1
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Norman K, Hemmings KE, Shawer H, Appleby HL, Burnett AJ, Hamzah N, Gosain R, Woodhouse EM, Beech DJ, Foster R, Bailey MA. Side-by-side comparison of published small molecule inhibitors against thapsigargin-induced store-operated Ca2+ entry in HEK293 cells. PLoS One 2024; 19:e0296065. [PMID: 38261554 PMCID: PMC10805320 DOI: 10.1371/journal.pone.0296065] [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: 05/12/2023] [Accepted: 12/05/2023] [Indexed: 01/25/2024] Open
Abstract
Calcium (Ca2+) is a key second messenger in eukaryotes, with store-operated Ca2+ entry (SOCE) being the main source of Ca2+ influx into non-excitable cells. ORAI1 is a highly Ca2+-selective plasma membrane channel that encodes SOCE. It is ubiquitously expressed in mammals and has been implicated in numerous diseases, including cardiovascular disease and cancer. A number of small molecules have been identified as inhibitors of SOCE with a variety of potential therapeutic uses proposed and validated in vitro and in vivo. These encompass both nonselective Ca2+ channel inhibitors and targeted selective inhibitors of SOCE. Inhibition of SOCE can be quantified both directly and indirectly with a variety of assay setups, making an accurate comparison of the activity of different SOCE inhibitors challenging. We have used a fluorescence based Ca2+ addback assay in native HEK293 cells to generate dose-response data for many published SOCE inhibitors. We were able to directly compare potency. Most compounds were validated with only minor and expected variations in potency, but some were not. This could be due to differences in assay setup relating to the mechanism of action of the inhibitors and highlights the value of a singular approach to compare these compounds, as well as the general need for biorthogonal validation of novel bioactive compounds. The compounds observed to be the most potent against SOCE in our study were: 7-azaindole 14d (12), JPIII (17), Synta-66 (6), Pyr 3 (5), GSK5503A (8), CM4620 (14) and RO2959 (7). These represent the most promising candidates for future development of SOCE inhibitors for therapeutic use.
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Affiliation(s)
- Katherine Norman
- School of Chemistry, University of Leeds, Leeds, West Yorkshire, United Kingdom
- Discovery and Translational Science Department, Leeds Institute of Cardiovascular and Metabolic Medicine, School of Medicine, University of Leeds, Leeds, West Yorkshire, United Kingdom
| | - Karen E. Hemmings
- Discovery and Translational Science Department, Leeds Institute of Cardiovascular and Metabolic Medicine, School of Medicine, University of Leeds, Leeds, West Yorkshire, United Kingdom
| | - Heba Shawer
- Discovery and Translational Science Department, Leeds Institute of Cardiovascular and Metabolic Medicine, School of Medicine, University of Leeds, Leeds, West Yorkshire, United Kingdom
| | - Hollie L. Appleby
- Discovery and Translational Science Department, Leeds Institute of Cardiovascular and Metabolic Medicine, School of Medicine, University of Leeds, Leeds, West Yorkshire, United Kingdom
| | - Alan J. Burnett
- Discovery and Translational Science Department, Leeds Institute of Cardiovascular and Metabolic Medicine, School of Medicine, University of Leeds, Leeds, West Yorkshire, United Kingdom
| | - Nurasyikin Hamzah
- School of Chemistry, University of Leeds, Leeds, West Yorkshire, United Kingdom
| | - Rajendra Gosain
- Discovery and Translational Science Department, Leeds Institute of Cardiovascular and Metabolic Medicine, School of Medicine, University of Leeds, Leeds, West Yorkshire, United Kingdom
| | - Emily M. Woodhouse
- Discovery and Translational Science Department, Leeds Institute of Cardiovascular and Metabolic Medicine, School of Medicine, University of Leeds, Leeds, West Yorkshire, United Kingdom
| | - David J. Beech
- Discovery and Translational Science Department, Leeds Institute of Cardiovascular and Metabolic Medicine, School of Medicine, University of Leeds, Leeds, West Yorkshire, United Kingdom
| | - Richard Foster
- School of Chemistry, University of Leeds, Leeds, West Yorkshire, United Kingdom
- Discovery and Translational Science Department, Leeds Institute of Cardiovascular and Metabolic Medicine, School of Medicine, University of Leeds, Leeds, West Yorkshire, United Kingdom
| | - Marc A. Bailey
- Discovery and Translational Science Department, Leeds Institute of Cardiovascular and Metabolic Medicine, School of Medicine, University of Leeds, Leeds, West Yorkshire, United Kingdom
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2
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Zhang T, Liu Q, Li Z, Tang S, An Q, Fan D, Xiang Y, Wu X, Jin Z, Ding J, Hu Y, Du Q, Xu J, Xie R. The role of ion channels in immune-related diseases. PROGRESS IN BIOPHYSICS AND MOLECULAR BIOLOGY 2023; 177:129-140. [PMID: 36417963 DOI: 10.1016/j.pbiomolbio.2022.11.003] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/07/2022] [Revised: 10/26/2022] [Accepted: 11/10/2022] [Indexed: 11/21/2022]
Abstract
Ion channel is an integral membrane protein that allows the permeation of charge ions across hydrophobic phospholipid membranes, including plasma membranes and organelle membranes (such as mitochondria, endoplasmic reticulum and vacuoles), which are widely distributed in various cells and tissues, such as cardiomyocytes, smooth muscle cells, and nerve cells. Ion channels establish membrane potential by regulating ion concentration and membrane potential. Membrane potential plays an important role in cells. Studies have shown that ion channels play a role in a number of immune-related diseases caused by functional defects in ion channels on immune or non-immune cells in major human organs, usually affecting specific organs or multiple organs. The present review discusses the relationship between ion channels and immune diseases in major organs of the human body.
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Affiliation(s)
- Ting Zhang
- Department of Gastroenterology, Digestive Disease Hospital, Affiliated Hospital of Zunyi Medical University, Zunyi, China
| | - Qi Liu
- Department of Gastroenterology, Digestive Disease Hospital, Affiliated Hospital of Zunyi Medical University, Zunyi, China
| | - Zhuo Li
- Department of Gastroenterology, Digestive Disease Hospital, Affiliated Hospital of Zunyi Medical University, Zunyi, China
| | - Siqi Tang
- Department of Gastroenterology, Digestive Disease Hospital, Affiliated Hospital of Zunyi Medical University, Zunyi, China
| | - Qimin An
- Department of Gastroenterology, Digestive Disease Hospital, Affiliated Hospital of Zunyi Medical University, Zunyi, China
| | - Dongdong Fan
- Department of Gastroenterology, Digestive Disease Hospital, Affiliated Hospital of Zunyi Medical University, Zunyi, China
| | - Yiwei Xiang
- Department of Gastroenterology, Digestive Disease Hospital, Affiliated Hospital of Zunyi Medical University, Zunyi, China
| | - Xianli Wu
- Department of Gastroenterology, Digestive Disease Hospital, Affiliated Hospital of Zunyi Medical University, Zunyi, China
| | - Zhe Jin
- Department of Gastroenterology, Digestive Disease Hospital, Affiliated Hospital of Zunyi Medical University, Zunyi, China
| | - Jianhong Ding
- Department of Gastroenterology, Digestive Disease Hospital, Affiliated Hospital of Zunyi Medical University, Zunyi, China
| | - Yanxia Hu
- Department of Gastroenterology, Digestive Disease Hospital, Affiliated Hospital of Zunyi Medical University, Zunyi, China
| | - Qian Du
- Department of Gastroenterology, Digestive Disease Hospital, Affiliated Hospital of Zunyi Medical University, Zunyi, China
| | - Jingyu Xu
- Department of Gastroenterology, Digestive Disease Hospital, Affiliated Hospital of Zunyi Medical University, Zunyi, China.
| | - Rui Xie
- Department of Gastroenterology, Digestive Disease Hospital, Affiliated Hospital of Zunyi Medical University, Zunyi, China.
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3
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Maltan L, Andova AM, Derler I. The Role of Lipids in CRAC Channel Function. Biomolecules 2022; 12:biom12030352. [PMID: 35327543 PMCID: PMC8944985 DOI: 10.3390/biom12030352] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/27/2022] [Revised: 02/12/2022] [Accepted: 02/20/2022] [Indexed: 11/28/2022] Open
Abstract
The composition and dynamics of the lipid membrane define the physical properties of the bilayer and consequently affect the function of the incorporated membrane transporters, which also applies for the prominent Ca2+ release-activated Ca2+ ion channel (CRAC). This channel is activated by receptor-induced Ca2+ store depletion of the endoplasmic reticulum (ER) and consists of two transmembrane proteins, STIM1 and Orai1. STIM1 is anchored in the ER membrane and senses changes in the ER luminal Ca2+ concentration. Orai1 is the Ca2+-selective, pore-forming CRAC channel component located in the plasma membrane (PM). Ca2+ store-depletion of the ER triggers activation of STIM1 proteins, which subsequently leads to a conformational change and oligomerization of STIM1 and its coupling to as well as activation of Orai1 channels at the ER-PM contact sites. Although STIM1 and Orai1 are sufficient for CRAC channel activation, their efficient activation and deactivation is fine-tuned by a variety of lipids and lipid- and/or ER-PM junction-dependent accessory proteins. The underlying mechanisms for lipid-mediated CRAC channel modulation as well as the still open questions, are presented in this review.
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4
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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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5
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Li Y, Yang X, Shen Y. Structural Insights into Ca 2+ Permeation through Orai Channels. Cells 2021; 10:cells10113062. [PMID: 34831285 PMCID: PMC8619096 DOI: 10.3390/cells10113062] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/20/2021] [Revised: 11/03/2021] [Accepted: 11/04/2021] [Indexed: 11/16/2022] Open
Abstract
Orai channels belong to the calcium release-activated calcium (CRAC) channel family. Orai channels are responsible for the influx of extracellular Ca2+ that is triggered by Ca2+ depletion from the endoplasmic reticulum (ER); this function is essential for many types of non-excitable cells. Extensive structural and functional studies have advanced the knowledge of the molecular mechanism by which Orai channels are activated. However, the gating mechanism that allows Ca2+ permeation through Orai channels is less well explained. Here, we reviewed and summarized the existing structural studies of Orai channels. We detailed the structural features of Orai channels, described structural comparisons of their closed and open states, and finally proposed a "push-pull" model of Ca2+ permeation.
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6
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Yu F, Agrebi N, Mackeh R, Abouhazima K, KhudaBakhsh K, Adeli M, Lo B, Hassan A, Machaca K. Novel ORAI1 Mutation Disrupts Channel Trafficking Resulting in Combined Immunodeficiency. J Clin Immunol 2021; 41:1004-1015. [PMID: 33650027 PMCID: PMC8249264 DOI: 10.1007/s10875-021-01004-8] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2020] [Accepted: 02/19/2021] [Indexed: 11/23/2022]
Abstract
Store-operated Ca2+ entry (SOCE) represents a predominant Ca2+ influx pathway in non-excitable cells. SOCE is required for immune cell activation and is mediated by the plasma membrane (PM) channel ORAI1 and the endoplasmic reticulum (ER) Ca2+ sensor STIM1. Mutations in the Orai1 or STIM1 genes abolish SOCE leading to combined immunodeficiency (CID), muscular hypotonia, and anhidrotic ectodermal dysplasia. Here, we identify a novel autosomal recessive mutation in ORAI1 in a child with CID. The patient is homozygous for p.C126R mutation in the second transmembrane domain (TM2) of ORAI1, a region with no previous loss-of-function mutations. SOCE is suppressed in the patient’s lymphocytes, which is associated with impaired T cell proliferation and cytokine production. Functional analyses demonstrate that the p.C126R mutation does not alter protein expression but disrupts ORAI1 trafficking. Orai1-C126R does not insert properly into the bilayer resulting in ER retention. Insertion of an Arg on the opposite face of TM2 (L135R) also results in defective folding and trafficking. We conclude that positive side chains within ORAI1 TM2 are not tolerated and result in misfolding, defective bilayer insertion, and channel trafficking thus abolishing SOCE and resulting in CID.
