Frog Skin Packs A Chemical Punch

The skin of tree frogs tells a story of peril. Constantly assaulted by predators, these amphibians survive by waging chemical warfare using skin secretions. The potent molecules within may help humans too, as a potential source of new medications. Researchers have now analyzed the skin secretions of Chinese tree frogs, Hyla simplex, and found a potent mix of deadly snake-venom-like toxins as well as therapeutic chemicals (J. Proteome Res., DOI: 10.1021/pr200393t).

Han Liu of the Kunming Institute of Zoology at the Chinese Academy of Sciences, and colleagues captured and collected secretions of tree frogs from forests in Guangxi province. They determined the amino acid sequences of 27 proteins and peptides using a standard sequencing method coupled with mass spectrometry. The researchers also confirmed the protein and peptide identities using DNA sequences derived from RNA samples in the skin secretions.

The researchers subjected the agents to a battery of tests to check whether they could act as antimicrobials, painkillers, neurotoxins, or promoters of blood vessel regrowth. These studies revealed that some skin secretions are toxic to mice, water snakes, insects, and birds. Others seemed capable of helping the frog heal its own wounded flesh or dull its perception of pain.

The researchers also found that the amino acid sequences of several of the proteins bear remarkable similarity to those of neurotoxins from snake venom. Because snakes are predators of tree frogs, Liu says that the similarity in their toxins may indicate an arms race in which each species evolves increasingly sophisticated chemical weaponry and resistance. Though more work is needed to confirm this relationship, Liu says, frog skin could shed light on how a small amphibian survives in a snaky wilderness.