Defective membrane insertion of mutant Na,K‐ATPase, a cause of fatal epilepsy

Abstract

Given its critical role in establishing ionic gradients in neurons and other excitable cells, functional disruption of the Na/K‐ATPase is expected to substantially compromise neurological homeostasis. However, to date only a few examples of spontaneous Na/K‐ATPase mutations have been identified in human patients. Here we describe a de novo Trp‐Arg mutation in the ATP1A1 gene, encoding the Na/K‐ATPase catalytic α1 subunit, in an infant who died at 10 months from therapy‐resistant epilepsy. Located in a conserved transmembrane helical region of the α1 subunit, the mutation was associated primarily with neurological symptoms and a low capacity to retain magnesium. Confocal imaging of the mutant Na/K‐ATPase α1 subunit expressed in rat hippocampal neurons revealed decreased but detectable membrane expression. Expressed in Xenopus oocytes, the mutant Na/K‐ATPase catalytic α1 subunit was associated with nonselective, ouabain‐resistant leak currents, consistent with a sizable, continuous hydration defect in the transmembrane domain. Indeed, molecular dynamics simulations in both POPC and mixed‐lipid bilayers showed accumulation of water at the protein periphery, particularly in the vicinity of crystallographic Na‐binding sites. These results provide evidence, from clinical diagnosis to atomistic simulation, for a mechanism of ion‐gradient disruption that could account for leak currents now observed in multiple pathological Na/K‐ATPase variants. Our finding of a pathological interaction between the mutated ion transporter and the membrane lipids has implications for development of new treatment strategy in many cases of genetic epilepsy.Support or Funding InformationSwedish Research Council to AA and to HB