title: Altered linkage of hydroxyacyl chains in lipid A of Campylobacter jejuni reduces TLR4 activation and antimicrobial resistance.
abstract: Modification of the lipid A moiety of bacterial lipopolysaccharide influences cell wall properties, endotoxic activity, and bacterial resistance to antimicrobial peptides. Known modifications are variation in the number or length of acyl chains and/or attached phosphoryl groups. Here we identified two genes (gnnA and gnnB) in the major foodborne pathogen Campylobacter jejuni that enable the synthesis of a GlcN3N precursor UDP 2-acetamido-3-amino-2,3-dideoxy-alpha-D-glucopyranose (UDP-GlcNAc3N) in the lipid A backbone. Mass spectrometry of purified lipooligosaccharide verified that the gene products facilitate the formation of a 2,3-diamino-2,3-dideoxy-D-glucose (GlcN3N) disaccharide lipid A backbone when compared with the beta-1'-6-linked D-glucosamine (GlcN) disaccharide observed in Escherichia coli lipid A. Functional assays showed that inactivation of the gnnA or gnnB gene enhanced the TLR4-MD2-mediated NF-kappaB activation. The mutants also displayed increased susceptibility to killing by the antimicrobial peptides polymyxin B, colistin and the chicken cathelicidin-1. The gnnA and gnnB genes are organized in one operon with hemH, encoding a ferrochelatase catalyzing the last step in heme biosynthesis. These results indicate that lipid A modification resulting in amide-linked acyl chains in the lipid A is an effective mechanism to evade activation of the innate host defense and killing by antimicrobial peptides.
authors.affiliation: Department of Infectious Diseases and Immunology, Utrecht University, Yalelaan 1, 3584 CL Utrecht, The Netherlands.
authors.forename: Andries
authors.initials: A
authors.lastname: van Mourik
authors.forename: Liana
authors.initials: L
authors.lastname: Steeghs
authors.forename: Jacoline
authors.initials: J
authors.lastname: van Laar
authors.forename: Hugo D
authors.initials: HD
authors.lastname: Meiring
authors.forename: Hendrik-Jan
authors.initials: HJ
authors.lastname: Hamstra
authors.forename: Jos P M
authors.initials: JP
authors.lastname: van Putten
authors.forename: Marc M S M
authors.initials: MM
authors.lastname: Wösten
mesh_terms: D000818:Animals; D000890:Anti-Infective Agents / Q000494:pharmacology*; D016123:Campylobacter jejuni / Q000235:genetics / Q000276:immunology / Q000378:metabolism* / Q000472:pathogenicity; D002236:Carbohydrate Conformation; D002645:Chickens; D024881:Drug Resistance, Bacterial / Q000187:drug effects* / Q000235:genetics; D006367:HeLa Cells; D006801:Humans; D008050:Lipid A / Q000235:genetics / Q000276:immunology / Q000378:metabolism*; D051218:Lymphocyte Antigen 96 / Q000235:genetics / Q000276:immunology / Q000378:metabolism; D016328:NF-kappa B / Q000235:genetics / Q000276:immunology / Q000378:metabolism; D009876:Operon / Q000276:immunology; D051197:Toll-Like Receptor 4 / Q000235:genetics / Q000276:immunology / Q000378:metabolism*; D014539:Uridine Diphosphate Sugars / Q000235:genetics / Q000378:metabolism*
chemical_list: D000890:Anti-Infective Agents; C495377:LY96 protein, human; D008050:Lipid A; D051218:Lymphocyte Antigen 96; D016328:NF-kappa B; C495345:TLR4 protein, human; D051197:Toll-Like Receptor 4; D014539:Uridine Diphosphate Sugars