Binding Structure & Dynamics for Toxins Modifying the Gating Mechanism of Kv Channels

Abstract

Voltage gated ion channels allow the flux of specific ions through the cell membrane to be controlled by the membrane potential, which makes them a critical component for electro-chemical signaling in the nervous system. The gating is regulated by the voltage sensor domains (VSD), in which the charged S4 helix moves to induce the conformational transition between open/closed states. This serves as an ideal model system for membrane proteins with multiple conformations, and if the gating can be modulated it would potentially enable a whole range of new drugs that could fine-tune the gating response. This is strikingly manifested in the case of tarantula spiders, which produce a potent venom that specifically target the VSD to causing dysfunctions in the neuronal and cardiac systems.Here, we report on molecular simulations of interactions between toxins and different Kv channels, in particular related to their influence of the gating transition. We have studied the binding to multiple intermediate states and effect of Stromatoxin (ScTx1) on gating transitions in both Kv2.1 and a mutant Shaker channel with enhanced toxin affinity. Results from toxin-protein docking show the toxin binding to S2 and S3 helices. An interaction pair is formed between E277 (Kv2.1 numbering) in the top-most part of S3 and either R4 or K22 on opposite sides of the toxin, resulting in two distinct poses in the binding site. In addition to docking, we have also explored multi-microsecond molecular dynamics simulations of toxins bound in both open and closed states.We propose a specific binding site for the toxin in the VSD of both channels, and predict that differences in residue interactions are responsible for selectively stabilizing S4 in either the open or closed state.