The Tarantula Venom Peptide Eo1a Binds to the Domain II S3-S4 Extracellular Loop of Voltage-Gated Sodium Channel NaV1.8 to Enhance Activation

Abstract

Venoms from cone snails and arachnids are a rich source of peptide modulators of voltage-gated sodium (NaV) channels, however relatively few venom-derived peptides with activity at the mammalian NaV1.8 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 NaV1.8. Eo1a is a 37-residue peptide that increases NaV1.8 peak current (EC50 894 ± 146 nM) and causes a large hyperpolarising shift in both the voltage-dependence of activation (ΔV50–20.5 ± 1.2 mV) and steady-state fast inactivation (ΔV50–15.5 ± 1.8 mV). At a concentration of 10 μM, Eo1a has varying effects on the peak current and channel gating of NaV1.1–NaV1.7, although its activity is most pronounced at NaV1.8. Investigations into the binding site of Eo1a using NaV1.7/NaV1.8 chimeras revealed a critical contribution of the DII S3-S4 extracellular loop of NaV1.8 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 NaV1.8.

Structural and Functional Characterization of a Novel Scorpion Toxin that Inhibits NaV1.8 via Interactions With the DI Voltage Sensor and DII Pore Module

“…For example, the scorpion β-toxin BMK I shifts the voltage dependence of both activation and fast inactivation gating to hyperpolarized potentials in rat Na V 1.8, causing an increase in small diameter DRG TTX-R Na + current and pain-related behavior ( Ye et al, 2015 ). Similarly, the recently described tarantula toxin β-theraphotoxin-Eo1a activates Na V 1.8 and causes pain in house mice by hyperpolarizing activation and steady-state fast inactivation ( Deuis et al, 2021 ). The DIV voltage-sensor-binding toxins Hm1a and LqqIV shift the voltage dependence of Na V 1.1 fast inactivation gating to depolarized potentials, increasing channel availability and window currents ( Osteen et al, 2017 ).…”

“…However, the mechanisms that regulate Na V 1.8 gating are not completely understood. While animal-derived toxins have provided tools for examining structure-activity relationships in several Na V , fewer toxins have been identified that modify Na V 1.8 gating ( Ye et al, 2015 ; Zhang et al, 2019 ; Deuis et al, 2021 ). AZ bark scorpions produce venoms rich in peptide toxins that modify the gating mechanisms of Na + ion channels in nerve and muscle tissue ( Jaimovich et al, 1982 ; Couraud et al, 1984 ; Possani et al, 1999 ; Corona et al, 2001 ; Rodríguez de la Vega and Possani, 2005 ; Carcamo-Noriega et al, 2018 ).…”

“…Electrophysiological analyses show that NaTx36 modulates OtNa V 1.8 activation and inactivation gating, while site-directed mutagenesis and computational modeling suggest that amino acids in the DI voltage sensor and the DII pore module are critical for channel inhibition. These results are significant because few toxins have been identified that target Na V 1.8 ( Ye et al, 2015 ; Zhang et al, 2019 ; Deuis et al, 2021 ). Moreover, few toxins have been described that modify Na V gating mechanisms via interaction with the DI voltage sensor ( Xiao et al, 2014 ; Clairfeuille et al, 2019 ).…”

“…However, until recently, few animal toxins had been identified that modify Na V 1.8 gating ( Ye et al, 2015 ), prompting efforts to construct chimeras of Na V 1.8 that could bind peptide toxins by exchanging extracellular loops on Na V 1.8 with corresponding toxin binding sites from Na V 1.2 ( Gilchrist and Bosmans, 2018 ). More recently, additional peptide toxins have been discovered that modify Na V 1.8 gating, providing insight into structure-activity relationships between voltage sensors and gating mechanisms ( Zhang et al, 2019 ; Deuis et al, 2021 ; Finol-Urdaneta et al, 2022 ).…”

Venom-derived pain-causing toxins: insights into sensory neuron function and pain mechanisms

“…97 Another example is b-theraphotoxin-Eo1a, a 37-amino acid residue ICK peptide from the Tanzanian black and olive baboon tarantula, Encyocratella olivacea, that selectively activates Na V 1.8 (EC 50 894 nM) by binding to the DII S3-S4 loop. 31 Although the role of Na V 1.8 in pain signalling is well established, relatively few modulators of Na V 1.8 have been described. Despite being an activator, Eo1a provides important structure-activity data that may be used for the rationale design of selective Na V 1.8 inhibitors.…”