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 β/δ-TRTX-Pre1a, a 35-residue tarantula peptide that selectively interacts with neuronal Na _V 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 Na _V 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.