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Patton BL, Zhu P, ElSheikh A, Driggers CM, Shyng SL. Dynamic duo: Kir6 and SUR in K ATP channel structure and function. Channels (Austin) 2024; 18:2327708. [PMID: 38489043 PMCID: PMC10950283 DOI: 10.1080/19336950.2024.2327708] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2023] [Accepted: 01/14/2024] [Indexed: 03/17/2024] Open
Abstract
KATP channels are ligand-gated potassium channels that couple cellular energetics with membrane potential to regulate cell activity. Each channel is an eight subunit complex comprising four central pore-forming Kir6 inward rectifier potassium channel subunits surrounded by four regulatory subunits known as the sulfonylurea receptor, SUR, which confer homeostatic metabolic control of KATP gating. SUR is an ATP binding cassette (ABC) protein family homolog that lacks membrane transport activity but is essential for KATP expression and function. For more than four decades, understanding the structure-function relationship of Kir6 and SUR has remained a central objective of clinical significance. Here, we review progress in correlating the wealth of functional data in the literature with recent KATP cryoEM structures.
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Affiliation(s)
- Bruce L. Patton
- Department of Chemical Physiology and Biochemistry, School of Medicine, Oregon Health and Science University, Portland, OR, USA
| | - Phillip Zhu
- Department of Chemical Physiology and Biochemistry, School of Medicine, Oregon Health and Science University, Portland, OR, USA
| | - Assmaa ElSheikh
- Department of Chemical Physiology and Biochemistry, School of Medicine, Oregon Health and Science University, Portland, OR, USA
- Department of Medical Biochemistry, Tanta University, Tanta, Egypt
| | - Camden M. Driggers
- Department of Chemical Physiology and Biochemistry, School of Medicine, Oregon Health and Science University, Portland, OR, USA
| | - Show-Ling Shyng
- Department of Chemical Physiology and Biochemistry, School of Medicine, Oregon Health and Science University, Portland, OR, USA
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2
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Niu B, Ma L, Yao L, Zhang Y, Su H. HCV affects K ATP channels through GnT-IVa-mediated N-glycosylation of GLUT2 on the surface of pancreatic β-cells leading to impaired insulin secretion. Endocrine 2024; 84:427-440. [PMID: 37962815 PMCID: PMC11076383 DOI: 10.1007/s12020-023-03589-z] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/03/2023] [Accepted: 10/29/2023] [Indexed: 11/15/2023]
Abstract
PURPOSE To explore the mechanism of insulin secretion dysfunction in pancreatic beta cells induced by N-glycosylation mediated by an infection from the hepatitis C virus (HCV). METHODS Min6 cell models infected with HCV and stimulated with glucose were constructed. Meanwhile, an HCV-infected animal model and a type 2 diabetes mellitus (T2DM) rat model were constructed. Glucose uptake in the Min6 cells was detected, and insulin secretion was detected by ELISA. Flow cytometry, immunofluorescence staining, Western blotting, RT-qPCR, and lectin blotting were used to detect the expression levels of related proteins and mRNA, as well as the level of N-glycosylation. HE staining was used to observe the pathological changes in the pancreatic tissue, and an oral glucose tolerance test (OGTT) was used to evaluate the glucose tolerance of the rats. RESULTS Compared with the NC group, the expression levels of GnT-IVa, GLUT2, galectin-9, and voltage-dependent calcium channel 1.2 (Cav1.2) were significantly downregulated in the HCV-infected group. The ATP-sensitive potassium channel (KATP) component proteins SUR1 and Kir6.2 were significantly upregulated, while intracellular glucose intake and insulin secretion decreased, N-glycosylation levels and ATP levels significantly decreased, and the overexpression of GnT-IVa reversed the effect of the HCV infection. However, treatment with the glycosylation inhibitor kifunensine (KIF) or the KATP channel activator diazine (Dia) reversed the effects of the overexpression of GnT-IVa. In the animal experiments, HE staining revealed serious pathological injuries in the pancreatic tissue of the HCV-infected rats, with decreased glucose tolerance and glycosylation levels, decreased insulin secretion, downregulated expression of GnT-IVa, GLUT2, and Cav1.2, and upregulated expression of SUR1 and Kir6.2. The overexpression treatment of GnT-IVa or the KATP channel antagonist miglinide reversed the effects of HCV. CONCLUSION HCV infection inhibits GLUT2 N-glycosylation on the pancreatic β cell surface by downregulating the expression of GnT-IVa and then activates the KATP pathway, which ultimately leads to disturbances in insulin secretion.
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Affiliation(s)
- Ben Niu
- Department of Endocrinology and Metabolism, The First People's Hospital of Yunnan Province, The Affiliated Hospital of Kunming University of Science and Technology, Kunming, 650032, Yunnan, China
| | - Lijing Ma
- Department of Endocrinology and Metabolism, The First People's Hospital of Yunnan Province, The Affiliated Hospital of Kunming University of Science and Technology, Kunming, 650032, Yunnan, China
| | - Lixuan Yao
- Department of Nephrology, Bao Ji People's Hospital, Baoji, 721000, Shaanxi, China
| | - Yating Zhang
- Department of Endocrinology and Metabolism, The First People's Hospital of Yunnan Province, The Affiliated Hospital of Kunming University of Science and Technology, Kunming, 650032, Yunnan, China
| | - Heng Su
- Department of Endocrinology and Metabolism, The First People's Hospital of Yunnan Province, The Affiliated Hospital of Kunming University of Science and Technology, Kunming, 650032, Yunnan, China.
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Driggers CM, Kuo YY, Zhu P, ElSheikh A, Shyng SL. Structure of an open K ATP channel reveals tandem PIP 2 binding sites mediating the Kir6.2 and SUR1 regulatory interface. Nat Commun 2024; 15:2502. [PMID: 38509107 PMCID: PMC10954709 DOI: 10.1038/s41467-024-46751-5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/18/2024] [Accepted: 03/08/2024] [Indexed: 03/22/2024] Open
Abstract
ATP-sensitive potassium (KATP) channels, composed of four pore-lining Kir6.2 subunits and four regulatory sulfonylurea receptor 1 (SUR1) subunits, control insulin secretion in pancreatic β-cells. KATP channel opening is stimulated by PIP2 and inhibited by ATP. Mutations that increase channel opening by PIP2 reduce ATP inhibition and cause neonatal diabetes. Although considerable evidence has implicated a role for PIP2 in KATP channel function, previously solved open-channel structures have lacked bound PIP2, and mechanisms by which PIP2 regulates KATP channels remain unresolved. Here, we report the cryoEM structure of a KATP channel harboring the neonatal diabetes mutation Kir6.2-Q52R, in the open conformation, bound to amphipathic molecules consistent with natural C18:0/C20:4 long-chain PI(4,5)P2 at two adjacent binding sites between SUR1 and Kir6.2. The canonical PIP2 binding site is conserved among PIP2-gated Kir channels. The non-canonical PIP2 binding site forms at the interface of Kir6.2 and SUR1. Functional studies demonstrate both binding sites determine channel activity. Kir6.2 pore opening is associated with a twist of the Kir6.2 cytoplasmic domain and a rotation of the N-terminal transmembrane domain of SUR1, which widens the inhibitory ATP binding pocket to disfavor ATP binding. The open conformation is particularly stabilized by the Kir6.2-Q52R residue through cation-π bonding with SUR1-W51. Together, these results uncover the cooperation between SUR1 and Kir6.2 in PIP2 binding and gating, explain the antagonistic regulation of KATP channels by PIP2 and ATP, and provide a putative mechanism by which Kir6.2-Q52R stabilizes an open channel to cause neonatal diabetes.
