Molecular cloning and antifungal activity of an inhibitor cysteine knot peptide from the bumblebee Bombus ignitus

Abstract

The honeybee inhibitor cysteine knot (ICK) peptide acts as an antifungal peptide and insecticidal venom toxin. However, the ICK peptide from bumblebees has not been characterized. Here, we report the molecular cloning and antifungal activity of a bumblebee (Bombus ignitus) ICK peptide (BiICK). We identified a BiICK that contains an ICK fold. The BiICK was expressed in the epidermis, fat body, and venom gland of B. ignitus worker bees. A 6.7-kDa recombinant BiICK peptide was expressed in baculovirus-infected insect cells. Recombinant BiICK peptides directly bound to Beauveria bassiana, Ascosphaera apis, and Fusarium graminearum, but they did not bind to Escherichia coli, Paenibacillus larvae, or Bacillus thuringiensis. Consistent with this finding, BiICK exhibited antifungal activity against fungi. These results demonstrate that BiICK acts as an antifungal peptide.