Expression and secretion in yeast of active insect defensin, an inducible antibacterial peptide from the fleshfly Phormia terranovae

Summary Insect defensin A is an inducible antibacterial peptide of the fleshfly Phormia terra-novae and has been recently characterized as a 40 residue basic peptide with six cysteines engaged in three intramolecular disulfide bridges. We report the expression of this peptide in Saccharomyces cerevisiae as a fusion protein carrying at its N-terminus leader sequences which are derived from the precursor of the yeast pheromone mating factor α (MFαl). These sequences allow the biologically active peptide to be secreted at high levels in a correctly processed form. Thus heterologous production of defensin A circumvents laborious purification of minute amounts of the peptide from its natural source. The insect defensin pro peptide can substitute for the MFαl pro peptide, indicating that yeast can process an insect pro sequence.