The tarantula toxin β/δ-TRTX-Pre1a highlights the importance of the S1-S2 voltage-sensor region for sodium channel subtype selectivity

Voltage-gated sodium (Na-V) channels are essential for the transmission of pain signals in humans making them prime targets for the development of new analgesics. Spider venoms are a rich source of peptide modulators useful to study ion channel structure and function. Here we describe beta/delta-TRTX-Pre1a, a 35-residue tarantula peptide that selectively interacts with neuronal NaV channels inhibiting peak current of hNa(V)1.1, rNa(V)1.2, hNa(V)1.6, and hNa(V)1.7 while concurrently inhibiting fast inactivation of hNa(V)1.1 and rNa(V)1.3. The DII and DIV S3-S4 loops of Na-V channel voltage sensors are important for the interaction of Pre1a with Na-V channels but cannot account for its unique subtype selectivity. Through analysis of the binding regions we ascertained that the variability of the S1-S2 loops between NaV channels contributes substantially to the selectivity profile observed for Pre1a, particularly with regards to fast inactivation. A serine residue on the DIV S2 helix was found to be sufficient to explain Pre1a's potent and selective inhibitory effect on the fast inactivation process of Na(V)1.1 and 1.3. This work highlights that interactions with both S1-S2 and S3-S4 of Na-V channels may be necessary for functional modulation, and that targeting the diverse S1-S2 region within voltage-sensing domains provides an avenue to develop subtype selective tools.