Multiple mechanisms underlie reduced potassium conductance in the p.T1019PfsX38 variant of hERG
Abstract Long QT syndrome type II (LQT2) is caused by loss‐of‐function mutations in the hERG K+ channel, leading to increased incidence of cardiac arrest and sudden death. Many genetic variants have been reported in the hERG gene with various consequences on channel expression, permeation, and gatin...
| Main Authors: | , , , |
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| Format: | Article |
| Language: | English |
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Wiley
2022-07-01
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| Series: | Physiological Reports |
| Subjects: | |
| Online Access: | https://doi.org/10.14814/phy2.15341 |
| _version_ | 1827589718492053504 |
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| author | Majid K. Al Salmani Rezvan Tavakoli Wajid Zaman Ahmed Al Harrasi |
| author_facet | Majid K. Al Salmani Rezvan Tavakoli Wajid Zaman Ahmed Al Harrasi |
| author_sort | Majid K. Al Salmani |
| collection | DOAJ |
| description | Abstract Long QT syndrome type II (LQT2) is caused by loss‐of‐function mutations in the hERG K+ channel, leading to increased incidence of cardiac arrest and sudden death. Many genetic variants have been reported in the hERG gene with various consequences on channel expression, permeation, and gating. Only a small number of LQT2 causing variants has been characterized to define the underlying pathophysiological causes of the disease. We sought to determine the characteristics of the frameshift variant p.Thr1019ProfsX38 (T1019PfsX38) which affects the C‐terminus of the protein. This mutation was identified in an extended Omani family of LQT2. It replaces the last 140 amino acids of hERG with 37 unique amino acids. T1019 is positioned at a distinguished region of the C‐terminal tail of hERG, as predicted from the deep learning system AlphaFold v2.0. We employed the whole‐cell configuration of the patch‐clamp technique to study wild‐type and mutant channels that were transiently expressed in human embryonic kidney 293 (HEK293) cells. Depolarizing voltages elicited slowly deactivating tail currents that appeared upon repolarization of cells that express either wild‐type‐ or T1019PfsX38‐hERG. There were no differences in the voltage and time dependencies of activation between the two variants. However, the rates of hERG channel deactivation at hyperpolarizing potentials were accelerated by T1019PfsX38. In addition, the voltage dependence of inactivation of T1019PfsX38‐hERG was shifted by 20 mV in the negative direction when compared with wild‐type hERG. The rates of channel inactivation were increased in the mutant channel variant. Next, we employed a step‐ramp protocol to mimic membrane repolarization by the cardiac action potential. The amplitudes of outward currents and their integrals were reduced in the mutant variant when compared with the wild‐type variant during repolarization. Thus, changes in the gating dynamics of hERG by the T1019PfsX38 variant contribute to the pathology seen in affected LQT2 patients. |
| first_indexed | 2024-03-09T01:05:54Z |
| format | Article |
| id | doaj.art-9dd8736a195d48b5b40d373a4d36549b |
| institution | Directory Open Access Journal |
| issn | 2051-817X |
| language | English |
| last_indexed | 2024-03-09T01:05:54Z |
| publishDate | 2022-07-01 |
| publisher | Wiley |
| record_format | Article |
| series | Physiological Reports |
| spelling | doaj.art-9dd8736a195d48b5b40d373a4d36549b2023-12-11T09:26:21ZengWileyPhysiological Reports2051-817X2022-07-011014n/an/a10.14814/phy2.15341Multiple mechanisms underlie reduced potassium conductance in the p.T1019PfsX38 variant of hERGMajid K. Al Salmani0Rezvan Tavakoli1Wajid Zaman2Ahmed Al Harrasi3Natural and Medical Sciences Research Center University of Nizwa Nizwa OmanNatural and Medical Sciences Research Center University of Nizwa Nizwa OmanNatural and Medical Sciences Research Center University of Nizwa Nizwa OmanNatural and Medical Sciences Research Center University of Nizwa Nizwa OmanAbstract Long QT syndrome type II (LQT2) is caused by loss‐of‐function mutations in the hERG K+ channel, leading to increased incidence of cardiac arrest and sudden death. Many genetic variants have been reported in the hERG gene with various consequences on channel expression, permeation, and gating. Only a small number of LQT2 causing variants has been characterized to define the underlying pathophysiological causes of the disease. We sought to determine the characteristics of the frameshift variant p.Thr1019ProfsX38 (T1019PfsX38) which affects the C‐terminus of the protein. This mutation was identified in an extended Omani family of LQT2. It replaces the last 140 amino acids of hERG with 37 unique amino acids. T1019 is positioned at a distinguished region of the C‐terminal tail of hERG, as predicted from the deep learning system AlphaFold v2.0. We employed the whole‐cell configuration of the patch‐clamp technique to study wild‐type and mutant channels that were transiently expressed in human embryonic kidney 293 (HEK293) cells. Depolarizing voltages elicited slowly deactivating tail currents that appeared upon repolarization of cells that express either wild‐type‐ or T1019PfsX38‐hERG. There were no differences in the voltage and time dependencies of activation between the two variants. However, the rates of hERG channel deactivation at hyperpolarizing potentials were accelerated by T1019PfsX38. In addition, the voltage dependence of inactivation of T1019PfsX38‐hERG was shifted by 20 mV in the negative direction when compared with wild‐type hERG. The rates of channel inactivation were increased in the mutant channel variant. Next, we employed a step‐ramp protocol to mimic membrane repolarization by the cardiac action potential. The amplitudes of outward currents and their integrals were reduced in the mutant variant when compared with the wild‐type variant during repolarization. Thus, changes in the gating dynamics of hERG by the T1019PfsX38 variant contribute to the pathology seen in affected LQT2 patients.https://doi.org/10.14814/phy2.15341arrhythmiahERGlong QT syndromepotassium channels |
| spellingShingle | Majid K. Al Salmani Rezvan Tavakoli Wajid Zaman Ahmed Al Harrasi Multiple mechanisms underlie reduced potassium conductance in the p.T1019PfsX38 variant of hERG Physiological Reports arrhythmia hERG long QT syndrome potassium channels |
| title | Multiple mechanisms underlie reduced potassium conductance in the p.T1019PfsX38 variant of hERG |
| title_full | Multiple mechanisms underlie reduced potassium conductance in the p.T1019PfsX38 variant of hERG |
| title_fullStr | Multiple mechanisms underlie reduced potassium conductance in the p.T1019PfsX38 variant of hERG |
| title_full_unstemmed | Multiple mechanisms underlie reduced potassium conductance in the p.T1019PfsX38 variant of hERG |
| title_short | Multiple mechanisms underlie reduced potassium conductance in the p.T1019PfsX38 variant of hERG |
| title_sort | multiple mechanisms underlie reduced potassium conductance in the p t1019pfsx38 variant of herg |
| topic | arrhythmia hERG long QT syndrome potassium channels |
| url | https://doi.org/10.14814/phy2.15341 |
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