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Affiliation(s)
- Camden M Driggers
- Department of Chemical Physiology and Biochemistry, School of Medicine, Oregon Health & Science University, Portland, OR, 97239, USA.
| | - Yi-Ying Kuo
- Department of Chemical Physiology and Biochemistry, School of Medicine, Oregon Health & Science University, Portland, OR, 97239, USA
| | - Phillip Zhu
- Department of Chemical Physiology and Biochemistry, School of Medicine, Oregon Health & Science University, Portland, OR, 97239, USA
| | - Assmaa ElSheikh
- Department of Chemical Physiology and Biochemistry, School of Medicine, Oregon Health & Science University, Portland, OR, 97239, USA
- Department of Medical Biochemistry, Tanta University, Tanta, Egypt
| | - Show-Ling Shyng
- Department of Chemical Physiology and Biochemistry, School of Medicine, Oregon Health & Science University, Portland, OR, 97239, USA.
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4
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Longden TA, Lederer WJ. Electro-metabolic signaling. J Gen Physiol 2024; 156:e202313451. [PMID: 38197953 PMCID: PMC10783436 DOI: 10.1085/jgp.202313451] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/26/2023] [Revised: 10/27/2023] [Accepted: 12/14/2023] [Indexed: 01/11/2024] Open
Abstract
Precise matching of energy substrate delivery to local metabolic needs is essential for the health and function of all tissues. Here, we outline a mechanistic framework for understanding this critical process, which we refer to as electro-metabolic signaling (EMS). All tissues exhibit changes in metabolism over varying spatiotemporal scales and have widely varying energetic needs and reserves. We propose that across tissues, common signatures of elevated metabolism or increases in energy substrate usage that exceed key local thresholds rapidly engage mechanisms that generate hyperpolarizing electrical signals in capillaries that then relax contractile elements throughout the vasculature to quickly adjust blood flow to meet changing needs. The attendant increase in energy substrate delivery serves to meet local metabolic requirements and thus avoids a mismatch in supply and demand and prevents metabolic stress. We discuss in detail key examples of EMS that our laboratories have discovered in the brain and the heart, and we outline potential further EMS mechanisms operating in tissues such as skeletal muscle, pancreas, and kidney. We suggest that the energy imbalance evoked by EMS uncoupling may be central to cellular dysfunction from which the hallmarks of aging and metabolic diseases emerge and may lead to generalized organ failure states-such as diverse flavors of heart failure and dementia. Understanding and manipulating EMS may be key to preventing or reversing these dysfunctions.
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Affiliation(s)
- Thomas A. Longden
- Department of Physiology, University of Maryland School of Medicine, Baltimore, MD, USA
- Laboratory of Neurovascular Interactions, Center for Biomedical Engineering and Technology, University of Maryland School of Medicine, Baltimore, MD, USA
| | - W. Jonathan Lederer
- Department of Physiology, University of Maryland School of Medicine, Baltimore, MD, USA
- Laboratory of Molecular Cardiology, Center for Biomedical Engineering and Technology, University of Maryland School of Medicine, Baltimore, MD, USA
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5
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Driggers CM, Kuo YY, Zhu P, ElSheikh A, Shyng SL. Structure of an open K ATP channel reveals tandem PIP 2 binding sites mediating the Kir6.2 and SUR1 regulatory interface. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2024:2023.08.01.551546. [PMID: 37577494 PMCID: PMC10418277 DOI: 10.1101/2023.08.01.551546] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 08/15/2023]
Abstract
ATP-sensitive potassium (K ATP ) channels, composed of four pore-lining Kir6.2 subunits and four regulatory sulfonylurea receptor 1 (SUR1) subunits, control insulin secretion in pancreatic β-cells. K ATP channel opening is stimulated by PIP 2 and inhibited by ATP. Mutations that increase channel opening by PIP 2 reduce ATP inhibition and cause neonatal diabetes. Although considerable evidence has indicated PIP 2 in K ATP channel function, previously solved open-channel structures have lacked bound PIP 2 , and mechanisms by which PIP 2 regulates K ATP channels remain unresolved. Here, we report the cryoEM structure of a K ATP channel harboring the neonatal diabetes mutation Kir6.2-Q52R, bound to natural C18:0/C20:4 long-chain PIP 2 in an open conformation. The structure reveals two adjacent PIP 2 molecules between SUR1 and Kir6.2. The first PIP 2 binding site is conserved among PIP 2 -gated Kir channels. The second site forms uniquely in K ATP at the interface of Kir6.2 and SUR1. Functional studies demonstrate both binding sites determine channel activity. Kir6.2 pore opening is associated with a twist of the Kir6.2 cytoplasmic domain and a rotation of the N-terminal transmembrane domain of SUR1, which widens the inhibitory ATP binding pocket to disfavor ATP binding. The open conformation is particularly stabilized by the Kir6.2-Q52R residue through cation-π bonding with SUR1-W51. Together, these results uncover the cooperation between SUR1 and Kir6.2 in PIP 2 binding and gating, explain the antagonistic regulation of K ATP channels by PIP 2 and ATP, and provide the mechanism by which Kir6.2-Q52R stabilizes an open channel to cause neonatal diabetes.
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Martin GM, Patton BL, Shyng SL. K ATP channels in focus: Progress toward a structural understanding of ligand regulation. Curr Opin Struct Biol 2023; 79:102541. [PMID: 36807078 PMCID: PMC10023423 DOI: 10.1016/j.sbi.2023.102541] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/05/2022] [Revised: 12/11/2022] [Accepted: 01/14/2023] [Indexed: 02/21/2023]
Abstract
KATP channels are hetero-octameric complexes of four inward rectifying potassium channels, Kir6.1 or Kir6.2, and four sulfonylurea receptors, SUR1, SUR2A, or SUR2B from the ABC transporter family. This unique combination enables KATP channels to couple intracellular ATP/ADP ratios, through gating, with membrane excitability, thus regulating a broad range of cellular activities. The prominence of KATP channels in human physiology, disease, and pharmacology has long attracted research interest. Since 2017, a steady flow of high-resolution KATP cryoEM structures has revealed complex and dynamic interactions between channel subunits and their ligands. Here, we highlight insights from recent structures that begin to provide mechanistic explanations for decades of experimental data and discuss the remaining knowledge gaps in our understanding of KATP channel regulation.
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Affiliation(s)
- Gregory M Martin
- Department of Integrative Structural and Computational Biology, The Scripps Research Institute, La Jolla, CA, 92037, USA
| | - Bruce L Patton
- Department of Chemical Physiology and Biochemistry, School of Medicine, Oregon Health and Science University, Portland, OR, 97239, USA
| | - Show-Ling Shyng
- Department of Chemical Physiology and Biochemistry, School of Medicine, Oregon Health and Science University, Portland, OR, 97239, USA.
