Non-Toxin Gating Modifiers Reveal the Promiscuous Nature of the Voltage Sensor of Kv7.2 and TRPV1 Channels

Abstract

Voltage-sensitive cation channel architecture consists of two main structural modules, the voltage sensor domain (VSD) and the pore domain. The VSDs are the target of various gating-modifier toxins and their paddle motifs are modular and transferable structures. Here we show that NH17 and NH29, two new Kv7.2 channel blocker and opener, respectively, act as non-toxin gating modifiers. Mutagenesis and modeling data suggest that in Kv7.2, NH29 docks to the external groove formed by the interface of helices S1, S2 and S4 in a way, which stabilizes the interaction between two conserved charged residues in S2, and S4, known to interact electrostatically, in the open state of Kv channels. Reflecting the promiscuous nature of the VSD, NH29 is also a potent blocker of TRPV1 channels, a feature similar to that described for tarantula toxins. TRPV1 channels appear to be weakly voltage-dependent. However, NH29 changes the linear TRPV1 current-voltage relation obtained with capsaicin, to an outwardly rectifying shape. Interestingly, mutations in linker S3-S4 of the TRPV1 VSD are significantly more resistant to the inhibitory effect of NH29. While compound NH17 potently blocks Kv7.2 channels, it sensitizes the TRPV1 current activated by capsaicin. Mutations in linker S3-S4 switch the TRPV1 sensitizing action of NH17 to a potent inhibition. Subtle modifications in the VSD or in the chemical structure of the molecule drastically change the attributes of the gating-modifier, thereby stabilizing the channel in either the closed or the open state. Data indicate that the novel compounds may operate via a voltage-sensor trapping mechanism similar to that suggested for scorpion and sea anemone toxins. Thus, the VSDs of Kv and TRPV1 channels are promiscuous and share some common structural and biophysical features.