Biosynthesis of inner core lipopolysaccharide in enteric bacteria identification and characterization of a conserved phosphoheptose isomerase.
The lpcA locus has been identified in Escherichia coli K12 novobiocin-supersensitive mutants that produce a short lipopolysaccharide (LPS) core which lacks glyceromannoheptose and terminal hexoses. We have characterized lpcA as a single gene mapping around 5.3 min (246 kilobases) on the E. coli K12 chromosome and encoding a 22.6-kDa cytosolic protein. Recombinant plasmids containing only lpcA restored a complete core LPS in the E. coli strain chi711. We show that this strain has an IS5-mediated chromosomal deletion of 35 kilobases that eliminates lpcA. The LpcA protein showed discrete similarities with a family of aldose/ketose isomerases and other proteins of unknown function. The isomerization of sedoheptulose 7-phosphate, into a phosphosugar presumed to be D-glycero-D-mannoheptose 7-phosphate, was detected in enzyme reactions with cell extracts of E. coli lpcA+ and of lpcA mutants containing the recombinant lpcA gene. We concluded that LpcA is the phosphoheptose isomerase used in the first step of glyceromannoheptose synthesis. We also demonstrated that lpcA is conserved among enteric bacteria, all of which contain glyceromannoheptose in the inner core LPS, indicating that LpcA is an essential component in a conserved biosynthetic pathway of inner core LPS.
Brooke
J S
JS
Department of Microbiology and Immunology, University of Western Ontario, London, Ontario, N6A 5C1 Canada.
Valvano
M A
MA
D019747:Aldose-Ketose Isomerases; D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D002238:Carbohydrate Epimerases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D050260:Carbohydrate Metabolism; D002241:Carbohydrates / Q000032:analysis; D002851:Chromatography, High Pressure Liquid; D002872:Chromosome Deletion; D002876:Chromosomes, Bacterial; D017124:Conserved Sequence; D004755:Enterobacteriaceae / Q000201:enzymology* / Q000235:genetics / Q000276:immunology; D004926:Escherichia coli / Q000201:enzymology* / Q000235:genetics / Q000276:immunology; D005798:Genes, Bacterial; D005838:Genotype; D008070:Lipopolysaccharides / Q000096:biosynthesis*; D008969:Molecular Sequence Data; D051381:Rats; D015183:Restriction Mapping; D017386:Sequence Homology, Amino Acid
D002241:Carbohydrates; D008070:Lipopolysaccharides; D002238:Carbohydrate Epimerases; D019747:Aldose-Ketose Isomerases; C023917:phosphoheptose isomerase