title: Bacterial β-Kdo glycosyltransferases represent a new glycosyltransferase family (GT99).
abstract: Kdo (3-deoxy-d-manno-oct-2-ulosonic acid) is an eight-carbon sugar mostly confined to Gram-negative bacteria. It is often involved in attaching surface polysaccharides to their lipid anchors. α-Kdo provides a bridge between lipid A and the core oligosaccharide in all bacterial LPSs, whereas an oligosaccharide of β-Kdo residues links "group 2" capsular polysaccharides to (lyso)phosphatidylglycerol. β-Kdo is also found in a small number of other bacterial polysaccharides. The structure and function of the prototypical cytidine monophosphate-Kdo-dependent α-Kdo glycosyltransferase from LPS assembly is well characterized. In contrast, the β-Kdo counterparts were not identified as glycosyltransferase enzymes by bioinformatics tools and were not represented among the 98 currently recognized glycosyltransferase families in the Carbohydrate-Active Enzymes database. We report the crystallographic structure and function of a prototype β-Kdo GT from WbbB, a modular protein participating in LPS O-antigen synthesis in Raoultella terrigena The β-Kdo GT has dual Rossmann-fold motifs typical of GT-B enzymes, but extensive deletions, insertions, and rearrangements result in a unique architecture that makes it a prototype for a new GT family (GT99). The cytidine monophosphate-binding site in the C-terminal α/β domain closely resembles the corresponding site in bacterial sialyltransferases, suggesting an evolutionary connection that is not immediately evident from the overall fold or sequence similarities.
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: Department of Molecular and Cellular Biology, University of Guelph, Guelph, ON, Canada N1G 2W1;
authors.forename: Evan
authors.initials: E
authors.lastname: Mallette
authors.affiliation: Department of Chemistry and Alberta Glycomics Centre, University of Alberta, Edmonton, AB, Canada T6G 2R3.
authors.forename: Akihiko
authors.initials: A
authors.lastname: Koizumi
authors.affiliation: Department of Chemistry and Alberta Glycomics Centre, 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; mkimber@uoguelph.ca cwhitfie@uoguelph.ca.
authors.forename: Matthew S
authors.initials: MS
authors.lastname: Kimber
authors.affiliation: Department of Molecular and Cellular Biology, University of Guelph, Guelph, ON, Canada N1G 2W1; mkimber@uoguelph.ca cwhitfie@uoguelph.ca.
authors.forename: Chris
authors.identifier: 0000-0002-5267-7027
authors.initials: C
authors.lastname: Whitfield
mesh_terms: D002236:Carbohydrate Conformation; D018360:Crystallography, X-Ray; D004755:Enterobacteriaceae / Q000201:enzymology*; D006031:Glycosylation; D016695:Glycosyltransferases / Q000737:chemistry* / Q000378:metabolism*; D010802:Phylogeny; D011134:Polysaccharides / Q000737:chemistry / Q000378:metabolism*; D011487:Protein Conformation; D013400:Sugar Acids / Q000737:chemistry / Q000378:metabolism*
chemical_list: D011134:Polysaccharides; D013400:Sugar Acids; C002532:2-keto-3-deoxyoctonate; D016695:Glycosyltransferases
keywords: 3-deoxy-D-manno-oct-2-ulosonic acid; Kdo; glycosyltransferase; microbial glycobiology; polysaccharide