Molecular Characterization of a Defensin-like Peptide from Larvae of a Beetle, Protaetia brevitarsis

Abstract

A cDNA encoding a defensin-like peptide (Protaetia-mycine) from the larvae of a beetle, Protaetia brevi-tarsis was cloned. The DNAs encoded the deduced propeptide of 79 amino acid residues with the pre-dicted molecular weight of 8.4 kDa and PI of 8.24. Overall amino acid sequence of this protein has 39% similarity to that of Rhodnius prolixus defensin, 43% similarity to that of Acalolepta luxuriosa defensin, and 72 % similarity to that of Oryctes rhinoceros defensin, suggesting that this gene is an insect defensin. In an attempt to apply the anti-bacterial peptide to the development of therapeutic agents, a 12-mer peptide amidated at its C-terminus, ACAAHCLAIGRG-NH 2 (Ala55-Lys66-NH 2, 12Pbn) was synthesized. This pep-tide showed some antifungal activity against Candida albicans. To increase antifungal activity, six 9-mer pep-tides were synthesized by modifying amino acid sequences of 12Pbn fragment. Among these peptides, 9Pbm3-9Pbm6 exhibited strong activity compared with Cecropin B and mellitin.