title: Wza the translocon for E. coli capsular polysaccharides defines a new class of membrane protein.
abstract: Many types of bacteria produce extracellular polysaccharides (EPSs). Some are secreted polymers and show only limited association with the cell surface, whereas others are firmly attached to the cell surface and form a discrete structural layer, the capsule, which envelopes the cell and allows the bacteria to evade or counteract the host immune system. EPSs have critical roles in bacterial colonization of surfaces, such as epithelia and medical implants; in addition some EPSs have important industrial and biomedical applications in their own right. Here we describe the 2.26 A resolution structure of the 340 kDa octamer of Wza, an integral outer membrane lipoprotein, which is essential for group 1 capsule export in Escherichia coli. The transmembrane region is a novel alpha-helical barrel. The bulk of the Wza structure is located in the periplasm and comprises three novel domains forming a large central cavity. Wza is open to the extracellular environment but closed to the periplasm. We propose a route and mechanism for translocation of the capsular polysaccharide. This work may provide insight into the export of other large polar molecules such as DNA and proteins.
authors.affiliation: Centre for Biomolecular Sciences, The University of St Andrews, Fife KY16 9RH, UK.
authors.forename: Changjiang
authors.initials: C
authors.lastname: Dong
authors.forename: Konstantinos
authors.initials: K
authors.lastname: Beis
authors.forename: Jutta
authors.initials: J
authors.lastname: Nesper
authors.forename: Anne L
authors.initials: AL
authors.lastname: Brunkan-Lamontagne
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 / Q000737:chemistry* / Q000378:metabolism; D001425:Bacterial Outer Membrane Proteins / Q000145:classification* / Q000378:metabolism*; D001692:Biological Transport; D004926:Escherichia coli / Q000378:metabolism*; D029968:Escherichia coli Proteins / Q000145:classification* / Q000378:metabolism*; D057927:Hydrophobic and Hydrophilic Interactions; D008958:Models, Molecular; D011135:Polysaccharides, Bacterial / Q000378:metabolism*; D011487:Protein Conformation; D013499:Surface Properties
chemical_list: D001425:Bacterial Outer Membrane Proteins; D029968:Escherichia coli Proteins; D011135:Polysaccharides, Bacterial; C404158:Wza protein, E coli