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Driggers CM, Shyng SL. Mechanistic insights on KATP channel regulation from cryo-EM structures. J Gen Physiol 2022; 155:213723. [PMID: 36441147 PMCID: PMC9700523 DOI: 10.1085/jgp.202113046] [Citation(s) in RCA: 9] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/02/2022] [Revised: 10/19/2022] [Accepted: 11/08/2022] [Indexed: 11/29/2022] Open
Abstract
Gated by intracellular ATP and ADP, ATP-sensitive potassium (KATP) channels couple cell energetics with membrane excitability in many cell types, enabling them to control a wide range of physiological processes based on metabolic demands. The KATP channel is a complex of four potassium channel subunits from the Kir channel family, Kir6.1 or Kir6.2, and four sulfonylurea receptor subunits, SUR1, SUR2A, or SUR2B, from the ATP-binding cassette (ABC) transporter family. Dysfunction of KATP channels underlies several human diseases. The importance of these channels in human health and disease has made them attractive drug targets. How the channel subunits interact with one another and how the ligands interact with the channel to regulate channel activity have been long-standing questions in the field. In the past 5 yr, a steady stream of high-resolution KATP channel structures has been published using single-particle cryo-electron microscopy (cryo-EM). Here, we review the advances these structures bring to our understanding of channel regulation by physiological and pharmacological ligands.
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Affiliation(s)
- Camden M. Driggers
- Department of Chemical Physiology and Biochemistry, School of Medicine, Oregon Health and Science University, Portland, OR
| | - Show-Ling Shyng
- Department of Chemical Physiology and Biochemistry, School of Medicine, Oregon Health and Science University, Portland, OR,Correspondence to Show-Ling Shyng:
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8
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Sung MW, Driggers CM, Mostofian B, Russo JD, Patton BL, Zuckerman DM, Shyng SL. Ligand-mediated Structural Dynamics of a Mammalian Pancreatic K ATP Channel. J Mol Biol 2022; 434:167789. [PMID: 35964676 PMCID: PMC9618280 DOI: 10.1016/j.jmb.2022.167789] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/12/2022] [Revised: 07/22/2022] [Accepted: 08/09/2022] [Indexed: 11/16/2022]
Abstract
Regulation of pancreatic KATP channels involves orchestrated interactions of their subunits, Kir6.2 and SUR1, and ligands. Previously we reported KATP channel cryo-EM structures in the presence and absence of pharmacological inhibitors and ATP, focusing on the mechanisms by which inhibitors act as pharmacological chaperones of KATP channels (Martin et al., 2019). Here we analyzed the same cryo-EM datasets with a focus on channel conformational dynamics to elucidate structural correlates pertinent to ligand interactions and channel gating. We found pharmacological inhibitors and ATP enrich a channel conformation in which the Kir6.2 cytoplasmic domain is closely associated with the transmembrane domain, while depleting one where the Kir6.2 cytoplasmic domain is extended away into the cytoplasm. This conformational change remodels a network of intra- and inter-subunit interactions as well as the ATP and PIP2 binding pockets. The structures resolved key contacts between the distal N-terminus of Kir6.2 and SUR1's ABC module involving residues implicated in channel function and showed a SUR1 residue, K134, participates in PIP2 binding. Molecular dynamics simulations revealed two Kir6.2 residues, K39 and R54, that mediate both ATP and PIP2 binding, suggesting a mechanism for competitive gating by ATP and PIP2.
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Affiliation(s)
- Min Woo Sung
- Department of Chemical Physiology and Biochemistry, School of Medicine, Oregon Health & Science University, Portland, OR, USA. https://twitter.com/MinWooSung5
| | - Camden M Driggers
- Department of Chemical Physiology and Biochemistry, School of Medicine, Oregon Health & Science University, Portland, OR, USA
| | - Barmak Mostofian
- Department of Biomedical Engineering, School of Medicine, Oregon Health & Science University, Portland, OR, USA
| | - John D Russo
- Department of Biomedical Engineering, School of Medicine, Oregon Health & Science University, Portland, OR, USA
| | - Bruce L Patton
- Department of Chemical Physiology and Biochemistry, School of Medicine, Oregon Health & Science University, Portland, OR, USA
| | - Daniel M Zuckerman
- Department of Biomedical Engineering, School of Medicine, Oregon Health & Science University, Portland, OR, USA.
| | - Show-Ling Shyng
- Department of Chemical Physiology and Biochemistry, School of Medicine, Oregon Health & Science University, Portland, OR, USA.
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9
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Structural insights into the mechanism of pancreatic K ATP channel regulation by nucleotides. Nat Commun 2022; 13:2770. [PMID: 35589716 PMCID: PMC9120461 DOI: 10.1038/s41467-022-30430-4] [Citation(s) in RCA: 13] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2021] [Accepted: 04/28/2022] [Indexed: 11/17/2022] Open
Abstract
ATP-sensitive potassium channels (KATP) are metabolic sensors that convert the intracellular ATP/ADP ratio to the excitability of cells. They are involved in many physiological processes and implicated in several human diseases. Here we present the cryo-EM structures of the pancreatic KATP channel in both the closed state and the pre-open state, resolved in the same sample. We observe the binding of nucleotides at the inhibitory sites of the Kir6.2 channel in the closed but not in the pre-open state. Structural comparisons reveal the mechanism for ATP inhibition and Mg-ADP activation, two fundamental properties of KATP channels. Moreover, the structures also uncover the activation mechanism of diazoxide-type KATP openers. KATP channels are energy sensors. Here, authors report the Cryo-EM structures of pancreatic KATP in both the closed state and the pre-open state. These structures illuminate the mechanism of KATP channel regulation by the intracellular nucleotides.
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10
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Houtman MJC, Friesacher T, Chen X, Zangerl-Plessl EM, van der Heyden MAG, Stary-Weinzinger A. Development of I KATP Ion Channel Blockers Targeting Sulfonylurea Resistant Mutant K IR6.2 Based Channels for Treating DEND Syndrome. Front Pharmacol 2022; 12:814066. [PMID: 35095528 PMCID: PMC8795863 DOI: 10.3389/fphar.2021.814066] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/12/2021] [Accepted: 12/23/2021] [Indexed: 11/13/2022] Open
Abstract
Introduction: DEND syndrome is a rare channelopathy characterized by a combination of developmental delay, epilepsy and severe neonatal diabetes. Gain of function mutations in the KCNJ11 gene, encoding the KIR6.2 subunit of the IKATP potassium channel, stand at the basis of most forms of DEND syndrome. In a previous search for existing drugs with the potential of targeting Cantú Syndrome, also resulting from increased IKATP, we found a set of candidate drugs that may also possess the potential to target DEND syndrome. In the current work, we combined Molecular Modelling including Molecular Dynamics simulations, with single cell patch clamp electrophysiology, in order to test the effect of selected drug candidates on the KIR6.2 WT and DEND mutant channels. Methods: Molecular dynamics simulations were performed to investigate potential drug binding sites. To conduct in vitro studies, KIR6.2 Q52R and L164P mutants were constructed. Inside/out patch clamp electrophysiology on transiently transfected HEK293T cells was performed for establishing drug-channel inhibition relationships. Results: Molecular Dynamics simulations provided insight in potential channel interaction and shed light on possible mechanisms of action of the tested drug candidates. Effective IKIR6.2/SUR2a inhibition was obtained with the pore-blocker betaxolol (IC50 values 27-37 μM). Levobetaxolol effectively inhibited WT and L164P (IC50 values 22 μM) and Q52R (IC50 55 μM) channels. Of the SUR binding prostaglandin series, travoprost was found to be the best blocker of WT and L164P channels (IC50 2-3 μM), while Q52R inhibition was 15-20% at 10 μM. Conclusion: Our combination of MD and inside-out electrophysiology provides the rationale for drug mediated IKATP inhibition, and will be the basis for 1) screening of additional existing drugs for repurposing to address DEND syndrome, and 2) rationalized medicinal chemistry to improve IKATP inhibitor efficacy and specificity.
