A serine protease inhibitor from the hornfaced bee, Osmia cornifrons, exhibits antimicrobial activities

•cDNA encoding for a serine protease inhibitor was cloned from the hornfaced bee Osmia cornifrons.•This serine protease inhibitor from O. cornifrons (OcSPI) inhibits chymotrypsin.•OcSPI inhibits microbial serine proteases, such as subtilisin A and proteinase K.•OcSPI demonstrates antimicrobial activities against bacteria and fungi.

Serine protease inhibitors play a critical role in physiological processes and immune responses by regulating serine protease activities. Here we describe the molecular cloning and antimicrobial activities of a serine protease inhibitor from the hornfaced bee, Osmia cornifrons (OcSPI). OcSPI consists of 405 amino acid residues and contains a potential reactive center loop (RCL) region in its C-terminus. Recombinant OcSPI was produced as a 64-kDa glycoprotein in baculovirus-infected insect cells and exhibited inhibitory activity against chymotrypsin. Additionally, OcSPI demonstrated inhibitory activity against microbial serine proteases, such as subtilisin A and proteinase K, but not against tissue plasminogen activator, thrombin, or plasmin. Recombinant OcSPI bound directly to Escherichia coli, Bacillus subtilis, and Beauveria bassiana and exhibited antimicrobial activity against both bacteria and fungi. Our results demonstrated the antimicrobial functions of OcSPI and suggest a role for OcSPI in the immune response of O. cornifrons bees.

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