title: Role of Rfe and RfbF in the initiation of biosynthesis of D-galactan I, the lipopolysaccharide O antigen from Klebsiella pneumoniae serotype O1.
abstract: The 6.6-kb rfb gene cluster from Klebsiella pneumoniae serotype O1 (rfbKpO1) contains six genes whose products are required for the biosynthesis of a lipopolysaccharide O antigen with the following repeating unit structure: -->3-beta-D-Galf-1-->3-alpha-D-Galp-1-->(D-galactan I). rfbFKpO1 is the last gene in the cluster, and its gene product is required for the initiation of D-galactan I synthesis. Escherichia coli K-12 strains expressing the RfbFKpO1 polypeptide contain dual galactopyranosyl and galactofuranosyl transferase activity. This activity modifies the host lipopolysaccharide core by adding the disaccharide beta-D-Galf-1-->3-alpha-D-Galp, representing a single repeating unit of D-galactan I. The formation of the lipopolysaccharide substituted either with the disaccharide or with authentic polymeric D-galactan I is dependent on the activity of the Rfe enzyme. Rfe (UDP-GlcpNAc::undecaprenylphosphate GlcpNAc-1-phosphate transferase) catalyzes the formation of the lipid-linked biosynthetic intermediate to which galactosyl residues are transferred during the initial steps of D-galactan I synthesis. The rfbFKpO1 gene comprises 1,131 nucleotides, and the predicted polypeptide consists of 373 amino acid residues with a predicted M(r) of 42,600. A polypeptide with an M(r) of 42,000 was evident in sodium dodecyl sulfate-polyacrylamide gels when rfbKpO1 was expressed behind the T7 promoter. The carboxy-terminal region of RfbFKpO1 shares similarity with the carboxy terminus of RfpB, a galactopyranosyl transferase which is involved in the synthesis of the type 1 O antigen of Shigella dysenteriae.
authors.affiliation: Department of Microbiology, University of Guelph, Ontario, Canada.
authors.forename: B R
authors.initials: BR
authors.lastname: Clarke
authors.forename: D
authors.initials: D
authors.lastname: Bronner
authors.forename: W J
authors.initials: WJ
authors.lastname: Keenleyside
authors.forename: W B
authors.initials: WB
authors.lastname: Severn
authors.forename: J C
authors.initials: JC
authors.lastname: Richards
authors.forename: C
authors.initials: C
authors.lastname: Whitfield
mesh_terms: D001483:Base Sequence; D002240:Carbohydrate Sequence; D003001:Cloning, Molecular; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism; D029968:Escherichia coli Proteins; D005685:Galactans / Q000096:biosynthesis*; D005700:Galactosyltransferases / Q000235:genetics / Q000378:metabolism*; D005798:Genes, Bacterial / Q000235:genetics; D007711:Klebsiella pneumoniae / Q000201:enzymology / Q000235:genetics*; D008969:Molecular Sequence Data; D005810:Multigene Family / Q000235:genetics; D019081:O Antigens / Q000096:biosynthesis*; D017422:Sequence Analysis, DNA; D012762:Shigella dysenteriae / Q000201:enzymology; D017855:Transferases (Other Substituted Phosphate Groups) / Q000378:metabolism*
chemical_list: D029968:Escherichia coli Proteins; D005685:Galactans; D019081:O Antigens; D005700:Galactosyltransferases; D017855:Transferases (Other Substituted Phosphate Groups); C083617:wecA protein, E coli