N1366S mutation of human skeletal muscle sodium channel causes paramyotonia congenita

Abstract

Paramyotonia congenita is an autosomal dominant skeletal muscle channelopathy caused by missense mutations in SCN4A, the gene encoding the α subunit of the human skeletal muscle voltage-gated sodium channel NaV1.4. We report a three-generation family in which six members present clinical symptoms of paramyotonia congenita characterized by a marked worsening of myotonia by cold and by the presence of clear episodes of paralysis. We identified a novel mutation in SCN4A (Asn1366Ser, N1366S) in all patients in the family but not in healthy relatives or in 500 normal control subjects. Functional analysis of the channel protein expressed in HEK293 cells by whole-cell patch clamp recording revealed that the N1366S mutation led to significant alterations in the gating process of the NaV1.4 channel. The N1366S mutant displayed a cold-induced hyperpolarizing shift in the voltage dependence of activation and a depolarizing shift in fast inactivation, as well as a reduced rate of fast inactivation and accelerated recovery from fast inactivation. In addition, homology modelling and molecular dynamic simulation of N1366S and wild-type NaV1.4 channels indicated that the arginine-to-serine substitution disrupted the hydrogen bond formed between N1366 and R1454. Together, our results suggest that N1366S is a gain-of-function mutation of NaV1.4 at low temperature and the mutation may be responsible for the clinical symptoms of paramyotonia congenita in the affected family and constitute a basis for studies into its pathogenesis.

Roles for Countercharge in the Voltage Sensor Domain of Ion Channels

“…The mutation produces a right shift in the midpoint of the activation curve, consistent with loss of function (hypoexcitability). In contrast, N1366S (DIVS1 ENC), identified in a family diagnosed with paramyotonia congenita, produces gain of function effects including enhanced activation, slowed entry into the fastinactivated state, and accelerated recovery (Ke et al, 2017). These effects are consistent with a hyperexcitable skeletal muscle fiber phenotype that characterizes the disease.…”

Modeling the Interactions Between Sodium Channels Provides Insight Into the Negative Dominance of Certain Channel Mutations

“…In a voltage-dependent manner, Na + channels change their conformation between permeable (open) and not permeable (e.g., closed, inactivated) states ( Hille, 2001 ), ultimately leading to the upstroke of the AP. Because of this crucial role in AP generation, genetic variants of voltage-gated Na + channels are frequently associated with pathologies of the central nervous system such as epilepsy ( Wei et al, 2017 ; Nolan and Fink, 2018 ) or pain syndromes ( Rühlmann et al, 2020 ), of skeletal muscle such as paramyotonia ( Ke et al, 2017 ), and of the heart, where they can cause arrhythmias ( Lieve and Wilde, 2015 ; Veerman et al, 2015 ).…”

Role of the voltage sensor module in Nav domain IV on fast inactivation in sodium channelopathies: The implication of closed-state inactivation

“…Of note, structural studies showed that N1366 in DIVS1 forms hydrogen bonds with R1457 (R4) in DIVS4, and a functional study of N1366D (replaced with a negatively charged residue) displayed a hyperpolarizing shift in steady-state availability, altered voltage-dependence of fast inactivation and delayed recovery from inactivation, causing a loss-offunction of Na v 1.4 [9,15] (Table 2). Conversely, N1366S (replaced with an uncharged residue), found in PC, displayed a cold-induced hyperpolarizing shift in activation, depolarizing shift in steady-state availability, delayed fast inactivation and accelerated recovery from inactivation, causing a gain-of-function of Na v 1.4 that can be associated with PC [54] (Table 2). Intriguingly, a structural study of N1366S demonstrated disrupted interactions of N1366S and an arginine residue in DIVS4 at low temperature [54].…”

“…Conversely, N1366S (replaced with an uncharged residue), found in PC, displayed a cold-induced hyperpolarizing shift in activation, depolarizing shift in steady-state availability, delayed fast inactivation and accelerated recovery from inactivation, causing a gain-of-function of Na v 1.4 that can be associated with PC [54] (Table 2). Intriguingly, a structural study of N1366S demonstrated disrupted interactions of N1366S and an arginine residue in DIVS4 at low temperature [54]. On the other hand, a structural study showed that D1420, one of the residues of pGCTC, in Na v 1.4 DIVS3 is in close proximity to R1635 (R5) in DIVS4, and a functional study showed that D1420K (replaced with a positively charged residue) displayed a delayed fast inactivation and altered voltage-dependence of recovery from inactivation (Table 2) [15].…”