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Affiliation(s)
- Fang Yu
- Department of Physiology and Biophysics, Weill Cornell Medicine Qatar, Education City, Qatar Foundation, Doha, Qatar.,Calcium Signaling Group, Weill Cornell Medicine Qatar, Education City, Qatar Foundation, Doha, Qatar
| | - Nourhen Agrebi
- Translational Medicine Department, Sidra Medicine, Doha, Qatar
| | - Rafah Mackeh
- Translational Medicine Department, Sidra Medicine, Doha, Qatar
| | - Khaled Abouhazima
- Pediatric Gastroenterology, Sidra Medicine, Education City, Doha, Qatar
| | | | - Mehdi Adeli
- Pediatric Allergy and Immunology Department, Sidra Medicine, Education City, Doha, Qatar
| | - Bernice Lo
- Translational Medicine Department, Sidra Medicine, Doha, Qatar. .,College of Health and Life Sciences, Hamad Bin Khalifa University, Doha, Qatar.
| | - Amel Hassan
- Pediatric Allergy and Immunology Department, Sidra Medicine, Education City, Doha, Qatar.
| | - Khaled Machaca
- Department of Physiology and Biophysics, Weill Cornell Medicine Qatar, Education City, Qatar Foundation, Doha, Qatar. .,Calcium Signaling Group, Weill Cornell Medicine Qatar, Education City, Qatar Foundation, Doha, Qatar.
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7
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Tiffner A, Maltan L, Fahrner M, Sallinger M, Weiß S, Grabmayr H, Höglinger C, Derler I. Transmembrane Domain 3 (TM3) Governs Orai1 and Orai3 Pore Opening in an Isoform-Specific Manner. Front Cell Dev Biol 2021; 9:635705. [PMID: 33644073 PMCID: PMC7905104 DOI: 10.3389/fcell.2021.635705] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2020] [Accepted: 01/21/2021] [Indexed: 12/17/2022] Open
Abstract
STIM1-mediated activation of calcium selective Orai channels is fundamental for life. The three Orai channel isoforms, Orai1-3, together with their multiple ways of interplay, ensure their highly versatile role in a variety of cellular functions and tissues in both, health and disease. While all three isoforms are activated in a store-operated manner by STIM1, they differ in diverse biophysical and structural properties. In the present study, we provide profound evidence that non-conserved residues in TM3 control together with the cytosolic loop2 region the maintenance of the closed state and the configuration of an opening-permissive channel conformation of Orai1 and Orai3 in an isoform-specific manner. Indeed, analogous amino acid substitutions of these non-conserved residues led to distinct extents of gain- (GoF) or loss-of-function (LoF). Moreover, we showed that enhanced overall hydrophobicity along TM3 correlates with an increase in GoF mutant currents. Conclusively, while the overall activation mechanisms of Orai channels appear comparable, there are considerable variations in gating checkpoints crucial for pore opening. The elucidation of regions responsible for isoform-specific functional differences provides valuable targets for drug development selective for one of the three Orai homologs.
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Affiliation(s)
| | | | | | | | | | | | | | - Isabella Derler
- JKU Life Science Center, Institute of Biophysics, Johannes Kepler University Linz, Linz, Austria
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8
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Yamashita M, Ing CE, Yeung PSW, Maneshi MM, Pomès R, Prakriya M. The basic residues in the Orai1 channel inner pore promote opening of the outer hydrophobic gate. J Gen Physiol 2021; 152:132615. [PMID: 31816637 PMCID: PMC7034092 DOI: 10.1085/jgp.201912397] [Citation(s) in RCA: 19] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/13/2019] [Revised: 09/25/2019] [Accepted: 11/05/2019] [Indexed: 12/12/2022] Open
Abstract
CRAC channels contain a cluster of positively charged residues in the inner pore whose function is not understood. Here, we show that these positive charges promote pore opening by enhancing hydration of the hydrophobic gate located at the outer end of the pore. Store-operated Orai1 channels regulate a wide range of cellular functions from gene expression to cell proliferation. Previous studies have shown that gating of Orai1 channels is regulated by the outer pore residues V102 and F99, which together function as a hydrophobic gate to block ion conduction in resting channels. Opening of this gate occurs through a conformational change that moves F99 away from the permeation pathway, leading to pore hydration and ion conduction. In addition to this outer hydrophobic gate, several studies have postulated the presence of an inner gate formed by the basic residues R91, K87, and R83 in the inner pore. These positively charged residues were suggested to block ion conduction in closed channels via mechanisms involving either electrostatic repulsion or steric occlusion by a bound anion plug. However, in contrast to this model, here we find that neutralization of the basic residues dose-dependently abolishes both STIM1-mediated and STIM1-independent activation of Orai1 channels. Molecular dynamics simulations show that loss of the basic residues dehydrates the pore around the hydrophobic gate and stabilizes the pore in a closed configuration. Likewise, the severe combined immunodeficiency mutation, Orai1 R91W, closes the channel by dewetting the hydrophobic stretch of the pore and stabilizing F99 in a pore-facing configuration. Loss of STIM1-gating in R91W and in the other basic residue mutants is rescued by a V102A mutation, which restores pore hydration at the hydrophobic gate to repermit ion conduction. These results indicate that the inner pore basic residues facilitate opening of the principal outer hydrophobic gate through a long-range effect involving hydration of the outer pore.
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Affiliation(s)
- Megumi Yamashita
- Department of Pharmacology, Northwestern University, Feinberg School of Medicine, Chicago, IL
| | - Christopher E Ing
- Molecular Medicine, Hospital for Sick Children, Toronto, Canada.,Department of Biochemistry, University of Toronto, Toronto, Canada
| | - Priscilla See-Wai Yeung
- Department of Pharmacology, Northwestern University, Feinberg School of Medicine, Chicago, IL
| | - Mohammad M Maneshi
- Department of Pharmacology, Northwestern University, Feinberg School of Medicine, Chicago, IL
| | - Régis Pomès
- Molecular Medicine, Hospital for Sick Children, Toronto, Canada.,Department of Biochemistry, University of Toronto, Toronto, Canada
| | - Murali Prakriya
- Department of Pharmacology, Northwestern University, Feinberg School of Medicine, Chicago, IL
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9
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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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10
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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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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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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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13
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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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14
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Fahrner M, Pandey SK, Muik M, Traxler L, Butorac C, Stadlbauer M, Zayats V, Krizova A, Plenk P, Frischauf I, Schindl R, Gruber HJ, Hinterdorfer P, Ettrich R, Romanin C, Derler I. Communication between N terminus and loop2 tunes Orai activation. J Biol Chem 2018; 293:1271-1285. [PMID: 29237733 PMCID: PMC5787804 DOI: 10.1074/jbc.m117.812693] [Citation(s) in RCA: 42] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2017] [Revised: 12/12/2017] [Indexed: 11/22/2022] Open
Abstract
Ca2+ release-activated Ca2+ (CRAC) channels constitute the major Ca2+ entry pathway into the cell. They are fully reconstituted via intermembrane coupling of the Ca2+-selective Orai channel and the Ca2+-sensing protein STIM1. In addition to the Orai C terminus, the main coupling site for STIM1, the Orai N terminus is indispensable for Orai channel gating. Although the extended transmembrane Orai N-terminal region (Orai1 amino acids 73-91; Orai3 amino acids 48-65) is fully conserved in the Orai1 and Orai3 isoforms, Orai3 tolerates larger N-terminal truncations than Orai1 in retaining store-operated activation. In an attempt to uncover the reason for these isoform-specific structural requirements, we analyzed a series of Orai mutants and chimeras. We discovered that it was not the N termini, but the loop2 regions connecting TM2 and TM3 of Orai1 and Orai3 that featured distinct properties, which explained the different, isoform-specific behavior of Orai N-truncation mutants. Atomic force microscopy studies and MD simulations suggested that the remaining N-terminal portion in the non-functional Orai1 N-truncation mutants formed new, inhibitory interactions with the Orai1-loop2 regions, but not with Orai3-loop2. Such a loop2 swap restored activation of the N-truncation Orai1 mutants. To mimic interactions between the N terminus and loop2 in full-length Orai1 channels, we induced close proximity of the N terminus and loop2 via cysteine cross-linking, which actually caused significant inhibition of STIM1-mediated Orai currents. In aggregate, maintenance of Orai activation required not only the conserved N-terminal region but also permissive communication of the Orai N terminus and loop2 in an isoform-specific manner.
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Affiliation(s)
- Marc Fahrner
- From the Institute of Biophysics, Johannes Kepler University of Linz, Gruberstrasse 40, 4020 Linz, Austria, and
| | - Saurabh K. Pandey
- the Center for Nanobiology and Structural Biology, Institute of Microbiology, Academy of Sciences of the Czech Republic, 373 33 Nove Hrady, Czech Republic
| | - Martin Muik
- From the Institute of Biophysics, Johannes Kepler University of Linz, Gruberstrasse 40, 4020 Linz, Austria, and
| | - Lukas Traxler
- From the Institute of Biophysics, Johannes Kepler University of Linz, Gruberstrasse 40, 4020 Linz, Austria, and
| | - Carmen Butorac
- From the Institute of Biophysics, Johannes Kepler University of Linz, Gruberstrasse 40, 4020 Linz, Austria, and
| | - Michael Stadlbauer
- From the Institute of Biophysics, Johannes Kepler University of Linz, Gruberstrasse 40, 4020 Linz, Austria, and
| | - Vasilina Zayats
- the Center for Nanobiology and Structural Biology, Institute of Microbiology, Academy of Sciences of the Czech Republic, 373 33 Nove Hrady, Czech Republic
| | - Adéla Krizova
- From the Institute of Biophysics, Johannes Kepler University of Linz, Gruberstrasse 40, 4020 Linz, Austria, and
| | - Peter Plenk
- From the Institute of Biophysics, Johannes Kepler University of Linz, Gruberstrasse 40, 4020 Linz, Austria, and
| | - Irene Frischauf
- From the Institute of Biophysics, Johannes Kepler University of Linz, Gruberstrasse 40, 4020 Linz, Austria, and
| | - Rainer Schindl
- From the Institute of Biophysics, Johannes Kepler University of Linz, Gruberstrasse 40, 4020 Linz, Austria, and
| | - Hermann J. Gruber
- From the Institute of Biophysics, Johannes Kepler University of Linz, Gruberstrasse 40, 4020 Linz, Austria, and
| | - Peter Hinterdorfer
- From the Institute of Biophysics, Johannes Kepler University of Linz, Gruberstrasse 40, 4020 Linz, Austria, and
| | - Rüdiger Ettrich
- the Center for Nanobiology and Structural Biology, Institute of Microbiology, Academy of Sciences of the Czech Republic, 373 33 Nove Hrady, Czech Republic
| | - Christoph Romanin
- From the Institute of Biophysics, Johannes Kepler University of Linz, Gruberstrasse 40, 4020 Linz, Austria, and
| | - Isabella Derler
- From the Institute of Biophysics, Johannes Kepler University of Linz, Gruberstrasse 40, 4020 Linz, Austria, and
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15
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Frischauf I, Litviňuková M, Schober R, Zayats V, Svobodová B, Bonhenry D, Lunz V, Cappello S, Tociu L, Reha D, Stallinger A, Hochreiter A, Pammer T, Butorac C, Muik M, Groschner K, Bogeski I, Ettrich RH, Romanin C, Schindl R. Transmembrane helix connectivity in Orai1 controls two gates for calcium-dependent transcription. Sci Signal 2017; 10:eaao0358. [PMID: 29184031 PMCID: PMC6433236 DOI: 10.1126/scisignal.aao0358] [Citation(s) in RCA: 59] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
The channel Orai1 requires Ca2+ store depletion in the endoplasmic reticulum and an interaction with the Ca2+ sensor STIM1 to mediate Ca2+ signaling. Alterations in Orai1-mediated Ca2+ influx have been linked to several pathological conditions including immunodeficiency, tubular myopathy, and cancer. We screened large-scale cancer genomics data sets for dysfunctional Orai1 mutants. Five of the identified Orai1 mutations resulted in constitutively active gating and transcriptional activation. Our analysis showed that certain Orai1 mutations were clustered in the transmembrane 2 helix surrounding the pore, which is a trigger site for Orai1 channel gating. Analysis of the constitutively open Orai1 mutant channels revealed two fundamental gates that enabled Ca2+ influx: Arginine side chains were displaced so they no longer blocked the pore, and a chain of water molecules formed in the hydrophobic pore region. Together, these results enabled us to identify a cluster of Orai1 mutations that trigger Ca2+ permeation associated with gene transcription and provide a gating mechanism for Orai1.