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Affiliation(s)
- Marien J C Houtman
- Department of Medical Physiology, Division of Heart and Lungs, University Medical Center Utrecht, Utrecht, Netherlands
| | - Theres Friesacher
- Department of Pharmaceutical Sciences, Division of Pharmacology and Toxicology, University of Vienna, Vienna, Austria
| | - Xingyu Chen
- Department of Pharmaceutical Sciences, Division of Pharmacology and Toxicology, University of Vienna, Vienna, Austria
| | - Eva-Maria Zangerl-Plessl
- Department of Pharmaceutical Sciences, Division of Pharmacology and Toxicology, University of Vienna, Vienna, Austria
| | - Marcel A G van der Heyden
- Department of Medical Physiology, Division of Heart and Lungs, University Medical Center Utrecht, Utrecht, Netherlands
| | - Anna Stary-Weinzinger
- Department of Pharmaceutical Sciences, Division of Pharmacology and Toxicology, University of Vienna, Vienna, Austria
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Zhao C, MacKinnon R. Molecular structure of an open human K ATP channel. Proc Natl Acad Sci U S A 2021; 118:e2112267118. [PMID: 34815345 PMCID: PMC8640745 DOI: 10.1073/pnas.2112267118] [Citation(s) in RCA: 40] [Impact Index Per Article: 13.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 10/02/2021] [Indexed: 11/18/2022] Open
Abstract
KATP channels are metabolic sensors that translate intracellular ATP/ADP balance into membrane excitability. The molecular composition of KATP includes an inward-rectifier potassium channel (Kir) and an ABC transporter-like sulfonylurea receptor (SUR). Although structures of KATP have been determined in many conformations, in all cases, the pore in Kir is closed. Here, we describe human pancreatic KATP (hKATP) structures with an open pore at 3.1- to 4.0-Å resolution using single-particle cryo-electron microscopy (cryo-EM). Pore opening is associated with coordinated structural changes within the ATP-binding site and the channel gate in Kir. Conformational changes in SUR are also observed, resulting in an area reduction of contact surfaces between SUR and Kir. We also observe that pancreatic hKATP exhibits the unique (among inward-rectifier channels) property of PIP2-independent opening, which appears to be correlated with a docked cytoplasmic domain in the absence of PIP2.
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Affiliation(s)
- Chen Zhao
- HHMI, The Rockefeller University, New York, NY 10065
- Laboratory of Molecular Neurobiology and Biophysics, The Rockefeller University, New York, NY 10065
| | - Roderick MacKinnon
- HHMI, The Rockefeller University, New York, NY 10065;
- Laboratory of Molecular Neurobiology and Biophysics, The Rockefeller University, New York, NY 10065
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12
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Production and purification of ATP-sensitive potassium channel particles for cryo-electron microscopy. Methods Enzymol 2021; 653:121-150. [PMID: 34099169 DOI: 10.1016/bs.mie.2021.02.008] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Abstract
ATP-sensitive potassium (KATP) channels are multimeric protein complexes made of four inward rectifying potassium channel (Kir6.x) subunits and four ABC protein sulfonylurea receptor (SURx) subunits. Kir6.x subunits form the potassium ion conducting pore of the channel, and SURx functions to regulate Kir6.x. Kir6.x and SURx are uniquely dependent on each other for expression and function. In pancreatic β-cells, channels comprising SUR1 and Kir6.2 mediate glucose-stimulated insulin secretion and are the targets of antidiabetic sulfonylureas. Mutations in genes encoding SUR1 or Kir6.2 are linked to insulin secretion disorders, with loss- or gain-of-function mutations causing congenital hyperinsulinism or neonatal diabetes mellitus, respectively. Defects in the KATP channel in other tissues underlie human diseases of the cardiovascular and nervous systems. Key to understanding how channels are regulated by physiological and pharmacological ligands and how mutations disrupt channel assembly or gating to cause disease is the ability to observe structural changes associated with subunit interactions and ligand binding. While recent advances in the structural method of single-particle cryo-electron microscopy (cryoEM) offers direct visualization of channel structures, success of obtaining high-resolution structures is dependent on highly concentrated, homogeneous KATP channel particles. In this chapter, we describe a method for expressing KATP channels in mammalian cell culture, solubilizing the channel in detergent micelles and purifying KATP channels using an affinity tag to the SURx subunit for cryoEM structural studies.
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Pipatpolkai T, Usher S, Stansfeld PJ, Ashcroft FM. New insights into K ATP channel gene mutations and neonatal diabetes mellitus. Nat Rev Endocrinol 2020; 16:378-393. [PMID: 32376986 DOI: 10.1038/s41574-020-0351-y] [Citation(s) in RCA: 72] [Impact Index Per Article: 18.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Accepted: 03/17/2020] [Indexed: 12/12/2022]
Abstract
The ATP-sensitive potassium channel (KATP channel) couples blood levels of glucose to insulin secretion from pancreatic β-cells. KATP channel closure triggers a cascade of events that results in insulin release. Metabolically generated changes in the intracellular concentrations of adenosine nucleotides are integral to this regulation, with ATP and ADP closing the channel and MgATP and MgADP increasing channel activity. Activating mutations in the genes encoding either of the two types of KATP channel subunit (Kir6.2 and SUR1) result in neonatal diabetes mellitus, whereas loss-of-function mutations cause hyperinsulinaemic hypoglycaemia of infancy. Sulfonylurea and glinide drugs, which bind to SUR1, close the channel through a pathway independent of ATP and are now the primary therapy for neonatal diabetes mellitus caused by mutations in the genes encoding KATP channel subunits. Insight into the molecular details of drug and nucleotide regulation of channel activity has been illuminated by cryo-electron microscopy structures that reveal the atomic-level organization of the KATP channel complex. Here we review how these structures aid our understanding of how the various mutations in the genes encoding Kir6.2 (KCNJ11) and SUR1 (ABCC8) lead to a reduction in ATP inhibition and thereby neonatal diabetes mellitus. We also provide an update on known mutations and sulfonylurea therapy in neonatal diabetes mellitus.
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Affiliation(s)
- Tanadet Pipatpolkai
- Department of Physiology, Anatomy and Genetics, University of Oxford, Oxford, UK
- Department of Biochemistry, University of Oxford, Oxford, UK
| | - Samuel Usher
- Department of Physiology, Anatomy and Genetics, University of Oxford, Oxford, UK
| | - Phillip J Stansfeld
- Department of Biochemistry, University of Oxford, Oxford, UK
- School of Life Sciences, University of Warwick, Coventry, UK
- Department of Chemistry, University of Warwick, Coventry, UK
| | - Frances M Ashcroft
- Department of Physiology, Anatomy and Genetics, University of Oxford, Oxford, UK.
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Ding D, Wang M, Wu JX, Kang Y, Chen L. The Structural Basis for the Binding of Repaglinide to the Pancreatic K ATP Channel. Cell Rep 2020; 27:1848-1857.e4. [PMID: 31067468 DOI: 10.1016/j.celrep.2019.04.050] [Citation(s) in RCA: 61] [Impact Index Per Article: 15.3] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/11/2019] [Revised: 03/15/2019] [Accepted: 04/10/2019] [Indexed: 01/13/2023] Open
Abstract
Repaglinide (RPG) is a short-acting insulin secretagogue widely prescribed for the treatment of type 2 diabetes. It boosts insulin secretion by inhibiting the pancreatic ATP-sensitive potassium channel (KATP). However, the mechanisms by which RPG binds to the KATP channel are poorly understood. Here, we describe two cryo-EM structures: the pancreatic KATP channel in complex with inhibitory RPG and adenosine-5'-(γ-thio)-triphosphate (ATPγS) at 3.3 Å and a medium-resolution structure of a RPG-bound mini SUR1 protein in which the N terminus of the inward-rectifying potassium channel 6.1 (Kir6.1) is fused to the ABC transporter module of the sulfonylurea receptor 1 (SUR1). These structures reveal the binding site of RPG in the SUR1 subunit. Furthermore, the high-resolution structure reveals the complex architecture of the ATP binding site, which is formed by both Kir6.2 and SUR1 subunits, and the domain-domain interaction interfaces.
