β1 subunit stabilises sodium channel Nav1.7 against mechanical stress

Abstract

Voltage-gated sodium channels are key players in neuronal excitability and pain signalling. Precise gating of these channels is crucial as even small functional alterations can lead to pathological phenotypes such as pain or heart failure. Mechanical stress has been shown to affect sodium channel activation and inactivation. This suggests that stabilising components are necessary to ensure precise channel gating in living organisms. Here, we show that mechanical shear stress affects voltage dependence of activation and fast inactivation of the Nav1.7 channel. Co-expression of the β1 subunit, however, protects both gating modes of Nav1.7 against mechanical shear stress. Using molecular dynamics simulation, homology modelling and site-directed mutagenesis, we identify an intramolecular disulfide bond of β1 (Cys21-Cys43) which is partially involved in this process: the β1-C43A mutant prevents mechanical modulation of voltage dependence of activation, but not of fast inactivation. Our data emphasise the unique role of segment 6 of domain IV for sodium channel fast inactivation and confirm previous reports that the intracellular process of fast inactivation can be modified by interfering with the extracellular end of segment 6 of domain IV. Thus, our data suggest that physiological gating of Nav1.7 may be protected against mechanical stress in a living organism by assembly with the β1 subunit.

Subcellular dynamics and functional activity of the cleaved intracellular domain of the Na+ channel β1 subunit

“…With the exception of the β1 alternative splice variant β1B, β subunits are single-pass transmembrane proteins with a large, extracellular immunoglobulin (Ig) domain and are thus members of the Ig superfamily of cell adhesion molecules (CAMs) ( 3 ). The β subunits regulate α subunit trafficking ( 4 , 5 , 6 ), cell type-specific gating and kinetics ( 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 ), mechanosensitivity ( 16 , 17 ), and glycosylation ( 18 ). In addition to regulating α subunit function, β subunits also function as CAMs, regulating cell-cell and cell-matrix adhesion via interaction with an array of other CAMs, neurite outgrowth, neuronal pathfinding, fasciculation, and cell migration ( 6 , 15 , 19 , 20 , 21 , 22 , 23 , 24 , 25 ).…”

Sodium Channels and Local Anesthetics—Old Friends With New Perspectives

“…This isoform of hNav1.7 was first cloned from the human medullary thyroid carcinoma cell line, and its transcripts were found to be present only in neuroendocrine cells ( Klugbauer et al, 1995 ). With Nav1.7 being a primary target for LAs and isoform 3 widely used in many functional studies of hNav1.7 ( Xiao et al, 2010 ; Theile et al, 2011 ; Walker et al, 2012 ; Wang et al, 2015 ; Körner et al, 2018 ; Rühlmann et al, 2020 ) the hNav1.7 isoform 3 is chosen as the reference numbering for Table 2 .…”

Uncoupling sodium channel dimers rescues phenotype of pain-linked Nav1.7 mutation

“…Two human embryonic kidney cell (HEK cell) lines were used: HEK293T cells and a HEK cell line stably expressing WT hNav1.7 (Hampl et al, 2016;Körner et al, 2018). To the second cell line we refer to as WT cell line.…”