title: Repeat unit polysaccharides of bacteria: a model for polymerization resembling that of ribosomes and fatty acid synthetase, with a novel mechanism for determining chain length.
abstract: We report the identification and sequence from Escherichia coli and Salmonella enterica strains of the cld gene, encoding the chain-length determinant (CLD) which confers a modal distribution of chain length on the O-antigen component of lipopolysaccharide (LPS). The distribution of chain lengths in the absence of this gene fits a model in which as the chain is extended there is a constant probability of 0.165 of transfer of growing chain to LPS core, with termination of chain extension. The data for E. coli O111 fit a model in which the CLD reduces this probability for short chains and increases it to 0.4 for longer chains, leading to a reduced number of short chain molecules but an increase in numbers of longer molecules and transfer of essentially all molecules by chain length 21. We put forward a model for O-antigen polymerase which resembles the ribosome and fatty acid synthetase in having two sites, with the growing chain being transferred from a D site onto the new unit at the R site to extend the chain and then back to the D site to repeat the process. It is proposed that the CLD protein and polymerase form a complex which has two states: 'E' facilitating extension and 'T' facilitating transfer to core. The complex is postulated to enter the E state as O-antigen polymerization starts, and to shift to the T state after a predetermined time, the CLD acting as a molecular clock. The CLD is not O-antigen or species-specific but the modal value does depend on the source of the cld gene.
authors.affiliation: Department of Microbiology, University of Sydney, NSW, Australia.
authors.forename: D A
authors.initials: DA
authors.lastname: Bastin
authors.forename: G
authors.initials: G
authors.lastname: Stevenson
authors.forename: P K
authors.initials: PK
authors.lastname: Brown
authors.forename: A
authors.initials: A
authors.lastname: Haase
authors.forename: P R
authors.initials: PR
authors.lastname: Reeves
mesh_terms: D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D001483:Base Sequence; D002240:Carbohydrate Sequence; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism*; D029968:Escherichia coli Proteins; D064429:Fatty Acid Synthases / Q000378:metabolism*; D006602:Hexosyltransferases / Q000378:metabolism; D008070:Lipopolysaccharides / Q000378:metabolism*; D008954:Models, Biological; D008958:Models, Molecular; D008969:Molecular Sequence Data; D019081:O Antigens; D011108:Polymers; D011135:Polysaccharides, Bacterial / Q000235:genetics / Q000378:metabolism*; D011487:Protein Conformation; D012270:Ribosomes / Q000378:metabolism*; D012486:Salmonella typhimurium / Q000235:genetics / Q000378:metabolism*; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid
chemical_list: D001426:Bacterial Proteins; D029968:Escherichia coli Proteins; D008070:Lipopolysaccharides; D019081:O Antigens; D011108:Polymers; D011135:Polysaccharides, Bacterial; C489587:rol protein, Salmonella typhimurium; C489586:wzzB protein, E coli; C075969:rol protein, Bacteria; D064429:Fatty Acid Synthases; D006602:Hexosyltransferases; C068252:O-antigen polymerase, Salmonella