title: Biochemical and structural analysis of bacterial O-antigen chain length regulator proteins reveals a conserved quaternary structure.
abstract: Lipopolysaccharide (LPS) is a major component of the Gram-negative outer membrane and is an important virulence determinant. The O-antigen polysaccharide of the LPS molecule provides protection from host defenses, and the length of O-antigen chains plays a pivotal role. In the Wzy-dependent O-antigen biosynthesis pathway, the integral inner membrane protein Wzz determines the O-antigen chain length. How these proteins function is currently unknown, but the hypothesis includes activities such as a "molecular ruler" or a "molecular stopwatch," and other possibilities may exist. Wzz homologs are membrane proteins with two transmembrane helices that flank a large periplasmic domain. Recent x-ray crystallographic studies of the periplasmic portions of Wzz proteins found multiple oligomeric forms, with quaternary structures favoring the "molecular ruler" interpretation. Here, we have studied full-length Wzz proteins with the transmembrane portions embedded in lipid membranes. Using electron microscopy and image analysis we find a unique hexameric state rather than differing oligomeric forms. The data suggest that in vivo Wzz proteins determine O-antigen chain length via subtle structure-function relationships at the level of primary, secondary, or tertiary structure within the context of a hexameric complex.
authors.affiliation: Department of Molecular and Cellular Biology, University of Guelph, Guelph, Ontario N1G 2W1, Canada.
authors.forename: Kane
authors.initials: K
authors.lastname: Larue
authors.forename: Matthew S
authors.initials: MS
authors.lastname: Kimber
authors.forename: Robert
authors.initials: R
authors.lastname: Ford
authors.forename: Chris
authors.initials: C
authors.lastname: Whitfield
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D002240:Carbohydrate Sequence; D002462:Cell Membrane / Q000201:enzymology* / Q000235:genetics; D016695:Glycosyltransferases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D019081:O Antigens / Q000096:biosynthesis / Q000737:chemistry*; D019897:Periplasm / Q000201:enzymology* / Q000235:genetics; D020836:Protein Structure, Quaternary / Q000502:physiology; D017434:Protein Structure, Tertiary / Q000502:physiology; D012486:Salmonella typhimurium / Q000201:enzymology* / Q000235:genetics; D013329:Structure-Activity Relationship
chemical_list: D001426:Bacterial Proteins; D019081:O Antigens; D016695:Glycosyltransferases