1
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Augustynek B, Gyimesi G, Dernič J, Sallinger M, Albano G, Klesse GJ, Kandasamy P, Grabmayr H, Frischauf I, Fuster DG, Peinelt C, Hediger MA, Bhardwaj R. Discovery of novel gating checkpoints in the Orai1 calcium channel by systematic analysis of constitutively active mutants of its paralogs and orthologs. Cell Calcium 2022; 105:102616. [PMID: 35792401 DOI: 10.1016/j.ceca.2022.102616] [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: 05/05/2022] [Revised: 06/17/2022] [Accepted: 06/20/2022] [Indexed: 11/24/2022]
Abstract
In humans, there are three paralogs of the Orai Ca2+ channel that form the core of the store-operated calcium entry (SOCE) machinery. While the STIM-mediated gating mechanism of Orai channels is still under active investigation, several artificial and natural variants are known to cause constitutive activity of the human Orai1 channel. Surprisingly, little is known about the conservation of the gating checkpoints among the different human Orai paralogs and orthologs in other species. In our work, we show that the mutation corresponding to the activating mutation H134A in transmembrane helix 2 (TM2) of human Orai1 also activates Orai2 and Orai3, likely via a similar mechanism. However, this cross-paralog conservation does not apply to the "ANSGA" nexus mutations in TM4 of human Orai1, which is reported to mimic the STIM1-activated state of the channel. In investigating the mechanistic background of these differences, we identified two positions, H171 and F246 in human Orai1, that are not conserved among paralogs and that seem to be crucial for the channel activation triggered by the "ANSGA" mutations in Orai1. However, mutations of the same residues still allow gating of Orai1 by STIM1, suggesting that the ANSGA mutant of Orai1 may not be a surrogate for the STIM1-activated state of the Orai1 channel. Our results shed new light on these important gating checkpoints and show that the gating mechanism of Orai channels is affected by multiple factors that are not necessarily conserved among orai homologs, such as the TM4-TM3 coupling.
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Affiliation(s)
- Bartłomiej Augustynek
- Membrane Transport Discovery Lab, Department of Nephrology and Hypertension and Department of Biomedical Research, Inselspital, University of Bern, Freiburgstrasse 15, CH-3010 Bern, Switzerland
| | - Gergely Gyimesi
- Membrane Transport Discovery Lab, Department of Nephrology and Hypertension and Department of Biomedical Research, Inselspital, University of Bern, Freiburgstrasse 15, CH-3010 Bern, Switzerland
| | - Jan Dernič
- Membrane Transport Discovery Lab, Department of Nephrology and Hypertension and Department of Biomedical Research, Inselspital, University of Bern, Freiburgstrasse 15, CH-3010 Bern, Switzerland
| | - Matthias Sallinger
- Institute of Biophysics, JKU Life Science Center, Johannes Kepler University Linz, A-4020 Linz, Austria
| | - Giuseppe Albano
- Membrane Transport Discovery Lab, Department of Nephrology and Hypertension and Department of Biomedical Research, Inselspital, University of Bern, Freiburgstrasse 15, CH-3010 Bern, Switzerland
| | - Gabriel J Klesse
- Membrane Transport Discovery Lab, Department of Nephrology and Hypertension and Department of Biomedical Research, Inselspital, University of Bern, Freiburgstrasse 15, CH-3010 Bern, Switzerland
| | - Palanivel Kandasamy
- Membrane Transport Discovery Lab, Department of Nephrology and Hypertension and Department of Biomedical Research, Inselspital, University of Bern, Freiburgstrasse 15, CH-3010 Bern, Switzerland
| | - Herwig Grabmayr
- Institute of Biophysics, JKU Life Science Center, Johannes Kepler University Linz, A-4020 Linz, Austria
| | - Irene Frischauf
- Institute of Biophysics, JKU Life Science Center, Johannes Kepler University Linz, A-4020 Linz, Austria
| | - Daniel G Fuster
- Membrane Transport Discovery Lab, Department of Nephrology and Hypertension and Department of Biomedical Research, Inselspital, University of Bern, Freiburgstrasse 15, CH-3010 Bern, Switzerland
| | - Christine Peinelt
- Institute of Biochemistry and Molecular Medicine, University of Bern, Bühlstrasse 28, 3012 Bern, Switzerland
| | - Matthias A Hediger
- Membrane Transport Discovery Lab, Department of Nephrology and Hypertension and Department of Biomedical Research, Inselspital, University of Bern, Freiburgstrasse 15, CH-3010 Bern, Switzerland.
| | - Rajesh Bhardwaj
- Membrane Transport Discovery Lab, Department of Nephrology and Hypertension and Department of Biomedical Research, Inselspital, University of Bern, Freiburgstrasse 15, CH-3010 Bern, Switzerland; Current address: Signal Transduction Laboratory, National Institute of Environmental Health Sciences, NIH, 111 TW Alexander Drive, NC 27709, USA.
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2
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Humer C, Romanin C, Höglinger C. Highlighting the Multifaceted Role of Orai1 N-Terminal- and Loop Regions for Proper CRAC Channel Functions. Cells 2022; 11:371. [PMID: 35159181 PMCID: PMC8834118 DOI: 10.3390/cells11030371] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2021] [Revised: 01/14/2022] [Accepted: 01/15/2022] [Indexed: 11/16/2022] Open
Abstract
Orai1, the Ca2+-selective pore in the plasma membrane, is one of the key components of the Ca2+release-activated Ca2+ (CRAC) channel complex. Activated by the Ca2+ sensor in the endoplasmic reticulum (ER) membrane, stromal interaction molecule 1 (STIM1), via direct interaction when ER luminal Ca2+ levels recede, Orai1 helps to maintain Ca2+ homeostasis within a cell. It has already been proven that the C-terminus of Orai1 is indispensable for channel activation. However, there is strong evidence that for CRAC channels to function properly and maintain all typical hallmarks, such as selectivity and reversal potential, additional parts of Orai1 are needed. In this review, we focus on these sites apart from the C-terminus; namely, the second loop and N-terminus of Orai1 and on their multifaceted role in the functioning of CRAC channels.
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Affiliation(s)
| | | | - Carmen Höglinger
- Institute of Biophysics, Johannes Kepler University Linz, Gruberstrasse 40, 4020 Linz, Austria; (C.H.); (C.R.)
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3
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Baraniak JH, Zhou Y, Nwokonko RM, Jennette MR, Kazzaz SA, Stenson JM, Whitsell AL, Wang Y, Trebak M, Gill DL. Orai channel C-terminal peptides are key modulators of STIM-Orai coupling and calcium signal generation. Cell Rep 2021; 35:109322. [PMID: 34192542 PMCID: PMC8462482 DOI: 10.1016/j.celrep.2021.109322] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/25/2020] [Revised: 03/17/2021] [Accepted: 06/07/2021] [Indexed: 11/03/2022] Open
Abstract
Junctional coupling between endoplasmic reticulum (ER) Ca2+-sensor STIM proteins and plasma membrane (PM) Orai channels mediates Ca2+ signals in most cells. We reveal that PM-tethered, fluorescently tagged C-terminal M4x (fourth transmembrane helix contains a cytoplasmic C-terminal extension) peptides from Orai channels undergo a Leu-specific signature of direct interaction with the STIM1 Orai-activating region (SOAR), exactly mimicking STIM1 binding to gate Orai channels. The 20-amino-acid Orai3-M4x peptide associates avidly with STIM1 within ER-PM junctions, functions to competitively block native Ca2+ signals, and mediates a key modification of STIM-Orai coupling induced by 2-aminoethoxydiphenyl borate. By blocking STIM-Orai coupling, the Orai3-M4x peptide reveals the critical role of Orai channels in driving Ca2+ oscillatory signals and transcriptional control through NFAT. The M4x peptides interact independently with SOAR dimers consistent with unimolecular coupling between Orai subunits and STIM1 dimers. We reveal the critical role of M4x helices in defining the coupling interface between STIM and Orai proteins to mediate store-operated Ca2+ signals.
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Affiliation(s)
- James H Baraniak
- Department of Cellular and Molecular Physiology, The Pennsylvania State University College of Medicine, Hershey, PA 17033, USA
| | - Yandong Zhou
- Department of Cellular and Molecular Physiology, The Pennsylvania State University College of Medicine, Hershey, PA 17033, USA.
| | - Robert M Nwokonko
- Department of Cellular and Molecular Physiology, The Pennsylvania State University College of Medicine, Hershey, PA 17033, USA
| | - Michelle R Jennette
- Department of Cellular and Molecular Physiology, The Pennsylvania State University College of Medicine, Hershey, PA 17033, USA
| | - Sarah A Kazzaz
- Department of Cellular and Molecular Physiology, The Pennsylvania State University College of Medicine, Hershey, PA 17033, USA
| | - Jazmin M Stenson
- Department of Cellular and Molecular Physiology, The Pennsylvania State University College of Medicine, Hershey, PA 17033, USA
| | - Abigale L Whitsell
- Department of Cellular and Molecular Physiology, The Pennsylvania State University College of Medicine, Hershey, PA 17033, USA
| | - Youjun Wang
- Beijing Key Laboratory of Gene Resources and Molecular Development College of Life Sciences, Beijing Normal University, Beijing 100875, People's Republic of China
| | - Mohamed Trebak
- Department of Cellular and Molecular Physiology, The Pennsylvania State University College of Medicine, Hershey, PA 17033, USA
| | - Donald L Gill
- Department of Cellular and Molecular Physiology, The Pennsylvania State University College of Medicine, Hershey, PA 17033, USA.
