Constitutive opening of the Kv7.2 pore activation gate causes KCNQ2-developmental encephalopathy

Proc Natl Acad Sci U S A. 2024 Dec 3;121(49):e2412388121. doi: 10.1073/pnas.2412388121. Epub 2024 Nov 27.

Abstract

Pathogenic variants in KCNQ2 encoding 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 S6 activation gate that undergoes large structural rearrangements during pore opening; the disease-causing A356T variant in KCNQ3, paralogous to the A317T variant in KCNQ2, was also investigated. Currents through KCNQ2 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 KCNQ2-related encephalopathies.

Keywords: Genotype–phenotype correlations; Molecular dynamics; channel gating; developmental and epileptic encephalopathies; potassium channels.

MeSH terms

  • Animals
  • Brain Diseases / genetics
  • Brain Diseases / metabolism
  • Female
  • Humans
  • Ion Channel Gating*
  • KCNQ2 Potassium Channel* / chemistry
  • KCNQ2 Potassium Channel* / genetics
  • KCNQ2 Potassium Channel* / metabolism
  • KCNQ3 Potassium Channel / chemistry
  • KCNQ3 Potassium Channel / genetics
  • KCNQ3 Potassium Channel / metabolism
  • Male
  • Molecular Dynamics Simulation*
  • Mutation
  • Phosphatidylinositol 4,5-Diphosphate / metabolism

Substances

  • KCNQ2 Potassium Channel
  • KCNQ2 protein, human
  • KCNQ3 Potassium Channel
  • KCNQ3 protein, human
  • Phosphatidylinositol 4,5-Diphosphate