title: Hemin-dependent modulation of the lipid A structure of Porphyromonas gingivalis lipopolysaccharide.
abstract: Porphyromonas gingivalis is a periopathogen strongly associated with the development of adult-type periodontitis. Both the virulence characteristics of periopathogens and host-related factors are believed to contribute to periodontitis. P. gingivalis lipopolysaccharide (LPS) displays a significant amount of lipid A structural heterogeneity, containing both penta- and tetra-acylated lipid A structures. However, little is known concerning how the lipid A structural content of P. gingivalis is regulated. Alterations in the lipid A content may facilitate the ability of P. gingivalis to modulate the innate host response to this bacterium. In this report, it is shown that the concentration of hemin in the growth medium significantly modulates the lipopolysaccharide lipid A structural content of P. gingivalis. Hemin is a key microenvironmental component of gingival cervicular fluid which is believed to vary depending upon the state of vascular ulceration. At low hemin concentrations, one major penta-acylated lipid A structure was found, whereas at high concentrations of hemin, multiple tetra- and penta-acylated lipid A structures were observed. Hemin concentrations, not iron acquisition, were responsible for the alterations in the lipid A structural content. The modifications of the lipid A structural content were independent of the LPS extraction procedure and occurred in a variety of laboratory strains as well as a freshly obtained clinical isolate. The known hemin binding proteins Kgp and HmuR contributed to the lipid A modulation sensing mechanism. To the best of our knowledge, this is the first report that hemin, a clinically relevant microenvironmental component for P. gingivalis, can modulate the lipid A structure found in a bacterium. Since tetra- and penta-acylated P. gingivalis lipid A structures have opposing effects on Toll-like receptor 4 activation, the alteration of the lipid A structural content may have significant effects on the host response to this bacterium.
authors.affiliation: Department of Periodontics, University of Washington, Box 357444, Seattle, Washington 98195, USA.
authors.forename: Montaser N
authors.initials: MN
authors.lastname: Al-Qutub
authors.forename: Pamela H
authors.initials: PH
authors.lastname: Braham
authors.forename: Lisa M
authors.initials: LM
authors.lastname: Karimi-Naser
authors.forename: Xinyan
authors.initials: X
authors.lastname: Liu
authors.forename: Caroline A
authors.initials: CA
authors.lastname: Genco
authors.forename: Richard P
authors.initials: RP
authors.lastname: Darveau
mesh_terms: D003470:Culture Media; D006427:Hemin / Q000737:chemistry / Q000378:metabolism*; D006801:Humans; D008050:Lipid A / Q000737:chemistry* / Q000378:metabolism*; D008070:Lipopolysaccharides / Q000737:chemistry* / Q000378:metabolism; D016966:Porphyromonas gingivalis / Q000254:growth & development / Q000378:metabolism*; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization / Q000379:methods
chemical_list: D003470:Culture Media; D008050:Lipid A; D008070:Lipopolysaccharides; D006427:Hemin