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Affiliation(s)
- Dian Ding
- State Key Laboratory of Membrane Biology, Institute of Molecular Medicine, Peking University, Beijing Key Laboratory of Cardiometabolic Molecular Medicine, Beijing 100871, China; Peking-Tsinghua Center for Life Sciences, Peking University, Beijing 100871, China; Academy for Advanced Interdisciplinary Studies, Peking University, Beijing 100871, China
| | - Mengmeng Wang
- State Key Laboratory of Membrane Biology, Institute of Molecular Medicine, Peking University, Beijing Key Laboratory of Cardiometabolic Molecular Medicine, Beijing 100871, China; Peking-Tsinghua Center for Life Sciences, Peking University, Beijing 100871, China; Academy for Advanced Interdisciplinary Studies, Peking University, Beijing 100871, China
| | - Jing-Xiang Wu
- State Key Laboratory of Membrane Biology, Institute of Molecular Medicine, Peking University, Beijing Key Laboratory of Cardiometabolic Molecular Medicine, Beijing 100871, China; Peking-Tsinghua Center for Life Sciences, Peking University, Beijing 100871, China
| | - Yunlu Kang
- State Key Laboratory of Membrane Biology, Institute of Molecular Medicine, Peking University, Beijing Key Laboratory of Cardiometabolic Molecular Medicine, Beijing 100871, China
| | - Lei Chen
- State Key Laboratory of Membrane Biology, Institute of Molecular Medicine, Peking University, Beijing Key Laboratory of Cardiometabolic Molecular Medicine, Beijing 100871, China; Peking-Tsinghua Center for Life Sciences, Peking University, Beijing 100871, China.
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15
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Usher SG, Ashcroft FM, Puljung MC. Nucleotide inhibition of the pancreatic ATP-sensitive K+ channel explored with patch-clamp fluorometry. eLife 2020; 9:52775. [PMID: 31909710 PMCID: PMC7004565 DOI: 10.7554/elife.52775] [Citation(s) in RCA: 13] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/16/2019] [Accepted: 01/07/2020] [Indexed: 12/20/2022] Open
Abstract
Pancreatic ATP-sensitive K+ channels (KATP) comprise four inward rectifier subunits (Kir6.2), each associated with a sulphonylurea receptor (SUR1). ATP/ADP binding to Kir6.2 shuts KATP. Mg-nucleotide binding to SUR1 stimulates KATP. In the absence of Mg2+, SUR1 increases the apparent affinity for nucleotide inhibition at Kir6.2 by an unknown mechanism. We simultaneously measured channel currents and nucleotide binding to Kir6.2. Fits to combined data sets suggest that KATP closes with only one nucleotide molecule bound. A Kir6.2 mutation (C166S) that increases channel activity did not affect nucleotide binding, but greatly perturbed the ability of bound nucleotide to inhibit KATP. Mutations at position K205 in SUR1 affected both nucleotide affinity and the ability of bound nucleotide to inhibit KATP. This suggests a dual role for SUR1 in KATP inhibition, both in directly contributing to nucleotide binding and in stabilising the nucleotide-bound closed state.
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Affiliation(s)
- Samuel G Usher
- Department of Physiology, Anatomy and Genetics, University of Oxford, Oxford, United Kingdom
| | - Frances M Ashcroft
- Department of Physiology, Anatomy and Genetics, University of Oxford, Oxford, United Kingdom
| | - Michael C Puljung
- Department of Physiology, Anatomy and Genetics, University of Oxford, Oxford, United Kingdom
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16
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Martin GM, Sung MW, Yang Z, Innes LM, Kandasamy B, David LL, Yoshioka C, Shyng SL. Mechanism of pharmacochaperoning in a mammalian K ATP channel revealed by cryo-EM. eLife 2019; 8:46417. [PMID: 31343405 PMCID: PMC6699824 DOI: 10.7554/elife.46417] [Citation(s) in RCA: 55] [Impact Index Per Article: 11.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/26/2019] [Accepted: 07/22/2019] [Indexed: 01/03/2023] Open
Abstract
ATP-sensitive potassium (KATP) channels composed of a pore-forming Kir6.2 potassium channel and a regulatory ABC transporter sulfonylurea receptor 1 (SUR1) regulate insulin secretion in pancreatic β-cells to maintain glucose homeostasis. Mutations that impair channel folding or assembly prevent cell surface expression and cause congenital hyperinsulinism. Structurally diverse KATP inhibitors are known to act as pharmacochaperones to correct mutant channel expression, but the mechanism is unknown. Here, we compare cryoEM structures of a mammalian KATP channel bound to pharmacochaperones glibenclamide, repaglinide, and carbamazepine. We found all three drugs bind within a common pocket in SUR1. Further, we found the N-terminus of Kir6.2 inserted within the central cavity of the SUR1 ABC core, adjacent the drug binding pocket. The findings reveal a common mechanism by which diverse compounds stabilize the Kir6.2 N-terminus within SUR1’s ABC core, allowing it to act as a firm ‘handle’ for the assembly of metastable mutant SUR1-Kir6.2 complexes.
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Affiliation(s)
- Gregory M Martin
- Department of Biochemistry and Molecular Biology, Oregon Health & Science University, Portland, United States
| | - Min Woo Sung
- Department of Biochemistry and Molecular Biology, Oregon Health & Science University, Portland, United States
| | - Zhongying Yang
- Department of Biochemistry and Molecular Biology, Oregon Health & Science University, Portland, United States
| | - Laura M Innes
- Department of Biochemistry and Molecular Biology, Oregon Health & Science University, Portland, United States
| | - Balamurugan Kandasamy
- Department of Biochemistry and Molecular Biology, Oregon Health & Science University, Portland, United States
| | - Larry L David
- Department of Biochemistry and Molecular Biology, Oregon Health & Science University, Portland, United States
| | - Craig Yoshioka
- Department of Biomedical Engineering, Oregon Health & Science University, Portland, United States
| | - Show-Ling Shyng
- Department of Biochemistry and Molecular Biology, Oregon Health & Science University, Portland, United States
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17
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Puljung MC. Cryo-electron microscopy structures and progress toward a dynamic understanding of K ATP channels. J Gen Physiol 2018; 150:653-669. [PMID: 29685928 PMCID: PMC5940251 DOI: 10.1085/jgp.201711978] [Citation(s) in RCA: 39] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/23/2018] [Accepted: 03/26/2018] [Indexed: 12/11/2022] Open
Abstract
Puljung reviews recent cryo-EM KATP channel structures and proposes a mechanism by which ligand binding results in channel opening. Adenosine triphosphate (ATP)–sensitive K+ (KATP) channels are molecular sensors of cell metabolism. These hetero-octameric channels, comprising four inward rectifier K+ channel subunits (Kir6.1 or Kir6.2) and four sulfonylurea receptor (SUR1 or SUR2A/B) subunits, detect metabolic changes via three classes of intracellular adenine nucleotide (ATP/ADP) binding site. One site, located on the Kir subunit, causes inhibition of the channel when ATP or ADP is bound. The other two sites, located on the SUR subunit, excite the channel when bound to Mg nucleotides. In pancreatic β cells, an increase in extracellular glucose causes a change in oxidative metabolism and thus turnover of adenine nucleotides in the cytoplasm. This leads to the closure of KATP channels, which depolarizes the plasma membrane and permits Ca2+ influx and insulin secretion. Many of the molecular details regarding the assembly of the KATP complex, and how changes in nucleotide concentrations affect gating, have recently been uncovered by several single-particle cryo-electron microscopy structures of the pancreatic KATP channel (Kir6.2/SUR1) at near-atomic resolution. Here, the author discusses the detailed picture of excitatory and inhibitory ligand binding to KATP that these structures present and suggests a possible mechanism by which channel activation may proceed from the ligand-binding domains of SUR to the channel pore.
