Multiple antimicrobial peptides and peptides related to bradykinin and neuromedin N isolated from skin secretions of the pickerel frog, Rana palustris

The skin secretions of the North American pickerel frog Rana palustris are toxic to both microorganisms and predators. A total of 22 peptides with dif ferential growth-inhibitory activity towards bacteria and yeast were isolat ed from the electrostimulated secretions of R palustris skin and were chara cterized structurally. Thirteen of the antimicrobial peptides belong to fiv e of the known families previously identified in the skins of other species of Ranid frogs: brevinin-1 (3 peptides), esculentin-1 (2 peptides), escule ntin-2 (1 peptide), ranatuerin-2 (6 peptides), and temporin (1 peptide). Ni ne peptides show little structural similarity towards other known antimicro bial peptides and so are classified in new families: palustrin-1 (4 peptide s) with 27-28 amino acid residues and a cystine-bridged heptapeptide ring; palustrin-2 (3 peptides) with 31 amino acids and a cyclic heptapeptide regi on and palustrin-3 (2 peptides) with 48 amino acids and a cyclic hexapeptid e region. Peptides belonging to the esculentin-1, esculentin-2 and palustri n-3 families are the most potent (minimal inhibitory concentrations approxi mately 1 muM against Escherichia coli) whereas peptides of the brevinin-1 a nd esculentin-2 families show the broadest spectrum of activity. As well as bradykinin that is identical to the human peptide, a further 4 peptides st ructurally related to [Leu(8)]bradykinin and two peptides related to neurom edin-N (the hexapeptide KKPYIL and a larger, cystine-containing form HLRRCG KKPYILMACS) were purified from the skin secretions. (C) 2000 Elsevier Scien ce B.V. All rights reserved.