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4
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Huo J, Dong H. Gating and regulation of the calcium release-activated calcium channel: Recent progress from experiments and molecular modeling. Biopolymers 2021; 111:e23392. [PMID: 33460071 DOI: 10.1002/bip.23392] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/18/2020] [Revised: 06/29/2020] [Accepted: 07/01/2020] [Indexed: 11/08/2022]
Abstract
Calcium release-activated calcium (CRAC) channels are highly calcium ion (Ca2+)-selective channels in the plasma membrane. The transient drop of endoplasmic reticulum Ca2+ level activates its calcium sensor stromal interaction molecule (STIM) and then triggers the gating of the CRAC channel pore unit Orai. This process involves a variety of activities of the immune system. Therefore, understanding how the activation and regulation of the CRAC channel can be accomplished is essential. Here we briefly summarize the recent progress on Orai gating and its regulation by 2-aminoethoxydiphenylborate (2-APB) obtained from structural biology studies, biochemical and electrophysiological measurements, as well as molecular modeling. Indeed, integration between experiments and computations has further deepened our understanding of the channel gating and regulation.
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Affiliation(s)
- Jun Huo
- Kuang Yaming Honors School, Nanjing University, Nanjing, China
| | - Hao Dong
- Kuang Yaming Honors School, Nanjing University, Nanjing, China.,Institute for Brain Sciences, Nanjing University, Nanjing, China
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5
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The Orai Pore Opening Mechanism. Int J Mol Sci 2021; 22:ijms22020533. [PMID: 33430308 PMCID: PMC7825772 DOI: 10.3390/ijms22020533] [Citation(s) in RCA: 11] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/29/2020] [Revised: 12/30/2020] [Accepted: 01/02/2021] [Indexed: 02/07/2023] Open
Abstract
Cell survival and normal cell function require a highly coordinated and precise regulation of basal cytosolic Ca2+ concentrations. The primary source of Ca2+ entry into the cell is mediated by the Ca2+ release-activated Ca2+ (CRAC) channel. Its action is stimulated in response to internal Ca2+ store depletion. The fundamental constituents of CRAC channels are the Ca2+ sensor, stromal interaction molecule 1 (STIM1) anchored in the endoplasmic reticulum, and a highly Ca2+-selective pore-forming subunit Orai1 in the plasma membrane. The precise nature of the Orai1 pore opening is currently a topic of intensive research. This review describes how Orai1 gating checkpoints in the middle and cytosolic extended transmembrane regions act together in a concerted manner to ensure an opening-permissive Orai1 channel conformation. In this context, we highlight the effects of the currently known multitude of Orai1 mutations, which led to the identification of a series of gating checkpoints and the determination of their role in diverse steps of the Orai1 activation cascade. The synergistic action of these gating checkpoints maintains an intact pore geometry, settles STIM1 coupling, and governs pore opening. We describe the current knowledge on Orai1 channel gating mechanisms and summarize still open questions of the STIM1-Orai1 machinery.
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6
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Tiffner A, Derler I. Molecular Choreography and Structure of Ca 2+ Release-Activated Ca 2+ (CRAC) and K Ca2+ Channels and Their Relevance in Disease with Special Focus on Cancer. MEMBRANES 2020; 10:E425. [PMID: 33333945 PMCID: PMC7765462 DOI: 10.3390/membranes10120425] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 11/04/2020] [Revised: 12/04/2020] [Accepted: 12/07/2020] [Indexed: 12/16/2022]
Abstract
Ca2+ ions play a variety of roles in the human body as well as within a single cell. Cellular Ca2+ signal transduction processes are governed by Ca2+ sensing and Ca2+ transporting proteins. In this review, we discuss the Ca2+ and the Ca2+-sensing ion channels with particular focus on the structure-function relationship of the Ca2+ release-activated Ca2+ (CRAC) ion channel, the Ca2+-activated K+ (KCa2+) ion channels, and their modulation via other cellular components. Moreover, we highlight their roles in healthy signaling processes as well as in disease with a special focus on cancer. As KCa2+ channels are activated via elevations of intracellular Ca2+ levels, we summarize the current knowledge on the action mechanisms of the interplay of CRAC and KCa2+ ion channels and their role in cancer cell development.
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Affiliation(s)
| | - Isabella Derler
- Institute of Biophysics, JKU Life Science Center, Johannes Kepler University Linz, A-4020 Linz, Austria;
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7
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Baraniak JH, Zhou Y, Nwokonko RM, Gill DL. The Intricate Coupling Between STIM Proteins and Orai Channels. CURRENT OPINION IN PHYSIOLOGY 2020; 17:106-114. [PMID: 32954113 DOI: 10.1016/j.cophys.2020.07.018] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
Store-operated Ca2+ entry signals are critical for cellular regulation. This intricate signaling pathway involves coupling of proteins in two different membranes: the ER-resident Ca2+-sensing STIM proteins and the highly Ca2+-selective PM Orai channels. The molecular nature of the STIM-Orai coupling interface in ER-PM junctions and consequent Orai channel gating, are processes under intense study. We describe recent developments in determining the mechanism of Orai activation through the key STIM-Orai Activating Region (SOAR) of STIM1. We describe the unexpected unimolecular coupling of STIM with Orai and explain the observed variable stoichiometry of STIM-Orai interactions. We also define the discrete C-terminal regions in Orai channels that initially latch onto STIM proteins and mediate allosteric activation of the channel. A critical "nexus" region closely associated with the STIM-activated C-terminus of Orai1, propagates the STIM-binding signal through the four tightly-associated transmembrane helices of Orai1, finally to modify the pore-forming helices and effect channel opening.
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Affiliation(s)
- James H Baraniak
- Department of Cellular and Molecular Physiology, The Pennsylvania State University College of Medicine, Hershey, PA 17033
| | - Yandong Zhou
- Department of Cellular and Molecular Physiology, The Pennsylvania State University College of Medicine, Hershey, PA 17033
| | - Robert M Nwokonko
- Department of Cellular and Molecular Physiology, The Pennsylvania State University College of Medicine, Hershey, PA 17033
| | - Donald L Gill
- Department of Cellular and Molecular Physiology, The Pennsylvania State University College of Medicine, Hershey, PA 17033
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8
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Niu L, Wu F, Li K, Li J, Zhang SL, Hu J, Wang Q. STIM1 interacts with termini of Orai channels in a sequential manner. J Cell Sci 2020; 133:jcs239491. [PMID: 32107289 DOI: 10.1242/jcs.239491] [Citation(s) in RCA: 12] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/23/2019] [Accepted: 02/24/2020] [Indexed: 12/20/2022] Open
Abstract
Store-operated Ca2+ entry (SOCE) is critical for numerous Ca2+-related processes. The activation of SOCE requires engagement between stromal interaction molecule 1 (STIM1) molecules on the endoplasmic reticulum and Ca2+ release-activated channel (CRAC) Orai on the plasma membrane. However, the molecular details of their interactions remain elusive. Here, we analyzed STIM1-Orai interactions using synthetic peptides derived from the N- and C-termini of Orai channels (Orai-NT and Orai-CT, respectively) and purified fragments of STIM1. The binding of STIM1 to Orai-NT is hydrophilic based, whereas binding to the Orai-CT is mostly hydrophobic. STIM1 decreases its affinity for Orai-CT when Orai-NT is present, supporting a stepwise interaction. Orai3-CT exhibits stronger binding to STIM1 than Orai1-CT, largely due to the shortness of one helical turn. The role of newly identified residues was confirmed by co-immunoprecipitation and Ca2+ imaging using full-length molecules. Our results provide important insight into CRAC gating by STIM1.
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Affiliation(s)
- Liling Niu
- Department of Immunology, School of Basic Medical Sciences, Tianjin Medical University, and Tianjin Key Laboratory of Cellular and Molecular Immunology, Tianjin 300070, China
- Department of Genetics and Cell Biology, College of Life Sciences, Nankai University, Tianjin 300071, China
| | - Fuyun Wu
- Department of Genetics and Cell Biology, College of Life Sciences, Nankai University, Tianjin 300071, China
- School of Basic Medical Sciences, Hubei University of Medicine, Shiyan 442000, China
| | - Kaili Li
- National Laboratory of Biomacromolecules, CAS Center for Excellence in Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing 100101, China
| | - Jing Li
- Department of Genetics and Cell Biology, College of Life Sciences, Nankai University, Tianjin 300071, China
| | - Shenyuan L Zhang
- Department of Medical Physiology, College of Medicine, Texas A&M Health Science Center, Temple, TX 76504, USA
| | - Junjie Hu
- Department of Genetics and Cell Biology, College of Life Sciences, Nankai University, Tianjin 300071, China
- National Laboratory of Biomacromolecules, CAS Center for Excellence in Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing 100101, China
| | - Qian Wang
- Department of Immunology, School of Basic Medical Sciences, Tianjin Medical University, and Tianjin Key Laboratory of Cellular and Molecular Immunology, Tianjin 300070, China
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9
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Butorac C, Krizova A, Derler I. Review: Structure and Activation Mechanisms of CRAC Channels. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2020; 1131:547-604. [PMID: 31646526 DOI: 10.1007/978-3-030-12457-1_23] [Citation(s) in RCA: 17] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
Ca2+ release activated Ca2+ (CRAC) channels represent a primary pathway for Ca2+ to enter non-excitable cells. The two key players in this process are the stromal interaction molecule (STIM), a Ca2+ sensor embedded in the membrane of the endoplasmic reticulum, and Orai, a highly Ca2+ selective ion channel located in the plasma membrane. Upon depletion of the internal Ca2+ stores, STIM is activated, oligomerizes, couples to and activates Orai. This review provides an overview of novel findings about the CRAC channel activation mechanisms, structure and gating. In addition, it highlights, among diverse STIM and Orai mutants, also the disease-related mutants and their implications.