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Affiliation(s)
- Michael C Puljung
- Department of Physiology, Anatomy, and Genetics, University of Oxford, Oxford, England, UK
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18
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Lee KPK, Chen J, MacKinnon R. Molecular structure of human KATP in complex with ATP and ADP. eLife 2017; 6:32481. [PMID: 29286281 PMCID: PMC5790381 DOI: 10.7554/elife.32481] [Citation(s) in RCA: 118] [Impact Index Per Article: 16.9] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/03/2017] [Accepted: 12/29/2017] [Indexed: 12/20/2022] Open
Abstract
In many excitable cells, KATP channels respond to intracellular adenosine nucleotides: ATP inhibits while ADP activates. We present two structures of the human pancreatic KATP channel, containing the ABC transporter SUR1 and the inward-rectifier K+ channel Kir6.2, in the presence of Mg2+ and nucleotides. These structures, referred to as quatrefoil and propeller forms, were determined by single-particle cryo-EM at 3.9 Å and 5.6 Å, respectively. In both forms, ATP occupies the inhibitory site in Kir6.2. The nucleotide-binding domains of SUR1 are dimerized with Mg2+-ATP in the degenerate site and Mg2+-ADP in the consensus site. A lasso extension forms an interface between SUR1 and Kir6.2 adjacent to the ATP site in the propeller form and is disrupted in the quatrefoil form. These structures support the role of SUR1 as an ADP sensor and highlight the lasso extension as a key regulatory element in ADP’s ability to override ATP inhibition. A hormone called insulin finely controls the amount of sugar in the blood. When the blood sugar content is high, a group of cells in the pancreas release insulin; when it is low, they stop. In these cells, the level of sugar in the blood modifies the ratio of two molecules: ATP, the body’s energy currency, and ADP, a molecule closely related to ATP. Changes in the ATP/ADP ratio are therefore a proxy of the variations in blood sugar levels. In these pancreatic cells, a membrane protein called ATP sensitive potassium channel, KATP channel for short, acts as a switch that turns on and off the production of insulin. ATP and ADP control that switch, with the two molecules having opposite effects on the channel – ATP deactivates it, ADP activates it. The changes in ATP/ADP ratio – and by extension in blood sugar levels – are therefore coupled with the release of insulin. However, how KATP channels sense the changes in the ATP/ADP ratio in these cells is still unclear. In particular, ATP levels are usually high and constant: ATP is then continuously deactivating the channels, and it is unclear how ADP ever activates them. Here, Lee et al. use a microscopy technique that can image biological molecules at the atomic scale to look at the structure of human pancreatic KATP channels. The 3D reconstruction maps show that KATP channels have binding sites for ATP but also one for ADP. This ADP site acts as a sensor that can detect even small changes in ADP levels in the cell. The maps also reveal a dynamic lasso-like structure connecting the ATP and ADP binding areas. This domain may play a vital role in allowing ADP to override ATP’s control of the channel. The presence of the ADP sensor and the lasso structure could explain how KATP channels monitor changes in the ATP/ADP ratio and can therefore control the release of insulin based on blood sugar levels. Defects in the KATP channels of the pancreas are present in genetic diseases where infants produce too much or too little insulin. Understanding the structure of these channels and how they work may help scientists to design new drugs to treat these conditions.
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Affiliation(s)
- Kenneth Pak Kin Lee
- Laboratory of Molecular Neurobiology and Biophysics, Howard Hughes Medical Institute, The Rockefeller University, New York, United States
| | - Jue Chen
- Laboratory of Membrane Biology and Biophysics, Howard Hughes Medical Institute, The Rockefeller University, New York, United States
| | - Roderick MacKinnon
- Laboratory of Molecular Neurobiology and Biophysics, Howard Hughes Medical Institute, The Rockefeller University, New York, United States
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19
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Martin GM, Kandasamy B, DiMaio F, Yoshioka C, Shyng SL. Anti-diabetic drug binding site in a mammalian K ATP channel revealed by Cryo-EM. eLife 2017; 6:31054. [PMID: 29035201 PMCID: PMC5655142 DOI: 10.7554/elife.31054] [Citation(s) in RCA: 103] [Impact Index Per Article: 14.7] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/05/2017] [Accepted: 10/11/2017] [Indexed: 12/25/2022] Open
Abstract
Sulfonylureas are anti-diabetic medications that act by inhibiting pancreatic KATP channels composed of SUR1 and Kir6.2. The mechanism by which these drugs interact with and inhibit the channel has been extensively investigated, yet it remains unclear where the drug binding pocket resides. Here, we present a cryo-EM structure of a hamster SUR1/rat Kir6.2 channel bound to a high-affinity sulfonylurea drug glibenclamide and ATP at 3.63 Å resolution, which reveals unprecedented details of the ATP and glibenclamide binding sites. Importantly, the structure shows for the first time that glibenclamide is lodged in the transmembrane bundle of the SUR1-ABC core connected to the first nucleotide binding domain near the inner leaflet of the lipid bilayer. Mutation of residues predicted to interact with glibenclamide in our model led to reduced sensitivity to glibenclamide. Our structure provides novel mechanistic insights of how sulfonylureas and ATP interact with the KATP channel complex to inhibit channel activity.
