The β3-subunit modulates the effect of venom peptides ProTx-II and OD1 on Na_V 1.7 gating

The voltage-gated sodium channel Na_V 1.7 is involved in various pain phenotypes and is physiologically regulated by the Na_V -β3-subunit. Venom toxins ProTx-II and OD1 modulate Na_V 1.7 channel function and may be useful as therapeutic agents and/or research tools. Here, we use patch-clamp recordings to investigate how the β3-subunit can influence and modulate the toxin-mediated effects on Na_V 1.7 function, and we propose a putative binding mode of OD1 on Na_V 1.7 to rationalise its activating effects. The inhibitor ProTx-II slowed the rate of Na_V 1.7 activation, whilst the activator OD1 reduced the rate of fast inactivation and accelerated recovery from inactivation. The β3-subunit partially abrogated these effects. OD1 induced a hyperpolarising shift in the V_1/2 of steady-state activation, which was not observed in the presence of β3. Consequently, OD1-treated Na_V 1.7 exhibited an enhanced window current compared with OD1-treated Na_V 1.7-β3 complex. We identify candidate OD1 residues that are likely to prevent the upward movement of the DIV S4 helix and thus impede fast inactivation. The binding sites for each of the toxins and the predicted location of the β3-subunit on the Na_V 1.7 channel are distinct. Therefore, we infer that the β3-subunit influences the interaction of toxins with Na_V 1.7 via indirect allosteric mechanisms. The enhanced window current shown by OD1-treated Na_V 1.7 compared with OD1-treated Na_V 1.7-β3 is discussed in the context of differing cellular expressions of Na_V 1.7 and the β3-subunit in dorsal root ganglion (DRG) neurons. We propose that β3, as the native binding partner for Na_V 1.7 in DRG neurons, should be included during screening of molecules against Na_V 1.7 in relevant analgesic discovery campaigns.