A phenylalanine at the extracellular side of Kir1.1 facilitates potassium permeation
The Kir1.1 (ROMK) family of weak inward rectifiers controls K secretion in the renal CCT and K recycling in the renal TALH. A single point mutant of the inward rectifier, F127V-Kir1.1b was used to investigate the K transition between the selectivity filter and the outer mouth of the channel. We hypo...
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| Format: | Article |
| Language: | English |
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Taylor & Francis Group
2024-12-01
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| Series: | Channels |
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| Online Access: | https://www.tandfonline.com/doi/10.1080/19336950.2023.2294661 |
| _version_ | 1826945131627937792 |
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| author | Henry Sackin Mikheil Nanazashvili |
| author_facet | Henry Sackin Mikheil Nanazashvili |
| author_sort | Henry Sackin |
| collection | DOAJ |
| description | The Kir1.1 (ROMK) family of weak inward rectifiers controls K secretion in the renal CCT and K recycling in the renal TALH. A single point mutant of the inward rectifier, F127V-Kir1.1b was used to investigate the K transition between the selectivity filter and the outer mouth of the channel. We hypothesize that normally an aromatic Phe at the external entryway of Kir1.1b facilitates outward K secretion. We tested this by replacing F127-Kir1.1b with a small aliphatic Val. Results indicate that removal of the Phe at 127 suppresses outward currents that normally contribute to K secretion. Results with the F127V mutant could be explained by increased polyamine block and/or a decrease in the avidity of Kir1.1 for K ions near the outer mouth of the channel. The latter is supported by F127V-Kir1.1b having a lower affinity (Km = 33 mM) for K than wild-type Kir1.1b (Km = 7 mM) during external K elevation. Conversely, chelation of K with 18-Crown-6 ether reduced K conductance faster in F127V (half-time = 6s) than in wt-Kir1.1b (half-time = 120s), implying that F127V is less hospitable to external K. In other experiments, positive membrane potentials gated the F127V mutant channel closed at physiological levels of external Ca, possibly by electrostatically depleting K adjacent to the membrane, suggesting that the Phe residue is critical for outward K secretion at physiological Ca. We speculate that the avidity of wt-Kir1.1b for external K could result from a cation-Pi interaction between K and the aromatic F127. |
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| format | Article |
| id | doaj.art-3872694bc47c4e1ea74c91f57a7076be |
| institution | Directory Open Access Journal |
| issn | 1933-6950 1933-6969 |
| language | English |
| last_indexed | 2025-02-17T20:49:56Z |
| publishDate | 2024-12-01 |
| publisher | Taylor & Francis Group |
| record_format | Article |
| series | Channels |
| spelling | doaj.art-3872694bc47c4e1ea74c91f57a7076be2024-12-09T07:27:27ZengTaylor & Francis GroupChannels1933-69501933-69692024-12-0118110.1080/19336950.2023.2294661A phenylalanine at the extracellular side of Kir1.1 facilitates potassium permeationHenry Sackin0Mikheil Nanazashvili1Department of Physiology and Biophysics and Center for Proteomics and Molecular Therapeutics, Chicago Medical School, Rosalind Franklin University, North Chicago, IL, USADepartment of Physiology and Biophysics and Center for Proteomics and Molecular Therapeutics, Chicago Medical School, Rosalind Franklin University, North Chicago, IL, USAThe Kir1.1 (ROMK) family of weak inward rectifiers controls K secretion in the renal CCT and K recycling in the renal TALH. A single point mutant of the inward rectifier, F127V-Kir1.1b was used to investigate the K transition between the selectivity filter and the outer mouth of the channel. We hypothesize that normally an aromatic Phe at the external entryway of Kir1.1b facilitates outward K secretion. We tested this by replacing F127-Kir1.1b with a small aliphatic Val. Results indicate that removal of the Phe at 127 suppresses outward currents that normally contribute to K secretion. Results with the F127V mutant could be explained by increased polyamine block and/or a decrease in the avidity of Kir1.1 for K ions near the outer mouth of the channel. The latter is supported by F127V-Kir1.1b having a lower affinity (Km = 33 mM) for K than wild-type Kir1.1b (Km = 7 mM) during external K elevation. Conversely, chelation of K with 18-Crown-6 ether reduced K conductance faster in F127V (half-time = 6s) than in wt-Kir1.1b (half-time = 120s), implying that F127V is less hospitable to external K. In other experiments, positive membrane potentials gated the F127V mutant channel closed at physiological levels of external Ca, possibly by electrostatically depleting K adjacent to the membrane, suggesting that the Phe residue is critical for outward K secretion at physiological Ca. We speculate that the avidity of wt-Kir1.1b for external K could result from a cation-Pi interaction between K and the aromatic F127.https://www.tandfonline.com/doi/10.1080/19336950.2023.2294661Inward rectifierROMKchannelselectivity filterrenalregulation |
| spellingShingle | Henry Sackin Mikheil Nanazashvili A phenylalanine at the extracellular side of Kir1.1 facilitates potassium permeation Channels Inward rectifier ROMK channel selectivity filter renal regulation |
| title | A phenylalanine at the extracellular side of Kir1.1 facilitates potassium permeation |
| title_full | A phenylalanine at the extracellular side of Kir1.1 facilitates potassium permeation |
| title_fullStr | A phenylalanine at the extracellular side of Kir1.1 facilitates potassium permeation |
| title_full_unstemmed | A phenylalanine at the extracellular side of Kir1.1 facilitates potassium permeation |
| title_short | A phenylalanine at the extracellular side of Kir1.1 facilitates potassium permeation |
| title_sort | phenylalanine at the extracellular side of kir1 1 facilitates potassium permeation |
| topic | Inward rectifier ROMK channel selectivity filter renal regulation |
| url | https://www.tandfonline.com/doi/10.1080/19336950.2023.2294661 |
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