title: Multifunctionality and mechanism of ligand binding in a mosquito antiinflammatory protein.
abstract: The mosquito D7 salivary proteins are encoded by a multigene family related to the arthropod odorant-binding protein (OBP) superfamily. Forms having either one or two OBP domains are found in mosquito saliva. Four single-domain and one two-domain D7 proteins from Anopheles gambiae and Aedes aegypti (AeD7), respectively, were shown to bind biogenic amines with high affinity and with a stoichiometry of one ligand per protein molecule. Sequence comparisons indicated that only the C-terminal domain of AeD7 is homologous to the single-domain proteins from A. gambiae, suggesting that the N-terminal domain may bind a different class of ligands. Here, we describe the 3D structure of AeD7 and examine the ligand-binding characteristics of the N- and C-terminal domains. Isothermal titration calorimetry and ligand complex crystal structures show that the N-terminal domain binds cysteinyl leukotrienes (cysLTs) with high affinities (50-60 nM) whereas the C-terminal domain binds biogenic amines. The lipid chain of the cysLT binds in a hydrophobic pocket of the N-terminal domain, whereas binding of norepinephrine leads to an ordering of the C-terminal portion of the C-terminal domain into an alpha-helix that, along with rotations of Arg-176 and Glu-268 side chains, acts to bury the bound ligand.
authors.affiliation: Laboratory of Malaria and Vector Research, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Rockville, MD 20852, USA.
authors.forename: Eric
authors.initials: E
authors.lastname: Calvo
authors.forename: Ben J
authors.initials: BJ
authors.lastname: Mans
authors.forename: José M C
authors.initials: JM
authors.lastname: Ribeiro
authors.forename: John F
authors.initials: JF
authors.lastname: Andersen
mesh_terms: D000330:Aedes / Q000737:chemistry*; D000818:Animals; D000852:Anopheles / Q000737:chemistry; D000893:Anti-Inflammatory Agents / Q000737:chemistry* / Q000378:metabolism*; D001665:Binding Sites; D002151:Calorimetry; D019476:Insect Proteins / Q000737:chemistry* / Q000378:metabolism*; D017999:Leukotriene E4 / Q000737:chemistry; D008024:Ligands; D008958:Models, Molecular; D009638:Norepinephrine / Q000737:chemistry; D011485:Protein Binding; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D055672:Static Electricity
chemical_list: D000893:Anti-Inflammatory Agents; D019476:Insect Proteins; D008024:Ligands; D017999:Leukotriene E4; D009638:Norepinephrine