Regulated covalent modifications of lipid A.
Regulated covalent modifications of lipid A are implicated in virulence of pathogenic Gram-negative bacteria. The Salmonella PhoP/PhoQ-activated gene pagP is required for resistance to cationic antimicrobial peptides and for biosynthesis of hepta-acylated lipid A species containing palmitate. Interestingly, pagP encodes an unusual enzyme of lipid A biosynthesis localized in the outer membrane, whereas all previously characterized lipid A enzymes are cytoplasmic or associated with the inner membrane. PagP is not unique, however, as pagL encodes another outer membrane enzyme in Salmonella that deacylates the 3 position of lipid A.S. typhimurium also synthesizes S-2-hydroxymyristate modified lipid A in a PhoP/PhoQ-dependent manner. We postulated that 2-hydroxylation might be catalyzed by a novel dioxygenase. Using well-characterized dioxygenase sequences as probes, tBLASTn searches revealed unassigned open reading frame(s) with similarity to mammalian aspartyl beta-hydroxylases in bacteria known to make 2-hydroxyacylated lipid A. The S. typhimurium aspartyl beta-hydroxylase homologue (lpxO) was cloned and expressed in Escherichia coli K-12, which does not contain lpxO. Analysis of the resulting construct revealed that lpxO expression induces O(2)-dependent formation of 2-hydroxymyristate-modified lipid A in E. coli. LpxO may be an inner membrane enzyme that catalyzes Fe(2+)/ascorbate/alpha-ketoglutarate dependent hydroxylation of lipid A. We propose that 2-hydroxymyristate released from LPS inside infected animal cells might be converted to 2-hydroxymyristoyl coenzyme A, a potent inhibitor of protein N-myristoyl transferase.
Raetz
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Department of Biochemistry, Duke University Medical Center, Durham, NC, USA. raetz@biochem.duke.edu
D001426:Bacterial Proteins / Q000737:chemistry; D002265:Carboxylic Ester Hydrolases / Q000737:chemistry*; D002384:Catalysis; D002413:Cations, Divalent; D004926:Escherichia coli / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D008050:Lipid A / Q000096:biosynthesis / Q000737:chemistry*; D008274:Magnesium; D006899:Mixed Function Oxygenases / Q000096:biosynthesis / Q000737:chemistry / Q000235:genetics; D008956:Models, Chemical; D015394:Molecular Structure; D009227:Myristic Acids / Q000737:chemistry; D012486:Salmonella typhimurium / Q000737:chemistry* / Q000201:enzymology; D014157:Transcription Factors / Q000737:chemistry
D001426:Bacterial Proteins; D002413:Cations, Divalent; D008050:Lipid A; D009227:Myristic Acids; C409039:PmrB protein, bacteria; D014157:Transcription Factors; C081902:pmrA protein, Bacteria; C017418:alpha-hydroxymyristic acid; D006899:Mixed Function Oxygenases; C058291:aspartic acid 2-oxoglutarate-dependent dioxygenase; D002265:Carboxylic Ester Hydrolases; C424702:PagL protein, Salmonella typhimurium; D008274:Magnesium