1
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Ismatullah H, Jabeen I, Kiani YS. Structural and functional insight into a new emerging target IP 3R in cancer. J Biomol Struct Dyn 2024; 42:2170-2196. [PMID: 37070253 DOI: 10.1080/07391102.2023.2201332] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/27/2023] [Accepted: 04/05/2023] [Indexed: 04/19/2023]
Abstract
Calcium signaling has been identified as an important phenomenon in a plethora of cellular processes. Inositol 1,4,5-trisphosphate receptors (IP3Rs) are ER-residing intracellular calcium (Ca2+) release channels responsible for cell bioenergetics by transferring calcium from the ER to the mitochondria. The recent availability of full-length IP3R channel structure has enabled the researchers to design the IP3 competitive ligands and reveal the channel gating mechanism by elucidating the conformational changes induced by ligands. However, limited knowledge is available for IP3R antagonists and the exact mechanism of action of these antagonists within a tumorigenic environment of a cell. Here in this review a summarized information about the role of IP3R in cell proliferation and apoptosis has been discussed. Moreover, structure and gating mechanism of IP3R in the presence of antagonists have been provided in this review. Additionally, compelling information about ligand-based studies (both agonists and antagonists) has been discussed. The shortcomings of these studies and the challenges toward the design of potent IP3R modulators have also been provided in this review. However, the conformational changes induced by antagonists for channel gating mechanism still display some major drawbacks that need to be addressed. However, the design, synthesis and availability of isoform-specific antagonists is a rather challenging one due to intra-structural similarity within the binding domain of each isoform. HighlightsThe intricate complexity of IP3R's in cellular processes declares them an important target whereby, the recently solved structure depicts the receptor's potential involvement in a complex network of processes spanning from cell proliferation to cell death.Pharmacological inhibition of IP3R attenuates the proliferation or invasiveness of cancers, thus inducing necrotic cell death.Despite significant advancements, there is a tremendous need to design new potential hits to target IP3R, based upon 3D structural features and pharmacophoric patterns.Communicated by Ramaswamy H. Sarma.
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Affiliation(s)
- Humaira Ismatullah
- Department of Sciences, School of Interdisciplinary Engineering and Sciences (SINES), National University of Sciences and Technology (NUST), Islamabad, Pakistan
| | - Ishrat Jabeen
- Department of Sciences, School of Interdisciplinary Engineering and Sciences (SINES), National University of Sciences and Technology (NUST), Islamabad, Pakistan
| | - Yusra Sajid Kiani
- Department of Sciences, School of Interdisciplinary Engineering and Sciences (SINES), National University of Sciences and Technology (NUST), Islamabad, Pakistan
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2
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Della-Felice F, de Andrade Bartolomeu A, Pilli RA. The phosphate ester group in secondary metabolites. Nat Prod Rep 2022; 39:1066-1107. [PMID: 35420073 DOI: 10.1039/d1np00078k] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Covering: 2000 to mid-2021The phosphate ester is a versatile, widespread functional group involved in a plethora of biological activities. Its presence in secondary metabolites, however, is relatively rare compared to other functionalities and thus is part of a rather unexplored chemical space. Herein, the chemistry of secondary metabolites containing the phosphate ester group is discussed. The text emphasizes their structural diversity, biological and pharmacological profiles, and synthetic approaches employed in the phosphorylation step during total synthesis campaigns, covering the literature from 2000 to mid-2021.
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Affiliation(s)
- Franco Della-Felice
- Institute of Chemistry, University of Campinas (UNICAMP), P.O. Box 6154, CEP 13083-970 Campinas, Sao Paulo, Brazil.,Institute of Chemical Research of Catalonia (ICIQ), Barcelona Institute of Science and Technology, Av. Països Catalans 16, 43007 Tarragona, Spain.
