title: Identification of an ATP-binding cassette transport system required for translocation of lipopolysaccharide O-antigen side-chains across the cytoplasmic membrane of Klebsiella pneumoniae serotype O1.
abstract: The rfbKpO1 gene cluster of Klebsiella pneumoniae O1 directs synthesis of the D-galactan I component of the lipopolysaccharide O-antigen. The first two genes in the rfbKpO1 cluster encode RfbAKpO1 and RfbBKpO1, with predicted sizes of 29.5 or 30.0 kDa and 27.4 kDa, respectively. RfbBKpO1 contains a consensus ATP-binding domain and shares homology with several proteins which function as ATP-binding components of cell surface polysaccharide transporters. RfbAKpO1 is predicted to be an integral membrane protein with five putative membrane-spanning domains and its transmembrane topology was confirmed by TnphoA mutagenesis. The hydropathy plot of RfbAKpO1 resembles KpsM, the transcytoplasmic membrane component of the capsular polysaccharide transporter from Escherichia coli K-1 and K-5. These relationships suggest that RfbAKpO1 and RfbBKpO1 belong to a family of two-component ABC (ATP-binding cassette) transporters. E. coli K-12 containing a plasmid carrying an rfbKpO1 gene cluster deleted in rfbAKpO1 and rfbBKpO1 expresses rough lipopolysaccharide molecules on its surface and accumulates cytoplasmic O-antigen. When RfbAKpO1 and RfbBKpO1 are supplied in trans by a compatible plasmid, O-polysaccharide transport is restored and smooth D-galactan I-substituted lipopolysaccharide is produced. RfbAKpO1 and RfbBKpO1 are, therefore, proposed to constitute a system required for transport of D-galactan I across the cytoplasmic membrane, where RfbAKpO1 represents the membrane-spanning translocator and RfbBKpO1 couples the energy of ATP hydrolysis ot the transport process.
authors.affiliation: Department of Microbiology, University of Guelph, Ontario, Canada.
authors.forename: D
authors.initials: D
authors.lastname: Bronner
authors.forename: B R
authors.initials: BR
authors.lastname: Clarke
authors.forename: C
authors.initials: C
authors.lastname: Whitfield
mesh_terms: D018528:ATP-Binding Cassette Transporters / Q000235:genetics / Q000378:metabolism*; D000255:Adenosine Triphosphate / Q000378:metabolism; D000595:Amino Acid Sequence; D001483:Base Sequence; D001693:Biological Transport, Active; D002240:Carbohydrate Sequence; D002462:Cell Membrane / Q000378:metabolism; D002874:Chromosome Mapping; D003001:Cloning, Molecular; D003062:Codon / Q000235:genetics; D004269:DNA, Bacterial / Q000235:genetics; D005798:Genes, Bacterial; D007711:Klebsiella pneumoniae / Q000145:classification / Q000235:genetics / Q000378:metabolism*; D016253:Microscopy, Immunoelectron; D008969:Molecular Sequence Data; D005810:Multigene Family; D019081:O Antigens; D011135:Polysaccharides, Bacterial / Q000737:chemistry / Q000378:metabolism*; D017386:Sequence Homology, Amino Acid; D012703:Serotyping
chemical_list: D018528:ATP-Binding Cassette Transporters; D003062:Codon; D004269:DNA, Bacterial; D019081:O Antigens; D011135:Polysaccharides, Bacterial; D000255:Adenosine Triphosphate