Tracking the motion of the K_V1.2 voltage sensor reveals the molecular perturbations caused by a de novo mutation in a case of epilepsy

Abstract

r 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. r Immunocytochemistry and flow cytometry showed that F302L does not impair KCNA2 subunit surface trafficking. r Molecular dynamics simulations indicated that F302L alters the exposure of S4 residues to membrane lipids. r 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. r 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. Antonios Pantazis: This project was Antonios' last at his previous position (UCLA; PI: Riccardo Olcese) and first at his first fully independent appointment, as Assistant Professor at Linköping University. He is particularly fond of this work because it combines highly diverse contributions from a truly international and multidisciplinary team of investigators, to address a case straight from the clinic. Antonios' research focus is on ion channel function and dysfunction. His team at LiU study how the intricate and dynamic structure of ion channels, their biophysical properties and their regulation relate to cellular excitability in health and, as in this article, disease.

Structural Determinants for Ligand Accommodation in Voltage Sensors

“…DOI: http://dx.doi.org/10.5772/intechopen.102094 flexibility of the S3a region facilitates movement of the segment S3b-S4, which in turn exhibits an even higher flexibility profile due to its composition rich in residues with small side-chain (Gly, Ser, Thr) and basic residues (Figure 1). Notably, these predictions have been experimentally confirmed elsewhere [9,10] and some reports also indicate that abnormal S4 movements cause pathological effects related for example to the development of epilepsy [11]. Therefore, it is becoming increasingly clear that the VSD is a flexible dynamic structure with evident relevance in physiological disorders.…”

An epilepsy-associated K V 1.2 charge-transfer-center mutation impairs K V 1.2 and K V 1.4 trafficking

“…Neuronal firing behavior can be further modulated by K V 1.2-subunit interaction with other K V 1 subunits: e.g., an A-type conductance is formed by K V 1.2 and K V 1.4 heteromeric channels ( 3 , 5 , 6 ). A growing number of both gain- and loss-of-function KCNA2 variants are implicated in epileptic encephalopathy ( 7 – 10 ).…”

“… Discovery of a KCNA2 mutation in a patient with epilepsy. ( A ) Membrane topology of the K V 1.2 subunit and model of a homotetrameric K V 1.2 channel ( 8 ). F233S is on helix S2, within the VSD.…”

A Novel KCNA2 Variant in a Patient with Non-Progressive Congenital Ataxia and Epilepsy: Functional Characterization and Sensitivity to 4-Aminopyridine

“…Kv1.2-containing channels are expressed at axon initial segment, juxtaparanodal regions and presynaptic terminals of both excitatory and inhibitory neurons where they increase the threshold for neuronal firing and terminate bursts of action potentials, thereby protecting cells from hyperexcitability [ 8 , 20 , 21 , 22 , 23 , 24 ]. The impact of Kv1.2 variants may be cell-type specific and cause variable phenotypes at different onset ages depending on compensatory mechanisms and still unknown factors [ 25 , 26 , 27 ].…”