution crystal structure of enteropathogenic Escherichia coli GfcC, a periplasmic protein encoded by the gfc operon, which is essential for assembly of group 4 polysaccharide capsule (O-antigen capsule). Presumed gene orthologs of gfcC are present in capsule-encoding regions of at least 29 genera of Gram-negative bacteria. GfcC, a member of the DUF1017 family, is comprised of tandem β-grasp (ubiquitin-like) domains (D2 and D3) and a carboxyl-terminal amphipathic helix, a domain arrangement reminiscent of that of Wza that forms an exit pore for group 1 capsule export. Unlike the membrane-spanning C-terminal helix from Wza, the GfcC C-terminal helix packs against D3. Previously unobserved in a β-grasp domain structure is a 48-residue helical hairpin insert in D2 that binds to D3, constraining its position and sequestering the carboxyl-terminal amphipathic helix. A centrally located and invariant Arg115 not only is essential for proper localization but also forms one of two mostly conserved pockets. Finally, we draw analogies between a GfcC protein fused to an outer membrane β-barrel pore in some species and fusion proteins necessary for secreting biofilm-forming exopolysaccharides.
authors: Program in Biophysics, University of Michigan, Ann Arbor, Michigan 48109-1055, USA.
authors: Karthik
authors: K
authors: Sathiyamoorthy
authors: Erez
authors: E
authors: Mills
authors: Titus M
authors: TM
authors: Franzmann
authors: Ilan
authors: I
authors: Rosenshine
authors: Mark A
authors: MA
authors: Saper
mesh_terms: D000595:Amino Acid Sequence; D016667:Bacterial Capsules / Q000737:chemistry; D001425:Bacterial Outer Membrane Proteins / Q000737:chemistry* / Q000235:genetics; D001483:Base Sequence; D017124:Conserved Sequence; D018360:Crystallography, X-Ray; D004269:DNA, Bacterial / Q000235:genetics; D019281:Dimerization; D054308:Enteropathogenic Escherichia coli / Q000737:chemistry / Q000235:genetics; D029968:Escherichia coli Proteins / Q000737:chemistry* / Q000235:genetics; D005798:Genes, Bacterial; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009876:Operon; D054730:Protein Interaction Domains and Motifs; D020836:Protein Structure, Quaternary; D017434:Protein Structure, Tertiary; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics; D017386:Sequence Homology, Amino Acid; D055672:Static Electricity
chemical_list: D001425:Bacterial Outer Membrane Proteins; D004269:DNA, Bacterial; D029968:Escherichia coli Proteins; D011994:Recombinant Proteins; C404158:Wza protein, E coli