A conserved threonine in the S1–S2 loop of KV7.2 and KV7.3 channels regulates voltage-dependent activation

Abstract

The voltage-gated potassium channels KV7.2 and KV7.3 (KCNQ2/3 genes) play an important role in regulating neuronal excitability. More than 50 KCNQ2/3 mutations have been identified to cause an inherited form of epilepsy in newborns. For two of those (E119G and S122L) found in the S1-S2 region of KV7.2, we previously showed a decreased channel availability mainly at action potential subthreshold voltages caused by a slight depolarizing shift of the activation curve. Interestingly, recent studies revealed that a threonine residue within the S1-S2 loop, highly conserved among different classes of KV channels, is crucial for both their function and surface expression. To investigate the functional role of the homologous threonine residues in KV7.2 (T114) and KV7.3 (T144) channels, we replaced them with alanine and examined the electrophysiological properties using heterologous expression in CHO cells and whole cell patch clamping. Channels comprising mutant subunits yielded decreased potassium currents with slowed activation and accelerated deactivation kinetics. However, the most striking effect was a depolarizing shift in the voltage dependence of activation reaching +30 mV upon co-expression of both mutant subunits. Potential interactions of T114 within the channel were analyzed by creating a 3D homology model of KV7.2 in an open state suggesting that this residue plays a central role in the formation of a stable interface between the S1-S2 and the S5 segment helices. This could be the explanation why substitution of the conserved threonine in KV7.2 and KV7.3 channels destabilizes the open and favors the closed state of these channels.

Spectrum of KV2.1 Dysfunction in KCNB1‐Associated Neurodevelopmental Disorders

“…The T210K/M variants resulted in loss of K + conductance and cell‐surface K V 2.1 expression. T210 is a critical residue forming the S1–pore interface . A hydroxyl group is required at this position for channel function .…”

“…T210 is a critical residue forming the S1-pore interface. 31,32 A hydroxyl group is required at this position for channel function. 32 Thus, substitution with either lysine or methionine would be incompatible with channel function.…”

Reciprocal voltage sensor-to-pore coupling leads to potassium channel C-type inactivation

“…1a,b) and has been implicated as a candidate for a functional VSD-to-pore domain connection2032. Further, residues in the neighborhood of F416 form an important, close, and rigid contact point between the VSD and the pore domain3334353637. Here we explore the hypothesis that residue F416 is a possible candidate in the reciprocal VSD-to-pore interaction that modulates C-type inactivation.…”

Effect of sodium ferulate on delayed rectifier K+ currents in PC12 cells

“…K + channel alterations may reflect the clinical antinociceptive action. A number of studies have shown that voltage-gated K + channels have a major role in the regulation of neuronal excitability (21,22). …”