| | | | - Ronaldo Aloise Pilli
- Institute of Chemistry, University of Campinas (UNICAMP), P.O. Box 6154, CEP 13083-970 Campinas, Sao Paulo, Brazil
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3
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Woll KA, Van Petegem F. Calcium Release Channels: Structure and Function of IP3 Receptors and Ryanodine Receptors. Physiol Rev 2021; 102:209-268. [PMID: 34280054 DOI: 10.1152/physrev.00033.2020] [Citation(s) in RCA: 87] [Impact Index Per Article: 29.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
Ca2+-release channels are giant membrane proteins that control the release of Ca2+ from the endoplasmic and sarcoplasmic reticulum. The two members, ryanodine receptors (RyRs) and inositol-1,4,5-trisphosphate Receptors (IP3Rs), are evolutionarily related and are both activated by cytosolic Ca2+. They share a common architecture, but RyRs have evolved additional modules in the cytosolic region. Their massive size allows for the regulation by tens of proteins and small molecules, which can affect the opening and closing of the channels. In addition to Ca2+, other major triggers include IP3 for the IP3Rs, and depolarization of the plasma membrane for a particular RyR subtype. Their size has made them popular targets for study via electron microscopic methods, with current structures culminating near 3Å. The available structures have provided many new mechanistic insights int the binding of auxiliary proteins and small molecules, how these can regulate channel opening, and the mechanisms of disease-associated mutations. They also help scrutinize previously proposed binding sites, as some of these are now incompatible with the structures. Many questions remain around the structural effects of post-translational modifications, additional binding partners, and the higher-order complexes these channels can make in situ. This review summarizes our current knowledge about the structures of Ca2+-release channels and how this informs on their function.
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Affiliation(s)
- Kellie A Woll
- Department of Biochemistry and Molecular Biology, University of British Columbia, Vancouver, BC, Canada
| | - Filip Van Petegem
- Department of Biochemistry and Molecular Biology, University of British Columbia, Vancouver, BC, Canada
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4
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Oguro A, Sugitani A, Kobayashi Y, Sakuma R, Imaoka S. Bisphenol A stabilizes Nrf2 via Ca 2+ influx by direct activation of the IP 3 receptor. J Toxicol Sci 2021; 46:1-10. [PMID: 33408296 DOI: 10.2131/jts.46.1] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
Bisphenol A (BPA) is an endocrine-disrupting chemical used in polycarbonate and epoxy resins. Previously, we found that BPA stabilized the protein levels of nuclear factor erythroid 2-related factor 2 (Nrf2) by inducing Ca2+ efflux into the cytosol, followed by nitric oxide synthase activation, resulting in the enhanced nitrosylation of Keap1, which is a negative regulator of Nrf2. However, the mechanisms behind the stimulation of Ca2+ efflux by BPA remain unknown. In the present study, we found that BPA stimulated Ca2+ efflux into the cytosol from the ER, but not from outside of cells through the plasma membrane in Hep3B cells. Ca2+ efflux and Nrf2 stabilization by BPA were inhibited by an inhibitor of the inositol 1,4,5-trisphosphate (IP3) receptor, 2-aminoethoxydiphenylborane, in the endoplasmic reticulum. IP3 is produced by activation of phospholipase C (PLC) from a membrane lipid, phosphatidylinositol 4,5-bisphosphate (PIP2). The induction of Nrf2 by BPA was not inhibited by a PLC inhibitor, U-73122, suggesting that BPA does not induce the production of IP3 via PLC activation. We found that BPA bound directly to the IP3 binding core domain of the IP3 receptor, and BPA competed with IP3 on this site. In addition, overexpression of this domain of the IP3 receptor in Hep3B cells inhibited the stabilization of Nrf2 by BPA. These results clarified that the IP3 receptor is a new target of BPA, and that BPA induces Ca2+ efflux from the endoplasmic reticulum via activation of the IP3 receptor.
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Affiliation(s)
- Ami Oguro
- Department of Biomedical Chemistry, School of Science and Technology, Kwansei Gakuin University.,Program of Biomedical Science, Graduate School of Integrated Sciences for Life, Hiroshima University
| | - Atsushi Sugitani
- Department of Biomedical Chemistry, School of Science and Technology, Kwansei Gakuin University
| | - Yukino Kobayashi
- Department of Biomedical Chemistry, School of Science and Technology, Kwansei Gakuin University
| | - Rika Sakuma
- Department of Biomedical Chemistry, School of Science and Technology, Kwansei Gakuin University
| | - Susumu Imaoka
- Department of Biomedical Chemistry, School of Science and Technology, Kwansei Gakuin University
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5
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Gambardella J, Morelli MB, Wang X, Castellanos V, Mone P, Santulli G. The discovery and development of IP3 receptor modulators: an update. Expert Opin Drug Discov 2021; 16:709-718. [PMID: 33356639 DOI: 10.1080/17460441.2021.1858792] [Citation(s) in RCA: 15] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
Introduction: Inositol 1,4,5-trisphosphate receptors (IP3Rs) are intracellular calcium (Ca2+) release channels located on the endoplasmic/sarcoplasmic reticulum. The availability of the structure of the ligand-binding domain of IP3Rs has enabled the design of compatible ligands, but the limiting step remains their actual effectiveness in a biological context.Areas covered: This article summarizes the compelling literature on both agonists and antagonists targeting IP3Rs, emphasizing their strengths and limitations. The main challenges toward the discovery and development of IP3 receptor modulators are also described.Expert opinion: Despite significant progress in recent years, the pharmacology of IP3R still has major drawbacks, especially concerning the availability of specific antag onists. Moreover, drugs specifically targeting the three different subtypes of IP3R are especially needed.