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Affiliation(s)
- Carmen Butorac
- Institute of Biophysics, Johannes Kepler University of Linz, Linz, Austria
| | - Adéla Krizova
- Institute of Biophysics, Johannes Kepler University of Linz, Linz, Austria
| | - Isabella Derler
- Institute of Biophysics, Johannes Kepler University of Linz, Linz, Austria.
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10
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Zhou Y, Nwokonko RM, Baraniak JH, Trebak M, Lee KPK, Gill DL. The remote allosteric control of Orai channel gating. PLoS Biol 2019; 17:e3000413. [PMID: 31469825 PMCID: PMC6742413 DOI: 10.1371/journal.pbio.3000413] [Citation(s) in RCA: 22] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Revised: 09/12/2019] [Indexed: 12/30/2022] Open
Abstract
Calcium signals drive an endless array of cellular responses including secretion, contraction, transcription, cell division, and growth. The ubiquitously expressed Orai family of plasma membrane (PM) ion channels mediate Ca2+ entry signals triggered by the Ca2+ sensor Stromal Interaction Molecule (STIM) proteins of the endoplasmic reticulum (ER). The 2 proteins interact within curiously obscure ER-PM junctions, driving an allosteric gating mechanism for the Orai channel. Although key to Ca2+ signal generation, molecular understanding of this activation process remain obscure. Crystallographic structural analyses reveal much about the exquisite hexameric core structure of Orai channels. But how STIM proteins bind to the channel periphery and remotely control opening of the central pore, has eluded such analysis. Recent studies apply both crystallography and single-particle cryogenic electron microscopy (cryo-EM) analyses to probe the structure of Orai mutants that mimic activation by STIM. The results provide new understanding on the open state of the channel and how STIM proteins may exert remote allosteric control of channel gating. Plasma membrane Orai channels are activated by endoplasmic reticulum calcium-sensing STIM proteins through a dynamic coupling mechanism within specialized inter-membrane junctions. This Primer explores new structural studies that hint at the extraordinary complexity of this crucial association that is critical to the generation of calcium signals.
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Affiliation(s)
- Yandong Zhou
- Department of Cellular and Molecular Physiology, The Pennsylvania State University College of Medicine, Hershey, Pennsylvania, United States of America
- * E-mail: (DLG); (YZ)
| | - Robert M. Nwokonko
- Department of Cellular and Molecular Physiology, The Pennsylvania State University College of Medicine, Hershey, Pennsylvania, United States of America
| | - James H. Baraniak
- Department of Cellular and Molecular Physiology, The Pennsylvania State University College of Medicine, Hershey, Pennsylvania, United States of America
| | - Mohamed Trebak
- Department of Cellular and Molecular Physiology, The Pennsylvania State University College of Medicine, Hershey, Pennsylvania, United States of America
| | - Kenneth P. K. Lee
- Department of Cellular and Molecular Physiology, The Pennsylvania State University College of Medicine, Hershey, Pennsylvania, United States of America
| | - Donald L. Gill
- Department of Cellular and Molecular Physiology, The Pennsylvania State University College of Medicine, Hershey, Pennsylvania, United States of America
- * E-mail: (DLG); (YZ)
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11
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Krizova A, Maltan L, Derler I. Critical parameters maintaining authentic CRAC channel hallmarks. EUROPEAN BIOPHYSICS JOURNAL : EBJ 2019; 48:425-445. [PMID: 30903264 PMCID: PMC6647248 DOI: 10.1007/s00249-019-01355-6] [Citation(s) in RCA: 20] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 10/15/2018] [Revised: 12/20/2018] [Accepted: 03/06/2019] [Indexed: 12/20/2022]
Abstract
Ca2+ ions represent versatile second messengers that regulate a huge diversity of processes throughout the cell's life. One prominent Ca2+ entry pathway into the cell is the Ca2+ release-activated Ca2+ (CRAC) ion channel. It is fully reconstituted by the two molecular key players: the stromal interaction molecule (STIM1) and Orai. STIM1 is a Ca2+ sensor located in the membrane of the endoplasmic reticulum, and Orai, a highly Ca2+ selective ion channel embedded in the plasma membrane. Ca2+ store-depletion leads initially to the activation of STIM1 which subsequently activates Orai channels via direct binding. Authentic CRAC channel hallmarks and biophysical characteristics include high Ca2+ selectivity with a reversal potential in the range of + 50 mV, small unitary conductance, fast Ca2+-dependent inactivation and enhancements in currents upon the switch from a Na+-containing divalent-free to a Ca2+-containing solution. This review provides an overview on the critical determinants and structures within the STIM1 and Orai proteins that establish these prominent CRAC channel characteristics.
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Affiliation(s)
- Adéla Krizova
- Institute of Biophysics, Johannes Kepler University of Linz, Gruberstrasse 40, 4020, Linz, Austria
| | - Lena Maltan
- Institute of Biophysics, Johannes Kepler University of Linz, Gruberstrasse 40, 4020, Linz, Austria
| | - Isabella Derler
- Institute of Biophysics, Johannes Kepler University of Linz, Gruberstrasse 40, 4020, Linz, Austria.
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12
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Dong H, Zhang Y, Song R, Xu J, Yuan Y, Liu J, Li J, Zheng S, Liu T, Lu B, Wang Y, Klein ML. Toward a Model for Activation of Orai Channel. iScience 2019; 16:356-367. [PMID: 31207498 PMCID: PMC6579751 DOI: 10.1016/j.isci.2019.05.041] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2018] [Revised: 04/29/2019] [Accepted: 05/29/2019] [Indexed: 12/22/2022] Open
Abstract
Store-operated calcium release-activated calcium (CRAC) channels mediate a variety of cellular signaling functions. The CRAC channel pore-forming protein, Orai1, is a hexamer arranged with 3-fold symmetry. Despite its importance in moving Ca2+ ions into cells, a detailed mechanistic understanding of Orai1 activation is lacking. Herein, a working model is proposed for the putative open state of Orai from Drosophila melanogaster (dOrai), which involves a “twist-to-open” gating mechanism. The proposed model is supported by energetic, structural, and experimental evidence. Fluorescent imaging demonstrates that each subunit on the intracellular side of the pore is inherently strongly cross-linked, which is important for coupling to STIM1, the pore activator, and graded activation of the Orai1 channel. The proposed model thus paves the way for understanding key aspects of calcium signaling at a molecular level. Mechanical coupling within the calcium channel pore is critical for its activation Molecular modeling could disclose gating mechanism of ion channels at atomic level The predicted open-state structure of the pore was further confirmed by experiments
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Affiliation(s)
- Hao Dong
- Kuang Yaming Honors School, Nanjing University, Nanjing 210023, People's Republic of China; Institute for Brain Sciences, Nanjing University, Nanjing 210023, People's Republic of China.
| | - Yiming Zhang
- Beijing Key Laboratory of Gene Resource and Molecular Development, College of Life Sciences, Beijing Normal University, Beijing 100875, People's Republic of China
| | - Ruiheng Song
- Kuang Yaming Honors School, Nanjing University, Nanjing 210023, People's Republic of China
| | - Jingjie Xu
- State Key Laboratory of Scientific and Engineering Computing, National Center for Mathematics and Interdisciplinary Sciences, Academy of Mathematics and Systems Science, Chinese Academy of Sciences, Beijing 100190, People's Republic of China
| | - Yigao Yuan
- Kuang Yaming Honors School, Nanjing University, Nanjing 210023, People's Republic of China
| | - Jindou Liu
- Beijing Key Laboratory of Gene Resource and Molecular Development, College of Life Sciences, Beijing Normal University, Beijing 100875, People's Republic of China
| | - Jia Li
- Beijing Key Laboratory of Gene Resource and Molecular Development, College of Life Sciences, Beijing Normal University, Beijing 100875, People's Republic of China
| | - Sisi Zheng
- Beijing Key Laboratory of Gene Resource and Molecular Development, College of Life Sciences, Beijing Normal University, Beijing 100875, People's Republic of China
| | - Tiantian Liu
- State Key Laboratory of Scientific and Engineering Computing, National Center for Mathematics and Interdisciplinary Sciences, Academy of Mathematics and Systems Science, Chinese Academy of Sciences, Beijing 100190, People's Republic of China; CAEP Software Center for High Performance Numerical Simulation, Beijing 100088, People's Republic of China
| | - Benzhuo Lu
- State Key Laboratory of Scientific and Engineering Computing, National Center for Mathematics and Interdisciplinary Sciences, Academy of Mathematics and Systems Science, Chinese Academy of Sciences, Beijing 100190, People's Republic of China.
| | - Youjun Wang
- Beijing Key Laboratory of Gene Resource and Molecular Development, College of Life Sciences, Beijing Normal University, Beijing 100875, People's Republic of China.
| | - Michael L Klein
- Institute for Computational Molecular Science, Temple University, Philadelphia, PA 19122, USA.
