title: Lipid A modifications in polymyxin-resistant Salmonella typhimurium: PMRA-dependent 4-amino-4-deoxy-L-arabinose, and phosphoethanolamine incorporation.
abstract: Lipid A of Salmonella typhimurium can be resolved into multiple molecular species. Many of these substances are more polar than the predominant hexa-acylated lipid A 1,4'-bisphosphate of Escherichia coli K-12. By using new isolation methods, we have purified six lipid A subtypes (St1 to St6) from wild type S. typhimurium. We demonstrate that these lipid A variants are covalently modified with one or two 4-amino-4-deoxy-l-arabinose (l-Ara4N) moieties. Each lipid A species with a defined set of polar modifications can be further derivatized with a palmitoyl moiety and/or a 2-hydroxymyristoyl residue in place of the secondary myristoyl chain at position 3'. The unexpected finding that St5 and St6 contain two l-Ara4N residues accounts for the anomalous structures of lipid A precursors seen in S. typhimurium mutants defective in 3-deoxy-d-manno-octulosonic acid biosynthesis in which only the 1-phosphate group is modified with the l-Ara4N moiety (Strain, S. M., Armitage, I. M., Anderson, L., Takayama, K., Quershi, N., and Raetz, C. R. H. (1985) J. Biol. Chem. 260, 16089-16098). Phosphoethanolamine (pEtN)-modified lipid A species are much less abundant than l-Ara4N containing forms in wild type S. typhimurium grown in broth but accumulate to high levels when l-Ara4N synthesis is blocked in pmrA(C)pmrE(-) and pmrA(C)pmrF(-) mutants. Purification and analysis of selected compounds demonstrate that one or two pEtN moieties may be present. Our findings show that S. typhimurium contains versatile enzymes capable of modifying both the 1- and 4'-phosphates of lipid A with l-Ara4N and/or pEtN groups. PmrA null mutants of S. typhimurium produce lipid A species without any pEtN or l-Ara4N substituents. However, PmrA is not needed for the incorporation of 2-hydroxymyristate or palmitate.
authors.affiliation: Department of Biochemistry and the Duke NMR Spectroscopy Center, Duke University Medical Center, Durham, North Carolina 27710, USA.
authors.forename: Z
authors.initials: Z
authors.lastname: Zhou
authors.forename: A A
authors.initials: AA
authors.lastname: Ribeiro
authors.forename: S
authors.initials: S
authors.lastname: Lin
authors.forename: R J
authors.initials: RJ
authors.lastname: Cotter
authors.forename: S I
authors.initials: SI
authors.lastname: Miller
authors.forename: C R
authors.initials: CR
authors.lastname: Raetz
mesh_terms: D000606:Amino Sugars / Q000302:isolation & purification* / Q000494:pharmacology*; D001426:Bacterial Proteins / Q000737:chemistry* / Q000235:genetics*; D002240:Carbohydrate Sequence; D002845:Chromatography; D004926:Escherichia coli / Q000378:metabolism; D004983:Ethanolamines / Q000737:chemistry* / Q000494:pharmacology; D006868:Hydrolysis; D008050:Lipid A / Q000737:chemistry* / Q000378:metabolism*; D008956:Models, Chemical; D008969:Molecular Sequence Data; D009154:Mutation; D009227:Myristic Acids / Q000494:pharmacology; D019308:Palmitic Acid / Q000494:pharmacology; D011485:Protein Binding; D011487:Protein Conformation; D012486:Salmonella typhimurium / Q000378:metabolism*; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization
chemical_list: D000606:Amino Sugars; D001426:Bacterial Proteins; D004983:Ethanolamines; D008050:Lipid A; D009227:Myristic Acids; C081902:pmrA protein, Bacteria; C017418:alpha-hydroxymyristic acid; D019308:Palmitic Acid; C040134:4-amino-4-deoxyarabinose; C005448:phosphorylethanolamine