Crystal structure of Sol I 2: a major allergen from fire ant venom

J Mol Biol. 2012 Jan 27;415(4):635-48. doi: 10.1016/j.jmb.2011.10.009. Epub 2011 Nov 12.


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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Allergens / chemistry*
  • Allergens / metabolism
  • Amino Acid Sequence
  • Animals
  • Ant Venoms / chemistry*
  • Ant Venoms / immunology
  • Ant Venoms / metabolism
  • Binding Sites
  • Binding, Competitive
  • Crystallography, X-Ray
  • Insect Proteins / chemistry*
  • Insect Proteins / metabolism
  • Ligands
  • Models, Biological
  • Models, Molecular
  • Molecular Sequence Data
  • Protein Binding
  • Protein Structure, Secondary
  • Sequence Homology, Amino Acid


  • Allergens
  • Ant Venoms
  • Insect Proteins
  • Ligands
  • Sol i II protein, Solenopsis invicta