Moving gating charges through the gating pore in a Kv channel voltage sensor

Abstract

Voltage sensor domains (VSDs) regulate ion channels and enzymes by transporting electrically charged residues across a hydrophobic VSD constriction called the gating pore or hydrophobic plug. How the gating pore controls the gating charge movement presently remains debated. Here, using saturation mutagenesis and detailed analysis of gating currents from gating pore mutations in the Shaker Kv channel, we identified statistically highly significant correlations between VSD function and physicochemical properties of gating pore residues. A necessary small residue at position S240 in S1 creates a "steric gap" that enables an intracellular access pathway for the transport of the S4 Arg residues. In addition, the stabilization of the depolarized VSD conformation, a hallmark for most Kv channels, requires large side chains at positions F290 in S2 and F244 in S1 acting as "molecular clamps," and a hydrophobic side chain at position I237 in S1 acting as a local intracellular hydrophobic barrier. Finally, both size and hydrophobicity of I287 are important to control the main VSD energy barrier underlying transitions between resting and active states. Taken together, our study emphasizes the contribution of several gating pore residues to catalyze the gating charge transfer. This work paves the way toward understanding physicochemical principles underlying conformational dynamics in voltage sensors.energy landscape | kinetic model | global fit

The Hv1 proton channel responds to mechanical stimuli

“…A previous study on bacterial stretch-activated ion channels proposed that wetting and dewetting of a hydrophobic region in the permeation pathway can play a major role in defining the thermodynamics and kinetics of mechanosensitive channel gating and can be the origin of hysteretic behavior (Anishkin et al, 2010). The hydration/wetting of the core of the Hv1 VSD appears to be an important requirement for proton conduction (Freites et al, 2006;Ramsey et al, 2010;Wood et al, 2012), and water penetration into the core of the channel's transmembrane module is believed to change considerably upon channel opening (Chamberlin et al, 2014(Chamberlin et al, , 2015Hong et al, 2014), especially in the proximity of the VSD charge transfer center or hydrophobic plug (Tao et al, 2010;Lacroix et al, 2014;Takeshita et al, 2014). So one possible origin for Hv1 mechanosensitivity could reside in changes of VSD wettability induced by membrane stretch, which would result in changes in the thermodynamic and kinetic properties of voltage-dependent gating (Fig.…”

Roles for Countercharge in the Voltage Sensor Domain of Ion Channels

“…Countercharge to S4 arginine residue interactions have been revealed with crystallographic data from Na V Ab, Na V Rh, and Na V Ms (Payandeh et al, 2011;Payandeh et al, 2012;Zhang et al, 2012;Sula et al, 2017;Wisedchaisri et al, 2019). It has also been hypothesized that negatively charged residues tune the hydrophilicity of the inner and outer vestibules of the VSD (Palovcak et al, 2014), while the central, hydrophobic region separates these vestibules and focuses the electric field (Starace and Bezanilla, 2004;Ahern and Horn, 2005;Chanda and Bezanilla, 2008;Lacroix et al, 2014).…”

“…Their results showed that S4 arginines R1 and R2 move through a hydrophilic environment toward their interaction with phospholipid heads of the bilayer as the S2 ENC (D60)/S4 R3 salt-bridge interaction is formed with activation of the channel. The significance of hydration in voltage-gating is further emphasized with the finding that S4 aspartate substitutions in the Shaker channel are remarkably tolerated with respect to gating function (Diaz-Franulic et al, 2018), and by the corollary observation that mutation of S1-S3 residues comprising the hydrophobic plug have dramatic effects on gating charge movement (Lacroix et al, 2014, andreviewed by Bezanilla, 2018).…”

Electron current recordings in living cells

“…In voltage-gated proteins, two distinct types of currents can be measured: 1) currents associated with the movement of the S4 segments, the so-called gating currents. This type of current is intrinsically transient, since the voltage sensor is anchored to the membrane, and difficult to detect, given the small amount of charge involved [6]; 2) currents associated with ion permeation, which have been investigated in cells of many organisms, including, for example, sponges [7,8] and mussels [9], marine [10,11] and aquatic [12] plants. These currents are modulated by a multitude of factors, i.e.…”