Defensins are one of the major families of antimicrobial peptides (AMPs), and have been reported from prokaryotic to eukaryotic kingdoms. But defensins are seldom found in amphibian which is a major resource of novel AMPs. A novel defensin-like AMP (defensin-TK) was isolated and characterized from skin secretions of the tree frog Theloderma kwangsiensis. The cDNA encoding defensin-TK precursor was cloned from the skin cDNA library of T. kwangsiensis. The deduced precursor of defensin-TK was composed of three domains, a signal peptide of 16 residues, a spacer peptide of 1 residues and a mature peptide of 42 residues. The mature peptide of defensin-TK shared the highest identity with the salamander (Cynops fudingensis) defensin CFBD-1. The six conserved cysteines which formed intramolecular disulfide bonds of defensins also exist in defensin-TK. Phylogenetic analysis indicated that defensin-TK was closely related to fish β-defensins. Defensin-TK showed potent and broad-spectrum antimicrobial activity. In addition, defensin-TK exerted a low hemolytic activity on human red cells. These results suggested defensin-TK might play an important role in defense the skin pathogenic microbes of tree frog T. kwangsiensis, and might be a promising candidate for development of novel antimicrobial agents.
Keywords: Amphibian; Antimicrobial peptide; Defensin; Skin secretion; Theloderma kwangsiensis.
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