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Affiliation(s)
- Irene Frischauf
- Institute of Biophysics, JKU Life Science Center, Johannes Kepler University Linz, Linz A-4020, Austria
| | - Monika Litviňuková
- Institute of Biophysics, JKU Life Science Center, Johannes Kepler University Linz, Linz A-4020, Austria
- Max Delbrück Center for Molecular Medicine in the Helmholtz Association, Cardiovascular and Metabolic Sciences, Berlin D-13125, Germany
| | - Romana Schober
- Institute of Biophysics, JKU Life Science Center, Johannes Kepler University Linz, Linz A-4020, Austria
| | - Vasilina Zayats
- Center for Nanobiology and Structural Biology, Institute of Microbiology, Academy of Sciences of the Czech Republic, Nové Hrady CZ-373 33, Czech Republic
- Center of New Technologies, University of Warsaw, Warsaw 02-097, Poland
| | - Barbora Svobodová
- Institute for Biophysics, Medical University of Graz, Graz A-8010, Austria
| | - Daniel Bonhenry
- Center for Nanobiology and Structural Biology, Institute of Microbiology, Academy of Sciences of the Czech Republic, Nové Hrady CZ-373 33, Czech Republic
| | - Victoria Lunz
- Institute of Biophysics, JKU Life Science Center, Johannes Kepler University Linz, Linz A-4020, Austria
| | - Sabrina Cappello
- Molecular Physiology, Institute of Cardiovascular Physiology, University Medical Center, Georg August University Göttingen, Göttingen, Niedersachsen 37073, Germany
- Department of Biophysics, Center for Integrative Physiology and Molecular Medicine, Medical Faculty, Saarland University, Homburg D-66421, Germany
| | - Laura Tociu
- Center for Nanobiology and Structural Biology, Institute of Microbiology, Academy of Sciences of the Czech Republic, Nové Hrady CZ-373 33, Czech Republic
- University of Chicago, Chicago, IL 60637, USA
| | - David Reha
- Center for Nanobiology and Structural Biology, Institute of Microbiology, Academy of Sciences of the Czech Republic, Nové Hrady CZ-373 33, Czech Republic
- Faculty of Sciences, University of South Bohemia, Nové Hrady CZ-373 33, Czech Republic
| | - Amrutha Stallinger
- Institute for Molecular Biosciences, Karl-Franzens-University Graz, Graz A-8010, Austria
| | - Anna Hochreiter
- Institute for Experimental and Clinical Cell Therapy, Paracelsus Medical University, Salzburg A-5020, Austria
| | - Teresa Pammer
- Institute of Biophysics, JKU Life Science Center, Johannes Kepler University Linz, Linz A-4020, Austria
| | - Carmen Butorac
- Institute of Biophysics, JKU Life Science Center, Johannes Kepler University Linz, Linz A-4020, Austria
| | - Martin Muik
- Institute of Biophysics, JKU Life Science Center, Johannes Kepler University Linz, Linz A-4020, Austria
| | - Klaus Groschner
- Institute for Biophysics, Medical University of Graz, Graz A-8010, Austria
| | - Ivan Bogeski
- Molecular Physiology, Institute of Cardiovascular Physiology, University Medical Center, Georg August University Göttingen, Göttingen, Niedersachsen 37073, Germany
| | - Rüdiger H Ettrich
- Center for Nanobiology and Structural Biology, Institute of Microbiology, Academy of Sciences of the Czech Republic, Nové Hrady CZ-373 33, Czech Republic
- Faculty of Sciences, University of South Bohemia, Nové Hrady CZ-373 33, Czech Republic
| | - Christoph Romanin
- Institute of Biophysics, JKU Life Science Center, Johannes Kepler University Linz, Linz A-4020, Austria
| | - Rainer Schindl
- Institute for Biophysics, Medical University of Graz, Graz A-8010, Austria.
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16
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Protein hydration: Investigation of globular protein crystal structures. Int J Biol Macromol 2017; 99:160-165. [DOI: 10.1016/j.ijbiomac.2017.02.073] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/10/2017] [Revised: 02/10/2017] [Indexed: 01/06/2023]
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17
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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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18
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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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19
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Mullins FM, Lewis RS. The inactivation domain of STIM1 is functionally coupled with the Orai1 pore to enable Ca2+-dependent inactivation. ACTA ACUST UNITED AC 2016; 147:153-64. [PMID: 26809794 PMCID: PMC4727943 DOI: 10.1085/jgp.201511438] [Citation(s) in RCA: 42] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
The inactivation domain of STIM1 (ID(STIM): amino acids 470-491) has been described as necessary for Ca(2+)-dependent inactivation (CDI) of Ca(2+) release-activated Ca(2+) (CRAC) channels, but its mechanism of action is unknown. Here we identify acidic residues within IDSTIM that control the extent of CDI and examine functional interactions of ID(STIM) with Orai1 pore residues W76 and Y80. Alanine scanning revealed three IDSTIM residues (D476/D478/D479) that are critical for generating full CDI. Disabling ID(STIM) by a triple alanine substitution for these three residues ("STIM1 3A") or by truncation of the entire domain (STIM1(1-469)) reduced CDI to the same residual level observed for the Orai1 pore mutant W76A (approximately one third of the extent seen with full-length STIM1). Results of noise analysis showed that STIM11-469 and Orai1 W76A mutants do not reduce channel open probability or unitary Ca(2+) conductance, factors that determine local Ca(2+) accumulation, suggesting that they diminish CDI instead by inhibiting the CDI gating mechanism. We tested for functional coupling between ID(STIM) and the Orai1 pore by double-mutant cycle analysis. The effects on CDI of mutations disabling ID(STIM) or W76 were not additive, demonstrating that ID(STIM) and W76 are strongly coupled and act in concert to generate full-strength CDI. Interestingly, disabling ID(STIM) and W76 separately gave opposite results in Orai1 Y80A channels: channels with W76 but lacking ID(STIM) generated approximately two thirds of the WT extent of CDI but those with ID(STIM) but lacking W76 completely failed to inactivate. Together, our results suggest that Y80 alone is sufficient to generate residual CDI, but acts as a barrier to full CDI. Although ID(STIM) is not required as a Ca(2+) sensor for CDI, it acts in concert with W76 to progress beyond the residual inactivated state and enable CRAC channels to reach the full extent of inactivation.
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Affiliation(s)
- Franklin M Mullins
- Department of Pathology and Department of Molecular and Cellular Physiology, Stanford University School of Medicine, Stanford, CA 94305
| | - Richard S Lewis
- Department of Pathology and Department of Molecular and Cellular Physiology, Stanford University School of Medicine, Stanford, CA 94305
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20
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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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21
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Derler I, Jardin I, Stathopulos PB, Muik M, Fahrner M, Zayats V, Pandey SK, Poteser M, Lackner B, Absolonova M, Schindl R, Groschner K, Ettrich R, Ikura M, Romanin C. Cholesterol modulates Orai1 channel function. Sci Signal 2016; 9:ra10. [PMID: 26814231 DOI: 10.1126/scisignal.aad7808] [Citation(s) in RCA: 76] [Impact Index Per Article: 9.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
STIM1 (stromal interaction molecule 1) and Orai proteins are the essential components of Ca(2+) release-activated Ca(2+) (CRAC) channels. We focused on the role of cholesterol in the regulation of STIM1-mediated Orai1 currents. Chemically induced cholesterol depletion enhanced store-operated Ca(2+) entry (SOCE) and Orai1 currents. Furthermore, cholesterol depletion in mucosal-type mast cells augmented endogenous CRAC currents, which were associated with increased degranulation, a process that requires calcium influx. Single point mutations in the Orai1 amino terminus that would be expected to abolish cholesterol binding enhanced SOCE to a similar extent as did cholesterol depletion. The increase in Orai1 activity in cells expressing these cholesterol-binding-deficient mutants occurred without affecting the amount in the plasma membrane or the coupling of STIM1 to Orai1. We detected cholesterol binding to an Orai1 amino-terminal fragment in vitro and to full-length Orai1 in cells. Thus, our data showed that Orai1 senses the amount of cholesterol in the plasma membrane and that the interaction of Orai1 with cholesterol inhibits its activity, thereby limiting SOCE.
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Affiliation(s)
- Isabella Derler
- Institute of Biophysics, Johannes Kepler University of Linz, Gruberstrasse 40, 4020 Linz, Austria.
| | - Isaac Jardin
- Institute of Biophysics, Johannes Kepler University of Linz, Gruberstrasse 40, 4020 Linz, Austria
| | - Peter B Stathopulos
- Department of Physiology and Pharmacology, Schulich School of Medicine and Dentistry, University of Western Ontario, London, Ontario N6A 5C1, Canada
| | - Martin Muik
- Institute of Biophysics, Johannes Kepler University of Linz, Gruberstrasse 40, 4020 Linz, Austria
| | - Marc Fahrner
- Institute of Biophysics, Johannes Kepler University of Linz, Gruberstrasse 40, 4020 Linz, Austria
| | - Vasilina Zayats
- Center for Nanobiology and Structural Biology, Institute of Microbiology, Academy of Sciences of the Czech Republic, CZ-373 33 Nové Hrady, Czech Republic
| | - Saurabh K Pandey
- Center for Nanobiology and Structural Biology, Institute of Microbiology, Academy of Sciences of the Czech Republic, CZ-373 33 Nové Hrady, Czech Republic
| | - Michael Poteser
- Institute of Biophysics, Medical University of Graz, Harrachgasse 21/4, 8010 Graz, Austria
| | - Barbara Lackner
- Institute of Biophysics, Johannes Kepler University of Linz, Gruberstrasse 40, 4020 Linz, Austria
| | - Marketa Absolonova
- Institute of Biophysics, Johannes Kepler University of Linz, Gruberstrasse 40, 4020 Linz, Austria
| | - Rainer Schindl
- Institute of Biophysics, Johannes Kepler University of Linz, Gruberstrasse 40, 4020 Linz, Austria
| | - Klaus Groschner
- Institute of Biophysics, Medical University of Graz, Harrachgasse 21/4, 8010 Graz, Austria
| | - Rüdiger Ettrich
- Center for Nanobiology and Structural Biology, Institute of Microbiology, Academy of Sciences of the Czech Republic, CZ-373 33 Nové Hrady, Czech Republic
| | - Mitsu Ikura
- Princess Margaret Cancer Centre and Department of Medical Biophysics, University of Toronto, Toronto, Ontario M5G 1L7, Canada
| | - Christoph Romanin
- Institute of Biophysics, Johannes Kepler University of Linz, Gruberstrasse 40, 4020 Linz, Austria.
