Using Potassium Channels As Reporters To Deconstruct The Function And Pharmacology Of Sodium Channel Voltage Sensors

Abstract

Voltage-activated sodium (Nav) channels found in both nerve and muscle cells are crucial for the generation and propagation of nerve impulses, and as such are amongst the most widely targeted ion channels by both toxins and drugs. The four voltage sensors in Nav channels have distinct amino acid sequences, raising fundamental questions about their relative contributions to the function and pharmacological sensitivities of the channel. Dissecting these contributions, however, has been problematic because the voltage sensors are contained within pseudosubunits (domain I to IV) of a single protein. Here we show that the four S3b-S4 paddle motifs within Nav channel voltage sensors can be transplanted into four-fold symmetric voltage-activated potassium (Kv) channels and can be used as reporters to individually examine the contributions of these paddle motifs to the kinetics of voltage sensor activation and their interactions with toxins. Our results show that each of the four Nav channel paddle motifs can interact with toxins from tarantula venom (PaurTx3, ProTx-I, ProTx-II, HaTx and SGTx1) or scorpion venom (AaHII and TsVII), that multiple paddle motifs are often targeted by a single toxin, and that the profiles of toxin-paddle interactions vary for different subtypes of Nav channels. The paddle motif from domain IV is unique because it slows voltage sensor activation and toxins must selectively target this motif to alter Nav channel fast inactivation. In contrast, toxins that interact with paddle motifs in domains I-III influence Nav channel opening. The influence of domain-specific interactions has important implications for developing strategies to reshape Nav channel activity. Therefore, our reporter approach and the principles that emerge will be useful in generating new drugs for treating pain and Nav channelopathies.