Antimicrobial activity of a newly identified Kazal-type serine proteinase inhibitor, CcKPI1, from the jellyfish Cyanea capillata.

In this study, we reported a jellyfish-derived Kazal-type serine protease inhibitor, named CcKPI1, from Cyanea capillata. CcKPI1 has a calculated molecular mass of 19.02kDa and contains three typical Kazal domains. Soluble recombinant CcKPI1 (rCcKPI1) was successfully expressed and purified. rCcKPI1 exhibited significant inhibitory activities against elastase, subtilisin A and proteinase K, but not against trypsin or chymotrypsin. Kinetic studies showed that all of the inhibitory effects of rCcKPI1 were competitive, indicating that it may be a microbial serine protease inhibitor and can exhibit antimicrobial activity. As predicted, rCcKPI1 directly bound to various microorganisms, including the Gram-positive bacteria Staphylococcus aureus and Bacillus subtilis, Gram-negative bacteria Escherichia coli, marine pathogenic vibrios Vibrio vulnificus, Vibrio cholerae, Vibrio natriegens, Vibrio mimicus, Vibrio alginolyticus and Vibrio parahaemolyticus, and fungi Candida albicans, Candida parapsilokis and Candida glabrata. In addition, rCcKPI1 inhibited the growth of most of the tested microorganisms that it bound to. These findings indicate that CcKPI1 possesses marked antibacterial and antifungal activities and may play an important role in the immune defence of C. capillata, providing a novel view for the understanding of the immune system of jellyfish and also facilitating future research on antimicrobial agents from marine natural products.