Constitutive opening of the Kv7.2 pore activation gate causes <i>KCNQ2</i>-developmental encephalopathy.

Abstract

Pathogenic variants in <i>KCNQ2</i> encoding Kv7.2 voltage-gated potassium channel subunits cause developmental encephalopathies (<i>KCNQ2</i>-encephalopathies), both with and without epilepsy. We herein describe the clinical, in vitro, and in silico features of two encephalopathy-causing variants (A317T, L318V) in Kv7.2 affecting two consecutive residues in the S₆ activation gate that undergoes large structural rearrangements during pore opening; the disease-causing A356T variant in <i>KCNQ3</i>, paralogous to the A317T variant in <i>KCNQ2</i>, was also investigated. Currents through <i>KCNQ2</i> mutant channels displayed increased density, hyperpolarizing shifts in activation gating, faster activation and slower deactivation kinetics, and resistance to changes in the cellular concentrations of phosphatidylinositol 4,5-bisphosphate (PIP₂), a critical regulator of Kv7 channel function; all these features are consistent with a strong gain-of-function effect. An increase in the probability of single-channel opening, with no change in membrane abundance or single-channel conductance, was responsible for the observed gain-of-function effects. All-atom molecular dynamics simulations revealed that the mutations widened the inner pore gate and stabilized a constitutively open channel configuration in the closed state, with minimal effects on the open conformation. Thus, mutation-induced stabilization of the inner pore gate open configuration is a molecular pathogenetic mechanism for <i>KCNQ2</i>-related encephalopathies.