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22
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Frischauf I, Zayats V, Deix M, Hochreiter A, Jardin I, Muik M, Lackner B, Svobodová B, Pammer T, Litviňuková M, Sridhar AA, Derler I, Bogeski I, Romanin C, Ettrich RH, Schindl R. A calcium-accumulating region, CAR, in the channel Orai1 enhances Ca(2+) permeation and SOCE-induced gene transcription. Sci Signal 2015; 8:ra131. [PMID: 26696631 DOI: 10.1126/scisignal.aab1901] [Citation(s) in RCA: 47] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
Abstract
The Ca(2+) release-activated Ca(2+) channel mediates Ca(2+) influx in a plethora of cell types, thereby controlling diverse cellular functions. The channel complex is composed of stromal interaction molecule 1 (STIM1), an endoplasmic reticulum Ca(2+)-sensing protein, and Orai1, a plasma membrane Ca(2+) channel. Channels composed of STIM1 and Orai1 mediate Ca(2+) influx even at low extracellular Ca(2+) concentrations. We investigated whether the activity of Orai1 adapted to different environmental Ca(2+) concentrations. We used homology modeling and molecular dynamics simulations to predict the presence of an extracellular Ca(2+)-accumulating region (CAR) at the pore entrance of Orai1. Furthermore, simulations of Orai1 proteins with mutations in CAR, along with live-cell experiments, or simulations and electrophysiological recordings of the channel with transient, electrostatic loop3 interacting with loop1 (the site of CAR) determined that CAR enhanced Ca(2+) permeation most efficiently at low external Ca(2+) concentrations. Consistent with these results, cells expressing Orai1 CAR mutants exhibited impaired gene expression stimulated by the Ca(2+)-activated transcription factor nuclear factor of activated T cells (NFAT). We propose that the Orai1 channel architecture with a close proximity of CAR to the selectivity filter, which enables Ca(2+)-selective ion permeation, enhances the local extracellular Ca(2+) concentration to maintain Ca(2+)-dependent gene regulation even in environments with relatively low Ca(2+)concentrations.
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Affiliation(s)
- Irene Frischauf
- Institute of Biophysics, JKU Life Science Center, Johannes Kepler University Linz, Gruberstrasse 40, 4020 Linz, Austria
| | - Vasilina Zayats
- Center for Nanobiology and Structural Biology, Institute of Microbiology, Academy of Sciences of the Czech Republic, Zamek 136, CZ-373 33, Nove Hrady, Czech Republic.,Faculty of Sciences, University of South Bohemia, Zamek 136, CZ-373 33, Nove Hrady, Czech Republic
| | - Michael Deix
- Institute of Biophysics, JKU Life Science Center, Johannes Kepler University Linz, Gruberstrasse 40, 4020 Linz, Austria
| | - Anna Hochreiter
- Institute of Biophysics, JKU Life Science Center, Johannes Kepler University Linz, Gruberstrasse 40, 4020 Linz, Austria.,Institute for Experimental and Clinical Cell Therapy, Paracelsus Medical University, A-5020 Salzburg, Austria
| | - Isaac Jardin
- Institute of Biophysics, JKU Life Science Center, Johannes Kepler University Linz, Gruberstrasse 40, 4020 Linz, Austria
| | - Martin Muik
- Institute of Biophysics, JKU Life Science Center, Johannes Kepler University Linz, Gruberstrasse 40, 4020 Linz, Austria
| | - Barbara Lackner
- Institute of Biophysics, JKU Life Science Center, Johannes Kepler University Linz, Gruberstrasse 40, 4020 Linz, Austria
| | - Barbora Svobodová
- Institute of Biophysics, JKU Life Science Center, Johannes Kepler University Linz, Gruberstrasse 40, 4020 Linz, Austria.,Institute for Biophysics of Medical University Graz, A-8010, Graz, Austria
| | - Teresa Pammer
- Institute of Biophysics, JKU Life Science Center, Johannes Kepler University Linz, Gruberstrasse 40, 4020 Linz, Austria
| | - Monika Litviňuková
- Institute of Biophysics, JKU Life Science Center, Johannes Kepler University Linz, Gruberstrasse 40, 4020 Linz, Austria
| | - Amrutha Arumbakam Sridhar
- Institute of Biophysics, JKU Life Science Center, Johannes Kepler University Linz, Gruberstrasse 40, 4020 Linz, Austria
| | - Isabella Derler
- Institute of Biophysics, JKU Life Science Center, Johannes Kepler University Linz, Gruberstrasse 40, 4020 Linz, Austria
| | - Ivan Bogeski
- Department of Biophysics, School of Medicine, University of Saarland, D-66421 Homburg, Germany
| | - Christoph Romanin
- Institute of Biophysics, JKU Life Science Center, Johannes Kepler University Linz, Gruberstrasse 40, 4020 Linz, Austria
| | - Rüdiger H Ettrich
- Center for Nanobiology and Structural Biology, Institute of Microbiology, Academy of Sciences of the Czech Republic, Zamek 136, CZ-373 33, Nove Hrady, Czech Republic.,Faculty of Sciences, University of South Bohemia, Zamek 136, CZ-373 33, Nove Hrady, Czech Republic
| | - Rainer Schindl
- Institute of Biophysics, JKU Life Science Center, Johannes Kepler University Linz, Gruberstrasse 40, 4020 Linz, Austria
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23
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Abstract
Ca(2+) release-activated Ca(2+) (CRAC) channels mediate a specific form of Ca(2+) influx called store-operated Ca(2+) entry (SOCE) that contributes to the function of many cell types. CRAC channels are composed of ORAI1 proteins located in the plasma membrane, which form its ion-conducting pore. ORAI1 channels are activated by stromal interaction molecule (STIM) 1 and STIM2 located in the endoplasmic reticulum. Loss- and gain-of-function gene mutations in ORAI1 and STIM1 in human patients cause distinct disease syndromes. CRAC channelopathy is caused by loss-of-function mutations in ORAI1 and STIM1 that abolish CRAC channel function and SOCE; it is characterized by severe combined immunodeficiency (SCID)-like disease, autoimmunity, muscular hypotonia, and ectodermal dysplasia, with defects in sweat gland function and dental enamel formation. The latter defect emphasizes an important role of CRAC channels in tooth development. By contrast, autosomal dominant gain-of-function mutations in ORAI1 and STIM1 result in constitutive CRAC channel activation, SOCE, and increased intracellular Ca(2+) levels that are associated with an overlapping spectrum of diseases, including nonsyndromic tubular aggregate myopathy (TAM) and York platelet and Stormorken syndromes. The latter two syndromes are defined, besides myopathy, by thrombocytopenia, thrombopathy, and bleeding diathesis. The fact that myopathy results from both loss- and gain-of-function mutations in ORAI1 and STIM1 highlights the importance of CRAC channels for Ca(2+) homeostasis in skeletal muscle function. The cellular dysfunction and clinical disease spectrum observed in mutant patients provide important information about the molecular regulation of ORAI1 and STIM1 proteins and the role of CRAC channels in human physiology.
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Affiliation(s)
- Rodrigo S Lacruz
- Department of Basic Science and Craniofacial Biology, New York University College of Dentistry, New York, New York
| | - Stefan Feske
- Department of Pathology, New York University School of Medicine, New York, New York
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24
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Amcheslavsky A, Wood ML, Yeromin AV, Parker I, Freites JA, Tobias DJ, Cahalan MD. Molecular biophysics of Orai store-operated Ca2+ channels. Biophys J 2015; 108:237-46. [PMID: 25606672 DOI: 10.1016/j.bpj.2014.11.3473] [Citation(s) in RCA: 51] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/05/2014] [Revised: 11/24/2014] [Accepted: 11/26/2014] [Indexed: 12/12/2022] Open
Abstract
Upon endoplasmic reticulum Ca(2+) store depletion, Orai channels in the plasma membrane are activated directly by endoplasmic reticulum-resident STIM proteins to generate the Ca(2+)-selective, Ca(2+) release-activated Ca(2+) (CRAC) current. After the molecular identification of Orai, a plethora of functional and biochemical studies sought to compare Orai homologs, determine their stoichiometry, identify structural domains responsible for the biophysical fingerprint of the CRAC current, identify the physiological functions, and investigate Orai homologs as potential therapeutic targets. Subsequently, the solved crystal structure of Drosophila Orai (dOrai) substantiated many findings from structure-function studies, but also revealed an unexpected hexameric structure. In this review, we explore Orai channels as elucidated by functional and biochemical studies, analyze the dOrai crystal structure and its implications for Orai channel function, and present newly available information from molecular dynamics simulations that shed light on Orai channel gating and permeation.
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Affiliation(s)
- Anna Amcheslavsky
- Department of Physiology and Biophysics, University of California at Irvine, Irvine, California
| | - Mona L Wood
- Department of Chemistry, University of California at Irvine, Irvine, California
| | - Andriy V Yeromin
- Department of Physiology and Biophysics, University of California at Irvine, Irvine, California
| | - Ian Parker
- Department of Physiology and Biophysics, University of California at Irvine, Irvine, California; Department of Neurobiology and Behavior, University of California at Irvine, Irvine, California
| | - J Alfredo Freites
- Department of Chemistry, University of California at Irvine, Irvine, California
| | - Douglas J Tobias
- Department of Chemistry, University of California at Irvine, Irvine, California
| | - Michael D Cahalan
- Department of Physiology and Biophysics, University of California at Irvine, Irvine, California; Institute for Immunology, University of California at Irvine, Irvine, California.
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25
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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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26
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Conformational Changes in the Orai1 C-Terminus Evoked by STIM1 Binding. PLoS One 2015; 10:e0128622. [PMID: 26035642 PMCID: PMC4452722 DOI: 10.1371/journal.pone.0128622] [Citation(s) in RCA: 36] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/24/2015] [Accepted: 04/29/2015] [Indexed: 01/09/2023] Open
Abstract
Store-operated CRAC channels regulate a wide range of cellular functions including gene expression, chemotaxis, and proliferation. CRAC channels consist of two components: the Orai proteins (Orai1-3), which form the ion-selective pore, and STIM proteins (STIM1-2), which form the endoplasmic reticulum (ER) Ca2+ sensors. Activation of CRAC channels is initiated by the migration of STIM1 to the ER-plasma membrane (PM) junctions, where it directly interacts with Orai1 to open the Ca2+-selective pores of the CRAC channels. The recent elucidation of the Drosophila Orai structure revealed a hexameric channel wherein the C-terminal helices of adjacent Orai subunits associate in an anti-parallel orientation. This association is maintained by hydrophobic interactions between the Drosophila equivalents of human Orai1 residues L273 and L276. Here, we used mutagenesis and chemical cross-linking to assess the nature and extent of conformational changes in the self-associated Orai1 C-termini during STIM1 binding. We find that linking the anti-parallel coiled-coils of the adjacent Orai1 C-termini through disulfide cross-links diminishes STIM1-Orai1 interaction, as assessed by FRET. Conversely, prior binding of STIM1 to the Orai1 C-terminus impairs cross-linking of the Orai1 C-termini. Mutational analysis indicated that a bend of the Orai1 helix located upstream of the self-associated coils (formed by the amino acid sequence SHK) establishes an appropriate orientation of the Orai1 C-termini that is required for STIM1 binding. Together, our results support a model wherein the self-associated Orai1 C-termini rearrange modestly to accommodate STIM1 binding.
