title: The Klebsiella pneumoniae O2a antigen defines a second mechanism for O antigen ATP-binding cassette transporters.
abstract: An ATP-binding cassette (ABC) transporter-dependent mechanism is responsible for the biosynthesis of polysaccharide O antigens in the lipopolysaccharides of many Gram-negative bacteria. In the Escherichia coli O9a prototype, addition of a non-reducing terminal modification regulates chain length. The terminal residue is an export signal recognized by the nucleotide-binding domain component of the cognate ABC transporter. The Klebsiella pneumoniae O2a antigen lacks a capping residue, and the corresponding nucleotide-binding protein does not contain a separate substrate-binding domain. Unlike the O9a transporter, the O2a transporter can export heterologous O antigens. Export of the O2a antigen is obligatorily coupled to chain elongation, and the O2a transporter is essential for establishing O antigen chain length. The E. coli O9a transporter operates after chain length has been determined. Furthermore biosynthesis and export can be uncoupled. O antigen chain length is a critical element in the ability of lipopolysaccharides to confer resistance to complement-mediated killing. This study establishes that two distinctly different approaches are available for the regulation of O antigen chain length and export via an ABC transporter.
authors.affiliation: Department of Molecular and Cellular Biology, University of Guelph, Guelph, Ontario N1G 2W1, Canada.
authors.forename: Veronica
authors.initials: V
authors.lastname: Kos
authors.affiliation: Department of Molecular and Cellular Biology, University of Guelph, Guelph, Ontario N1G 2W1, Canada.
authors.forename: Leslie
authors.initials: L
authors.lastname: Cuthbertson
authors.affiliation: Department of Molecular and Cellular Biology, University of Guelph, Guelph, Ontario N1G 2W1, Canada. Electronic address: cwhitfie@uoguelph.ca.
authors.forename: Chris
authors.initials: C
authors.lastname: Whitfield
mesh_terms: D018528:ATP-Binding Cassette Transporters / Q000737:chemistry / Q000502:physiology*; D000595:Amino Acid Sequence; D002240:Carbohydrate Sequence; D007711:Klebsiella pneumoniae / Q000276:immunology*; D008856:Microscopy, Fluorescence; D008969:Molecular Sequence Data; D019081:O Antigens / Q000276:immunology*; D017386:Sequence Homology, Amino Acid
chemical_list: D018528:ATP-Binding Cassette Transporters; D019081:O Antigens