Expression of a recombinant Phoneutria toxin active in calcium channels

► Heterologous expression and purification of PnTx3-4, a toxin that blocks N-, P/Q-, and R-type voltage-gated calcium channels. ► Demonstration that recombinant PnTx3-4 shows biological activity similar to the native peptide using two different assays. ► Suggestion that PnTx3-4 adopts a knottin scaffold based on primary sequence analysis. ► Circular dichroism analysis showing that the peptide is composed of about 53% turns/unordered, 31% α-helix and 16% β-strand.