ACUTE TRANSCRIPTIONAL RESPONSE OF THE HONEYBEE PEPTIDE-ANTIBIOTICS GENE REPERTOIRE AND REQUIRED POSTTRANSLATIONAL CONVERSION OF THE PRECURSOR STRUCTURES

The cell free immune repertoire of honeybees (Apis mellifera) consists of four polypeptides that are induced by bacterial infection and, thr ough complementarity, provide broad-spectrum antibacterial defense. ap idaecin is overproduced by a combination of low threshold transcriptio nal activation and a unique, genetically encoded amplification mechani sm. In contrast, sizable experimental infections are required for indu ction of the normally silent hymenoptaecin, abaecin, and bee defensin genes; even so, bee defensin transcription is minimal and delayed, and only minute quantities of corresponding peptide are produced. The spe cific, temporal organization of the multi component immune response in bees has therefore likely been selected to cope with infection of pre valent, plant-associated Gram-negative bacteria. Post-translational pr ocessing and modifications are substantially different for each of the four antibacterial peptides. While no similarities were observed amon g precursor structures of the various bee peptides, surprisingly, the signal sequences of abaecin (bee) and drosocin (Drosophila) shared unm istakable homology, possibly indicating common ancestral secretion/pro cessing mechanisms. Finally, we report that bee defensin contains a ty pical disulfide-rich structure (40 amino acids) but also a unique, amp hipathic, putatively amidated carboxyl-terminal tail (10 amino acids). We speculate that this structure is a ''co-drug'' assembled by fusing ''disulfide-rich'' and ''alpha-helical'' class peptide antibiotics, a novel concept in naturally occurring antibacterials.