New caerin antibiotic peptides from the skin secretion of the Dainty Green Tree Frog Litoria gracilenta. Identification using positive and negative ion electrospray mass spectrometry

The skin secretion of the Dainty Green Tree Frog Litoria gracilenta contains 16 peptides, which protect the animal from predators, both large and small. A combination of negative and positive ion electrospray mass spectrometry together with Lys-C enzymic digest and Edman sequencing identifies three new wide-spectrum caerin 1 antibiotics, namelyCaerin 1.17[GLFSVLGSVAKHLLPHVAPIIAEKL-NH2],Caerin 1.18[GLFSVLGSVAKHLLPHVVPVIAEKL-NH2], andCaerin 1.19[GLFKVLGSVAKHLLPHVAPIIAEKL-NH2], and a narrow spectrum antibioticCaerin 3.5[GLWEKVKEKANELVSGIVEGVK-NH2].