Molecular Modeling of Cardiac Sodium Channel with Mexiletine
A sodium channel blocker mexiletine (MEX) is used to treat chronic pain, myotonia and some arrhythmias. Mutations in the pore domain (PD) of voltage-gated sodium channels differently affect tonic block (TB) and use-dependent block (UDB) by MEX. Previous studies identified several MEX-sensing residue...
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| Format: | Article |
| Language: | English |
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MDPI AG
2022-12-01
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| Series: | Membranes |
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| Online Access: | https://www.mdpi.com/2077-0375/12/12/1252 |
| _version_ | 1797456400472866816 |
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| author | Boris S. Zhorov |
| author_facet | Boris S. Zhorov |
| author_sort | Boris S. Zhorov |
| collection | DOAJ |
| description | A sodium channel blocker mexiletine (MEX) is used to treat chronic pain, myotonia and some arrhythmias. Mutations in the pore domain (PD) of voltage-gated sodium channels differently affect tonic block (TB) and use-dependent block (UDB) by MEX. Previous studies identified several MEX-sensing residues in the hNav1.5 channel and demonstrated that the channel block by MEX increases with activation of the voltage-sensing domain III (VSD<sub>III</sub>), whereas MEX stabilizes the activated state of VSD<sub>III</sub>. Structural rationales for these observations are unclear. Here, Monte Carlo (MC) energy minimizations were used to dock MEX and its more potent analog, Thio-Me2, into the hNav1.5 cryo-EM structure with activated VSDs and presumably inactivated PD. Computations yielded two ensembles of ligand binding poses in close contacts with known MEX-sensing residues in helices S6<sub>III</sub>, S6<sub>IV</sub> and P1<sub>IV</sub>. In both ensembles, the ligand NH<sub>3</sub> group approached the cation-attractive site between backbone carbonyls at the outer-pore bottom, while the aromatic ring protruded ether into the inner pore (putative UDB pose) or into the III/IV fenestration (putative TB pose). In silico deactivation of VSD<sub>III</sub> shifted helices S4–S5<sub>III</sub>, S5<sub>III</sub>, S6<sub>III</sub> and S6<sub>IV</sub> and tightened the TB site. In a model with activated VSD<sub>III</sub> and three resting VSDs, MC-minimized energy profile of MEX pulled from the TB site towards lipids shows a deep local minimum due to interactions with 11 residues in S5<sub>III</sub>, P1<sub>III</sub>, S6<sub>III</sub> and S6<sub>IV</sub>. The minimum may correspond to an interim binding site for MEX in the hydrophobic path to the TB site along the lipid-exposed sides of repeats III and IV where 15 polar and aromatic residues would attract cationic blockers. The study explains numerous experimental data and suggests the mechanism of allosteric modification of the MEX binding site by VSD<sub>III</sub>. |
| first_indexed | 2024-03-09T16:06:59Z |
| format | Article |
| id | doaj.art-8dffb45850f54a8f90dfb9d3f1536235 |
| institution | Directory Open Access Journal |
| issn | 2077-0375 |
| language | English |
| last_indexed | 2024-03-09T16:06:59Z |
| publishDate | 2022-12-01 |
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| record_format | Article |
| series | Membranes |
| spelling | doaj.art-8dffb45850f54a8f90dfb9d3f15362352023-11-24T16:36:03ZengMDPI AGMembranes2077-03752022-12-011212125210.3390/membranes12121252Molecular Modeling of Cardiac Sodium Channel with MexiletineBoris S. Zhorov0Department of Biochemistry and Biomedical Sciences, McMaster University, Hamilton, ON L8S 4K1, CanadaA sodium channel blocker mexiletine (MEX) is used to treat chronic pain, myotonia and some arrhythmias. Mutations in the pore domain (PD) of voltage-gated sodium channels differently affect tonic block (TB) and use-dependent block (UDB) by MEX. Previous studies identified several MEX-sensing residues in the hNav1.5 channel and demonstrated that the channel block by MEX increases with activation of the voltage-sensing domain III (VSD<sub>III</sub>), whereas MEX stabilizes the activated state of VSD<sub>III</sub>. Structural rationales for these observations are unclear. Here, Monte Carlo (MC) energy minimizations were used to dock MEX and its more potent analog, Thio-Me2, into the hNav1.5 cryo-EM structure with activated VSDs and presumably inactivated PD. Computations yielded two ensembles of ligand binding poses in close contacts with known MEX-sensing residues in helices S6<sub>III</sub>, S6<sub>IV</sub> and P1<sub>IV</sub>. In both ensembles, the ligand NH<sub>3</sub> group approached the cation-attractive site between backbone carbonyls at the outer-pore bottom, while the aromatic ring protruded ether into the inner pore (putative UDB pose) or into the III/IV fenestration (putative TB pose). In silico deactivation of VSD<sub>III</sub> shifted helices S4–S5<sub>III</sub>, S5<sub>III</sub>, S6<sub>III</sub> and S6<sub>IV</sub> and tightened the TB site. In a model with activated VSD<sub>III</sub> and three resting VSDs, MC-minimized energy profile of MEX pulled from the TB site towards lipids shows a deep local minimum due to interactions with 11 residues in S5<sub>III</sub>, P1<sub>III</sub>, S6<sub>III</sub> and S6<sub>IV</sub>. The minimum may correspond to an interim binding site for MEX in the hydrophobic path to the TB site along the lipid-exposed sides of repeats III and IV where 15 polar and aromatic residues would attract cationic blockers. The study explains numerous experimental data and suggests the mechanism of allosteric modification of the MEX binding site by VSD<sub>III</sub>.https://www.mdpi.com/2077-0375/12/12/1252tonic blockuse-dependent blocklocal anestheticsmolecular modelingMonte Carlo energy minimizationsvoltage-sensing domains |
| spellingShingle | Boris S. Zhorov Molecular Modeling of Cardiac Sodium Channel with Mexiletine Membranes tonic block use-dependent block local anesthetics molecular modeling Monte Carlo energy minimizations voltage-sensing domains |
| title | Molecular Modeling of Cardiac Sodium Channel with Mexiletine |
| title_full | Molecular Modeling of Cardiac Sodium Channel with Mexiletine |
| title_fullStr | Molecular Modeling of Cardiac Sodium Channel with Mexiletine |
| title_full_unstemmed | Molecular Modeling of Cardiac Sodium Channel with Mexiletine |
| title_short | Molecular Modeling of Cardiac Sodium Channel with Mexiletine |
| title_sort | molecular modeling of cardiac sodium channel with mexiletine |
| topic | tonic block use-dependent block local anesthetics molecular modeling Monte Carlo energy minimizations voltage-sensing domains |
| url | https://www.mdpi.com/2077-0375/12/12/1252 |
| work_keys_str_mv | AT borisszhorov molecularmodelingofcardiacsodiumchannelwithmexiletine |