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27
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Dong H, Klein ML, Fiorin G. Counterion-Assisted Cation Transport in a Biological Calcium Channel. J Phys Chem B 2014; 118:9668-76. [DOI: 10.1021/jp5059897] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Affiliation(s)
- Hao Dong
- Institute for Computational
Molecular Science, Temple University, Philadelphia, Pennsylvania 19122, United States
| | - Michael L. Klein
- Institute for Computational
Molecular Science, Temple University, Philadelphia, Pennsylvania 19122, United States
| | - Giacomo Fiorin
- Institute for Computational
Molecular Science, Temple University, Philadelphia, Pennsylvania 19122, United States
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28
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Amcheslavsky A, Safrina O, Cahalan MD. Orai3 TM3 point mutation G158C alters kinetics of 2-APB-induced gating by disulfide bridge formation with TM2 C101. ACTA ACUST UNITED AC 2014; 142:405-12. [PMID: 24081982 PMCID: PMC3787773 DOI: 10.1085/jgp.201311030] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/05/2022]
Abstract
After endoplasmic reticulum (ER) Ca2+ store depletion, Orai channels in the plasma membrane (PM) are activated directly by ER-resident STIM proteins to form the Ca2+-selective Ca2+ release–activated Ca2+ (CRAC) channel. However, in the absence of Ca2+ store depletion and STIM interaction, the mammalian homologue Orai3 can be activated by 2-aminoethyl diphenylborinate (2-APB), resulting in a nonselective cation conductance characterized by biphasic inward and outward rectification. Here, we use site-directed mutagenesis and patch-clamp analysis to better understand the mechanism by which 2-APB activates Orai3. We find that point mutation of glycine 158 in the third transmembrane (TM) segment to cysteine, but not alanine, slows the kinetics of 2-APB activation and prevents complete channel closure upon 2-APB washout. The “slow” phenotype exhibited by Orai3 mutant G158C reveals distinct open states, characterized by variable reversal potentials. The slow phenotype can be reversed by application of the reducing reagent bis(2-mercaptoethylsulfone) (BMS), but in a state-dependent manner, only during 2-APB activation. Moreover, the double mutant C101G/G158C, in which an endogenous TM2 cysteine is changed to glycine, does not exhibit altered kinetics of 2-APB activation. We suggest that a disulfide bridge, formed between the introduced cysteine at TM3 position 158 and the endogenous cysteine at TM2 position 101, hinders transitions between Orai3 open and closed states. Our data provide functional confirmation of the proximity of these two residues and suggest a location within the Orai3 protein that is sensitive to the actions of 2-APB.
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Affiliation(s)
- Anna Amcheslavsky
- Department of Physiology and Biophysics, University of California, Irvine, Irvine, CA 92697
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29
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Amcheslavsky A, Safrina O, Cahalan MD. State-dependent block of Orai3 TM1 and TM3 cysteine mutants: insights into 2-APB activation. ACTA ACUST UNITED AC 2014; 143:621-31. [PMID: 24733836 PMCID: PMC4003185 DOI: 10.1085/jgp.201411171] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
Residue E165, in transmembrane helix 3, participates in formation of the dilated pore of the 2-APB–activated Orai3 channel but not that of the more selective store-operated Orai3 pore. After endoplasmic reticulum (ER) Ca2+ store depletion, Orai channels in the plasma membrane (PM) are activated directly by ER-resident stromal interacting molecule (STIM) proteins to form the Ca2+-selective Ca2+ release-activated Ca2+ (CRAC) channel. Of the three human Orai channel homologues, only Orai3 can be activated by high concentrations (>50 µM) of 2-aminoethyl diphenylborinate (2-APB). 2-APB activation of Orai3 occurs without STIM1–Orai3 interaction or store depletion, and results in a cationic, nonselective current characterized by biphasic inward and outward rectification. Here we use cysteine scanning mutagenesis, thiol-reactive reagents, and patch-clamp analysis to define the residues that assist in formation of the 2-APB–activated Orai3 pore. Mutating transmembrane (TM) 1 residues Q83, V77, and L70 to cysteine results in potentiated block by cadmium ions (Cd2+). TM1 mutants E81C, G73A, G73C, and R66C form channels that are not sensitive to 2-APB activation. We also find that Orai3 mutant V77C is sensitive to block by 2-aminoethyl methanethiosulfonate (MTSEA), but not 2-(trimethylammonium)ethyl methanethiosulfonate (MTSET). Block induced by reaction with MTSEA is state dependent, as it occurs only when Orai3-V77C channels are opened by either 2-APB or by cotransfection with STIM1 and concurrent passive store depletion. We also analyzed TM3 residue E165. Mutation E165A in Orai3 results in diminished 2-APB–activated currents. However, it has little effect on store-operated current density. Furthermore, mutation E165C results in Cd2+-induced block that is state dependent: Cd2+ only blocks 2-APB–activated, not store-operated, mutant channels. Our data suggest that the dilated pore of 2-APB–activated Orai3 is lined by TM1 residues, but also allows for TM3 E165 to approach the central axis of the channel that forms the conducting pathway, or pore.
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Affiliation(s)
- Anna Amcheslavsky
- Department of Physiology and Biophysics, University of California, Irvine, Irvine, CA 92697
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30
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Derler I, Plenk P, Fahrner M, Muik M, Jardin I, Schindl R, Gruber HJ, Groschner K, Romanin C. The extended transmembrane Orai1 N-terminal (ETON) region combines binding interface and gate for Orai1 activation by STIM1. J Biol Chem 2013; 288:29025-34. [PMID: 23943619 PMCID: PMC3790000 DOI: 10.1074/jbc.m113.501510] [Citation(s) in RCA: 93] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2013] [Revised: 08/09/2013] [Indexed: 11/21/2022] Open
Abstract
STIM1 and Orai1 represent the two molecular key components of the Ca(2+) release-activated Ca(2+) channels. Their activation involves STIM1 C terminus coupling to both the N terminus and the C terminus of Orai. Here we focused on the extended transmembrane Orai1 N-terminal (ETON, aa73-90) region, conserved among the Orai family forming an elongated helix of TM1 as recently shown by x-ray crystallography. To identify "hot spot" residues in the ETON binding interface for STIM1 interaction, numerous Orai1 constructs with N-terminal truncations or point mutations within the ETON region were generated. N-terminal truncations of the first four residues of the ETON region or beyond completely abolished STIM1-dependent Orai1 function. Loss of Orai1 function resulted from neither an impairment of plasma membrane targeting nor pore damage, but from a disruption of STIM1 interaction. In a complementary approach, we monitored STIM1-Orai interaction via Orai1 V102A by determining restored Ca(2+) selectivity as a consequence of STIM1 coupling. Orai1 N-terminal truncations that led to a loss of function consistently failed to restore Ca(2+) selectivity of Orai1 V102A in the presence of STIM1, demonstrating impairment of STIM1 binding. Hence, the major portion of the ETON region (aa76-90) is essential for STIM1 binding and Orai1 activation. Mutagenesis within the ETON region revealed several hydrophobic and basic hot spot residues that appear to control STIM1 coupling to Orai1 in a concerted manner. Moreover, we identified two basic residues, which protrude into the elongated pore to redound to Orai1 gating. We suggest that several hot spot residues in the ETON region contribute in aggregate to the binding of STIM1, which in turn is coupled to a conformational reorientation of the gate.
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Affiliation(s)
- Isabella Derler
- From the Institute of Biophysics, Johannes Kepler University of Linz, Gruberstrasse 40, 4020 Linz and
| | - Peter Plenk
- From the Institute of Biophysics, Johannes Kepler University of Linz, Gruberstrasse 40, 4020 Linz and
| | - Marc Fahrner
- From the Institute of Biophysics, Johannes Kepler University of Linz, Gruberstrasse 40, 4020 Linz and
| | - Martin Muik
- From the Institute of Biophysics, Johannes Kepler University of Linz, Gruberstrasse 40, 4020 Linz and
| | - Isaac Jardin
- From the Institute of Biophysics, Johannes Kepler University of Linz, Gruberstrasse 40, 4020 Linz and
| | - Rainer Schindl
- From the Institute of Biophysics, Johannes Kepler University of Linz, Gruberstrasse 40, 4020 Linz and
| | - Hermann J. Gruber
- From the Institute of Biophysics, Johannes Kepler University of Linz, Gruberstrasse 40, 4020 Linz and
| | - Klaus Groschner
- the Institute of Biophysics, Medical University of Graz, Harrachgasse 21/4, 8010 Graz, Austria
| | - Christoph Romanin
- From the Institute of Biophysics, Johannes Kepler University of Linz, Gruberstrasse 40, 4020 Linz and
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31
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Abstract
Ca(2+) influx via store-operated Ca(2+) release activated Ca(2+) (CRAC) channels represents a main signaling pathway for T-cell activation as well as mast-cell degranulation. The ER-located Ca(2+)-sensor, STIM1 and the Ca(2+)-selective ion pore, Orai1 in the membrane are sufficient to fully reconstitute CRAC currents. Their identification, but even more the recent structural resolution of both proteins by X-ray crystallography has substantially advanced the understanding of the activation mechanism of CRAC channels. In this review, we provide a detailed description of the STIM1/Orai1 signaling pathway thereby focusing on the critical domains mediating both, intra- as well as intermolecular interactions and on the ion permeation pathway. Based on the results of functional studies as well as the recently published crystal structures, we portray a mechanistic view of the steps in the CRAC channel signaling cascade ranging from STIM1 oligomerization over STIM1-Orai1 coupling to the ultimate Orai1 channel activation and permeation.
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Affiliation(s)
- Marc Fahrner
- Institute of Biophysics; Johannes Kepler University Linz; Linz, Austria
| | - Isabella Derler
- Institute of Biophysics; Johannes Kepler University Linz; Linz, Austria
| | - Isaac Jardin
- Institute of Biophysics; Johannes Kepler University Linz; Linz, Austria
| | - Christoph Romanin
- Institute of Biophysics; Johannes Kepler University Linz; Linz, Austria
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32
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Srikanth S, Ribalet B, Gwack Y. Regulation of CRAC channels by protein interactions and post-translational modification. Channels (Austin) 2013; 7:354-63. [PMID: 23454861 DOI: 10.4161/chan.23801] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
Store-operated Ca(2+) entry (SOCE) is a widespread mechanism to elevate the intracellular Ca(2+) concentrations and stimulate downstream signaling pathways affecting proliferation, secretion, differentiation and death in different cell types. In immune cells, immune receptor stimulation induces intracellular Ca(2+) store depletion that subsequently activates Ca(2+)-release-activated-Ca(2+) (CRAC) channels, a prototype of store-operated Ca(2+) (SOC) channels. CRAC channel opening leads to activation of diverse downstream signaling pathways affecting proliferation, differentiation, cytokine production and cell death. Recent identification of STIM1 as the endoplasmic reticulum Ca(2+) sensor and Orai1 as the pore subunit of CRAC channels has provided the much-needed molecular tools to dissect the mechanism of activation and regulation of CRAC channels. In this review, we discuss the recent advances in understanding the associating partners and posttranslational modifications of Orai1 and STIM1 proteins that regulate diverse aspects of CRAC channel function.