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13
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Yeung PSW, Yamashita M, Prakriya M. Molecular basis of allosteric Orai1 channel activation by STIM1. J Physiol 2019; 598:1707-1723. [PMID: 30950063 DOI: 10.1113/jp276550] [Citation(s) in RCA: 42] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/03/2018] [Accepted: 03/19/2019] [Indexed: 12/13/2022] Open
Abstract
Store-operated Ca2+ entry through Orai1 channels is a primary mechanism for Ca2+ entry in many cells and mediates numerous cellular effector functions ranging from gene transcription to exocytosis. Orai1 channels are amongst the most Ca2+ -selective channels known and are activated by direct physical interactions with the endoplasmic reticulum Ca2+ sensor stromal interaction molecule 1 (STIM1) in response to store depletion triggered by stimulation of a variety of cell surface G-protein coupled and tyrosine kinase receptors. Work in the last decade has revealed that the Orai1 gating process is highly cooperative and strongly allosteric, likely driven by a wave of interdependent conformational changes throughout the protein originating in the peripheral C-terminal ligand binding site and culminating in pore opening. In this review, we survey the structural and molecular features in Orai1 that contribute to channel gating and consider how they give rise to the unique biophysical fingerprint of Orai1 currents.
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Affiliation(s)
- Priscilla See-Wai Yeung
- Department of Pharmacology, Northwestern University, Feinberg School of Medicine, Chicago, IL, 60611, USA
| | - Megumi Yamashita
- Department of Pharmacology, Northwestern University, Feinberg School of Medicine, Chicago, IL, 60611, USA
| | - Murali Prakriya
- Department of Pharmacology, Northwestern University, Feinberg School of Medicine, Chicago, IL, 60611, USA
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14
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Lunz V, Romanin C, Frischauf I. STIM1 activation of Orai1. Cell Calcium 2019; 77:29-38. [PMID: 30530091 DOI: 10.1016/j.ceca.2018.11.009] [Citation(s) in RCA: 67] [Impact Index Per Article: 13.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/07/2018] [Revised: 11/20/2018] [Accepted: 11/28/2018] [Indexed: 11/23/2022]
Abstract
A primary calcium (Ca2+) entry pathway into non-excitable cells is through the store-operated Ca2+ release activated Ca2+ (CRAC) channel. Ca2+ entry into cells is responsible for the initiation of diverse signalling cascades that affect essential cellular processes like gene regulation, cell growth and death, secretion and gene transcription. Upon depletion of intracellular Ca2+ stores within the endoplasmic reticulum (ER), the CRAC channel opens to refill depleted stores. The two key limiting molecular players of the CRAC channel are the stromal interaction molecule (STIM1) embedded in the ER-membrane and Orai1, residing in the plasma membrane (PM), respectively. Together, they form a highly Ca2+ selective ion channel complex. STIM1 senses the Ca2+ content of the ER and confers Ca2+ store-depletion into the opening of Orai1 channels in the PM for triggering Ca2+-dependent gene transcription, T-cell activation or mast cell degranulation. The interplay of Orai and STIM proteins in the CRAC channel signalling cascade has been the main focus of research for more than twelve years. This chapter focuses on current knowledge and main experimental advances in the understanding of Orai1 activation by STIM1, thereby portraying key mechanistic steps in the CRAC channel signalling cascade.
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Affiliation(s)
- Victoria Lunz
- Institute of Biophysics, Johannes Kepler University Linz, A-4020, Linz, Austria
| | - Christoph Romanin
- Institute of Biophysics, Johannes Kepler University Linz, A-4020, Linz, Austria.
| | - Irene Frischauf
- Institute of Biophysics, Johannes Kepler University Linz, A-4020, Linz, Austria.
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15
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Song X, Liu Y, Dong L, Wang Y. Stromal-Interacting Molecule 1 (Stim1)/Orai1 Modulates Endothelial Permeability in Ventilator-Induced Lung Injury. Med Sci Monit 2018; 24:9413-9423. [PMID: 30589833 PMCID: PMC6322368 DOI: 10.12659/msm.911268] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
Background Increased endothelial permeability is involved in ventilator-induced lung injury (VILI). Stim1/Orai1 mediates store-operated Ca2+ activation, which modulates endothelial permeability. However, the underlying mechanisms of the Stim1/Orai1 pathway in VILI are poorly understood. Material/Methods Wistar rats were exposed to low tidal volume (7 mL/kg) or high tidal volume (40 mL/kg) ventilation. Human Lung Microvascular Endothelial Cells (HULEC) were subjected to 8% or 18% cyclic stretching (CS). BTP2 pretreatment was performed. Lung wet/dry weight ratio, histological changes of lung injury, and bronchoalveolar lavage fluid (BALF) protein were measured. Endothelial permeability and intracellular calcium concentration were evaluated in HULECs. Protein expression was determined by Western blotting. Results High tidal volume mechanical ventilation-induced lung injury (such as severe congestion and hemorrhage) and BTP2 pretreatment protected lungs from injury. The expression of Stim1, Orai1, and PKCα, lung wet/dry weight ratio, and BALF protein level significantly increased in the high tidal volume group compared to the control group and low tidal volume group. Importantly, BTP2 pretreatment alleviated the above-mentioned effects. Compared with exposure to 8% CS, the protein levels of Stim1, Orai1, and PKCα in HULECs significantly increased after exposure to 18% CS for 4 h, whereas BTP2 pretreatment significantly inhibited the increase (P<0.05). BTP2 pretreatment also suppressed increase of endothelial permeability and the intracellular calcium induced by 18% CS (P<0.05). Conclusions When exposed to high tidal volume or large-magnitude CS, Stim1 and Orai1 expression are upregulated, which further activates calcium-sensitive PKCα and results in calcium overload, endothelial hyperpermeability, and, finally, lung injury.
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Affiliation(s)
- Xiumei Song
- Department of Anesthesiology, Qianfoshan Hospital, Shandong University, Jinan, Shandong, China (mainland)
| | - Yang Liu
- Department of Anesthesiology, Qianfoshan Hospital, Shandong University, Jinan, Shandong, China (mainland)
| | - Ling Dong
- Department of Anesthesiology, Qianfoshan Hospital, Shandong University, Jinan, Shandong, China (mainland)
| | - Yuelan Wang
- Department of Anesthesiology, Qianfoshan Hospital, Shandong University, Jinan, Shandong, China (mainland)
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16
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Bulla M, Gyimesi G, Kim JH, Bhardwaj R, Hediger MA, Frieden M, Demaurex N. ORAI1 channel gating and selectivity is differentially altered by natural mutations in the first or third transmembrane domain. J Physiol 2018; 597:561-582. [PMID: 30382595 PMCID: PMC6332830 DOI: 10.1113/jp277079] [Citation(s) in RCA: 32] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/07/2018] [Accepted: 10/31/2018] [Indexed: 12/12/2022] Open
Abstract
KEY POINTS Gain-of-function mutations in the highly selective Ca2+ channel ORAI1 cause tubular aggregate myopathy (TAM) characterized by muscular pain, weakness and cramping. TAM-associated mutations in ORAI1 first and third transmembrane domain facilitate channel opening by STIM1, causing constitutive Ca2+ influx and increasing the currents evoked by Ca2+ store depletion. Mutation V107M additionally decreases the channel selectivity for Ca2+ ions and its inhibition by acidic pH, while mutation T184M does not alter the channel sensitivity to pH or to reactive oxygen species. The ORAI blocker GSK-7975A prevents the constitutive activity of TAM-associated channels and might be used in therapy for patients suffering from TAM. ABSTRACT Skeletal muscle differentiation relies on store-operated Ca2+ entry (SOCE) mediated by STIM proteins linking the depletion of endoplasmic/sarcoplasmic reticulum Ca2+ stores to the activation of membrane Ca2+ -permeable ORAI channels. Gain-of-function mutations in STIM1 or ORAI1 isoforms cause tubular aggregate myopathy (TAM), a skeletal muscle disorder with muscular pain, weakness and cramping. Here, we characterize two overactive ORAI1 mutants from patients with TAM: V107M and T184M, located in the first and third transmembrane domain of the channel. When ectopically expressed in HEK-293T cells or human primary myoblasts, the mutated channels increased basal and store-operated Ca2+ entry. The constitutive activity of V107M, L138F, T184M and P245L mutants was prevented by low concentrations of GSK-7975A while the G98S mutant was resistant to inhibition. Electrophysiological recordings confirmed ORAI1-V107M constitutive activity and revealed larger STIM1-gated V107M- and T184M-mediated currents with conserved fast and slow Ca2+ -dependent inactivation. Mutation V107M altered the channel selectivity for Ca2+ ions and conferred resistance to acidic inhibition. Ca2+ imaging and molecular dynamics simulations showed a preserved sensitivity of T184M to the negative regulation by reactive oxygen species. Both mutants were able to mediate SOCE in Stim1-/- /Stim2-/- mouse embryonic fibroblasts expressing the binding-deficient STIM1-F394H mutant, indicating a higher sensitivity for STIM1-mediated gating, with ORAI1-T184M gain-of-function being strictly dependent on STIM1. These findings provide new insights into the permeation and regulatory properties of ORAI1 mutants that might translate into therapies against diseases with gain-of-function mutations in ORAI1.
