Solution structure of drosomycin, the first inducible antifungal protein from insects.

Drosomycin is the first antifungal protein characterized recently among the broad family of inducible peptides and proteins produced by insects to respond to bacterial or septic injuries. It is a small protein of 44 amino acid residues extracted from Drosophila melanogaster that exhibits a potent activity against filamentous fungi. Its three-dimensional structure in aqueous solution was determined using 1H 2D NMR. This structure, involving an alpha-helix and a twisted three-stranded beta-sheet, is stabilized by three disulfide bridges. The corresponding Cysteine Stabilized alpha beta (CS alpha beta) motif, which was found in other defense proteins such as the antibacterial insect defensin A, short- and long-chain scorpion toxins, as well as in plant thionins and potent antifungal plant defensins, appears as remarkably persistent along evolution.