Variable K(+) channel subunit dysfunction in inherited mutations of KCNA1.
Mutations of KCNA1, which codes for the K(+) channel subunit hKv1.1, are associated with the human autosomal dominant disease episodic ataxia type 1 (EA1). Five recently described mutations are associated with a broad range of phenotypes: neuromyotonia alone or with seizures, EA1 with seizures, or very drug-resistant EA1. Here we investigated the consequences of each mutation for channel assembly, trafficking, gating and permeation. We related data obtained from co-expression of mutant and wild-type hKv1.1 to the results of expressing mutant-wild-type fusion proteins, and combined electrophysiological recordings in Xenopus oocytes with a pharmacological discrimination of the contribution of mutant and wild-type subunits to channels expressed at the membrane. We also applied confocal laser scanning microscopy to measure the level of expression of either wild-type or mutant subunits tagged with green fluorescent protein (GFP). R417stop truncates most of the C-terminus and is associated with severe drug-resistant EA1. Electrophysiological and pharmacological measurements indicated that the mutation impairs both tetramerisation of R417stop with wild-type subunits, and membrane targeting of heterotetramers. This conclusion was supported by confocal laser scanning imaging of enhanced GFP (EGFP)-tagged hKv1.1 subunits. Co-expression of R417stop with wild-type hKv1.2 subunits yielded similar results to co-expression with wild-type hKv1.1. Mutations associated with typical EA1 (V404I) or with neuromyotonia alone (P244H) significantly affected neither tetramerisation nor trafficking, and only altered channel kinetics. Two other mutations associated with a severe phenotype (T226R, A242P) yielded an intermediate result. The phenotypic variability of KCNA1 mutations is reflected in a wide range of disorders of channel assembly, trafficking and kinetics.
Rea
Ruth
R
University Department of Clinical Neurology, Institute of Neurology, UCL, Queen Square, London WC1N 3BG, UK.
Spauschus
Alexander
A
Eunson
Louise H
LH
Hanna
Michael G
MG
Kullmann
Dimitri M
DM
D000818:Animals; D004594:Electrophysiology; D005260:Female; D005453:Fluorescence; D006801:Humans; D007700:Kinetics; D051662:Kv1.1 Potassium Channel; D051663:Kv1.2 Potassium Channel; D008954:Models, Biological; D009154:Mutation / Q000502:physiology*; D009865:Oocytes; D018408:Patch-Clamp Techniques; D026902:Potassium Channel Blockers / Q000494:pharmacology; D015221:Potassium Channels / Q000187:drug effects / Q000235:genetics* / Q000502:physiology*; D024642:Potassium Channels, Voltage-Gated; D011499:Protein Processing, Post-Translational; D012016:Reference Values; D019789:Tetraethylammonium / Q000494:pharmacology; D014982:Xenopus laevis
C496946:KCNA1 protein, human; D051663:Kv1.2 Potassium Channel; D026902:Potassium Channel Blockers; D015221:Potassium Channels; D024642:Potassium Channels, Voltage-Gated; D051662:Kv1.1 Potassium Channel; D019789:Tetraethylammonium