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Affiliation(s)
- M Bulla
- Department of Cell Physiology and Metabolism, University of Geneva, Geneva, Switzerland
| | - G Gyimesi
- Institute of Biochemistry and Molecular Medicine, University of Bern, Bern, Switzerland
| | - J H Kim
- Departments of Physiology and Global Medical Science, Yonsei University Wonju College of Medicine, Wonju, Republic of Korea.,Mitohormesis Research Center, Yonsei University Wonju College of Medicine, Wonju, Republic of Korea
| | - R Bhardwaj
- Institute of Biochemistry and Molecular Medicine, University of Bern, Bern, Switzerland
| | - M A Hediger
- Institute of Biochemistry and Molecular Medicine, University of Bern, Bern, Switzerland
| | - M Frieden
- Department of Cell Physiology and Metabolism, University of Geneva, Geneva, Switzerland
| | - N Demaurex
- Department of Cell Physiology and Metabolism, University of Geneva, Geneva, Switzerland
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17
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Abstract
Yeung and Prakriya highlight new research showing that STIM1 must bind to all six Orai1 subunits to effectively activate the channel.
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Affiliation(s)
- Priscilla See-Wai Yeung
- Department of Pharmacology, Feinberg School of Medicine, Northwestern University, Chicago, IL
| | - Murali Prakriya
- Department of Pharmacology, Feinberg School of Medicine, Northwestern University, Chicago, IL
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18
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Hou X, Burstein SR, Long SB. Structures reveal opening of the store-operated calcium channel Orai. eLife 2018; 7:36758. [PMID: 30160233 PMCID: PMC6170153 DOI: 10.7554/elife.36758] [Citation(s) in RCA: 62] [Impact Index Per Article: 10.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/18/2018] [Accepted: 08/29/2018] [Indexed: 12/21/2022] Open
Abstract
The store-operated calcium (Ca2+) channel Orai governs Ca2+ influx through the plasma membrane of many non-excitable cells in metazoans. The channel opens in response to the depletion of Ca2+ stored in the endoplasmic reticulum (ER). Loss- and gain-of-function mutants of Orai cause disease. Our previous work revealed the structure of Orai with a closed pore. Here, using a gain-of-function mutation that constitutively activates the channel, we present an X-ray structure of Drosophila melanogaster Orai in an open conformation. Well-defined electron density maps reveal that the pore is dramatically dilated on its cytosolic side in comparison to the slender closed pore. Cations and anions bind in different regions of the open pore, informing mechanisms for ion permeation and Ca2+ selectivity. Opening of the pore requires the release of cytosolic latches. Together with additional X-ray structures of an unlatched-but-closed conformation, we propose a sequence for store-operated activation.
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Affiliation(s)
- Xiaowei Hou
- Structural Biology Program, Memorial Sloan Kettering Cancer Center, New York, United States
| | - Shana R Burstein
- Structural Biology Program, Memorial Sloan Kettering Cancer Center, New York, United States
| | - Stephen Barstow Long
- Structural Biology Program, Memorial Sloan Kettering Cancer Center, New York, United States
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19
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Yen M, Lewis RS. Physiological CRAC channel activation and pore properties require STIM1 binding to all six Orai1 subunits. J Gen Physiol 2018; 150:1373-1385. [PMID: 30120197 PMCID: PMC6168240 DOI: 10.1085/jgp.201711985] [Citation(s) in RCA: 26] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/22/2017] [Revised: 06/08/2018] [Accepted: 07/30/2018] [Indexed: 11/22/2022] Open
Abstract
The quantitative relation between STIM1 binding to Orai1 and store-operated CRAC channel activation is not well understood. Yen and Lewis find that STIM1 must bind to all six Orai1 subunits to effectively open the channel and generate the high ion selectivity and low conductance seen in native cells. The binding of STIM1 to Orai1 controls the opening of store-operated CRAC channels as well as their extremely high Ca2+ selectivity. Although STIM1 dimers are known to bind directly to the cytosolic C termini of the six Orai1 subunits (SUs) that form the channel hexamer, the dependence of channel activation and selectivity on the number of occupied binding sites is not well understood. Here we address these questions using dimeric and hexameric Orai1 concatemers in which L273D mutations were introduced to inhibit STIM1 binding to specific Orai1 SUs. By measuring FRET between fluorescently labeled STIM1 and Orai1, we find that homomeric L273D mutant channels fail to bind STIM1 appreciably; however, the L273D SU does bind STIM1 and contribute to channel activation when located adjacent to a WT SU. These results suggest that STIM1 dimers can interact with pairs of neighboring Orai1 SUs. Surprisingly, a single L273D mutation within the Orai1 hexamer reduces channel open probability by ∼90%, triples the size of the single-channel current, weakens the Ca2+ binding affinity of the selectivity filter, and lowers the selectivity for Na+ over Cs+ in the absence of divalent cations. These findings reveal a surprisingly strong functional coupling between STIM1 binding and CRAC channel gating and pore properties. We conclude that under physiological conditions, all six Orai1 SUs of the native CRAC channel bind STIM1 to effectively open the pore and generate the signature properties of extremely low conductance and high ion selectivity.
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Affiliation(s)
- Michelle Yen
- Department of Molecular and Cellular Physiology, Stanford University School of Medicine, Stanford, CA
| | - Richard S Lewis
- Department of Molecular and Cellular Physiology, Stanford University School of Medicine, Stanford, CA
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20
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Cai X, Nwokonko RM, Loktionova NA, Abdulqadir R, Baraniak JH, Wang Y, Trebak M, Zhou Y, Gill DL. Pore properties of Orai1 calcium channel dimers and their activation by the STIM1 ER calcium sensor. J Biol Chem 2018; 293:12962-12974. [PMID: 29954946 PMCID: PMC6102135 DOI: 10.1074/jbc.ra118.003424] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/11/2018] [Revised: 05/31/2018] [Indexed: 11/06/2022] Open
Abstract
Store-operated Ca2+ entry signals are mediated by plasma membrane Orai channels activated through intermembrane coupling with Ca2+-sensing STIM proteins in the endoplasmic reticulum (ER). The nature of this elaborate Orai-gating mechanism has remained enigmatic. Based on the Drosophila Orai structure, mammalian Orai1 channels are hexamers comprising three dimeric subunit pairs. We utilized concatenated Orai1 dimers to probe the function of key domains within the channel pore and gating regions. The Orai1-E106Q selectivity-filter mutant, widely considered a dominant pore blocker, was surprisingly nondominant within concatenated heterodimers with Orai1-WT. The Orai1-E106Q/WT heterodimer formed STIM1-activated nonselective cation channels with significantly enlarged apparent pore diameter. Other Glu-106 substitutions entirely blocked the function of heterodimers with Orai1-WT. The hydrophobic pore-lining mutation V102C, which constitutively opens channels, was suppressed by Orai1-WT in the heterodimer. In contrast, the naturally occurring R91W pore-lining mutation associated with human immunodeficiency was completely dominant-negative over Orai-WT in heterodimers. Heterodimers containing the inhibitory K85E mutation extending outward from the pore helix gave an interesting partial effect on both channel activation and STIM1 binding, indicating an important allosteric link between the cytosolic Orai1 domains. The Orai1 C-terminal STIM1-binding domain mutation L273D powerfully blocked STIM1-induced channel activation. The Orai1-L273D/WT heterodimer had drastically impaired STIM1-induced channel gating but, unexpectedly, retained full STIM1 binding. This reveals the critical role of Leu-273 in transducing the STIM1-binding signal into the allosteric conformational change that initiates channel gating. Overall, our results provide important new insights into the role of key functional domains that mediate STIM1-induced gating of the Orai1 channel.
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Affiliation(s)
- Xiangyu Cai
- Department of Cellular and Molecular Physiology, Pennsylvania State University College of Medicine, Hershey, Pennsylvania 17033
| | - Robert M Nwokonko
- Department of Cellular and Molecular Physiology, Pennsylvania State University College of Medicine, Hershey, Pennsylvania 17033
| | - Natalia A Loktionova
- Department of Cellular and Molecular Physiology, Pennsylvania State University College of Medicine, Hershey, Pennsylvania 17033
| | - Raz Abdulqadir
- Department of Cellular and Molecular Physiology, Pennsylvania State University College of Medicine, Hershey, Pennsylvania 17033
| | - James H Baraniak
- Department of Cellular and Molecular Physiology, Pennsylvania State University College of Medicine, Hershey, Pennsylvania 17033
| | - Youjun Wang
- Beijing Key Laboratory of Gene Resources and Molecular Development College of Life Sciences, Beijing Normal University, Beijing 100875, China
| | - Mohamed Trebak
- Department of Cellular and Molecular Physiology, Pennsylvania State University College of Medicine, Hershey, Pennsylvania 17033
| | - Yandong Zhou
- Department of Cellular and Molecular Physiology, Pennsylvania State University College of Medicine, Hershey, Pennsylvania 17033.
| | - Donald L Gill
- Department of Cellular and Molecular Physiology, Pennsylvania State University College of Medicine, Hershey, Pennsylvania 17033.
