Structural and biochemical characterization of chemosensory proteins from the red imported fire ant, Solenopsis invicta.

Social insects including the red imported fire ant, Solenopsis invicta, rely on the sensing of a variety of odorants to interpret numerous environmental cues and to communicate with each other.  Chemosensory proteins (CSPs) represent a category of small hydrophobic ligand binding proteins with the potential to bind a broad range of different odorants and chemicals.  CSPs facilitate the reception and clearing of molecules from the odorant receptors found in the membranes of odorant receptor neurons.  A number of S. invicta CSPs were expressed and purified from a recombinant E. coli host. S. invicta CSPs appeared remarkably stable retaining structure at high temperatures (up to 80^oC).  A number of approaches were used to probe the stability of the purified CSPs. Since CSPs have a set of conserved disulfide linkages, quantitative cysteine reactivity, a method used to analyze protein stability during denaturation via reactivity of exposed cysteine was explored. In addition, circular dichroism spectroscopy was used to examine protein secondary structure in the presence of specific potential ligands.  Ligand binding was also assessed using thermal denaturation profiles via Sypro Orange melting curves, with the goal of developing a facile assay for testing the specificities of individual CSPs.