Identification, chemical synthesis and heterologous expression of an antinociceptive peptide from the veined tree frog Trachycephalus typhonius.

A proteinic fraction from the skin secretion of Trachycephalus typhonius showed antinociceptive activity in mice when tested by the Hot Plate method. This fraction was purified, and a peptide named Tt7 with a molecular mass of 6,509.7 Da was identified. The primary structure of Tt7 was elucidated. Comparing Tt7 with the structure of other analgesic peptides, it exhibits a strong relationship with the family of anntoxins, which are peptides isolated from the skin secretions of Asian frogs of the genus Hyla, whereas T. typhonius is located only in the Americas. Tt7 contains a disulfide pattern Cys1-Cys4/Cys2-Cys3, a secondary structure defined by a β-hairpin, and a N-terminal α-helix, which are characteristic motifs of Kunitz-type structures. The peptide Tt7 was both chemically and biologically synthesized. The recombinant peptides (rTt7 and HisrTt7) showed analgesic effects. Electrophysiological analyses of Tt7 on the voltage-gated sodium channel (Nav) subtype 1.7 reduced the Na+ current by ca 10%. Further studies showed that Tt7 inhibits the pH gated Ca-fluorescence increase in dorsal root ganglion neurons of the rat, indicating an inhibitory action of Tt7 in the acid gated currents which may account for the observed analgesic action of Tt7, suggesting that this peptide might affect various pain-related receptors.