New antibiotic uperin peptides from the dorsal glands of the Australian toadlet Uperoleia mjobergii

The dorsal glandular extract of the toadlet Uperoleia mjobergii contains more than 20 peptides. We report the amino acid sequences of the seven major peptides: these were determined by a combination of mass spectrometry and automated Edman sequencing. Three of these peptides have 19 amino acid residues and belong to the uperin 2 group of peptides [e.g. uperin 2.6, GlyIleLeuAspIleAlaLysLysLeuValGlyGlyIleArgAsnValLeuGlyIle (OH)], while the other four have 17 residues and are classified as uperins 3 [e.g. uperin 3.4, GlyValGlyAspLeuIleArgLysAlaValAlaAlaIleLysAsnIleVal (NH2)]. Several of these cationic peptides have been synthesized in order for bioassays to be carried out: they show significant antibiotic activity against a range of Gram-positive microorganisms. A major skin peptide from the related species Uperoleia inundata is a powerful neuropeptide named uperin 1.1 ([Ala(2)]uperolein): no corresponding neuropeptide is detected in the skin glands of Uperoleia mjobergii.