The active site of drosomycin, a small insect antifungal protein, delineated by comparison with the modeled structure of Rs-AFP2, a plant antifungal protein

Drosomycin is the first strictly antifungal protein isolated from an insect (Drosophila melanogaster). The solution structure of this 44-residue prote in has been reported previously. It involves a three-stranded beta-sheet an d an a-helix, the protein global fold being maintained by four disulfide br idges. Rs-AFP2 is a plant antifungal protein exhibiting 41% sequence simila rity with drosomycin. Mutational analysis of Rs-AFP2 showed the importance of some residues in the antifungal activity of the protein against the fung us target. In order to determine the structural features responsible for an tifungal activity in both drosomycin and Rs-AFP2, we modeled the three-dime nsional structure of Rs-AFP2, and of other antifungal proteins, using the s olution structure of drosomycin as a template. Structure analysis of drosom ycin and Rs-AFP2, and comparisons with the other modeled antifungal structu res, revealed that the two proteins shared a hydrophobic cluster located at the protein surface in which a lysine residue is embedded. Based on these close structural similarities and the experimental data available for Rs-AF P2 mutants, an antifungal active site of the insect protein is proposed.