cDNA cloning and functional characterisation of four antimicrobial peptides from Paa spinosa

Antimicrobial peptides (AMPs) are small peptides found in many organisms defending themselves against pathogens. AMPs form the first line of host defence against pathogenic infections and are key components of the innate immune system of amphibians. In the current study, cDNAs of precursors of four novel antimicrobial peptides in the skin of Paa spinosa were cloned and sequenced using the 3'-RACE technique. Mature peptides, named spinosan A-D, encoded by the cDNAs were chemically synthesized and their chemical properties were predicted. The antimicrobial, antioxidative, cyotoxic and haemolytic activities of these four AMPs were determined. While the synthesised spinosans A-C exhibited no activity towards any of the bacterial strains tested, spinosan-D exhibited weak but broad-spectrum antimicrobial activities against Gram-positive and Gram-negative bacteria. All peptides were weakly haemolytic towards rabbit erythrocytes, had a strong antioxidative activity, and a low cytotoxic activity against HeLa cells. These findings provide helpful insights that may be useful in the future design of anti-infective peptide agents.