Regulation and drug modulation of a voltage-gated sodium channel: Pivotal role of the S4–S5 linker in activation and slow inactivation

Abstract

Voltage-gated sodium (NaV) channels control excitable cell functions. While structural investigations have revealed conformation details of different functional states, the mechanisms of both activation and slow inactivation remain unclear. Here, we identify residue T140 in the S4–S5 linker of the bacterial voltage-gated sodium channel NaChBac as critical for channel activation and drug effects on inactivation. Mutations at T140 either attenuate activation or render the channel nonfunctional. Propofol, a clinical anesthetic known to inhibit NaChBac by promoting slow inactivation, binds to a pocket between the S4–S5 linker and S6 helix in a conformation-dependent manner. Using 19F-NMR to quantify site-specific binding by saturation transfer differences (STDs), we found strong STDs in inactivated, but not activated, NaChBac. Molecular dynamics simulations show a highly dynamic pocket in the activated conformation, limiting STD buildup. In contrast, drug binding to this pocket promotes and stabilizes the inactivated states. Our results provide direct experimental evidence showing distinctly different associations between the S4–S5 linker and S6 helix in activated and inactivated states. Specifically, an exchange occurs between interaction partners T140 and N234 of the same subunit in activation, and T140 and N225 of the domain-swapped subunit in slow inactivation. The drug action on slow inactivation of prokaryotic NaV channels seems to have a mechanism similar to the recently proposed “door-wedge” action of the isoleucine-phenylalanine-methionine (IFM) motif on the fast inactivation of eukaryotic NaV channels. Elucidating this gating mechanism points to a possible direction for conformation-dependent drug development.

Relationship among surface electric double layer of cardiomyocyte membrane and toxicology of digoxin and opening of ion channels

“…EPM can reflect the amount of ions lost on the cell surface (in the external electric field, a shear plane is formed on the cell surface); and indirectly reflect the characteristics of the surface potential change of cells under different experimental conditions 15 . In studies related to the electrical activity of cardiomyocytes, the reason for using single-cell electrophoresis technology is because the changes in the surface electric double layer of cardiomyocytes membrane in an external electric field are the same as the initiation of the electrical activity of cardiomyocytes in vivo (the external electric field in the body comes from sinoatrial node cells or charged cells around or pacemakers) 14,16 . In general, the opening of gated ion channels in cardiomyocytes involves two elements: the presence of an external electric field or changes in transmembrane potential; and a change in the Table 1.…”

“…And the significant increase in transmembrane potential and the Na + -K + exchange on the cell surface of the action potential phase 4 caused by digoxin poisoning are the causes of cardiac ectopic beats. The adsorbed ions on the cell surface are an important part of the cell surface structure 16,36,37 , and the size and shape of the surface electric double layer of the cell (or membrane) are equally important, which depends on the multi-component surface potential of the cell and the composition and changes of the ions in the suspension. For example, chemical-gated channels: chemical substances compete with ions and bind to membrane proteins, which makes the surface electric double layer on the cell smaller and thinner; intracellular sarcoplasmic reticulum Ca 2+ channel: ions flow into the cell, changes the ion concentration of intracellular fluid, resulting in deformation of the electric double layer of the sarcoplasmic reticulum surface (because the electric double layer of the sarcoplasmic reticulum surface has only one ion adsorption layer-the influence of the transmembrane potential, and the characteristics of the ionic composition in this layer, the deformation is more easily induced by the change of Ca 2+ concentration in the suspension).…”

Volatile Anesthetics and O2 Activate TASK-1/3 by Weak H-Bonding with X-Gate Uncharged Arg-245: The Major Molecular Mechanism for Carotid Body Hypoxic Sensitivity and Further Insights into Fighter Pilot +Gz-Induced LOC

“…163 These effects are also seen with propofol binding to voltage-gated sodium channels. 39,164 Similarly sevoflurane effects on the voltage-gated potassium channel Kv1.2 alter open-closed conformation states increasing open probability. 165 VA affecting MT conformation states 62 and consequently "conformation resonance" of PLC 66 and PI3k 10 has been explored.…”

Recent advances in computational studies on voltage‐gated sodium channels: Drug design and mechanism studies

“…Recent studies show that the S4-S5 linker plays a key role in activation and slow inactivation. 36 Bacterial VGSCs, which contain 24 transmembrane (TM) segments, are relatively simple compared with eukaryotic VGSCs. Four polypeptide chains are included in the structure of bacterial VGSCs, and TM1-TM4 in each chain form the voltage sensors.…”