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21
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Mapping the functional anatomy of Orai1 transmembrane domains for CRAC channel gating. Proc Natl Acad Sci U S A 2018; 115:E5193-E5202. [PMID: 29760086 DOI: 10.1073/pnas.1718373115] [Citation(s) in RCA: 45] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
Store-operated Orai1 channels are activated through a unique inside-out mechanism involving binding of the endoplasmic reticulum Ca2+ sensor STIM1 to cytoplasmic sites on Orai1. Although atomic-level details of Orai structure, including the pore and putative ligand binding domains, are resolved, how the gating signal is communicated to the pore and opens the gate is unknown. To address this issue, we used scanning mutagenesis to identify 15 residues in transmembrane domains (TMs) 1-4 whose perturbation activates Orai1 channels independently of STIM1. Cysteine accessibility analysis and molecular-dynamics simulations indicated that constitutive activation of the most robust variant, H134S, arises from a pore conformational change that opens a hydrophobic gate to augment pore hydration, similar to gating evoked by STIM1. Mutational analysis of this locus suggests that H134 acts as steric brake to stabilize the closed state of the channel. In addition, atomic packing analysis revealed distinct functional contacts between the TM1 pore helix and the surrounding TM2/3 helices, including one set mediated by a cluster of interdigitating hydrophobic residues and another by alternative ridges of polar and hydrophobic residues. Perturbing these contacts via mutagenesis destabilizes STIM1-mediated Orai1 channel gating, indicating that these bridges between TM1 and the surrounding TM2/3 ring are critical for conveying the gating signal to the pore. These findings help develop a framework for understanding the global conformational changes and allosteric interactions between topologically distinct domains that are essential for activation of Orai1 channels.
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22
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Distinct gating mechanism of SOC channel involving STIM-Orai coupling and an intramolecular interaction of Orai in Caenorhabditis elegans. Proc Natl Acad Sci U S A 2018; 115:E4623-E4632. [PMID: 29712850 DOI: 10.1073/pnas.1714986115] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Store-operated calcium entry (SOCE), an important mechanism of Ca2+ signaling in a wide range of cell types, is mediated by stromal interaction molecule (STIM), which senses the depletion of endoplasmic reticulum Ca2+ stores and binds and activates Orai channels in the plasma membrane. This inside-out mechanism of Ca2+ signaling raises an interesting question about the evolution of SOCE: How did these two proteins existing in different cellular compartments evolve to interact with each other? We investigated the gating mechanism of Caenorhabditis elegans Orai channels. Our analysis revealed a mechanism of Orai gating by STIM binding to the intracellular 2-3 loop of Orai in C. elegans that is radically different from Orai gating by STIM binding to the N and C termini of Orai in mammals. In addition, we found that the conserved hydrophobic amino acids in the 2-3 loop of Orai1 are important for the oligomerization and gating of channels and are regulated via an intramolecular interaction mechanism mediated by the N and C termini of Orai1. This study identifies a previously unknown SOCE mechanism in C. elegans and suggests that, while the STIM-Orai interaction is conserved between invertebrates and mammals, the gating mechanism for Orai channels differs considerably.
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23
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Palty R, Fu Z, Isacoff EY. Sequential Steps of CRAC Channel Activation. Cell Rep 2018; 19:1929-1939. [PMID: 28564609 DOI: 10.1016/j.celrep.2017.05.025] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/08/2016] [Revised: 03/27/2017] [Accepted: 05/05/2017] [Indexed: 10/19/2022] Open
Abstract
Interaction between the endoplasmic reticulum protein STIM1 and the plasma membrane channel ORAI1 generates calcium signals that are central for diverse cellular functions. How STIM1 binds and activates ORAI1 remains poorly understood. Using electrophysiological, optical, and biochemical techniques, we examined the effects of mutations in the STIM1-ORAI1 activating region (SOAR) of STIM1. We find that SOAR mutants that are deficient in binding to resting ORAI1 channels are able to bind to and boost activation of partially activated ORAI1 channels. We further show that the STIM1 binding regions on ORAI1 undergo structural rearrangement during channel activation. The results suggest that activation of ORAI1 by SOAR occurs in multiple steps. In the first step, SOAR binds to ORAI1, partially activates the channel, and induces a rearrangement in the SOAR-binding site of ORAI1. That rearrangement of ORAI1 then permits sequential steps of SOAR binding, via distinct molecular interactions, to fully activate the channel.
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Affiliation(s)
- Raz Palty
- Department of Biochemistry, Ruth and Bruce Rappaport Faculty of Medicine, Technion - Israel Institute of Technology, Haifa 31096, Israel.
| | - Zhu Fu
- Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, CA 94720, USA
| | - Ehud Y Isacoff
- Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, CA 94720, USA; Helen Wills Neuroscience Institute, University of California, Berkeley, Berkeley, CA 94720, USA; Bioscience Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA.
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24
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Zhu J, Feng Q, Stathopulos PB. The STIM-Orai Pathway: STIM-Orai Structures: Isolated and in Complex. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2017; 993:15-38. [PMID: 28900907 DOI: 10.1007/978-3-319-57732-6_2] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/27/2023]
Abstract
Considerable progress has been made elucidating the molecular mechanisms of calcium (Ca2+) sensing by stromal interaction molecules (STIMs) and the basis for Orai channel activity. This chapter focuses on the available high-resolution structural details of STIM and Orai proteins with respect to the regulation of store-operated Ca2+ entry (SOCE). Solution structures of the Ca2+-sensing domains of STIM1 and STIM2 are reviewed in detail, crystal structures of cytosolic coiled-coil STIM fragments are discussed, and an overview of the closed Drosophila melanogaster Orai hexameric structure is provided. Additionally, we highlight structures of human Orai1 N-terminal and C-terminal domains in complex with calmodulin and human STIM1, respectively. Ultimately, the accessible structural data are discussed in terms of potential mechanisms of action and cohesiveness with functional observations.
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Affiliation(s)
- Jinhui Zhu
- Department of Physiology and Pharmacology, Schulich School of Medicine and Dentistry, Western University, London, ON, Canada, N6A 5C1
| | - Qingping Feng
- Department of Physiology and Pharmacology, Schulich School of Medicine and Dentistry, Western University, London, ON, Canada, N6A 5C1
| | - Peter B Stathopulos
- Department of Physiology and Pharmacology, Schulich School of Medicine and Dentistry, Western University, London, ON, Canada, N6A 5C1.
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25
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Stathopulos PB, Ikura M. Store operated calcium entry: From concept to structural mechanisms. Cell Calcium 2017; 63:3-7. [DOI: 10.1016/j.ceca.2016.11.005] [Citation(s) in RCA: 35] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/03/2016] [Revised: 11/24/2016] [Accepted: 11/24/2016] [Indexed: 11/16/2022]
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26
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Zhou Y, Cai X, Nwokonko RM, Loktionova NA, Wang Y, Gill DL. The STIM-Orai coupling interface and gating of the Orai1 channel. Cell Calcium 2017; 63:8-13. [PMID: 28087079 PMCID: PMC5466457 DOI: 10.1016/j.ceca.2017.01.001] [Citation(s) in RCA: 43] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/16/2016] [Revised: 01/05/2017] [Accepted: 01/05/2017] [Indexed: 10/25/2022]
Abstract
In virtually all cells, store-operated Ca2+ entry signals are vital in controlling a spectrum of functions. The signals are mediated by STIM proteins in the ER and Orai channels in the PM which undergo a dynamic coupling process within discrete ER-PM junctional regions. This coupling is initiated by depletion of ER stored Ca2+ triggering STIM proteins to undergo an intricate activation process. Thereafter, STIM proteins become trapped in the ER-PM junctions where they tether and gate PM Orai Ca2+ channels. STIM1 exists as a dimer, with a single STIM-Orai activating region (SOAR) buried in the resting protein that becomes exposed upon activation. An exposed region on SOAR including the Phe-394 residue forms a critical Orai1 interacting site. Using dimeric SOAR concatemers, we reveal only one of the two sites in the SOAR dimer is needed for Orai1 activation. This unimolecular interaction of SOAR with Orai1 suggests STIM1 can cross-link Orai channels with important significance for Ca2+ signaling. A critical "nexus" region in Orai1 close to the STIM1-binding site can be mutated to constitutively activate the channel mimicking the gating action of STIM1. This indicates STIM1 remotely controls Orai1 channel gating through an allosteric switch triggered by STIM1 binding only to the exposed C-terminal tail of the Orai1 channel.
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Affiliation(s)
- Yandong Zhou
- Department of Cellular and Molecular Physiology, The Pennsylvania State University College of Medicine, Hershey, PA 17033, USA.
| | - Xiangyu Cai
- Department of Cellular and Molecular Physiology, The Pennsylvania State University College of Medicine, Hershey, PA 17033, USA
| | - Robert M Nwokonko
- Department of Cellular and Molecular Physiology, The Pennsylvania State University College of Medicine, Hershey, PA 17033, USA
| | - Natalia A Loktionova
- Department of Cellular and Molecular Physiology, The Pennsylvania State University College of Medicine, Hershey, PA 17033, USA
| | - Youjun Wang
- Beijing Key Laboratory of Gene Resources and Molecular Development, College of Life Sciences, Beijing Normal University, Beijing 100875, PR China
| | - Donald L Gill
- Department of Cellular and Molecular Physiology, The Pennsylvania State University College of Medicine, Hershey, PA 17033, USA.
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27
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Fahrner M, Schindl R, Muik M, Derler I, Romanin C. The STIM-Orai Pathway: The Interactions Between STIM and Orai. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2017; 993:59-81. [PMID: 28900909 DOI: 10.1007/978-3-319-57732-6_4] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
A primary Ca2+ entry pathway in non-excitable cells is established by the Ca2+ release-activated Ca2+ channels. Their two limiting molecular components include the Ca2+-sensor protein STIM1 located in the endoplasmic reticulum and the Orai channel in the plasma membrane. STIM1 senses the luminal Ca2+ content, and store depletion induces its oligomerization into puncta-like structures, thereby triggering coupling to as well as activation of Orai channels. A C-terminal STIM1 domain is assumed to couple to both C- and N-terminal, cytosolic strands of Orai, accomplishing gating of the channel. Here we highlight the inter- and intramolecular steps of the STIM1-Orai signaling cascade together with critical sites of the pore structure that accomplishes Ca2+ permeation.
