The fallaxidin peptides from the skin secretion of the Eastern Dwarf Tree Frog Litoria fallax. Sequence determination by positive and negative ion electrospray mass spectrometry: antimicrobial activity and cDNA cloning of the fallaxidins.

The glandular skin secretion of the Eastern Dwarf Tree Frog Litoria fallax contains nine peptides named fallaxidins. The sequences of these peptides were elucidated using a combination of positive and negative electrospray mass spectrometry together with Edman sequencing. Among these peptides are: (i) fallaxidins 1.1 and 2.1 which have the sequences YFPIPI-NH2 and FWPFM-NH2. The activities of these peptides are unknown, but it has been shown that they are not smooth muscle active, opioids or antimicrobially active, nor do they effect proliferation of lymphocytes; (ii) two weakly active antibiotics, fallaxidins 3.1 and 3.2 (e.g. fallaxidin 3.1, GLLDLAKHVIGIASKL-NH2), and a moderately active antibiotic fallaxidin 4.1 (GLLSFLPKVIGVIGHLIHPPS-OH). Fallaxidin 4.1 has an unusual sequence for an antibiotic, containing three Pro residues together with a C-terminal CO2H group. cDNA cloning has confirmed the identity of the nine isolated peptides from L. fallax, together with five additional peptides not detected in the peptide profile. The pre-regions of the nine preprofallaxidins are conserved and similar to those of the caerin peptides from L. caerulea and L. splendida, suggesting that the fallaxidin and caerin peptides, although significantly different in sequence, originated from a common ancestor gene.