Biomolecular identification of beta-defensin-like peptides from the skin of the soft-shelled turtle Apalone spinifera.

Numerous bacteria are frequently observed in the superficial corneocytes forming the corneous layer of the soft-shelled turtle Apalona spinifera. The resistance to bacterial penetration through the living epidermis in this turtle suggests the presence of an antimicrobial barrier, possibly derived from the presence of anti-microbial peptides in the epidermis. Four beta-defensin-like peptides, named As-BD-1 to 4, have been characterized from skin tissues using molecular and bioinformatics methods. The precursor peptides contain the beta-defensin motif with the typical cysteine localization pattern. The analysis of the expression for the four different beta-defensin-like proteins show that these molecules are expressed in the skin (epidermis and dermis) of the carapace, neck, digit, and tail but are apparently not expressed in the liver or intestine under normal conditions. These data suggest that in the skin of the soft-shelled turtle there are potential effective anti-microbial peptides against epidermal bacteria.