CONSTITUTIVE OPENING OF THE Kv7.2 PORE ACTIVATION GATE CAUSES KCNQ2 -DEVELOPMENTAL ENCEPHALOPATHY

Pathogenic variants in KCNQ2 encoding for Kv7.2 voltage-gated potassium channel subunits cause developmental encephalopathies ( KCNQ2 -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 S ₆ activation 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 (PIP ₂ ), 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 PIP ₂ -independent stabilization of the inner pore gate open configuration is a novel molecular pathogenetic mechanism for KCNQ2 -developmental encephalopathies.