Resin-acid derivatives bind to multiple sites on the voltage-sensor domain of the Saker channel

Abstract

Resin acids and their derivatives open voltage-gated potassium (KV) channels by attracting the positively charged voltage sensor helix of the channel (S4) towards the extracellular leaflet of the cellular membrane and thereby favoring gate opening. The resin acids have been proposed to primarily bind in a pocket in the periphery of the channel, located between the lipid-facing extracellular ends of the transmembrane segments S3 and S4. However, neutralization of the top gating charge of the Shaker KV channel unexpectedly increases the resin-acid induced opening, suggesting other mechanisms and possibly other sites of action.Here we explored the binding of two resin-acid derivatives, Wu50 and Wu161, to the Shaker KV channel by a combination of in-silico docking, molecular dynamics simulations, and electrophysiological study of mutated channels. We identified three potential resin-acid binding sites around the voltage sensor helix S4: (1) the S3/S4 site identified in our previous work, (2) a site located in the cleft between S4 and the pore domain (the S4/pore site), and (3) a site located at the extracellular side of the voltage-sensor domain in a cleft formed by S1-S4 (the top-VSD site). The presence of multiple binding sites around S4 and the anticipated helical-screw motion of the helix during activation makes the effect of resin acid derivatives on channel function intricate. The propensity of a specific resin acid to open/close a voltagegated channel likely depends on its exact binding pose and the types of interactions it can form with the protein in a state-specific manner.