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Affiliation(s)
- Jessica Gambardella
- Department of Medicine (Division of Cardiology), Wilf Family Cardiovascular Research Institute, Einstein Institute for Aging Research, Albert Einstein College of Medicine, Montefiore University Hospital, New York City, USA.,Department of Molecular Pharmacology, Fleischer Institute for Diabetes and Metabolism, Einstein-Sinai Diabetes Research Center (ES-DRC), Albert Einstein College of Medicine, New York City, USA.,Department of Advanced Biomedical Sciences, "Federico II" University, Naples, Italy.,International Translational Research and Medical Education (ITME), Naples, Italy
| | - Marco B Morelli
- Department of Medicine (Division of Cardiology), Wilf Family Cardiovascular Research Institute, Einstein Institute for Aging Research, Albert Einstein College of Medicine, Montefiore University Hospital, New York City, USA.,Department of Molecular Pharmacology, Fleischer Institute for Diabetes and Metabolism, Einstein-Sinai Diabetes Research Center (ES-DRC), Albert Einstein College of Medicine, New York City, USA
| | - Xujun Wang
- Department of Medicine (Division of Cardiology), Wilf Family Cardiovascular Research Institute, Einstein Institute for Aging Research, Albert Einstein College of Medicine, Montefiore University Hospital, New York City, USA
| | - Vanessa Castellanos
- Department of Medicine (Division of Cardiology), Wilf Family Cardiovascular Research Institute, Einstein Institute for Aging Research, Albert Einstein College of Medicine, Montefiore University Hospital, New York City, USA
| | - Pasquale Mone
- University of Campania "Luigi Vanvitelli", Naples, Italy
| | - Gaetano Santulli
- Department of Medicine (Division of Cardiology), Wilf Family Cardiovascular Research Institute, Einstein Institute for Aging Research, Albert Einstein College of Medicine, Montefiore University Hospital, New York City, USA.,Department of Molecular Pharmacology, Fleischer Institute for Diabetes and Metabolism, Einstein-Sinai Diabetes Research Center (ES-DRC), Albert Einstein College of Medicine, New York City, USA.,Department of Advanced Biomedical Sciences, "Federico II" University, Naples, Italy.,International Translational Research and Medical Education (ITME), Naples, Italy
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6
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Su X, Dohle W, Mills SJ, Watt JM, Rossi AM, Taylor CW, Potter BVL. Inositol Adenophostin: Convergent Synthesis of a Potent Agonist of d- myo-Inositol 1,4,5-Trisphosphate Receptors. ACS OMEGA 2020; 5:28793-28811. [PMID: 33195933 PMCID: PMC7659177 DOI: 10.1021/acsomega.0c04145] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 08/27/2020] [Accepted: 10/08/2020] [Indexed: 06/11/2023]
Abstract
d-myo-Inositol 1,4,5-trisphosphate receptors (IP3Rs) are Ca2+ channels activated by the intracellular messenger inositol 1,4,5-trisphosphate (IP3, 1). The glyconucleotide adenophostin A (AdA, 2) is a potent agonist of IP3Rs. A recent synthesis of d-chiro-inositol adenophostin (InsAdA, 5) employed suitably protected chiral building blocks and replaced the d-glucose core by d-chiro-inositol. An alternative approach to fully chiral material is now reported using intrinsic sugar chirality to avoid early isomer resolution, involving the coupling of a protected and activated racemic myo-inositol derivative to a d-ribose derivative. Diastereoisomer separation was achieved after trans-isopropylidene group removal and the absolute ribose-inositol conjugate stereochemistry assigned with reference to the earlier synthesis. Optimization of stannylene-mediated regiospecific benzylation was explored using the model 1,2-O-isopropylidene-3,6-di-O-benzyl-myo-inositol and conditions successfully transferred to one conjugate diastereoisomer with 3:1 selectivity. However, only roughly 1:1 regiospecificity was achieved on the required diastereoisomer. The conjugate regioisomers of benzyl derivatives 39 and 40 were successfully separated and 39 was transformed subsequently to InsAdA after amination, pan-phosphorylation, and deprotection. InsAdA from this synthetic route bound with greater affinity than AdA to IP3R1 and was more potent in releasing Ca2+ from intracellular stores through IP3Rs. It is the most potent full agonist of IP3R1 known and .equipotent with material from the fully chiral synthetic route.