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Affiliation(s)
- Sonal Srikanth
- Department of Physiology; David Geffen School of Medicine at UCLA; Los Angeles, CA USA
| | - Bernard Ribalet
- Department of Physiology; David Geffen School of Medicine at UCLA; Los Angeles, CA USA
| | - Yousang Gwack
- Department of Physiology; David Geffen School of Medicine at UCLA; Los Angeles, CA USA
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33
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Abstract
Severe combined immunodeficiency (SCID) comprises a group of disorders that are fatal owing to genetic defects that abrogate T cell development. Numerous related defects have recently been identified that allow T cell development but that compromise T cell function by affecting proximal or distal steps in intracellular signaling. These functional T cell immunodeficiencies are characterized by immune dysregulation and increased risk of malignancies, in addition to infections. The study of patients with these rare conditions, and of corresponding animal models, illustrates the importance of intracellular signaling to maintain T cell homeostasis.
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Affiliation(s)
- Luigi D Notarangelo
- Division of Immunology and The Manton Center for Orphan Disease Research, Boston Children's Hospital, Boston, Massachusetts 02115, USA.
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34
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Gudlur A, Zhou Y, Hogan PG. STIM-ORAI interactions that control the CRAC channel. CURRENT TOPICS IN MEMBRANES 2013; 71:33-58. [PMID: 23890110 DOI: 10.1016/b978-0-12-407870-3.00002-0] [Citation(s) in RCA: 41] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
The Ca(2+) sensor STIM1 and the Ca(2+) channel ORAI1 are the fundamental working machinery of the CRAC channel, a classical pathway for store-operated Ca(2+) entry. This chapter focuses on the protein-protein interactions of STIM and ORAI proteins that control the channel.
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Affiliation(s)
- Aparna Gudlur
- La Jolla Institute for Allergy & Immunology, La Jolla, California, USA
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35
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Schleifer H, Doleschal B, Lichtenegger M, Oppenrieder R, Derler I, Frischauf I, Glasnov TN, Kappe CO, Romanin C, Groschner K. Novel pyrazole compounds for pharmacological discrimination between receptor-operated and store-operated Ca(2+) entry pathways. Br J Pharmacol 2012; 167:1712-22. [PMID: 22862290 PMCID: PMC3525873 DOI: 10.1111/j.1476-5381.2012.02126.x] [Citation(s) in RCA: 147] [Impact Index Per Article: 12.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2012] [Revised: 07/04/2012] [Accepted: 07/11/2012] [Indexed: 12/12/2022] Open
Abstract
BACKGROUND AND PURPOSE Pyrazole derivatives have recently been suggested as selective blockers of transient receptor potential cation (TRPC) channels but their ability to distinguish between the TRPC and Orai pore complexes is ill-defined. This study was designed to characterize a series of pyrazole derivatives in terms of TRPC/Orai selectivity and to delineate consequences of selective suppression of these pathways for mast cell activation. EXPERIMENTAL APPROACH Pyrazoles were generated by microwave-assisted synthesis and tested for effects on Ca(2+) entry by Fura-2 imaging and membrane currents by patch-clamp recording. Experiments were performed in HEK293 cells overexpressing TRPC3 and in RBL-2H3 mast cells, which express classical store-operated Ca(2+) entry mediated by Orai channels. The consequences of inhibitory effects on Ca(2+) signalling in RBL-2H3 cells were investigated at the level of both degranulation and nuclear factor of activated T-cells activation. KEY RESULTS Pyr3, a previously suggested selective inhibitor of TRPC3, inhibited Orai1- and TRPC3-mediated Ca(2+) entry and currents as well as mast cell activation with similar potency. By contrast, Pyr6 exhibited a 37-fold higher potency to inhibit Orai1-mediated Ca(2+) entry as compared with TRPC3-mediated Ca(2+) entry and potently suppressed mast cell activation. The novel pyrazole Pyr10 displayed substantial selectivity for TRPC3-mediated responses (18-fold) and the selective block of TRPC3 channels by Pyr10 barely affected mast cell activation. CONCLUSIONS AND IMPLICATIONS The pyrazole derivatives Pyr6 and Pyr10 are able to distinguish between TRPC and Orai-mediated Ca(2+) entry and may serve as useful tools for the analysis of cellular functions of the underlying Ca(2+) channels.
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Affiliation(s)
- H Schleifer
- Institute of Biophysics, Medical University of Graz, Graz, Austria
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36
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Hou X, Pedi L, Diver MM, Long SB. Crystal structure of the calcium release-activated calcium channel Orai. Science 2012. [PMID: 23180775 DOI: 10.1126/science.1228757] [Citation(s) in RCA: 449] [Impact Index Per Article: 37.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
The plasma membrane protein Orai forms the pore of the calcium release-activated calcium (CRAC) channel and generates sustained cytosolic calcium signals when triggered by depletion of calcium from the endoplasmic reticulum. The crystal structure of Orai from Drosophila melanogaster, determined at 3.35 angstrom resolution, reveals that the calcium channel is composed of a hexameric assembly of Orai subunits arranged around a central ion pore. The pore traverses the membrane and extends into the cytosol. A ring of glutamate residues on its extracellular side forms the selectivity filter. A basic region near the intracellular side can bind anions that may stabilize the closed state. The architecture of the channel differs markedly from other ion channels and gives insight into the principles of selective calcium permeation and gating.
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Affiliation(s)
- Xiaowei Hou
- Structural Biology Program, Memorial Sloan-Kettering Cancer Center, 1275 York Avenue, New York, NY 10065, USA
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37
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Shaw PJ, Qu B, Hoth M, Feske S. Molecular regulation of CRAC channels and their role in lymphocyte function. Cell Mol Life Sci 2012; 70:2637-56. [PMID: 23052215 DOI: 10.1007/s00018-012-1175-2] [Citation(s) in RCA: 77] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/15/2012] [Revised: 09/16/2012] [Accepted: 09/17/2012] [Indexed: 12/12/2022]
Abstract
Calcium (Ca(2+)) influx is required for the activation and function of all cells in the immune system. It is mediated mainly by store-operated Ca(2+) entry (SOCE) through Ca(2+) release-activated Ca(2+) (CRAC) channels located in the plasma membrane. CRAC channels are composed of ORAI proteins that form the channel pore and are activated by stromal interaction molecules (STIM) 1 and 2. Located in the membrane of the endoplasmic reticulum, STIM1 and STIM2 have the dual function of sensing the intraluminal Ca(2+) concentration in the ER and to activate CRAC channels. A decrease in the ER's Ca(2+) concentration induces STIM multimerization and translocation into puncta close to the plasma membrane where they bind to and activate ORAI channels. Since the identification of ORAI and STIM genes as the principal mediators of CRAC channel function, substantial advances have been achieved in understanding the molecular regulation and physiological role of CRAC channels in cells of the immune system and other organs. In this review, we discuss the mechanisms that regulate CRAC channel function and SOCE, the role of recently identified proteins and mechanisms that modulate the activation of ORAI/STIM proteins and the consequences of CRAC channel dysregulation for lymphocyte function and immunity.
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Affiliation(s)
- Patrick J Shaw
- Department of Pathology, New York University Medical Center, 550 First Avenue, SRB 316, New York, NY 10016, USA
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38
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Muik M, Schindl R, Fahrner M, Romanin C. Ca(2+) release-activated Ca(2+) (CRAC) current, structure, and function. Cell Mol Life Sci 2012; 69:4163-76. [PMID: 22802126 PMCID: PMC3505497 DOI: 10.1007/s00018-012-1072-8] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2012] [Revised: 06/07/2012] [Accepted: 06/21/2012] [Indexed: 10/28/2022]
Abstract
Store-operated Ca(2+) entry describes the phenomenon that connects a depletion of internal Ca(2+) stores to an activation of plasma membrane-located Ca(2+) selective ion channels. Tremendous progress towards the underlying molecular mechanism came with the discovery of the two respective limiting components, STIM and Orai. STIM1 represents the ER-located Ca(2+) sensor and transmits the signal of store depletion to the plasma membrane. Here it couples to and activates Orai, the highly Ca(2+)-selective pore-forming subunit of Ca(2+) release-activated Ca(2+) channels. In this review, we focus on the molecular steps that these two proteins undergo from store-depletion to their coupling, the activation, and regulation of Ca(2+) currents.
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Affiliation(s)
- Martin Muik
- Institute of Biophysics, University of Linz, Gruberstrasse 40, 4020 Linz, Austria
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39
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McKeown L, Moss NK, Turner P, Li J, Heath N, Burke D, O’Regan D, Gilthorpe MS, Porter KE, Beech DJ. Platelet-derived growth factor maintains stored calcium through a nonclustering Orai1 mechanism but evokes clustering if the endoplasmic reticulum is stressed by store depletion. Circ Res 2012; 111:66-76. [PMID: 22556336 PMCID: PMC3605802 DOI: 10.1161/circresaha.111.263616] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
RATIONALE Calcium entry through Orai1 channels drives vascular smooth muscle cell migration and neointimal hyperplasia. The channels are activated by the important growth factor platelet-derived growth factor (PDGF). Channel activation is suggested to depend on store depletion, which redistributes and clusters stromal interaction molecule 1 (STIM1), which then coclusters and activates Orai1. OBJECTIVE To determine the relevance of STIM1 and Orai1 redistribution in PDGF responses. METHODS AND RESULTS Vascular smooth muscle cells were cultured from human saphenous vein. STIM1 and Orai1 were tagged with green and red fluorescent proteins to track them in live cells. Under basal conditions, the proteins were mobile but mostly independent of each other. Inhibition of sarco-endoplasmic reticulum calcium ATPase led to store depletion and dramatic redistribution of STIM1 and Orai1 into coclusters. PDGF did not evoke redistribution, even though it caused calcium release and Orai1-mediated calcium entry in the same time period. After chemical blockade of Orai1-mediated calcium entry, however, PDGF caused redistribution. Similarly, mutagenic disruption of calcium flux through Orai1 caused PDGF to evoke redistribution, showing that calcium flux through the wild-type channels had been filling the stores. Acidification of the extracellular medium to pH 6.4 caused inhibition of Orai1-mediated calcium entry and conferred capability for PDGF to evoke complete redistribution and coclustering. CONCLUSIONS The data suggest that PDGF has a nonclustering mechanism by which to activate Orai1 channels and maintain calcium stores replete. Redistribution and clustering become important, however, when the endoplasmic reticulum stress signal of store depletion arises, for example when acidosis inhibits Orai1 channels.