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Affiliation(s)
- Gregory M Martin
- Department of Biochemistry and Molecular Biology, Oregon Health and Science University, Portland, United States
| | - Balamurugan Kandasamy
- Department of Biochemistry and Molecular Biology, Oregon Health and Science University, Portland, United States
| | - Frank DiMaio
- Department of Biochemistry, University of Washington, Seattle, United States
| | - Craig Yoshioka
- Department of Biomedical Engineering, Oregon Health and Science University, Portland, United States
| | - Show-Ling Shyng
- Department of Biochemistry and Molecular Biology, Oregon Health and Science University, Portland, United States
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20
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Martin GM, Yoshioka C, Rex EA, Fay JF, Xie Q, Whorton MR, Chen JZ, Shyng SL. Cryo-EM structure of the ATP-sensitive potassium channel illuminates mechanisms of assembly and gating. eLife 2017; 6. [PMID: 28092267 PMCID: PMC5344670 DOI: 10.7554/elife.24149] [Citation(s) in RCA: 131] [Impact Index Per Article: 18.7] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/12/2016] [Accepted: 01/11/2017] [Indexed: 12/18/2022] Open
Abstract
KATP channels are metabolic sensors that couple cell energetics to membrane excitability. In pancreatic β-cells, channels formed by SUR1 and Kir6.2 regulate insulin secretion and are the targets of antidiabetic sulfonylureas. Here, we used cryo-EM to elucidate structural basis of channel assembly and gating. The structure, determined in the presence of ATP and the sulfonylurea glibenclamide, at ~6 Å resolution reveals a closed Kir6.2 tetrameric core with four peripheral SUR1s each anchored to a Kir6.2 by its N-terminal transmembrane domain (TMD0). Intricate interactions between TMD0, the loop following TMD0, and Kir6.2 near the proposed PIP2 binding site, and where ATP density is observed, suggest SUR1 may contribute to ATP and PIP2 binding to enhance Kir6.2 sensitivity to both. The SUR1-ABC core is found in an unusual inward-facing conformation whereby the two nucleotide binding domains are misaligned along a two-fold symmetry axis, revealing a possible mechanism by which glibenclamide inhibits channel activity. DOI:http://dx.doi.org/10.7554/eLife.24149.001 The hormone insulin reduces blood sugar levels by encouraging fat, muscle and other body cells to take up sugar. When blood sugar levels rise following a meal, cells within the pancreas known as beta cells should release insulin. In people with diabetes, the beta cells fail to release insulin, meaning that the high blood sugar levels are not corrected. When blood sugar levels are high, beta cells generate more energy in the form of ATP molecules. The increased level of ATP causes channels called ATP-sensitive potassium (KATP) channels in the membrane of the cell to close. This triggers a cascade of events that leads to the release of insulin. Some treatments for diabetes alter how the KATP channels work. For example, a widely prescribed medication called glibenclamide (also known as glyburide in the United States) stimulates the release of insulin by preventing the flow of potassium through KATP channels. It remains unknown exactly how ATP and glibenclamide interact with the channel’s molecular structure to stop the flow of potassium ions. KATP channels are made up of two proteins called SUR1 and Kir6.2. To investigate the structure of the KATP channel, Martin et al. purified channels made of the hamster form of the SUR1 protein and the mouse form of Kir6.2, which each closely resemble their human counterparts. The channels were purified in the presence of ATP and glibenclamide and were then rapidly frozen to preserve their structure, which allowed them to be visualized individually using electron microscopy. By analyzing the images taken from many channels, Martin et al. constructed a highly detailed, three-dimensional map of the KATP channel. The structure revealed by this map shows how SUR1 and Kir6.2 work together and provides insight into how ATP and glibenclamide interact with the channel to block the flow of potassium, and hence stimulate the release of insulin. An important next step will be to improve the structure to more clearly identify where ATP and glibenclamide bind to the KATP channel. It will also be important to study the structures of channels that are bound to other regulatory molecules. This will help researchers to fully understand how KATP channels located throughout the body operate under healthy and diseased conditions. This knowledge will aid in the design of more effective drugs to treat several devastating diseases caused by defective KATP channels. DOI:http://dx.doi.org/10.7554/eLife.24149.002
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Affiliation(s)
- Gregory M Martin
- Department of Biochemistry and Molecular Biology, Oregon Health and Science University, Portland, Oregon, United States
| | - Craig Yoshioka
- Department of Biomedical Engineering, Oregon Health and Science University, Portland, Oregon, United States
| | - Emily A Rex
- Department of Biochemistry and Molecular Biology, Oregon Health and Science University, Portland, Oregon, United States
| | - Jonathan F Fay
- Department of Biochemistry and Molecular Biology, Oregon Health and Science University, Portland, Oregon, United States
| | - Qing Xie
- Department of Biochemistry and Molecular Biology, Oregon Health and Science University, Portland, Oregon, United States
| | - Matthew R Whorton
- Vollum Institute, Oregon Health and Science University, Portland, Oregon, United States
| | - James Z Chen
- Department of Biochemistry and Molecular Biology, Oregon Health and Science University, Portland, Oregon, United States
| | - Show-Ling Shyng
- Department of Biochemistry and Molecular Biology, Oregon Health and Science University, Portland, Oregon, United States
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21
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Li N, Wu JX, Ding D, Cheng J, Gao N, Chen L. Structure of a Pancreatic ATP-Sensitive Potassium Channel. Cell 2017; 168:101-110.e10. [DOI: 10.1016/j.cell.2016.12.028] [Citation(s) in RCA: 133] [Impact Index Per Article: 19.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/09/2016] [Revised: 12/19/2016] [Accepted: 12/20/2016] [Indexed: 10/20/2022]
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22
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Vedovato N, Ashcroft FM, Puljung MC. The Nucleotide-Binding Sites of SUR1: A Mechanistic Model. Biophys J 2016; 109:2452-2460. [PMID: 26682803 PMCID: PMC4699857 DOI: 10.1016/j.bpj.2015.10.026] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/07/2015] [Revised: 10/22/2015] [Accepted: 10/22/2015] [Indexed: 12/19/2022] Open
Abstract
ATP-sensitive potassium (KATP) channels comprise four pore-forming Kir6.2 subunits and four modulatory sulfonylurea receptor (SUR) subunits. The latter belong to the ATP-binding cassette family of transporters. KATP channels are inhibited by ATP (or ADP) binding to Kir6.2 and activated by Mg-nucleotide interactions with SUR. This dual regulation enables the KATP channel to couple the metabolic state of a cell to its electrical excitability and is crucial for the KATP channel’s role in regulating insulin secretion, cardiac and neuronal excitability, and vascular tone. Here, we review the regulation of the KATP channel by adenine nucleotides and present an equilibrium allosteric model for nucleotide activation and inhibition. The model can account for many experimental observations in the literature and provides testable predictions for future experiments.
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Affiliation(s)
- Natascia Vedovato
- Department of Physiology, Anatomy and Genetics, University of Oxford, Oxford, United Kingdom
| | - Frances M Ashcroft
- Department of Physiology, Anatomy and Genetics, University of Oxford, Oxford, United Kingdom
| | - Michael C Puljung
- Department of Physiology, Anatomy and Genetics, University of Oxford, Oxford, United Kingdom.
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23
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Lee SJ, Ren F, Zangerl-Plessl EM, Heyman S, Stary-Weinzinger A, Yuan P, Nichols CG. Structural basis of control of inward rectifier Kir2 channel gating by bulk anionic phospholipids. J Gen Physiol 2016; 148:227-37. [PMID: 27527100 PMCID: PMC5004336 DOI: 10.1085/jgp.201611616] [Citation(s) in RCA: 53] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/02/2016] [Accepted: 07/12/2016] [Indexed: 01/11/2023] Open
Abstract
Phospholipids are required to bind to two distinct sites on the inward rectifier potassium channel for maximal efficacy. Lee et al. show that a membrane-associating tryptophan residue in the second site can mimic the effect of phospholipid binding and cause a conformational change to reveal the primary binding site. Inward rectifier potassium (Kir) channel activity is controlled by plasma membrane lipids. Phosphatidylinositol-4,5-bisphosphate (PIP2) binding to a primary site is required for opening of classic inward rectifier Kir2.1 and Kir2.2 channels, but interaction of bulk anionic phospholipid (PL−) with a distinct second site is required for high PIP2 sensitivity. Here we show that introduction of a lipid-partitioning tryptophan at the second site (K62W) generates high PIP2 sensitivity, even in the absence of PL−. Furthermore, high-resolution x-ray crystal structures of Kir2.2[K62W], with or without added PIP2 (2.8- and 2.0-Å resolution, respectively), reveal tight tethering of the C-terminal domain (CTD) to the transmembrane domain (TMD) in each condition. Our results suggest a refined model for phospholipid gating in which PL− binding at the second site pulls the CTD toward the membrane, inducing the formation of the high-affinity primary PIP2 site and explaining the positive allostery between PL− binding and PIP2 sensitivity.
