title: The Combining Sites of Anti-lipid A Antibodies Reveal a Widely Utilized Motif Specific for Negatively Charged Groups.
abstract: Lipopolysaccharide dispersed in the blood by Gram-negative bacteria can be a potent inducer of septic shock. One research focus has been based on antibody sequestration of lipid A (the endotoxic principle of LPS); however, none have been successfully developed into a clinical treatment. Comparison of a panel of anti-lipid A antibodies reveals highly specific antibodies produced through distinct germ line precursors. The structures of antigen-binding fragments for two homologous mAbs specific for lipid A, S55-3 and S55-5, have been determined both in complex with lipid A disaccharide backbone and unliganded. These high resolution structures reveal a conserved positively charged pocket formed within the complementarity determining region H2 loops that binds the terminal phosphates of lipid A. Significantly, this motif occurs in unrelated antibodies where it mediates binding to negatively charged moieties through a range of epitopes, including phosphorylated peptides used in diagnostics and therapeutics. S55-3 and S55-5 have combining sites distinct from anti-lipid A antibodies previously described (as a result of their separate germ line origin), which are nevertheless complementary both in shape and charge to the antigen. S55-3 and S55-5 display similar avidity toward lipid A despite possessing a number of different amino acid residues in their combining sites. Binding of lipid A occurs independent of the acyl chains, although the GlcN-O6 attachment point for the core oligosaccharide is buried in the combining site, which explains their inability to recognize LPS. Despite their lack of therapeutic potential, the observed motif may have significant immunological implications as a tool for engineering recombinant antibodies.
authors.affiliation: From the Department of Biochemistry and Microbiology, University of Victoria, Victoria, British Columbia V8P 3P6, Canada and.
authors.forename: Omid
authors.initials: O
authors.lastname: Haji-Ghassemi
authors.affiliation: the Research Center Borstel, Leibniz-Center for Medicine and Biosciences, Parkallee 22, Borstel D-23845, Germany sml@fz-borstel.de.
authors.forename: Sven
authors.initials: S
authors.lastname: Müller-Loennies
authors.affiliation: From the Department of Biochemistry and Microbiology, University of Victoria, Victoria, British Columbia V8P 3P6, Canada and.
authors.forename: Teresa
authors.initials: T
authors.lastname: Rodriguez
authors.affiliation: the Research Center Borstel, Leibniz-Center for Medicine and Biosciences, Parkallee 22, Borstel D-23845, Germany.
authors.forename: Lore
authors.initials: L
authors.lastname: Brade
authors.affiliation: the Research Center Borstel, Leibniz-Center for Medicine and Biosciences, Parkallee 22, Borstel D-23845, Germany.
authors.forename: Hans-Dieter
authors.initials: HD
authors.lastname: Grimmecke
authors.affiliation: the Research Center Borstel, Leibniz-Center for Medicine and Biosciences, Parkallee 22, Borstel D-23845, Germany.
authors.forename: Helmut
authors.initials: H
authors.lastname: Brade
authors.affiliation: From the Department of Biochemistry and Microbiology, University of Victoria, Victoria, British Columbia V8P 3P6, Canada and svevans@uvic.ca.
authors.forename: Stephen V
authors.initials: SV
authors.lastname: Evans
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D000911:Antibodies, Monoclonal / Q000737:chemistry / Q000276:immunology* / Q000378:metabolism; D001666:Binding Sites, Antibody; D022801:Complementarity Determining Regions / Q000737:chemistry / Q000276:immunology* / Q000378:metabolism; D018360:Crystallography, X-Ray; D000939:Epitopes / Q000737:chemistry / Q000276:immunology* / Q000378:metabolism; D007140:Immunoglobulin Fab Fragments / Q000737:chemistry / Q000276:immunology* / Q000378:metabolism; D008050:Lipid A / Q000737:chemistry / Q000276:immunology* / Q000378:metabolism; D008070:Lipopolysaccharides / Q000737:chemistry / Q000276:immunology* / Q000378:metabolism; D051379:Mice; D008807:Mice, Inbred BALB C; D008958:Models, Molecular; D008969:Molecular Sequence Data; D017434:Protein Structure, Tertiary; D017386:Sequence Homology, Amino Acid
chemical_list: D000911:Antibodies, Monoclonal; D022801:Complementarity Determining Regions; D000939:Epitopes; D007140:Immunoglobulin Fab Fragments; D008050:Lipid A; D008070:Lipopolysaccharides
keywords: X-ray crystallography; lipid A; lipopolysaccharide (LPS); monoclonal antibody; protein structure; recognition pocket