title: Three-dimensional structure of Wza, the protein required for translocation of group 1 capsular polysaccharide across the outer membrane of Escherichia coli.
abstract: Wza is a highly conserved multimeric outer membrane protein complex required for the surface expression of the serotype K30 group 1 capsular polysaccharide in Escherichia coli. Here we present the first three-dimensional structure of this type of polysaccharide exporter at a 15.5-A resolution obtained using single particle averaging on a dataset of cryo-negatively stained protein. Previous structural studies on purified Wza have revealed a homo-oligomeric ring structure that is most probably composed of eight subunits. Symmetry analysis of the three-dimensional structure combined with biochemical two- and three-dimensional crystallographic data strongly suggest that Wza is an octameric complex with a C4 quasi-rotational symmetry and is organized as a tetramer of dimeric subunits. Wza is best described as a stack of two 4-A high rings with differing diameters providing a mushroom-like aspect from the side. The larger ring has a distinctive square shape with a diameter of 115 A, whereas the smaller is almost circular with a diameter of 90 A. In the center of the complex and enclosed by the four symmetrical arms is a small elliptical cagelike cavity of approximately 40 A in diameter. The central cavity is effectively sealed at the top and bottom of the complex but has small inter-arm holes when viewed from the side. We discuss the structure of this complex and implications in the surface translocation of cell-surface polysaccharide.
authors.affiliation: Centre for Biomolecular Sciences, University of St. Andrews, North Haugh, St. Andrews, Fife KY16 9ST, Scotland, United Kingdom.
authors.forename: Konstantinos
authors.initials: K
authors.lastname: Beis
authors.forename: Richard F
authors.initials: RF
authors.lastname: Collins
authors.forename: Robert C
authors.initials: RC
authors.lastname: Ford
authors.forename: Alhaji B
authors.initials: AB
authors.lastname: Kamis
authors.forename: Chris
authors.initials: C
authors.lastname: Whitfield
authors.forename: James H
authors.initials: JH
authors.lastname: Naismith
mesh_terms: D001425:Bacterial Outer Membrane Proteins / Q000737:chemistry*; D001692:Biological Transport; D020285:Cryoelectron Microscopy; D003460:Crystallization; D018360:Crystallography, X-Ray; D019281:Dimerization; D029968:Escherichia coli Proteins / Q000737:chemistry*; D007091:Image Processing, Computer-Assisted; D008854:Microscopy, Electron; D008958:Models, Molecular; D011134:Polysaccharides / Q000737:chemistry*; D011487:Protein Conformation; D017434:Protein Structure, Tertiary; D021381:Protein Transport
chemical_list: D001425:Bacterial Outer Membrane Proteins; D029968:Escherichia coli Proteins; D011134:Polysaccharides; C404158:Wza protein, E coli