The beta 3-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-beta 3-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 beta 3-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 beta 3-subunit partially abrogated these effects. OD1 induced a hyperpolarising shift in the V1/ 2 of steady-state activation, which was not observed in the presence of beta 3. Consequently, OD1-treated Na(V)1.7 exhibited an enhanced window current compared with OD1-treated Na(V)1.7-beta 3 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 beta 3-subunit on the Na(V)1.7 channel are distinct. Therefore, we infer that the beta 3-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-beta 3 is discussed in the context of differing cellular expressions of Na(V)1.7 and the beta 3-subunit in dorsal root ganglion (DRG) neurons. We propose that beta 3, 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.