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MESH Headings
- Bacterial Proteins/genetics
- Bacterial Proteins/metabolism
- Calcium/metabolism
- Calcium Channels/metabolism
- Cells, Cultured
- Endoplasmic Reticulum/drug effects
- Endoplasmic Reticulum/metabolism
- Green Fluorescent Proteins/genetics
- Green Fluorescent Proteins/metabolism
- Humans
- Hydrogen-Ion Concentration
- Luminescent Proteins/genetics
- Luminescent Proteins/metabolism
- Membrane Proteins/genetics
- Membrane Proteins/metabolism
- Microscopy, Fluorescence
- Microscopy, Video
- Muscle, Smooth, Vascular/drug effects
- Muscle, Smooth, Vascular/metabolism
- Mutation
- Myocytes, Smooth Muscle/drug effects
- Myocytes, Smooth Muscle/metabolism
- Neoplasm Proteins/genetics
- Neoplasm Proteins/metabolism
- ORAI1 Protein
- Platelet-Derived Growth Factor/metabolism
- Protein Transport
- Recombinant Fusion Proteins/metabolism
- Saphenous Vein/metabolism
- Stress, Physiological
- Stromal Interaction Molecule 1
- Thapsigargin/pharmacology
- Time Factors
- Transfection
- Red Fluorescent Protein
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Affiliation(s)
- Lynn McKeown
- Multidisciplinary Cardiovascular Research Centre, University of Leeds, Leeds, LS2 9JT, UK
- Faculty of Biological Sciences, University of Leeds, Leeds, LS2 9JT, UK
| | - Nicholas K Moss
- Multidisciplinary Cardiovascular Research Centre, University of Leeds, Leeds, LS2 9JT, UK
- Faculty of Biological Sciences, University of Leeds, Leeds, LS2 9JT, UK
| | - Paul Turner
- Multidisciplinary Cardiovascular Research Centre, University of Leeds, Leeds, LS2 9JT, UK
- Faculty of Biological Sciences, University of Leeds, Leeds, LS2 9JT, UK
| | - Jing Li
- Multidisciplinary Cardiovascular Research Centre, University of Leeds, Leeds, LS2 9JT, UK
- Faculty of Biological Sciences, University of Leeds, Leeds, LS2 9JT, UK
| | - Nikki Heath
- Multidisciplinary Cardiovascular Research Centre, University of Leeds, Leeds, LS2 9JT, UK
- Faculty of Biological Sciences, University of Leeds, Leeds, LS2 9JT, UK
| | - Dermot Burke
- Leeds Teaching Hospitals, General Infirmary, Great George Street, Leeds, LS1 3EX
| | - David O’Regan
- Leeds Teaching Hospitals, General Infirmary, Great George Street, Leeds, LS1 3EX
| | - Mark S Gilthorpe
- Faculty of Medicine & Health, University of Leeds, Leeds, LS2 9JT, UK
| | - Karen E Porter
- Multidisciplinary Cardiovascular Research Centre, University of Leeds, Leeds, LS2 9JT, UK
- Faculty of Medicine & Health, University of Leeds, Leeds, LS2 9JT, UK
| | - David J Beech
- Multidisciplinary Cardiovascular Research Centre, University of Leeds, Leeds, LS2 9JT, UK
- Faculty of Biological Sciences, University of Leeds, Leeds, LS2 9JT, UK
- Faculty of Medicine & Health, University of Leeds, Leeds, LS2 9JT, UK
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40
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McNally BA, Prakriya M. Permeation, selectivity and gating in store-operated CRAC channels. J Physiol 2012; 590:4179-91. [PMID: 22586221 DOI: 10.1113/jphysiol.2012.233098] [Citation(s) in RCA: 45] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
Store-operated Ca(2+) release-activated Ca(2+) (CRAC) channels are a widespread mechanism for generating cellular Ca(2+) signals and regulate many Ca(2+)-dependent functions, including transcription, motility and proliferation. The opening of CRAC channels in response to depletion of intracellular Ca(2+) stores involves a cascade of cellular events that culminate in direct interactions between STIM1, the endoplasmic reticulum Ca(2+) sensor, and the channels composed of Orai proteins. Evidence gathered over the last two decades indicates that CRAC channels display a unique functional pore fingerprint characterized by exquisite Ca(2+) selectivity, low unitary conductance, and low permeability to large cations. Here, we review the key pore properties of CRAC channels and discuss recent progress in addressing the molecular foundations of these properties. Structure-function and cysteine-scanning studies have revealed the identity and organization of pore-lining residues, including those that form the selectivity filter, providing a structural framework for understanding CRAC channel pore properties. Recent studies in pore mutants that produce STIM1-independent constitutive channel activation indicate that exquisite Ca(2+) selectivity in CRAC channels is not hardwired into Orai proteins, but is instead manifested only following the binding of STIM1 to the intrinsically poorly Ca(2+)-selective Orai channels. These findings reveal new functional aspects of CRAC channels and suggest that the selectivity filter of the CRAC channel is a dynamic structure whose conformation and functional properties are powerfully regulated by the channel activation stimulus.
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Affiliation(s)
- Beth A McNally
- Department of Molecular Pharmacology and Biological Chemistry, Northwestern University, Feinberg School of Medicine, Chicago, IL 60611, USA
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41
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Abstract
Mutations in genes encoding the calcium-release activated calcium (CRAC) channel abolish calcium influx in cells of the immune system and cause severe congenital immunodeficiency. Patients with autosomal recessive mutations in the CRAC channel gene ORAI1, its activator stromal interaction molecule 1 (STIM1), and mice with targeted deletion of Orai1, Stim1, and Stim2 genes reveal important roles for CRAC channels in adaptive and innate immune responses to infection and in autoimmunity. Because CRAC channels have important functions outside the immune system, deficiency of either ORAI1 or STIM1 is associated with a unique clinical phenotype. This review will give an overview of CRAC channel function in the immune system, examine the consequences of CRAC channel deficiency for immunity in human patients and mice, and discuss genetic defects in immunoreceptor-associated signaling molecules that compromise calcium influx and cause immunodeficiency.
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Affiliation(s)
- Stefan Feske
- Department of Pathology, New York University Langone Medical Center, New York, USA.
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42
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Structure, regulation and biophysics of I(CRAC), STIM/Orai1. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2012; 740:383-410. [PMID: 22453951 DOI: 10.1007/978-94-007-2888-2_16] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
Ca(2+) release activated Ca(2+) (CRAC) channels mediate robust Ca(2+) influx when the endoplasmic reticulum Ca(2+) stores are depleted. This essential process for T-cell activation as well as degranulation of mast cells involves the Ca(2+) sensor STIM1, located in the endoplasmic reticulum and the Ca(2+) selective Orai1 channel in the plasma membrane. Our review describes the CRAC signaling pathway, the activation of which is initiated by a drop in the endoplasmic Ca(2+) level sensed by STIM1. This in term induces multimerisation and puncta-formation of STIM1 proteins is followed by their coupling to and activation of Orai channels. Consequently Ca(2+) entry is triggered through the Orai pore into the cytosol with subsequent closure of the channel by Ca(2+)-dependent inactivation. We will portray a mechanistic view of the events coupling STIM1 to Orai activation based on their structure and biophysics.
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43
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Shaw PJ, Feske S. Physiological and pathophysiological functions of SOCE in the immune system. Front Biosci (Elite Ed) 2012; 4:2253-2268. [PMID: 22202035 PMCID: PMC3774593 DOI: 10.2741/e540] [Citation(s) in RCA: 58] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
Calcium signals play a critical role in many cell-type specific effector functions during innate and adaptive immune responses. The predominant mechanism to raise intracellular (Ca²⁺) used by most immune cells is store-operated Ca²⁺ entry (SOCE), whereby the depletion of endoplasmic reticulum (ER) Ca²⁺ stores triggers the influx of extracellular Ca²⁺. SOCE in immune cells is mediated by the highly Ca²⁺ selective Ca²⁺-release-activated Ca²⁺ (CRAC) channel, encoded by ORAI1, ORAI2 and ORAI3 genes. ORAI proteins are activated by stromal interaction molecules (STIM) 1 and 2, which act as sensors of ER Ca²⁺ store depletion. The importance of SOCE mediated by STIM and ORAI proteins for immune function is evident from the immunodeficiency and autoimmunity in patients with mutations in STIM1 and ORAI1 genes. These patients and studies in gene-targeted mice have revealed an essential role for ORAI/STIM proteins in the function of several immune cells. This review focuses on recent advances made towards understanding the role of SOCE in immune cells with an emphasis on the immune dysregulation that results from defects in SOCE in human patients and transgenic mice.
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Affiliation(s)
- Patrick J. Shaw
- Department of Pathology, New York University Langone Medical Center, New York, NY 10016
| | - Stefan Feske
- Department of Pathology, New York University Langone Medical Center, New York, NY 10016
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44
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Shaw PJ, Feske S. Physiological and pathophysiological functions of SOCE in the immune system. Front Biosci (Elite Ed) 2012. [PMID: 22202035 DOI: 10.2741/540] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
Calcium signals play a critical role in many cell-type specific effector functions during innate and adaptive immune responses. The predominant mechanism to raise intracellular (Ca²⁺) used by most immune cells is store-operated Ca²⁺ entry (SOCE), whereby the depletion of endoplasmic reticulum (ER) Ca²⁺ stores triggers the influx of extracellular Ca²⁺. SOCE in immune cells is mediated by the highly Ca²⁺ selective Ca²⁺-release-activated Ca²⁺ (CRAC) channel, encoded by ORAI1, ORAI2 and ORAI3 genes. ORAI proteins are activated by stromal interaction molecules (STIM) 1 and 2, which act as sensors of ER Ca²⁺ store depletion. The importance of SOCE mediated by STIM and ORAI proteins for immune function is evident from the immunodeficiency and autoimmunity in patients with mutations in STIM1 and ORAI1 genes. These patients and studies in gene-targeted mice have revealed an essential role for ORAI/STIM proteins in the function of several immune cells. This review focuses on recent advances made towards understanding the role of SOCE in immune cells with an emphasis on the immune dysregulation that results from defects in SOCE in human patients and transgenic mice.
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Affiliation(s)
- Patrick J Shaw
- Department of Pathology, New York University Langone Medical Center, New York, NY 10016, USA
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45
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Lewis RS. Store-operated calcium channels: new perspectives on mechanism and function. Cold Spring Harb Perspect Biol 2011; 3:cshperspect.a003970. [PMID: 21791698 DOI: 10.1101/cshperspect.a003970] [Citation(s) in RCA: 160] [Impact Index Per Article: 12.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023]
Abstract
Store-operated calcium channels (SOCs) are a nearly ubiquitous Ca(2+) entry pathway stimulated by numerous cell surface receptors via the reduction of Ca(2+) concentration in the ER. The discovery of STIM proteins as ER Ca(2+) sensors and Orai proteins as structural components of the Ca(2+) release-activated Ca(2+) (CRAC) channel, a prototypic SOC, opened the floodgates for exploring the molecular mechanism of this pathway and its functions. This review focuses on recent advances made possible by the use of STIM and Orai as molecular tools. I will describe our current understanding of the store-operated Ca(2+) entry mechanism and its emerging roles in physiology and disease, areas of uncertainty in which further progress is needed, and recent findings that are opening new directions for research in this rapidly growing field.
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Affiliation(s)
- Richard S Lewis
- Department of Molecular and Cellular Physiology, Stanford University School of Medicine, California 94305, USA.
