title: Modification of the 1-Phosphate Group during Biosynthesis of Capnocytophaga canimorsus Lipid A.
abstract: Capnocytophaga canimorsus, a commensal bacterium of dog's mouth flora causing severe infections in humans after dog bites or scratches, has a lipopolysaccharide (LPS) (endotoxin) with low-inflammatory lipid A. In particular, it contains a phosphoethanolamine (P-Etn) instead of a free phosphate group at the C-1 position of the lipid A backbone, usually present in highly toxic enterobacterial Gram-negative lipid A. Here we show that the C. canimorsus genome comprises a single operon encoding a lipid A 1-phosphatase (LpxE) and a lipid A 1 P-Etn transferase (EptA). This suggests that lipid A is modified during biosynthesis after completing acylation of the backbone by removal of the 1-phosphate and subsequent addition of an P-Etn group. As endotoxicity of lipid A is known to depend largely on the degree of unsubstituted or unmodified phosphate residues, deletion of lpxE or eptA led to mutants lacking the P-Etn group, with consequently increased endotoxicity and decreased resistance to cationic antimicrobial peptides (CAMP). Consistent with the proposed sequential biosynthetic mechanism, the endotoxicity and CAMP resistance of a double deletion mutant of lpxE-eptA was similar to that of a single lpxE mutant. Finally, the proposed enzymatic activities of LpxE and EptA based on sequence similarity could be successfully validated by mass spectrometry (MS)-based analysis of lipid A isolated from the corresponding deletion mutant strains.
authors.affiliation: Université de Namur, Namur, Belgium.
authors.forename: Francesco
authors.initials: F
authors.lastname: Renzi
authors.affiliation: Division of Immunochemistry, Research Center Borstel, Leibniz Center for Medicine and Biosciences, Borstel, Germany.
authors.forename: Ulrich
authors.initials: U
authors.lastname: Zähringer
authors.affiliation: Department of Microbial Pathogenesis, University of Maryland, Baltimore, Maryland, USA.
authors.forename: Courtney E
authors.initials: CE
authors.lastname: Chandler
authors.affiliation: Department of Microbial Pathogenesis, University of Maryland, Baltimore, Maryland, USA.
authors.forename: Robert K
authors.initials: RK
authors.lastname: Ernst
authors.affiliation: Université de Namur, Namur, Belgium Biozentrum der Universität Basel, Basel, Switzerland.
authors.forename: Guy R
authors.initials: GR
authors.lastname: Cornelis
authors.affiliation: Biozentrum der Universität Basel, Basel, Switzerland simon.ittig@unibas.ch.
authors.forename: Simon J
authors.initials: SJ
authors.lastname: Ittig
mesh_terms: D000818:Animals; D023181:Antimicrobial Cationic Peptides / Q000494:pharmacology; D002206:Capnocytophaga / Q000187:drug effects / Q000201:enzymology / Q000235:genetics* / Q000378:metabolism*; D004285:Dogs; D005798:Genes, Bacterial / Q000235:genetics; D005816:Genetic Complementation Test; D016680:Genome, Bacterial; D006801:Humans; D008050:Lipid A / Q000096:biosynthesis* / Q000737:chemistry / Q000235:genetics; D013058:Mass Spectrometry; D009876:Operon; D010710:Phosphates / Q000378:metabolism*; D017384:Sequence Deletion
chemical_list: D023181:Antimicrobial Cationic Peptides; D008050:Lipid A; D010710:Phosphates