title: Function of the Escherichia coli msbB gene, a multicopy suppressor of htrB knockouts, in the acylation of lipid A. Acylation by MsbB follows laurate incorporation by HtrB.
abstract: Overexpression of the Escherichia coli msbB gene on high copy plasmids suppresses the temperature-sensitive growth associated with mutations in the htrB gene. htrB encodes the lauroyl transferase of lipid A biosynthesis that acylates the intermediate (Kdo)2-lipid IVA (Brozek, K. A., and Raetz, C. R. H. (1990) J. Biol. Chem. 265, 15410-15417). Since msbB displays 27.5% identity and 42.2% similarity to htrB, we explored the possibility that msbB encodes a related acyltransferase. In contrast to htrB, extracts of strains with insertion mutations in msbB are not defective in transferring laurate from lauroyl acyl carrier protein to (Kdo)2-lipid IVA. However, extracts of msbB mutants do not efficiently acylate the product formed by HtrB, designated (Kdo)2-(lauroyl)-lipid IVA. Extracts of strains harboring msbB+ bearing plasmids acylate (Kdo)2-(lauroyl)-lipid IVA very rapidly compared with wild type. We solubilized and partially purified MsbB from an overproducing strain, lacking HtrB. MsbB transfers myristate or laurate, activated on ACP, to (Kdo)2-(lauroyl)-lipid IVA. Decanoyl, palmitoyl, palmitoleoyl, and (R)-3-hydroxymyristoyl-ACP are poor acyl donors. MsbB acylates (Kdo)2-(lauroyl)-lipid IVA about 100 times faster than (Kdo)2-lipid IVA. The slow, but measurable, rate whereby MsbB acts on (Kdo)2-lipid IVA may explain why overexpression of MsbB suppresses the temperature-sensitive phenotype of htrB mutations. Presumably, the acyloxyacyl group generated by excess MsbB substitutes for the one normally formed by HtrB.
authors.affiliation: Department of Biochemistry, Duke University Medical Center, Durham, North Carolina 27710, USA.
authors.forename: T
authors.initials: T
authors.lastname: Clementz
authors.forename: Z
authors.initials: Z
authors.lastname: Zhou
authors.forename: C R
authors.initials: CR
authors.lastname: Raetz
mesh_terms: D000215:Acylation; D000217:Acyltransferases; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism; D002236:Carbohydrate Conformation; D002240:Carbohydrate Sequence; D002474:Cell-Free System; D002852:Chromatography, Ion Exchange; D004926:Escherichia coli / Q000235:genetics* / Q000378:metabolism*; D029968:Escherichia coli Proteins; D005798:Genes, Bacterial; D016153:Genes, Suppressor; D005838:Genotype; D007850:Lauric Acids / Q000378:metabolism*; D008050:Lipid A / Q000031:analogs & derivatives* / Q000737:chemistry / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D008969:Molecular Sequence Data; D005810:Multigene Family; D013379:Substrate Specificity
chemical_list: D001426:Bacterial Proteins; D029968:Escherichia coli Proteins; D007850:Lauric Acids; D008050:Lipid A; C030358:lauric acid; D000217:Acyltransferases; C097895:MsbB protein, E coli