Distinct regions that control ion selectivity and calcium-dependent activation in the bestrophin ion channel Journal Article
| Authors: | Vaisey, G.; Miller, A. N.; Long, S. B. |
| Article Title: | Distinct regions that control ion selectivity and calcium-dependent activation in the bestrophin ion channel |
| Abstract: | Cytoplasmic calcium (Ca2+) activates the bestrophin anion channel, allowing chloride ions to flow down their electrochemical gradient. Mutations in bestrophin 1 (BEST1) cause macular degenerative disorders. Previously, we determined an X-ray structure of chicken BEST1 that revealed the architecture of the channel. Here, we present electrophysiological studies of purified wild-type and mutant BEST1 channels and an X-ray structure of a Ca2+-independent mutant. From these experiments, we identify regions of BEST1 responsible for Ca2+ activation and ion selectivity. A "Ca2+ clasp" within the channel's intracellular region acts as a sensor of cytoplasmic Ca2+. Alanine substitutions within a hydrophobic "neck" of the pore, which widen it, cause the channel to be constitutively active, irrespective of Ca2+. We conclude that the primary function of the neck is as a "gate" that controls chloride permeation in a Ca2+-dependent manner. In contrast to what others have proposed, we find that the neck is not a major contributor to the channel's ion selectivity. We find that mutation of a cytosolic "aperture" of the pore does not perturb the Ca2+ dependence of the channel or its preference for anions over cations, but its mutation dramatically alters relative permeabilities among anions. The data suggest that the aperture functions as a size-selective filter that permits the passage of small entities such as partially dehydrated chloride ions while excluding larger molecules such as amino acids. Thus, unlike ion channels that have a single "selectivity filter," in bestrophin, distinct regions of the pore govern anion-vs.-cation selectivity and the relative permeabilities among anions. |
| Keywords: | family; mutations; identification; disease; anion; permeation; gating; conduction; channel; ion selectivity; chloride channels; mouse bestrophin-2; calcium-activated chloride channel; cacc; ion channel biophysics; macular dystrophy; cl-channels |
| Journal Title: | Proceedings of the National Academy of Sciences of the United States of America |
| Volume: | 113 |
| Issue: | 47 |
| ISSN: | 0027-8424 |
| Publisher: | National Academy of Sciences |
| Date Published: | 2016-11-22 |
| Start Page: | E7399 |
| End Page: | E7408 |
| Language: | English |
| ACCESSION: | WOS:000388830700009 |
| DOI: | 10.1073/pnas.1614688113 |
| PROVIDER: | wos |
| PMCID: | PMC5127342 |
| PUBMED: | 27821745 |
| Notes: | Article -- Source: Wos |
Altmetric
Citation Impact
BMJ Impact Analytics
Related MSK Work