title: Single polysaccharide assembly protein that integrates polymerization, termination, and chain-length quality control.
abstract: Lipopolysaccharides (LPS) are essential outer membrane glycolipids in most gram-negative bacteria. Biosynthesis of the O-antigenic polysaccharide (OPS) component of LPS follows one of three widely distributed strategies, and similar processes are used to assemble other bacterial surface glycoconjugates. This study focuses on the ATP-binding cassette (ABC) transporter-dependent pathway, where glycans are completed on undecaprenyl diphosphate carriers at the cytosol:membrane interface, before export by the ABC transporter. We describeRaoultella terrigenaWbbB, a prototype for a family of proteins that, remarkably, integrates several key activities in polysaccharide biosynthesis into a single polypeptide. WbbB contains three glycosyltransferase (GT) modules. Each of the GT102 and GT103 modules characterized here represents a previously unrecognized GT family. They form a polymerase, generating a polysaccharide of [4)-α-Rhap-(1→3)-β-GlcpNAc-(1→] repeat units. The polymer chain is terminated by a β-linked Kdo (3-deoxy-d-manno-oct-2-ulosonic acid) residue added by a third GT module belonging to the recently discovered GT99 family. The polymerase GT modules are separated from the GT99 chain terminator by a coiled-coil structure that forms a molecular ruler to determine product length. Different GT modules in the polymerase domains of other family members produce diversified OPS structures. These findings offer insight into glycan assembly mechanisms and the generation of antigenic diversity as well as potential tools for glycoengineering.
authors.affiliation: Department of Molecular and Cellular Biology, University of Guelph, Guelph, ON, Canada N1G 2W1.
authors.forename: Danielle M
authors.initials: DM
authors.lastname: Williams
authors.affiliation: Department of Molecular and Cellular Biology, University of Guelph, Guelph, ON, Canada N1G 2W1.
authors.forename: Olga G
authors.initials: OG
authors.lastname: Ovchinnikova
authors.affiliation: Alberta Glycomics Centre, University of Alberta, Edmonton, AB, Canada T6G 2R3.|Department of Chemistry, University of Alberta, Edmonton, AB, Canada T6G 2R3.
authors.forename: Akihiko
authors.initials: A
authors.lastname: Koizumi
authors.affiliation: Department of Molecular and Cellular Biology, University of Guelph, Guelph, ON, Canada N1G 2W1.
authors.forename: Iain L
authors.initials: IL
authors.lastname: Mainprize
authors.affiliation: Department of Molecular and Cellular Biology, University of Guelph, Guelph, ON, Canada N1G 2W1.
authors.forename: Matthew S
authors.initials: MS
authors.lastname: Kimber
authors.affiliation: Alberta Glycomics Centre, University of Alberta, Edmonton, AB, Canada T6G 2R3.|Department of Chemistry, University of Alberta, Edmonton, AB, Canada T6G 2R3.
authors.forename: Todd L
authors.initials: TL
authors.lastname: Lowary
authors.affiliation: Department of Molecular and Cellular Biology, University of Guelph, Guelph, ON, Canada N1G 2W1; cwhitfie@uoguelph.ca.
authors.forename: Chris
authors.identifier: 0000-0002-5267-7027
authors.initials: C
authors.lastname: Whitfield
mesh_terms: D018528:ATP-Binding Cassette Transporters / Q000378:metabolism; D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D053898:Biosynthetic Pathways / Q000235:genetics; D002240:Carbohydrate Sequence; D004755:Enterobacteriaceae / Q000235:genetics / Q000378:metabolism*; D016695:Glycosyltransferases / Q000235:genetics / Q000378:metabolism; D008070:Lipopolysaccharides / Q000737:chemistry / Q000378:metabolism*; D015394:Molecular Structure; D019081:O Antigens / Q000737:chemistry / Q000378:metabolism*; D058105:Polymerization; D011134:Polysaccharides / Q000737:chemistry / Q000378:metabolism; D011786:Quality Control; D017386:Sequence Homology, Amino Acid
chemical_list: D018528:ATP-Binding Cassette Transporters; D001426:Bacterial Proteins; D008070:Lipopolysaccharides; D019081:O Antigens; D011134:Polysaccharides; D016695:Glycosyltransferases
keywords: glycan biosynthesis; glycosyltransferases; lipopolysaccharides; microbial glycobiology; molecular ruler