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46
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Mutations in Orai1 transmembrane segment 1 cause STIM1-independent activation of Orai1 channels at glycine 98 and channel closure at arginine 91. Proc Natl Acad Sci U S A 2011; 108:17838-43. [PMID: 21987804 DOI: 10.1073/pnas.1114821108] [Citation(s) in RCA: 86] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023] Open
Abstract
Stim and Orai proteins comprise the molecular machinery of Ca(2+) release-activated Ca(2+) (CRAC) channels. As an approach toward understanding the gating of Orai1 channels, we investigated effects of selected mutations at two conserved sites in the first transmembrane segment (TM1): arginine 91 located near the cytosolic end of TM1 and glycine 98 near the middle of TM1. Orai1 R91C, when coexpressed with STIM1, was activated normally by Ca(2+)-store depletion. Treatment with diamide, a thiol-oxidizing agent, induced formation of disulfide bonds between R91C residues in adjacent Orai1 subunits and rapidly blocked STIM1-operated Ca(2+) current. Diamide-induced blocking was reversed by disulfide bond-reducing agents. These results indicate that R91 forms a very narrow part of the conducting pore at the cytosolic side. Alanine replacement at G98 prevented STIM1-induced channel activity. Interestingly, mutation to aspartate (G98D) or proline (G98P) caused constitutive channel activation in a STIM1-independent manner. Both Orai1 G98 mutants formed a nonselective Ca(2+)-permeable conductance that was relatively resistant to block by Gd(3+). The double mutant R91W/G98D was also constitutively active, overcoming the normal inhibition of channel activity by tryptophan at the 91 position found in some patients with severe combined immunodeficiency (SCID), and the double mutant R91C/G98D was resistant to diamide block. These data suggest that the channel pore is widened and ion selectivity is altered by mutations at the G98 site that may perturb α-helical structure. We propose distinct functional roles for G98 as a gating hinge and R91 as part of the physical gate at the narrow inner mouth of the channel.
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47
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Srikanth S, Yee MKW, Gwack Y, Ribalet B. The third transmembrane segment of orai1 protein modulates Ca2+ release-activated Ca2+ (CRAC) channel gating and permeation properties. J Biol Chem 2011; 286:35318-28. [PMID: 21865174 PMCID: PMC3186358 DOI: 10.1074/jbc.m111.265884] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/27/2011] [Revised: 07/19/2011] [Indexed: 11/06/2022] Open
Abstract
Orai1, the pore subunit of Ca(2+) release-activated Ca(2+) channels, has four transmembrane segments (TMs). The first segment, TMI, lines the pore and plays an important role in channel activation and ion permeation. TMIII, on the other hand, does not line the pore but still regulates channel gating and permeation properties. To understand the role of TMIII, we have mutated and characterized several residues in this domain. Mutation of Trp-176 to Cys (W176C) and Gly-183 to Ala (G183A) had dramatic effects. Unlike wild-type channels, which exhibit little outward current and are activated by STIM1, W176C mutant channels exhibited a large outward current at positive potentials and were constitutively active in the absence of STIM1. G183A mutant channels also exhibited substantial outward currents but were active only in the presence of 2-aminoethoxydiphenyl borate (2-APB), irrespective of STIM1. With W176C mutant channels inward, monovalent currents were blocked by Ca(2+) with a high affinity similar to the wild type, but the Ca(2+)-dependent blocking of outward currents differed in the two cases. Although a 50% block of the WT outward current required 250 μm Ca(2+), more than 6 mm was necessary to have the same effect on W176C mutant channels. In the presence of extracellular Ca(2+), W176C and G183A outward currents developed slowly in a voltage-dependent manner, whereas they developed almost instantaneously in the absence of Ca(2+). These changes in permeation and gating properties mimic the changes induced by mutations of Glu-190 in TMIII and Asp-110/Asp-112 in the TMI/TMII loop. On the basis of these data, we propose that TMIII maintains negatively charged residues at or near the selectivity filter in a conformation that facilitates Ca(2+) inward currents and prevents outward currents of monovalent cations. In addition, to controlling selectivity, TMIII may also stabilize channel gating in a closed state in the absence of STIM1 in a Trp-176-dependent manner.
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Affiliation(s)
- Sonal Srikanth
- From the Department of Physiology, University of California, Los Angeles, California 90095
| | - Ma-Khin Win Yee
- From the Department of Physiology, University of California, Los Angeles, California 90095
| | - Yousang Gwack
- From the Department of Physiology, University of California, Los Angeles, California 90095
| | - Bernard Ribalet
- From the Department of Physiology, University of California, Los Angeles, California 90095
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48
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Li J, McKeown L, Ojelabi O, Stacey M, Foster R, O'Regan D, Porter KE, Beech DJ. Nanomolar potency and selectivity of a Ca²⁺ release-activated Ca²⁺ channel inhibitor against store-operated Ca²⁺ entry and migration of vascular smooth muscle cells. Br J Pharmacol 2011; 164:382-93. [PMID: 21545575 PMCID: PMC3174418 DOI: 10.1111/j.1476-5381.2011.01368.x] [Citation(s) in RCA: 50] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/04/2010] [Revised: 02/16/2011] [Accepted: 02/28/2011] [Indexed: 01/05/2023] Open
Abstract
BACKGROUND AND PURPOSE The aim was to advance the understanding of Orai proteins and identify a specific inhibitor of the associated calcium entry mechanism in vascular smooth muscle cells (VSMCs). EXPERIMENTAL APPROACH Proliferating VSMCs were cultured from human saphenous veins. Intracellular calcium was measured using fura-2, whole-cell current was recorded using patch-clamp and cell migration quantified in modified Boyden chambers. Subcellular protein localization was determined by microscopy. Isometric tension was recorded from mouse aortic rings. KEY RESULTS Molecular disruption and rescue experiments indicated the importance of Orai1 in calcium entry caused by store depletion evoked passively or by platelet-derived growth factor (PDGF), suggesting the presence of Ca(2+) release-activated Ca(2+) (CRAC) channels like those of the immune system. The CRAC channel blocker, S66, was a potent inhibitor of the VSMC signals, IC(50) 26 nM, which was almost two orders of magnitude greater than with leucocytes. S66 had no effect on PDGF- and ATP-evoked calcium release, overexpressed transient receptor potential canonical (TRPC)5 channels, native TRPC1/5-containing channels, stromal interaction molecule 1 clustering, non-selective cationic current evoked by store depletion and phenylephrine-evoked aortic contraction. S66 reduced PDGF-evoked VSMC migration while having only modest effects on cell proliferation and no effect on cell viability. CONCLUSIONS AND IMPLICATIONS The data suggest that Orai1 has a role in human VSMC migration, and that a CRAC channel inhibitor has high potency and selectivity for the associated calcium entry, suggesting a distinct characteristic of vascular CRAC channels and the potential for selective chemical suppression of vascular remodelling.
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Affiliation(s)
- Jing Li
- Multidisciplinary Cardiovascular Research Centre, University of LeedsLeeds, UK
- Faculty of Biological Sciences, University of LeedsLeeds, UK
| | - Lynn McKeown
- Multidisciplinary Cardiovascular Research Centre, University of LeedsLeeds, UK
- Faculty of Biological Sciences, University of LeedsLeeds, UK
| | - Ogooluwa Ojelabi
- Multidisciplinary Cardiovascular Research Centre, University of LeedsLeeds, UK
- Faculty of Biological Sciences, University of LeedsLeeds, UK
| | - Martin Stacey
- Multidisciplinary Cardiovascular Research Centre, University of LeedsLeeds, UK
- Faculty of Biological Sciences, University of LeedsLeeds, UK
| | - Richard Foster
- Multidisciplinary Cardiovascular Research Centre, University of LeedsLeeds, UK
- School of Chemistry, University of LeedsLeeds, UK
| | - David O'Regan
- Yorkshire Heart Centre, General Infirmary at LeedsLeeds, UK
| | - Karen E Porter
- Multidisciplinary Cardiovascular Research Centre, University of LeedsLeeds, UK
- Faculty of Medicine & Health, University of LeedsLeeds, UK
| | - David J Beech
- Multidisciplinary Cardiovascular Research Centre, University of LeedsLeeds, UK
- Faculty of Biological Sciences, University of LeedsLeeds, UK
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49
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Bergsmann J, Derler I, Muik M, Frischauf I, Fahrner M, Pollheimer P, Schwarzinger C, Gruber HJ, Groschner K, Romanin C. Molecular determinants within N terminus of Orai3 protein that control channel activation and gating. J Biol Chem 2011; 286:31565-75. [PMID: 21724845 PMCID: PMC3173129 DOI: 10.1074/jbc.m111.227546] [Citation(s) in RCA: 40] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
STIM1 and Orai represent the key components of Ca2+ release-activated Ca2+ channels. Activation of Orai channels requires coupling of the C terminus of STIM1 to the N and C termini of Orai. Although the latter appears to be central in the interaction with STIM1, the role of the N terminus and particularly of the conserved region close to the first transmembrane sequence is less well understood. Here, we investigated in detail the functional role of this conserved region in Orai3 by stepwise deletions. Molecular determinants were mapped for the two modes of Orai3 activation via STIM1 or 2-aminoethoxydiphenyl borate (2-APB) and for current gating characteristics. Increasing N-terminal truncations revealed a progressive decrease of the specific fast inactivation of Orai3 concomitant with diminished binding to calmodulin. STIM1-dependent activation of Orai3 was maintained as long as the second half of this conserved N-terminal domain was present. Further truncations abolished it, whereas Orai3 stimulation via 2-APB was partially retained. In aggregate, the N-terminal conserved region plays a multifaceted role in Orai3 current gating with distinct structural requirements for STIM1- and 2-APB-stimulated activation.
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Affiliation(s)
- Judith Bergsmann
- Institute of Biophysics, University of Linz, Altenbergerstrasse 69, 4040 Linz, Austria
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50
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Li J, Cubbon RM, Wilson LA, Amer MS, McKeown L, Hou B, Majeed Y, Tumova S, Seymour VAL, Taylor H, Stacey M, O'Regan D, Foster R, Porter KE, Kearney MT, Beech DJ. Orai1 and CRAC channel dependence of VEGF-activated Ca2+ entry and endothelial tube formation. Circ Res 2011; 108:1190-8. [PMID: 21441136 DOI: 10.1161/circresaha.111.243352] [Citation(s) in RCA: 155] [Impact Index Per Article: 11.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
RATIONALE Orai1 and the associated calcium release-activated calcium (CRAC) channel were discovered in the immune system. Existence also in endothelial cells has been suggested, but the relevance to endothelial biology is mostly unknown. OBJECTIVE The aim of this study was to investigate the relevance of Orai1 and CRAC channels to vascular endothelial growth factor (VEGF) and endothelial tube formation. METHODS AND RESULTS In human umbilical vein endothelial cells, Orai1 disruption by short-interfering RNA or dominant-negative mutant Orai1 inhibited calcium release-activated (store-operated) calcium entry, VEGF-evoked calcium entry, cell migration, and in vitro tube formation. Expression of exogenous wild-type Orai1 rescued the tube formation. VEGF receptor-2 and Orai1 partially colocalized. Orai1 disruption also inhibited calcium entry and tube formation in endothelial progenitor cells from human blood. A known blocker of the immune cell CRAC channel (3-fluoropyridine-4-carboxylic acid (2',5'-dimethoxybiphenyl-4-yl)amide) was a strong blocker of store-operated calcium entry in endothelial cells and inhibited calcium entry evoked by VEGF in 3 types of human endothelial cell. The compound lacked effect on VEGF-evoked calcium-release, STIM1 clustering, and 2 types of transient receptor potential channels, TRPC6 and TRPV4. Without effect on cell viability, the compound inhibited human endothelial cell migration and tube formation in vitro and suppressed angiogenesis in vivo in the chick chorioallantoic membrane. The compound showed 100-fold greater potency for endothelial compared with immune cell calcium entry. CONCLUSIONS The data suggest positive roles for Orai1 and CRAC channels in VEGF-evoked calcium entry and new opportunity for chemical modulation of angiogenesis.
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Affiliation(s)
- Jing Li
- Institute of Membrane & Systems Biology, Faculty of Biological Sciences, University of Leeds, Leeds LS2 9JT, United Kingdom
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