Structure and Protein-ligand Binding Studies of Pheromone Binding Protein-like Sol g 2.1 Protein from Solenopsis geminata Fire Ant Venom

Abstract

Abstract Sol g 2 is the major protein in Solenopsis geminata fire ant venom. It shares the highest sequence identity with Sol i 2 (S. invicta), and shares high structural homology with LmaPBP (pheromone binding protein (PBP) from the cockroach, Leucophaea maderae). We examined the specific Sol g 2 protein ligands from the fire ant venom. The results revealed that the protein naturally formed complexes with hydrocarbons, including decane undecane, dodecane, and tridecane, in aqueous venom solutions. We found that decane has a higher affinity binding with the recombinant Sol g 2.1 protein (rSol g 2.1) than other specific ligands. Surprisingly, the mixture of the alkanes showed higher binding affinity with rSol g 2.1 protein than any single one, a positive blend effect. The ligands were examined further by molecular docking simulations, which showed allosteric binding sites in the Sol g 2.1 protein model. We also performed a trail-following bioassay and found that rSol g 2.1 and the mixture of hydrocarbons elicited S. geminata worker ants to follow the trails for a longer time and distance than only a mixture of hydrocarbons, which suggests that Sol g 2.1 protein may delay the evaporation of the hydrocarbons. Interestingly, the fully reconstituted venom, which contained piperidine alkaloids and trail pheromones, has the highest attraction to the ants. Therefore, the mixture of hydrocarbons and the piperidines have a synergistic effect on the trail-following of the ants when both were added to the protein.