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Owji AP, Wang J, Kittredge A, Clark Z, Zhang Y, Hendrickson WA, Yang T. Structures and gating mechanisms of human bestrophin anion channels. Nat Commun 2022; 13:3836. [PMID: 35789156 PMCID: PMC9253114 DOI: 10.1038/s41467-022-31437-7] [Citation(s) in RCA: 7] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/28/2022] [Accepted: 06/17/2022] [Indexed: 01/16/2023] Open
Abstract
Bestrophin-1 (Best1) and bestrophin-2 (Best2) are two members of the bestrophin family of calcium (Ca2+)-activated chloride (Cl−) channels with critical involvement in ocular physiology and direct pathological relevance. Here, we report cryo-EM structures of wild-type human Best1 and Best2 in various states at up to 1.8 Å resolution. Ca2+-bound Best1 structures illustrate partially open conformations at the two Ca2+-dependent gates of the channels, in contrast to the fully open conformations observed in Ca2+-bound Best2, which is in accord with the significantly smaller currents conducted by Best1 in electrophysiological recordings. Comparison of the closed and open states reveals a C-terminal auto-inhibitory segment (AS), which constricts the channel concentrically by wrapping around the channel periphery in an inter-protomer manner and must be released to allow channel opening. Our results demonstrate that removing the AS from Best1 and Best2 results in truncation mutants with similar activities, while swapping the AS between Best1 and Best2 results in chimeric mutants with swapped activities, underlying a key role of the AS in determining paralog specificity among bestrophins. Bestrophin channels are critical for physiology of the eye. Here, authors report cryo-EM structures of human bestrophins in various states at up to 1.8 Å resolution, revealing paralog-specific features that underlie molecular mechanisms of permeation.
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Affiliation(s)
- Aaron P Owji
- Department of Ophthalmology, Columbia University, New York, NY, USA.,Department of Pharmacology, Columbia University, New York, NY, USA
| | - Jiali Wang
- Department of Ophthalmology, Columbia University, New York, NY, USA
| | - Alec Kittredge
- Department of Ophthalmology, Columbia University, New York, NY, USA.,Department of Pharmacology, Columbia University, New York, NY, USA
| | - Zada Clark
- Department of Ophthalmology, Columbia University, New York, NY, USA
| | - Yu Zhang
- Department of Ophthalmology, Columbia University, New York, NY, USA.
| | - Wayne A Hendrickson
- Department of Biochemistry and Molecular Biophysics, Columbia University, New York, NY, USA. .,Department of Physiology and Cellular Biophysics, Columbia University, New York, NY, USA. .,New York Structural Biology Center, New York, NY, USA.
| | - Tingting Yang
- Department of Ophthalmology, Columbia University, New York, NY, USA.
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Owji AP, Kittredge A, Zhang Y, Yang T. Structure and Function of the Bestrophin family of calcium-activated chloride channels. Channels (Austin) 2021; 15:604-623. [PMID: 34612806 PMCID: PMC8496536 DOI: 10.1080/19336950.2021.1981625] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2022] Open
Abstract
Bestrophins are a family of calcium-activated chloride channels (CaCCs) with relevance to human physiology and a myriad of eye diseases termed "bestrophinopathies". Since the identification of bestrophins as CaCCs nearly two decades ago, extensive studies from electrophysiological and structural biology perspectives have sought to define their key channel features including calcium sensing, gating, inactivation, and anion selectivity. The initial X-ray crystallography studies on the prokaryotic homolog of Best1, Klebsiella pneumoniae (KpBest), and the Best1 homolog from Gallus gallus (chicken Best1, cBest1), laid the foundational groundwork for establishing the architecture of Best1. Recent progress utilizing single-particle cryogenic electron microscopy has further elucidated the molecular mechanism of gating in cBest1 and, separately, the structure of Best2 from Bos taurus (bovine Best2, bBest2). Meanwhile, whole-cell patch clamp, planar lipid bilayer, and other electrophysiologic analyses using these models as well as the human Best1 (hBest1) have provided ample evidence describing the functional properties of the bestrophin channels. This review seeks to consolidate these structural and functional results to paint a broad picture of the underlying mechanisms comprising the bestrophin family's structure-function relationship.
