Pi5 and Pi6, two undescribed peptides from the venom of the scorpion Pandinus imperator and their effects on K+-channels

- Two short length peptides: Pi5 and Pi6 were purified and characterized from Pandinus imperator scorpion venom.
- Pi5 has 33 amino acids and constitutes a new subfamily of α-KTx, (systematic number α-KTx 24.1).
- Pi6 contains 28 amino acids, two disulfide bonds, and is a new member of the κ-KTx (systematic number κ-KTx2.9).
- Pi5 inhibited Shaker B, hKv1, Kv1.2 and hKv1.3 channels at nanomolar concentrations.
- Pi6 is a non-selective blocker of hKv1.2 and hKv1.3 channels.

This work reports the isolation, chemical and functional characterization of two previously unknown peptides purified from the venom of the scorpion Pandinus imperator, denominated Pi5 and Pi6. Pi5 is a classical K+-channel blocking peptide containing 33 amino acid residues with 4 disulfide bonds. It is the first member of a new subfamily, here defined by the systematic number α-KTx 24.1. Pi6 is a peptide of unknown real function, containing only two disulfide bonds and 28 amino acid residues, but showing sequence similarities to the κ-family of K-channel toxins. The systematic number assigned is κ-KTx2.9. The function of both peptides was assayed on Drosophila Shab and Shaker K+-channels, as well as four different subtypes of voltage-dependent K+-channels: hKv1.1, hKv1.2, hKv1.3 and hKv1.4. The electrophysiological assays showed that Pi5 inhibited Shaker B, hKv1.1, hKv1.2 and hKv1.3 channels with Kd = 540 nM, Kd = 92 nM and Kd = 77 nM, respectively, other studied channels were not affected. Of the channels tested only hKv1.2 and hKv1.3 were inhibited at 100 nM concentration of Pi6, the remaining current fractions were 68% and 77%, respectively. Thus, Pi5 and Pi6 are high nanomolar affinity non-selective blockers of hKv1.2 and hKv1.3 channels.