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Affiliation(s)
- Sun-Joo Lee
- Department of Cell Biology and Physiology, Washington University School of Medicine, St. Louis, MO 63110 Center for the Investigation of Membrane Excitability Diseases, Washington University School of Medicine, St. Louis, MO 63110
| | - Feifei Ren
- Department of Cell Biology and Physiology, Washington University School of Medicine, St. Louis, MO 63110 Center for the Investigation of Membrane Excitability Diseases, Washington University School of Medicine, St. Louis, MO 63110
| | | | - Sarah Heyman
- Department of Cell Biology and Physiology, Washington University School of Medicine, St. Louis, MO 63110 Center for the Investigation of Membrane Excitability Diseases, Washington University School of Medicine, St. Louis, MO 63110
| | - Anna Stary-Weinzinger
- Department of Pharmacology and Toxicology, University of Vienna, A-1090 Vienna, Austria
| | - Peng Yuan
- Department of Cell Biology and Physiology, Washington University School of Medicine, St. Louis, MO 63110 Center for the Investigation of Membrane Excitability Diseases, Washington University School of Medicine, St. Louis, MO 63110
| | - Colin G Nichols
- Department of Cell Biology and Physiology, Washington University School of Medicine, St. Louis, MO 63110 Center for the Investigation of Membrane Excitability Diseases, Washington University School of Medicine, St. Louis, MO 63110
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24
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Abstract
KATP channels are integral to the functions of many cells and tissues. The use of electrophysiological methods has allowed for a detailed characterization of KATP channels in terms of their biophysical properties, nucleotide sensitivities, and modification by pharmacological compounds. However, even though they were first described almost 25 years ago (Noma 1983, Trube and Hescheler 1984), the physiological and pathophysiological roles of these channels, and their regulation by complex biological systems, are only now emerging for many tissues. Even in tissues where their roles have been best defined, there are still many unanswered questions. This review aims to summarize the properties, molecular composition, and pharmacology of KATP channels in various cardiovascular components (atria, specialized conduction system, ventricles, smooth muscle, endothelium, and mitochondria). We will summarize the lessons learned from available genetic mouse models and address the known roles of KATP channels in cardiovascular pathologies and how genetic variation in KATP channel genes contribute to human disease.
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Affiliation(s)
- Monique N Foster
- Departments of Pediatrics, Physiology & Neuroscience, and Biochemistry and Molecular Pharmacology, NYU School of Medicine, New York, New York
| | - William A Coetzee
- Departments of Pediatrics, Physiology & Neuroscience, and Biochemistry and Molecular Pharmacology, NYU School of Medicine, New York, New York
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25
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Sulfonylurea receptors regulate the channel pore in ATP-sensitive potassium channels via an intersubunit salt bridge. Biochem J 2015; 464:343-54. [PMID: 25236767 DOI: 10.1042/bj20140273] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023]
Abstract
ATP-sensitive potassium channels play key roles in many tissues by coupling metabolic status to membrane potential. In contrast with other potassium channels, the pore-forming Kir6 subunits must co-assemble in hetero-octameric complexes with ATP-binding cassette (ABC) family sulfonylurea receptor (SUR) subunits to facilitate cell surface expression. Binding of nucleotides and drugs to SUR regulates channel gating but how these responses are communicated within the complex has remained elusive to date. We have now identified an electrostatic interaction, forming part of a functional interface between the cytoplasmic nucleotide-binding domain-2 of SUR2 subunits and the distal C-terminus of Kir6 polypeptides that determines channel response to nucleotide, potassium channel opener and antagonist. Mutation of participating residues disrupted physical interaction and regulation of expressed channels, properties that were restored in paired charge-swap mutants. Equivalent interactions were identified in Kir6.1- and Kir6.2-containing channels suggesting a conserved mechanism of allosteric regulation.
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26
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Devaraneni PK, Martin GM, Olson EM, Zhou Q, Shyng SL. Structurally distinct ligands rescue biogenesis defects of the KATP channel complex via a converging mechanism. J Biol Chem 2015; 290:7980-91. [PMID: 25637631 DOI: 10.1074/jbc.m114.634576] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Small molecules that correct protein misfolding and misprocessing defects offer a potential therapy for numerous human diseases. However, mechanisms underlying pharmacological correction of such defects, especially in heteromeric complexes with structurally diverse constituent proteins, are not well understood. Here we investigate how two chemically distinct compounds, glibenclamide and carbamazepine, correct biogenesis defects in ATP-sensitive potassium (KATP) channels composed of sulfonylurea receptor 1 (SUR1) and Kir6.2. We present evidence that despite structural differences, carbamazepine and glibenclamide compete for binding to KATP channels, and both drugs share a binding pocket in SUR1 to exert their effects. Moreover, both compounds engage Kir6.2, in particular the distal N terminus of Kir6.2, which is involved in normal channel biogenesis, for their chaperoning effects on SUR1 mutants. Conversely, both drugs can correct channel biogenesis defects caused by Kir6.2 mutations in a SUR1-dependent manner. Using an unnatural, photocross-linkable amino acid, azidophenylalanine, genetically encoded in Kir6.2, we demonstrate in living cells that both drugs promote interactions between the distal N terminus of Kir6.2 and SUR1. These findings reveal a converging pharmacological chaperoning mechanism wherein glibenclamide and carbamazepine stabilize the heteromeric subunit interface critical for channel biogenesis to overcome defective biogenesis caused by mutations in individual subunits.
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Affiliation(s)
- Prasanna K Devaraneni
- From the Department of Biochemistry and Molecular Biology, Oregon Health and Science University, Portland, Oregon 97239
| | - Gregory M Martin
- From the Department of Biochemistry and Molecular Biology, Oregon Health and Science University, Portland, Oregon 97239
| | - Erik M Olson
- From the Department of Biochemistry and Molecular Biology, Oregon Health and Science University, Portland, Oregon 97239
| | - Qing Zhou
- From the Department of Biochemistry and Molecular Biology, Oregon Health and Science University, Portland, Oregon 97239
| | - Show-Ling Shyng
- From the Department of Biochemistry and Molecular Biology, Oregon Health and Science University, Portland, Oregon 97239
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27
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Zhou Q, Pratt EB, Shyng SL. Engineered Kir6.2 mutations that correct the trafficking defect of K(ATP) channels caused by specific SUR1 mutations. Channels (Austin) 2013; 7:313-7. [PMID: 23695995 DOI: 10.4161/chan.25003] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
Abstract
KATP channels consisting of Kir6.2 and SUR1 couple cell metabolism to membrane excitability and regulate insulin secretion. The molecular interactions between SUR1 and Kir6.2 that govern channel gating and biogenesis are incompletely understood. In a recent study, we showed that a SUR1 and Kir6.2 mutation pair, E203K-SUR1 and Q52E-Kir6.2, at the SUR1/Kir6.2 interface near the plasma membrane increases the ATP-sensitivity of the channel by nearly 100-fold. Here, we report the finding that the same mutation pair also suppresses channel folding/trafficking defects caused by select SUR1 mutations in the first transmembrane domain of SUR1. Analysis of the contributions from individual mutations, however, revealed that the correction effect is attributed largely to Q52E-Kir6.2 alone. Moreover, the correction is dependent on the negative charge of the substituting amino acid at the Q52 position in Kir6.2. Our study demonstrates for the first time that engineered mutations in Kir6.2 can correct the biogenesis defect caused by specific mutations in the SUR1 subunit.
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Affiliation(s)
- Qing Zhou
- Department of Biochemistry and Molecular Biology; Oregon Health & Science University; Portland, OR USA
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