Journal article
Distinct regions that control ion selectivity and calcium-dependent activation in the bestrophin ion channel
Proceedings of the National Academy of Sciences - PNAS, Vol.113(47), pp.E7399-E7408
11/22/2016
DOI: 10.1073/pnas.1614688113
PMCID: PMC5127342
PMID: 27821745
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.
Details
- Title: Subtitle
- Distinct regions that control ion selectivity and calcium-dependent activation in the bestrophin ion channel
- Creators
- George Vaisey - Memorial Sloan Kettering Cancer CenterAlexandria N. Miller - Memorial Sloan Kettering Cancer CenterStephen B. Long - Memorial Sloan Kettering Cancer Center
- Resource Type
- Journal article
- Publication Details
- Proceedings of the National Academy of Sciences - PNAS, Vol.113(47), pp.E7399-E7408
- Publisher
- Natl Acad Sciences
- DOI
- 10.1073/pnas.1614688113
- PMID
- 27821745
- PMCID
- PMC5127342
- ISSN
- 0027-8424
- eISSN
- 1091-6490
- Number of pages
- 10
- Grant note
- Boehringer Ingelheim Fonds Predoctoral Fellowship Program; Boehringer Ingelheim DE-AC02-06CH11357 / NIH under Department of Energy P30CA008748 / NATIONAL CANCER INSTITUTE; United States Department of Health & Human Services; National Institutes of Health (NIH) - USA; NIH National Cancer Institute (NCI) S10RR029205 / NATIONAL CENTER FOR RESEARCH RESOURCES; United States Department of Health & Human Services; National Institutes of Health (NIH) - USA; NIH National Center for Research Resources (NCRR) R01GM110396 / NATIONAL INSTITUTE OF GENERAL MEDICAL SCIENCES; United States Department of Health & Human Services; National Institutes of Health (NIH) - USA; NIH National Institute of General Medical Sciences (NIGMS) R01 GM110396; P30 CA008748; ACB-12002; AGM-12006; P41 GM103403; S10 RR029205 / NIH Grant; United States Department of Health & Human Services; National Institutes of Health (NIH) - USA
- Language
- English
- Date published
- 11/22/2016
- Academic Unit
- Molecular Physiology and Biophysics
- Record Identifier
- 9984446422602771
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