title: From agonist to antagonist: structure and dynamics of innate immune glycoprotein MD-2 upon recognition of variably acylated bacterial endotoxins.
abstract: The human immune response to an infection by Gram-negative bacteria involves detection of lipopolysaccharides (LPS), also known as endotoxins, which comprise the bacterial outer cell wall. Distinct from mammalian glycolipid structures, LPS have a conserved chemical pattern that is recognized by the pattern recognition receptor complex formed by myeloid differentiation protein 2 (MD-2) and toll-like receptor 4 (TLR4). A remarkable immune-mediated structure-toxicity relationship has been defined that relates to the number of acyl chains in the endotoxin. While there is a clear correlation between endotoxin acylation and elicited agonist or antagonist responses, the 3D structural basis of this relationship remains unclear. In order to explore, at atomic-resolution, the effects of a range of chemically distinct endotoxins on the structure and dynamics of their MD-2·endotoxin complexes, we examined a series of variably acylated lipid A molecules from Escherichia coli and Neisseria meningitidis in complex with human MD-2. Through the application of molecular dynamics simulations, in concert with experimental data, we have identified specific structural and dynamic features of the MD-2-endotoxin complexes that may control dimerization of TLR4 molecules. As dimerization is central to the release of downstream chemical mediators, the results provide a structural foundation for the ability of endotoxins to act as either agonists or antagonists of the TLR4 pathway.
authors.affiliation: Complex Carbohydrate Research Center, University of Georgia, GA 30602, USA. mdemarco@wustl.edu
authors.forename: Mari L
authors.initials: ML
authors.lastname: DeMarco
authors.forename: Robert J
authors.initials: RJ
authors.lastname: Woods
mesh_terms: D000215:Acylation; D006801:Humans; D007113:Immunity, Innate / Q000276:immunology; D008050:Lipid A / Q000737:chemistry* / Q000276:immunology* / Q000378:metabolism; D051218:Lymphocyte Antigen 96 / Q000737:chemistry* / Q000276:immunology* / Q000378:metabolism; D008958:Models, Molecular; D020836:Protein Structure, Quaternary; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D051197:Toll-Like Receptor 4 / Q000737:chemistry* / Q000276:immunology / Q000378:metabolism
chemical_list: C495377:LY96 protein, human; D008050:Lipid A; D051218:Lymphocyte Antigen 96; C495345:TLR4 protein, human; D051197:Toll-Like Receptor 4