Frog Skin Derived Peptides With Potential Protective Effects on Ultraviolet B-Induced Cutaneous Photodamage.

Hyla annectans is a tree frog living in the southwestern plateau area of China where there is strong ultraviolet radiation and long duration of sunshine. So their naked skin may possess chemical defense components that protect it from acute photo-damage. However, no such peptide or components has been identified till to date. In the current work, two novel peptides (FW-1, FWPLI-NH2 and FW-2, FWPMI-NH2) were identified from the skin of the tree frog. Five copies of FW-1 and four copies of FW-2 are encoded by an identical gene and released from the same protein precursor, which possess 167 amino acid residues. FW-1 and -2 can exert significant anti-inflammatory functions by directly inhibiting Ultraviolet B irradiation (UVB)-induced secretion of inflammatory cytokines such as tumor necrosis factor-α (TNF-α) and interleukin-6 (IL-6). They may achieve this function by modulating the UV-induced stress signaling pathways such as Mitogen-activated protein kinases (MAPK) and Nuclear Factor Kappa B (NF-κB). Besides, FW-1 and -2 showed potential antioxidant effects on epidermis by attenuating the UVB-induced reactive oxygen species (ROS) production through an unknown mechanism. Considering small peptides' easy production, storage, and potential photo-protective activity, FW-1/2 might be exciting leading compounds or templates for the development of novel pharmacological agents for the suppression of UVB-induced skin inflammation. Moreover, this study might expand our knowledge on skin defensive mechanism of tree frog upon UVB irradiation.

A novel Kunitz-type neurotoxin peptide identified from skin secretions of the frog Amolops loloensis.

A novel Kunitz-type neurotoxin peptide that inhibited voltage-gated sodium channel was purified and characterized from the skin secretions of rufous-spotted torrent frog, Amolops loloensis. It has a 240-bp cDNA encoding an 79-amino acid residue (aa) precursor protein containing 6 half-cysteines. The precursor was proven to release a 57-aa mature peptide with amino acid sequence, DRNPICNLPPKEGFCLWMMRRSFFNPSKGRCDTFGYRGCGGNKNNFETPRACKEACG. The mature was named amotoxin. Amotoxin shares sequence homology with other Kunitz-type toxins and also has three cysteine bridges. Amotoxin showed an inhibitory ability against trypsin with an inhibitory constant (Ki) of 0.087 µM. To the best of our knowledge, this is the first gene-encoded neurotoxin found in Amolops loloensis. Recombinant amotoxin showed similar functional properties as the native amotoxin. The functional properties of amotoxin may provide insights into the ecological adaptation of amphibians and deepen our understanding about the biological function spectrum of amphibian skin peptides.