CONSTITUTIVE OPENING OF THE Kv7.2 PORE ACTIVATION GATE CAUSESKCNQ2-DEVELOPMENTAL ENCEPHALOPATHY

Abstract

ABSTRACTPathogenic variants inKCNQ2encoding for Kv7.2 voltage-gated potassium channel subunits cause developmental encephalopathies (KCNQ2-encephalopathies), both with and without epilepsy. We herein describe the clinical,in vitroandin silicofeatures of two encephalopathy-causing variants (A317T, L318V) in Kv7.2 affecting two consecutive residues in the S6activation gate undergoing large structural rearrangements during pore opening. Currents through these mutant channels displayed increased density, hyperpolarizing shifts in activation gating, and insensitivity to 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 single-channel open probability, with no change in membrane abundance or single-channel conductance, was responsible for the observed gain-of-function effects. All-atoms 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, a PIP2-independent stabilization of the inner pore gate open configuration is a novel molecular pathogenetic mechanism forKCNQ2-developmental encephalopathies.