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Affiliation(s)
- Marc Fahrner
- Institute of Biophysics, Johannes Kepler University Linz, 4020, Linz, Austria.
| | - Rainer Schindl
- Institute of Biophysics, Johannes Kepler University Linz, 4020, Linz, Austria
| | - Martin Muik
- Institute of Biophysics, Johannes Kepler University Linz, 4020, Linz, Austria
| | - Isabella Derler
- Institute of Biophysics, Johannes Kepler University Linz, 4020, Linz, Austria
| | - Christoph Romanin
- Institute of Biophysics, Johannes Kepler University Linz, 4020, Linz, Austria.
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The STIM-Orai Pathway: Conformational Coupling Between STIM and Orai in the Activation of Store-Operated Ca 2+ Entry. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2017; 993:83-98. [PMID: 28900910 DOI: 10.1007/978-3-319-57732-6_5] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
Store-operated Ca2+ entry fulfills a crucial role in controlling Ca2+ signals in almost all cells. The Ca2+-sensing stromal interaction molecule (STIM) proteins in the endoplasmic reticulum (ER) undergo complex conformational changes in response to depleted ER luminal Ca2+, allowing them to unfold and become trapped in ER-plasma membrane (PM) junctions. Dimers of STIM proteins trap and gate the plasma membrane Orai Ca2+ channels within these junctions to generate discrete zones of high Ca2+ and regulate sensitive Ca2+-dependent intracellular signaling pathways. The STIM-Orai activating region (SOAR) of STIM1 becomes exposed upon store depletion and promotes trapping of Orai1 at the PM. Residue Phe-394 within SOAR forms an integral part of the high-affinity Orai1-interacting site. Our results demonstrate that only a single active site within the dimeric SOAR domain of STIM1 is required for the activation of Orai1 channel activity. This unimolecular model is strongly supported by evidence of variable STIM1:Orai1 stoichiometry reported in many studies. We hypothesize that unimolecular coupling promotes cross-linking of channels, localizing Ca2+ signals, and regulating channel activity. We have also identified a key "nexus" region in Orai1 near the C-terminal STIM1-binding site that can be mutated to constitutively activate Ca2+ entry, mimicking STIM1 activated channels. This suggests that STIM1 mediates gating of Orai1 in an allosteric manner via interaction with the Orai1 C-terminus alone. This model suggests the dual role of STIM1 in regulating both localization and gating of Orai1 channels and has important implications for the regulation of SOCE-mediated downstream signaling and the kinetics of channel activation.
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Gudlur A, Hogan PG. The STIM-Orai Pathway: Orai, the Pore-Forming Subunit of the CRAC Channel. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2017; 993:39-57. [PMID: 28900908 DOI: 10.1007/978-3-319-57732-6_3] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
This chapter focuses on the Orai proteins, Orai1-Orai3, with special emphasis on Orai1, in humans and other mammals, and on the definitive evidence that Orai is the pore subunit of the CRAC channel. It begins by reviewing briefly the defining characteristics of the CRAC channel, then discusses the studies that implicated Orai as part of the store-operated Ca2+ entry pathway and as the CRAC channel pore subunit, and finally examines ongoing work that is providing insights into CRAC channel structure and gating.
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Affiliation(s)
- Aparna Gudlur
- Division of Signalling and Gene Expression, La Jolla Institute for Allergy and Immunology, 9420 Athena Circle, La Jolla, CA, USA.
| | - Patrick G Hogan
- Division of Signalling and Gene Expression, La Jolla Institute for Allergy and Immunology, 9420 Athena Circle, La Jolla, CA, USA.
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The STIM1-binding site nexus remotely controls Orai1 channel gating. Nat Commun 2016; 7:13725. [PMID: 27929067 PMCID: PMC5155162 DOI: 10.1038/ncomms13725] [Citation(s) in RCA: 63] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/11/2016] [Accepted: 10/26/2016] [Indexed: 01/17/2023] Open
Abstract
The ubiquitously expressed Orai Ca2+ channels are gated through a unique process of intermembrane coupling with the Ca2+-sensing STIM proteins. Despite the significance of Orai1-mediated Ca2+ signals, how gating of Orai1 is triggered by STIM1 remains unknown. A widely held gating model invokes STIM1 binding directly to Orai1 pore-forming helix. Here we report that an Orai1 C-terminal STIM1-binding site, situated far from the N-terminal pore helix, alone provides the trigger that is necessary and sufficient for channel gating. We identify a critical ‘nexus' within Orai1 connecting the peripheral C-terminal STIM1-binding site to the Orai1 core helices. Mutation of the nexus transforms Orai1 into a persistently open state exactly mimicking the action of STIM1. We suggest that the Orai1 nexus transduces the STIM1-binding signal through a conformational change in the inner core helices, and that STIM1 remotely gates the Orai1 channel without the necessity for direct STIM1 contact with the pore-forming helix.
How plasma membrane Orai Ca2+ channels are activated by STIM proteins to activate Ca2+ signals is still not fully known. Here the authors show that a nexus region located at the Orai1 C-terminus allows channel gating without a direct interaction of STIM1 with the channel pore.
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Ali S, Xu T, Xu X. CRAC channel gating and its modulation by STIM1 and 2-aminoethoxydiphenyl borate. J Physiol 2016; 595:3085-3095. [PMID: 27753099 DOI: 10.1113/jp273130] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/08/2016] [Accepted: 10/27/2016] [Indexed: 11/08/2022] Open
Abstract
Ca2+ release-activated Ca2+ (CRAC) channels play an essential role in the immune system. The pore-forming subunit, Orai1, is an important pharmacological target. Here, we summarize the recent discoveries on the structure-function relationship of Orai1, as well as its interaction with the native channel opener STIM1 and chemical modulator 2-aminoethoxydiphenyl borate (2-APB). We first introduce the critical structural elements of Orai1, which include a Ca2+ accumulating region, ion selectivity filter, hydrophobic centre, basic region, extended transmembrane Orai1 N-terminal (ETON) region, transmembrane (TM) regions 2 and 3, P245 bend, 263 SHK265 hinge linker and L273-L276 hydrophobic patch. We then hypothesize the possible mechanisms by which STIM1 triggers the conformational transitions of TM regions and exquisitely shapes the ion conduction pathway during generation of the CRAC current (Icrac ) with high Ca2+ selectivity. Finally, we propose mechanisms by which 2-APB modulates Icrac . On the STIM1-activated Orai1 channel, a low dose of 2-APB acts directly, dilating its extremely narrow pore diameter from 3.8 to 4.6 Å, increasing its unitary channel conductance, and potentiating the Icrac . Further elucidation of the structure of the opened CRAC channel and a better understanding of structure-function relationship will benefit the future development of novel immune modulators.
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Affiliation(s)
- Sher Ali
- National Key Laboratory of Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing, 100101, China.,University of Chinese Academy of Science, Beijing, 100049, China
| | - Tao Xu
- National Key Laboratory of Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing, 100101, China
| | - Xiaolan Xu
- National Key Laboratory of Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing, 100101, China
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Cai X, Zhou Y, Nwokonko RM, Loktionova NA, Wang X, Xin P, Trebak M, Wang Y, Gill DL. The Orai1 Store-operated Calcium Channel Functions as a Hexamer. J Biol Chem 2016; 291:25764-25775. [PMID: 27780862 DOI: 10.1074/jbc.m116.758813] [Citation(s) in RCA: 86] [Impact Index Per Article: 10.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/14/2016] [Revised: 10/17/2016] [Indexed: 12/17/2022] Open
Abstract
Orai channels mediate store-operated Ca2+ signals crucial in regulating transcription in many cell types, and implicated in numerous immunological and inflammatory disorders. Despite their central importance, controversy surrounds the basic subunit structure of Orai channels, with several biochemical and biophysical studies suggesting a tetrameric structure yet crystallographic evidence indicating a hexamer. We systematically investigated the subunit configuration of the functional Orai1 channel, generating a series of tdTomato-tagged concatenated Orai1 channel constructs (dimers to hexamers) expressed in CRISPR-derived ORAI1 knock-out HEK cells, stably expressing STIM1-YFP. Surface biotinylation demonstrated that the full-length concatemers were surface membrane-expressed. Unexpectedly, Orai1 dimers, trimers, tetramers, pentamers, and hexamers all mediated similar and substantial store-operated Ca2+ entry. Moreover, each Orai1 concatemer mediated Ca2+ currents with inward rectification and reversal potentials almost identical to those observed with expressed Orai1 monomer. In Orai1 tetramers, subunit-specific replacement with Orai1 E106A "pore-inactive" subunits revealed that functional channels utilize only the N-terminal dimer from the tetramer. In contrast, Orai1 E106A replacement in Orai1 hexamers established that all the subunits can contribute to channel formation, indicating a hexameric channel configuration. The critical Ca2+ selectivity filter-forming Glu-106 residue may mediate Orai1 channel assembly around a central Ca2+ ion within the pore. Thus, multiple E106A substitutions in the Orai1 hexamer may promote an alternative "trimer-of-dimers" channel configuration in which the C-terminal E106A subunits are excluded from the hexameric core. Our results argue strongly against a tetrameric configuration for Orai1 channels and indicate that the Orai1 channel functions as a hexamer.
