The Tarantula Venom Peptide Eo1a Binds to the Domain II S3-S4 Extracellular Loop of Voltage-Gated Sodium Channel Na(V)1.8 to Enhance Activation

Venoms from cone snails and arachnids are a rich source of peptide modulators of voltage-gated sodium (Na(V)) channels, however relatively few venom-derived peptides with activity at the mammalian Na(V)1.8 subtype have been isolated. Here, we describe the discovery and functional characterisation of β-theraphotoxin-Eo1a, a peptide from the venom of the Tanzanian black and olive baboon tarantula Encyocratella olivacea that modulates Na(V)1.8. Eo1a is a 37-residue peptide that increases Na(V)1.8 peak current (EC(50) 894 ± 146 nM) and causes a large hyperpolarising shift in both the voltage-dependence of activation (ΔV(50)–20.5 ± 1.2 mV) and steady-state fast inactivation (ΔV(50)–15.5 ± 1.8 mV). At a concentration of 10 μM, Eo1a has varying effects on the peak current and channel gating of Na(V)1.1–Na(V)1.7, although its activity is most pronounced at Na(V)1.8. Investigations into the binding site of Eo1a using Na(V)1.7/Na(V)1.8 chimeras revealed a critical contribution of the DII S3-S4 extracellular loop of Na(V)1.8 to toxin activity. Results from this work may form the basis for future studies that lead to the rational design of spider venom-derived peptides with improved potency and selectivity at Na(V)1.8.