Molecular cloning and characterisation of three antimicrobial peptides from the skin secretion of the broad-folded frog, Hylarana latouchii

In this study, three antimicrobial peptides are reported, whose primary structures were deduced from cDNAs cloned from a skin secretion-derived cDNA library of the broad-folded frog, Hylarana latouchii, by adopting a “shotgun” cloning technique. All of the mature peptides were subsequently structurally-characterised following their location in chromatographic fractions of skin secretion. Their respective synthetic replicates were also subjected to a series of biological assays. Primary structural characterisations of mature peptides revealed that they are homologues of brevinin-1 and temporin family peptides and were named accordingly as brevinin-1HL, temporin-HL1 and temporin-HL2, respectively. Brevinin-1HL exhibited broad-spectrum antimicrobial activity against three strains of model test microorganisms with different potencies (MICs between 3.2 - 51.3 μM) and relatively strong haemolytic activity (82.4% at 51.3 μM). Temporin-HL1 had selective activity against the Gram-positive bacterium, Staphylococcus aureus (MIC 8.5 μM) and the yeast, Candida albicans (17.1 μM) with moderate haemolytic activity (24.8% at 17.1 μM). In contrast, temporin-HL2 was of specific potency against Staphylococcus aureus (MIC 10.7 μM) exhibiting only weak cytotoxicity toward erythrocytes (as low as 1% at 10.7 μM). In terms of anticancer activity, brevinin-1HL was effective against only one of eleven human cancer cell lines tested (H23) with an IC50 of 10-6 M; temporin-HL1 inhibited the growth of three cancer cell lines (H23, H157 and H460) with IC50 values ranging between 10-6 and 10-5 M; whereas, temporin-HL2 was ineffective against all tested cancer cell lines.