The rothein peptides from the skin secretion of Roth's tree frog Litoria rothii. Sequence determination using positive and negative ion electrospray mass spectrometry

Abstract

The secretion from the dorsal glands of the frog Litoria rothii contains a series of new peptides including rothein 1 (SVSNIPESIGF-OH, a neuropeptide which contracts smooth muscle), a number of inactive rothein 2 and 3 peptides (e.g. rothein 2.1, AGGLDDLLEPVLNSADNLVHGL-OH), and a new proline rich peptide, named rothein 4.1 (AEILFGDVRPPWMPPPIFPEMP-OH), which shows neither antimicrobial nor neuronal nitric oxide synthase (nNOS) activity. Two known neuropeptides of the caerulein family [e.g. caerulein, pEQDY(SO3)TGWMDF-NH2] together with a series of known caerin 1 antibiotic and nNOS-inhibiting peptides (e.g. caerin 1.1, GLLSVLGSVAKHVLPHVVPVIAEHL-NH2) were also identified. Positive ion electrospray mass spectrometry (ES-MS) was used as the primary method to investigate the sequences of the new peptides. Negative ion ES-MS was used to fill in any gaps in the positive ion data and, finally, Edman automated sequencing was used to differentiate between Leu and Ile and to confirm the sequences determined by mass spectrometry.