Mating-increases trypsin in female Drosophila hemolymph

Male-derived accessory gland proteins (Acps) are transferred to the female reproductive tract during mating and affect female reproductive maturation and behavior. Some Acps subsequently enter the female hemolymph. We hypothesized that humoral proteases are the primary effectors of Acp bioactivity by processing (activating) and/or degrading them. To test this hypothesis we examined the fate of one Acp, Drosophila melanogaster Sex Peptide (Acp70A, DrmSP), which possesses several putative serine-protease cleavage sites, in hemolymph of unmated and mated females. In D. melanogaster, DrmSP induces post-mating non-receptivity and enhances oogenesis. To determine if serine proteases regulate the duration of DrmSP activity in mated females, we performed kinetic analysis of cleavage of a synthetic N-terminal truncated DrmSP_8-36 (T-SP) with hemolymph of unmated versus mated females. We found that T-SP is cleaved more rapidly and completely in mated female hemolymph. Using LC-MS/MS analyses, we identified its primary cleavage sites, indicating that trypsin was the major endopeptidase regulating T-SP in hemolymph. This was verified in vitro by utilizing specific chromogenic serine-protease substrates and inhibitors. We propose that post-mating cleavage of DrmSP in the female hemolymph regulates the duration of the rapidly induced post-mating responses in D. melanogaster and that this is a specific example of Acp bioactivity regulated by hemolymph serine proteases.