title: The 3D structure of a periplasm-spanning platform required for assembly of group 1 capsular polysaccharides in Escherichia coli.
abstract: Capsular polysaccharides (CPSs) are essential virulence determinants of many pathogenic bacteria. Escherichia coli group 1 CPSs provide paradigms for widespread surface polysaccharide assembly systems in Gram-negative bacteria. In these systems, complex carbohydrate polymers must be exported across the periplasm and outer membrane to the cell surface. Group 1 CPS export requires oligomers of the outer membrane protein, Wza, for translocation across the outer membrane. Assembly also depends on Wzc, an inner membrane tyrosine autokinase known to regulate export and synthesis of group 1 CPS. Here, we provide a structural view of a complex comprising Wzc and Wza that spans the periplasm, connecting the inner and outer membranes. Examination of transmembrane sections of the complex suggests that the periplasm is compressed at the site of complex formation. An important feature of CPS production is the coupling of steps involved in biosynthesis and export. We propose that the Wza-Wzc complex provides the structural and regulatory core of a larger macromolecular machine. We suggest a mechanism by which CPS may move from the periplasm through the outer membrane.
authors.affiliation: Faculty of Life Science, University of Manchester, Manchester M60 1QD, United Kingdom.
authors.forename: Richard F
authors.initials: RF
authors.lastname: Collins
authors.forename: Konstantinos
authors.initials: K
authors.lastname: Beis
authors.forename: Changjiang
authors.initials: C
authors.lastname: Dong
authors.forename: Catherine H
authors.initials: CH
authors.lastname: Botting
authors.forename: Catherine
authors.initials: C
authors.lastname: McDonnell
authors.forename: Robert C
authors.initials: RC
authors.lastname: Ford
authors.forename: Bradley R
authors.initials: BR
authors.lastname: Clarke
authors.forename: Chris
authors.initials: C
authors.lastname: Whitfield
authors.forename: James H
authors.initials: JH
authors.lastname: Naismith
mesh_terms: D016667:Bacterial Capsules / Q000096:biosynthesis*; D001425:Bacterial Outer Membrane Proteins / Q000378:metabolism* / Q000502:physiology; D001692:Biological Transport; D019281:Dimerization; D004926:Escherichia coli / Q000737:chemistry / Q000378:metabolism; D029968:Escherichia coli Proteins / Q000378:metabolism* / Q000502:physiology; D008565:Membrane Proteins / Q000378:metabolism* / Q000502:physiology; D046912:Multiprotein Complexes / Q000378:metabolism / Q000502:physiology; D019897:Periplasm / Q000737:chemistry* / Q000378:metabolism; D011135:Polysaccharides, Bacterial / Q000378:metabolism*; D011505:Protein-Tyrosine Kinases / Q000378:metabolism* / Q000502:physiology
chemical_list: D001425:Bacterial Outer Membrane Proteins; D029968:Escherichia coli Proteins; D008565:Membrane Proteins; D046912:Multiprotein Complexes; D011135:Polysaccharides, Bacterial; C404158:Wza protein, E coli; D011505:Protein-Tyrosine Kinases; C499615:wzc protein, E coli