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Affiliation(s)
- Aaron P Owji
- Department of Pharmacology, Columbia University, NY, USA
| | - Alec Kittredge
- Department of Pharmacology, Columbia University, NY, USA
| | - Yu Zhang
- Department of Ophthalmology, Columbia University, NY, USA
| | - Tingting Yang
- Department of Ophthalmology, Columbia University, NY, USA
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Ji C, Kittredge A, Hopiavuori A, Ward N, Chen S, Fukuda Y, Zhang Y, Yang T. Dual Ca 2+-dependent gates in human Bestrophin1 underlie disease-causing mechanisms of gain-of-function mutations. Commun Biol 2019; 2:240. [PMID: 31263784 PMCID: PMC6591409 DOI: 10.1038/s42003-019-0433-3] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/18/2018] [Accepted: 04/17/2019] [Indexed: 01/22/2023] Open
Abstract
Mutations of human BEST1, encoding a Ca2+-activated Cl- channel (hBest1), cause macular degenerative disorders. Best1 homolog structures reveal an evolutionarily conserved channel architecture highlighted by two landmark restrictions (named the "neck" and "aperture", respectively) in the ion conducting pathway, suggesting a unique dual-switch gating mechanism, which, however, has not been characterized well. Using patch clamp and crystallography, we demonstrate that both the neck and aperture in hBest1 are Ca2+-dependent gates essential for preventing channel leakage resulting from Ca2+-independent, spontaneous gate opening. Importantly, three patient-derived mutations (D203A, I205T and Y236C) lead to Ca2+-independent leakage and elevated Ca2+-dependent anion currents due to enhanced opening of the gates. Moreover, we identify a network of residues critically involved in gate operation. Together, our results suggest an indispensable role of the neck and aperture of hBest1 for channel gating, and uncover disease-causing mechanisms of hBest1 gain-of-function mutations.
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Affiliation(s)
- Changyi Ji
- Department of Pharmacology and Physiology, University of Rochester, School of Medicine and Dentistry, Rochester, NY 14642 USA
| | - Alec Kittredge
- Department of Pharmacology and Physiology, University of Rochester, School of Medicine and Dentistry, Rochester, NY 14642 USA
| | - Austin Hopiavuori
- Department of Pharmacology and Physiology, University of Rochester, School of Medicine and Dentistry, Rochester, NY 14642 USA
| | - Nancy Ward
- Department of Pharmacology and Physiology, University of Rochester, School of Medicine and Dentistry, Rochester, NY 14642 USA
| | - Shoudeng Chen
- Guangdong Provincial Key Laboratory of Biomedical Imaging, Department of Experimental Medicine, The Fifth Affiliated Hospital of Sun Yat-sen University, 519000 Zhuhai, Guangzhou China
| | - Yohta Fukuda
- Division of Advance Pharmaco-Science, Graduate School of Pharmaceutical Science, Osaka University, Yamadaoka 1-6, Suita, Osaka 565-0871 Japan
| | - Yu Zhang
- Department of Pharmacology and Physiology, University of Rochester, School of Medicine and Dentistry, Rochester, NY 14642 USA
| | - Tingting Yang
- Department of Pharmacology and Physiology, University of Rochester, School of Medicine and Dentistry, Rochester, NY 14642 USA
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Zhang Y, Kittredge A, Ward N, Ji C, Chen S, Yang T. ATP activates bestrophin ion channels through direct interaction. Nat Commun 2018; 9:3126. [PMID: 30087350 PMCID: PMC6081419 DOI: 10.1038/s41467-018-05616-4] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/20/2018] [Accepted: 07/09/2018] [Indexed: 11/13/2022] Open
Abstract
Human Bestrophin1 (hBest1) is a Ca2+-activated Cl- channel in retinal pigment epithelium (RPE) essential for retina physiology, and its mutation results in retinal degenerative diseases that have no available treatments. Here, we discover that hBest1's channel activity in human RPE is significantly enhanced by adenosine triphosphate (ATP) in a dose-dependent manner. We further demonstrate a direct interaction between ATP and bestrophins, and map the ATP-binding motif on hBest1 to an intracellular loop adjacent to the channel activation gate. Importantly, a disease-causing mutation of hBest1 located within the ATP-binding motif, p.I201T, diminishes ATP-dependent activation of the channel in patient-derived RPE, while the corresponding mutants in bestrophin homologs display defective ATP binding and a conformational change in the ATP-binding motif. Taken together, our results identify ATP as a critical activator of bestrophins, and reveal the molecular mechanism of an hBest1 patient-specific mutation.
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Affiliation(s)
- Yu Zhang
- Department of Pharmacology and Physiology, University of Rochester, School of Medicine and Dentistry, Rochester, NY, 14642, USA
| | - Alec Kittredge
- Department of Pharmacology and Physiology, University of Rochester, School of Medicine and Dentistry, Rochester, NY, 14642, USA
| | - Nancy Ward
- Department of Pharmacology and Physiology, University of Rochester, School of Medicine and Dentistry, Rochester, NY, 14642, USA
| | - Changyi Ji
- Department of Pharmacology and Physiology, University of Rochester, School of Medicine and Dentistry, Rochester, NY, 14642, USA
| | - Shoudeng Chen
- Molecular Imaging Center, Department of Experimental Medicine, The Fifth Affiliated Hospital of Sun Yat-sen University, Zhuhai, Guangzhou, 519000, China
| | - Tingting Yang
- Department of Pharmacology and Physiology, University of Rochester, School of Medicine and Dentistry, Rochester, NY, 14642, USA.
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