title: Crystal structure of Sol I 2: a major allergen from fire ant venom.
abstract: Sol i 2 is a potent allergen from the venom of red imported fire ant, which contains allergens Sol i 1, Sol i 2, Sol i 3, and Sol i 4 that are known to be powerful triggers of anaphylaxis. Sol i 2 causes IgE antibody production in about one-third of individuals stung by fire ants. Baculovirus recombinant dimeric Sol i 2 was crystallized as a native and selenomethionyl-derivatized protein, and its structure has been determined by single-wavelength anomalous dispersion at 2.6 Å resolution. The overall fold of each subunit consists of five helices that enclose a central hydrophobic cavity. The structure is stabilized by three intramolecular disulfide bridges and one intermolecular disulfide bridge. The nearest structural homologue is the sequence-unrelated odorant binding protein and pheromone binding protein LUSH of the fruit fly Drosophila, which may suggest a similar biological function. To test this hypothesis, we measured the reversible binding of various pheromones, plant odorants, and other ligands to Sol i 2 by the changes in N-phenyl-1-naphthylamine fluorescence emission upon binding of ligands that compete with N-phenyl-1-naphthylamine. The highest binding affinity was observed for hydrophobic ligands such as aphid alarm pheromone (E)-β-farnesene, analogs of ant alarm pheromones, and plant volatiles decane, undecane, and β-caryophyllene. Conceivably, Sol i 2 may play a role in capturing and/or transporting small hydrophobic ligands such as pheromones, odors, fatty acids, or short-living hydrophobic primers. Molecular surface analysis, in combination with sequence alignment, can explain the serological cross-reactivity observed between some ant species.
authors.affiliation: Department of Structural Biology, Biozentrum, University of Basel, Basel, Switzerland.
authors.forename: Aline S
authors.initials: AS
authors.lastname: Borer
authors.forename: Paul
authors.initials: P
authors.lastname: Wassmann
authors.forename: Margit
authors.initials: M
authors.lastname: Schmidt
authors.forename: Donald R
authors.initials: DR
authors.lastname: Hoffman
authors.forename: Jing-Jiang
authors.initials: JJ
authors.lastname: Zhou
authors.forename: Christine
authors.initials: C
authors.lastname: Wright
authors.forename: Tilman
authors.initials: T
authors.lastname: Schirmer
authors.forename: Zora
authors.initials: Z
authors.lastname: Marković-Housley
mesh_terms: D000485:Allergens / Q000737:chemistry* / Q000378:metabolism; D000595:Amino Acid Sequence; D000818:Animals; D000862:Ant Venoms / Q000737:chemistry* / Q000276:immunology / Q000378:metabolism; D001665:Binding Sites; D001667:Binding, Competitive; D018360:Crystallography, X-Ray; D019476:Insect Proteins / Q000737:chemistry* / Q000378:metabolism; D008024:Ligands; D008954:Models, Biological; D008958:Models, Molecular; D008969:Molecular Sequence Data; D011485:Protein Binding; D017433:Protein Structure, Secondary; D017386:Sequence Homology, Amino Acid
chemical_list: D000485:Allergens; D000862:Ant Venoms; D019476:Insect Proteins; D008024:Ligands; C080289:Sol i II protein, Solenopsis invicta