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Affiliation(s)
- Xiangyu Cai
- From the Department of Cellular and Molecular Physiology, the Pennsylvania State University College of Medicine, Hershey, Pennsylvania 17033 and
| | - Yandong Zhou
- From the Department of Cellular and Molecular Physiology, the Pennsylvania State University College of Medicine, Hershey, Pennsylvania 17033 and
| | - Robert M Nwokonko
- From the Department of Cellular and Molecular Physiology, the Pennsylvania State University College of Medicine, Hershey, Pennsylvania 17033 and
| | - Natalia A Loktionova
- From the Department of Cellular and Molecular Physiology, the Pennsylvania State University College of Medicine, Hershey, Pennsylvania 17033 and
| | - Xianming Wang
- From the Department of Cellular and Molecular Physiology, the Pennsylvania State University College of Medicine, Hershey, Pennsylvania 17033 and
| | - Ping Xin
- From the Department of Cellular and Molecular Physiology, the Pennsylvania State University College of Medicine, Hershey, Pennsylvania 17033 and
| | - Mohamed Trebak
- From the Department of Cellular and Molecular Physiology, the Pennsylvania State University College of Medicine, Hershey, Pennsylvania 17033 and
| | - Youjun Wang
- the Beijing Key Laboratory of Gene Resources and Molecular Development, College of Life Sciences, Beijing Normal University, Beijing 100875, China
| | - Donald L Gill
- From the Department of Cellular and Molecular Physiology, the Pennsylvania State University College of Medicine, Hershey, Pennsylvania 17033 and
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33
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Alansary D, Schmidt B, Dörr K, Bogeski I, Rieger H, Kless A, Niemeyer BA. Thiol dependent intramolecular locking of Orai1 channels. Sci Rep 2016; 6:33347. [PMID: 27624281 PMCID: PMC5022029 DOI: 10.1038/srep33347] [Citation(s) in RCA: 28] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/11/2016] [Accepted: 08/25/2016] [Indexed: 12/11/2022] Open
Abstract
Store-operated Ca(2+) entry mediated by STIM1-gated Orai1 channels is essential to activate immune cells and its inhibition or gain-of-function can lead to immune dysfunction and other pathologies. Reactive oxygen species interacting with cysteine residues can alter protein function. Pretreatment of the Ca(2+) selective Orai1 with the oxidant H2O2 reduces ICRAC with C195, distant to the pore, being its major redox sensor. However, the mechanism of inhibition remained elusive. Here we combine experimental and theoretical approaches and show that oxidation of Orai1 leads to reduced subunit interaction, slows diffusion and that either oxidized C195 or its oxidomimetic mutation C195D located at the exit of transmembrane helix 3 virtually eliminates channel activation by intramolecular interaction with S239 of transmembrane helix 4, thereby locking the channel in a closed conformation. Our results demonstrate a novel mechanistic model for ROS-mediated inhibition of Orai1 and identify a candidate residue for pharmaceutical intervention.
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Affiliation(s)
- Dalia Alansary
- Molecular Biophysics, Saarland University, 66421 Homburg, Germany
| | - Barbara Schmidt
- Molecular Biophysics, Saarland University, 66421 Homburg, Germany
- Department of Biophysics, Saarland University, 66421 Homburg, Germany
- Department of Theoretical Physics, Saarland University, 66041 Saarbrücken, Germany
| | - Kathrin Dörr
- Molecular Biophysics, Saarland University, 66421 Homburg, Germany
| | - Ivan Bogeski
- Department of Biophysics, Saarland University, 66421 Homburg, Germany
| | - Heiko Rieger
- Department of Theoretical Physics, Saarland University, 66041 Saarbrücken, Germany
| | - Achim Kless
- Gruenenthal Innovation, Drug Discovery Technologies, Gruenenthal GmbH, 52078 Aachen, Germany
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Abstract
Ca2+ entry into the cell via store-operated Ca2+ release-activated Ca2+ (CRAC) channels triggers diverse signaling cascades that affect cellular processes like cell growth, gene regulation, secretion, and cell death. These store-operated Ca2+ channels open after depletion of intracellular Ca2+ stores, and their main features are fully reconstituted by the two molecular key players: the stromal interaction molecule (STIM) and Orai. STIM represents an endoplasmic reticulum-located Ca2+ sensor, while Orai forms a highly Ca2+-selective ion channel in the plasma membrane. Functional as well as mutagenesis studies together with structural insights about STIM and Orai proteins provide a molecular picture of the interplay of these two key players in the CRAC signaling cascade. This review focuses on the main experimental advances in the understanding of the STIM1-Orai choreography, thereby establishing a portrait of key mechanistic steps in the CRAC channel signaling cascade. The focus is on the activation of the STIM proteins, the subsequent coupling of STIM1 to Orai1, and the consequent structural rearrangements that gate the Orai channels into the open state to allow Ca2+ permeation into the cell.
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Affiliation(s)
- Isabella Derler
- Institute of Biophysics, Johannes Kepler University of Linz, Linz, Austria; and
| | - Isaac Jardin
- Department of Physiology, University of Extremadura, Cáceres, Spain
| | - Christoph Romanin
- Institute of Biophysics, Johannes Kepler University of Linz, Linz, Austria; and
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35
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Shin DM, Son A, Park S, Kim MS, Ahuja M, Muallem S. The TRPCs, Orais and STIMs in ER/PM Junctions. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2016; 898:47-66. [PMID: 27161224 DOI: 10.1007/978-3-319-26974-0_3] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
The Ca(2+) second messenger is initiated at ER/PM junctions and propagates into the cell interior to convey the receptor information. The signal is maintained by Ca(2+) influx across the plasma membrane through the Orai and TRPC channels. These Ca(2+) influx channels form complexes at ER/PM junctions with the ER Ca(2+) sensor STIM1, which activates the channels. The function of STIM1 is modulated by other STIM isoforms like STIM1L, STIM2 and STIM2.1/STIM2β and by SARAF, which mediates the Ca(2+)-dependent inhibition of Orai channels. The ER/PM junctions are formed at membrane contact sites by tethering proteins that generate several types of ER/PM junctions, such as PI(4,5)P2-poor and PI(4,5)P2-rich domains. This chapter discusses several properties of the TRPC channels, the Orai channels and the STIMs, their key interacting proteins and how interaction of the STIMs with the channels gates their activity. The chapter closes by highlighting open questions and potential future directions in this field.
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Affiliation(s)
- Dong Min Shin
- Department of Oral Biology, BK 21 PLUS Project, Yonsei University College of Dentistry, Seoul, 120-752, South Korea.
| | - Aran Son
- Epithelial Signaling and Transport Section, Molecular Physiology and Therapeutics Branch, National Institute of Dental and Craniofacial Research, National Institute of Health, Bethesda, MD, 20892, USA
| | - Seonghee Park
- Department of Physiology, School of Medicine, EwhaWomans University, 911-1 Mok-6-dong, Yang Chun-gu, Seoul, 158-710, South Korea
| | - Min Seuk Kim
- Department of Oral Physiology, School of Dentistry, Wonkwang University, Iksan City, Jeonbuk, South Korea
| | - Malini Ahuja
- Epithelial Signaling and Transport Section, Molecular Physiology and Therapeutics Branch, National Institute of Dental and Craniofacial Research, National Institute of Health, Bethesda, MD, 20892, USA
| | - Shmuel Muallem
- Epithelial Signaling and Transport Section, Molecular Physiology and Therapeutics Branch, National Institute of Dental and Craniofacial Research, National Institute of Health, Bethesda, MD, 20892, USA.
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Abstract
Store-operated calcium channels (SOCs) are a major pathway for calcium signaling in virtually all metozoan cells and serve a wide variety of functions ranging from gene expression, motility, and secretion to tissue and organ development and the immune response. SOCs are activated by the depletion of Ca(2+) from the endoplasmic reticulum (ER), triggered physiologically through stimulation of a diverse set of surface receptors. Over 15 years after the first characterization of SOCs through electrophysiology, the identification of the STIM proteins as ER Ca(2+) sensors and the Orai proteins as store-operated channels has enabled rapid progress in understanding the unique mechanism of store-operate calcium entry (SOCE). Depletion of Ca(2+) from the ER causes STIM to accumulate at ER-plasma membrane (PM) junctions where it traps and activates Orai channels diffusing in the closely apposed PM. Mutagenesis studies combined with recent structural insights about STIM and Orai proteins are now beginning to reveal the molecular underpinnings of these choreographic events. This review describes the major experimental advances underlying our current understanding of how ER Ca(2+) depletion is coupled to the activation of SOCs. Particular emphasis is placed on the molecular mechanisms of STIM and Orai activation, Orai channel properties, modulation of STIM and Orai function, pharmacological inhibitors of SOCE, and the functions of STIM and Orai in physiology and disease.
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Affiliation(s)
- Murali Prakriya
- Department of Pharmacology, Feinberg School of Medicine, Northwestern University, Chicago, Illinois; and Department of Molecular and Cellular Physiology, Stanford University School of Medicine, Stanford, California
| | - Richard S Lewis
- Department of Pharmacology, Feinberg School of Medicine, Northwestern University, Chicago, Illinois; and Department of Molecular and Cellular Physiology, Stanford University School of Medicine, Stanford, California
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