Anti-fibrinolytic and anti-microbial activities of a serine protease inhibitor from honeybee (Apis cerana) venom.

Bee venom contains a variety of peptide constituents, including low-molecular-weight protease inhibitors. While the putative low-molecular-weight serine protease inhibitor Api m 6 containing a trypsin inhibitor-like cysteine-rich domain was identified from honeybee (Apis mellifera) venom, no anti-fibrinolytic or anti-microbial roles for this inhibitor have been elucidated. In this study, we identified an Asiatic honeybee (A. cerana) venom serine protease inhibitor (AcVSPI) that was shown to act as a microbial serine protease inhibitor and plasmin inhibitor. AcVSPI was found to consist of a trypsin inhibitor-like domain that displays ten cysteine residues. Interestingly, the AcVSPI peptide sequence exhibited high similarity to the putative low-molecular-weight serine protease inhibitor Api m 6, which suggests that AcVSPI is an allergen Api m 6-like peptide. Recombinant AcVSPI was expressed in baculovirus-infected insect cells, and it demonstrated inhibitory activity against trypsin, but not chymotrypsin. Additionally, AcVSPI has inhibitory effects against plasmin and microbial serine proteases; however, it does not have any detectable inhibitory effects on thrombin or elastase. Consistent with these inhibitory effects, AcVSPI inhibited the plasmin-mediated degradation of fibrin to fibrin degradation products. AcVSPI also bound to bacterial and fungal surfaces and exhibited anti-microbial activity against fungi as well as gram-positive and gram-negative bacteria. These findings demonstrate the anti-fibrinolytic and anti-microbial roles of AcVSPI as a serine protease inhibitor.