Biosynthesis of uronamide sugars in Pseudomonas aeruginosa O6 and Escherichia coli O121 O antigens

Environ Microbiol. 2010 Jun;12(6):1531-44. doi: 10.1111/j.1462-2920.2010.02182.x. Epub 2010 Feb 25.

Abstract

The major component of the outer leaflet of the outer membrane of Gram-negative bacteria is lipopolysaccharide (LPS). The outermost domain of LPS is a polysaccharide called O antigen. Pseudomonas aeruginosa establishes biofilms on wet surfaces in a wide range of habitats and mutations in O-antigen biosynthesis genes affect bacterial adhesion and the structure of these biofilms. The P. aeruginosa O6 O antigen contains a 2-acetamido-2-deoxy-d-galacturonamide (d-GalNAcAN) residue. O-antigen biosynthesis in this serotype requires the wbpS gene, which encodes a protein with conserved domains of the glutamine-dependent amidotransferase family. Replacement of conserved amino acids in the N-terminal glutaminase conserved domain of WbpS inhibited O-antigen biosynthesis under restricted-ammonia conditions, but not in rich media; suggesting that this domain functions to provide ammonia for O-antigen biosynthesis under restricted-ammonia conditions, by hydrolysis of glutamine. Escherichia coli O121 also produces a d-GalNAcAN-containing O antigen, and possesses a homologue of wbpS called wbqG. An E. coli O121 wbqG mutant was cross-complemented by providing wbpS in trans, and vice versa, showing that these two genes are functionally interchangeable. The E. coli O121 wbqG mutant O antigen contains 2-acetamido-2-deoxy-d-galacturonate (d-GalNAcA), instead of d-GalNAcAN, demonstrating that wbqG is specifically required for biosynthesis of the carboxamide in this sugar.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Bacterial Proteins / genetics
  • Bacterial Proteins / metabolism
  • Carbohydrate Conformation
  • Carbohydrate Sequence
  • Escherichia coli / cytology
  • Escherichia coli / genetics
  • Escherichia coli / metabolism*
  • Genetic Complementation Test
  • Glutaminase / metabolism
  • Molecular Sequence Data
  • Mutagenesis, Site-Directed
  • Mutation
  • O Antigens / biosynthesis*
  • O Antigens / chemistry*
  • O Antigens / immunology
  • Pseudomonas aeruginosa / cytology
  • Pseudomonas aeruginosa / genetics
  • Pseudomonas aeruginosa / metabolism*
  • Uronic Acids / chemistry
  • Uronic Acids / metabolism*

Substances

  • Bacterial Proteins
  • O Antigens
  • O-antigen, E.coli O121
  • Uronic Acids
  • Glutaminase