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Tracking the motion of the K V 1.2 voltage sensor reveals the molecular perturbations caused by a de novo mutation in a case of epilepsy
Author(s) -
Pantazis Antonios,
Kaneko Maki,
Angelini Marina,
Steccanella Federica,
Westerlund Annie M.,
Lindström Sarah H.,
Nilsson Michelle,
Delemotte Lucie,
Saitta Sulagna C.,
Olcese Riccardo
Publication year - 2020
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1113/jp280438
Subject(s) - depolarization , biophysics , membrane potential , excitatory postsynaptic potential , missense mutation , epilepsy , voltage clamp , voltage gated ion channel , biology , protein subunit , loss function , chemistry , mutation , microbiology and biotechnology , ion channel , biochemistry , neuroscience , gene , receptor , phenotype
Key points K V 1.2 channels, encoded by the KCNA2 gene, regulate neuronal excitability by conducting K + upon depolarization. A new KCNA2 missense variant was discovered in a patient with epilepsy, causing amino acid substitution F302L at helix S4, in the K V 1.2 voltage‐sensing domain. Immunocytochemistry and flow cytometry showed that F302L does not impair KCNA2 subunit surface trafficking. Molecular dynamics simulations indicated that F302L alters the exposure of S4 residues to membrane lipids. Voltage clamp fluorometry revealed that the voltage‐sensing domain of K V 1.2‐F302L channels is more sensitive to depolarization. Accordingly, K V 1.2‐F302L channels opened faster and at more negative potentials; however, they also exhibited enhanced inactivation: that is, F302L causes both gain‐ and loss‐of‐function effects. Coexpression of KCNA2‐WT and ‐F302L did not fully rescue these effects. The proband's symptoms are more characteristic of patients with loss of KCNA2 function. Enhanced K V 1.2 inactivation could lead to increased synaptic release in excitatory neurons, steering neuronal circuits towards epilepsy.Abstract An exome‐based diagnostic panel in an infant with epilepsy revealed a previously unreported de novo missense variant in KCNA2 , which encodes voltage‐gated K + channel K V 1.2. This variant causes substitution F302L, in helix S4 of the K V 1.2 voltage‐sensing domain (VSD). F302L does not affect KCNA2 subunit membrane trafficking. However, it does alter channel functional properties, accelerating channel opening at more hyperpolarized membrane potentials, indicating gain of function. F302L also caused loss of K V 1.2 function via accelerated inactivation onset, decelerated recovery and shifted inactivation voltage dependence to more negative potentials. These effects, which are not fully rescued by coexpression of wild‐type and mutant KCNA2 subunits, probably result from the enhancement of VSD function, as demonstrated by optically tracking VSD depolarization‐evoked conformational rearrangements. In turn, molecular dynamics simulations suggest altered VSD exposure to membrane lipids. Compared to other encephalopathy patients with KCNA2 mutations, the proband exhibits mild neurological impairment, more characteristic of patients with KCNA2 loss of function. Based on this information, we propose a mechanism of epileptogenesis based on enhanced K V 1.2 inactivation leading to increased synaptic release preferentially in excitatory neurons, and hence the perturbation of the excitatory/inhibitory balance of neuronal circuits.