Peptides with potent cytolytic activity from the skin secretions of the North American leopard frogs, Lithobates blairi and Lithobates yavapaiensis
Abstract
Six structurally similar and strongly cationic peptides belonging to the brevinin-1 family were isolated from skin secretions of the plains leopard frog Lithobates blairi and the lowland leopard frog Lithobates yavapaiensis on the basis of their antimicrobial activities. Brevinin-1BLc (FLPIIAGIAAKFLPKIFCTISKKC) from L. blairi represented the most potent peptide (MIC=25microM Escherichia coli, MIC=1.5microM Staphylococcus aureus, MIC=3microM Candida albicans, LC(50)=9microM human erythrocytes and LC(50)=6microM HepG2 human hepatoma-derived cells). The appreciably lower antimicrobial potencies of brevinin-1Ya and -1Yc from L. yavapaiensis correlate with the decreases in cationicity produced by the amino acid substitutions Lys(11)-->Asn (brevinin-1Ya) and Pro(14)-->Glu (brevinin-1Yc). In addition, a peptide isolated from the skin secretions of L. yavapaiensis belonging to the ranatuerin-2 family (ranatuerin-2Ya; GLMDTIKGVAKTVAASWLDKLKCKIT GC) inhibited the growth of E. coli (MIC=50microM) and S. aureus (MIC=50microM). In contrast to brevinin-1BLc, ranatuerin-2Ya showed appreciably greater cytolytic activity against HepG2 cells (LC(50)=20microM) than against erythrocytes (LC(50)>100microM).