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Affiliation(s)
- Xiangdong Su
- Medicinal
Chemistry & Drug Discovery, Department of Pharmacology, University of Oxford, Mansfield Road, Oxford OX1 3QT, U.K.
| | - Wolfgang Dohle
- Medicinal
Chemistry & Drug Discovery, Department of Pharmacology, University of Oxford, Mansfield Road, Oxford OX1 3QT, U.K.
| | - Stephen J. Mills
- Medicinal
Chemistry & Drug Discovery, Department of Pharmacology, University of Oxford, Mansfield Road, Oxford OX1 3QT, U.K.
| | - Joanna M. Watt
- Medicinal
Chemistry & Drug Discovery, Department of Pharmacology, University of Oxford, Mansfield Road, Oxford OX1 3QT, U.K.
- Wolfson
Laboratory of Medicinal Chemistry, Department of Pharmacy and Pharmacology, University of Bath, Claverton Down, Bath BA2 7AY, U.K.
| | - Ana M. Rossi
- Department
of Pharmacology, University of Cambridge, Tennis Court Road, Cambridge CB2 1PD, U.K.
| | - Colin W. Taylor
- Department
of Pharmacology, University of Cambridge, Tennis Court Road, Cambridge CB2 1PD, U.K.
| | - Barry V. L. Potter
- Medicinal
Chemistry & Drug Discovery, Department of Pharmacology, University of Oxford, Mansfield Road, Oxford OX1 3QT, U.K.
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7
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Mills SJ, Rossi AM, Konieczny V, Bakowski D, Taylor CW, Potter BVL. d- chiro-Inositol Ribophostin: A Highly Potent Agonist of d- myo-Inositol 1,4,5-Trisphosphate Receptors: Synthesis and Biological Activities. J Med Chem 2020; 63:3238-3251. [PMID: 32052631 PMCID: PMC7104261 DOI: 10.1021/acs.jmedchem.9b01986] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
![]()
Analogues
of the Ca2+-releasing intracellular messenger d-myo-inositol 1,4,5-trisphosphate [1, Ins(1,4,5)P3] are important synthetic targets. Replacement
of the α-glucopyranosyl motif in the natural product mimic adenophostin 2 by d-chiro-inositol in d-chiro-inositol adenophostin 4 increased
the potency. Similar modification of the non-nucleotide Ins(1,4,5)P3 mimic ribophostin 6 may increase the activity. d-chiro-Inositol ribophostin 10 was synthesized by coupling as building blocks suitably protected
ribose 12 with l-(+)-3-O-trifluoromethylsulfonyl-6-O-p-methoxybenzyl-1,2:4,5-di-O-isopropylidene-myo-inositol 11. Separable
diastereoisomeric 3-O-camphanate esters of (±)-6-O-p-methoxy-benzyl-1,2:4,5-di-O-isopropylidene-myo-inositol allowed the preparation
of 11. Selective trans-isopropylidene
deprotection in coupled 13, then monobenzylation gave
separable regioisomers 15 and 16. p-Methoxybenzyl group deprotection of 16, phosphitylation/oxidation,
then deprotection afforded 10, which was a full agonist
in Ca2+-release assays; its potency and binding affinity
for Ins(1,4,5)P3R were similar to those of adenophostin.
Both 4 and 10 elicited a store-operated
Ca2+ current ICRAC in patch-clamped cells, unlike
Ins(1,4,5)P3 consistent with resistance to metabolism. d-chiro-Inositol ribophostin is the most potent
small-molecule Ins(1,4,5)P3 receptor agonist without a
nucleobase yet synthesized.
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Affiliation(s)
- Stephen J Mills
- Drug Discovery & Medicinal Chemistry, Department of Pharmacology, University of Oxford, Mansfield Road, Oxford OX1 3QT, United Kingdom
| | - Ana M Rossi
- Department of Pharmacology, University of Cambridge, Tennis Court Road, Cambridge CB2 1PD, United Kingdom
| | - Vera Konieczny
- Department of Pharmacology, University of Cambridge, Tennis Court Road, Cambridge CB2 1PD, United Kingdom
| | - Daniel Bakowski
- Centre of Integrative Physiology, Department of Physiology, Anatomy and Genetics, University of Oxford, Oxford OX1 3PT, United Kingdom
| | - Colin W Taylor
- Department of Pharmacology, University of Cambridge, Tennis Court Road, Cambridge CB2 1PD, United Kingdom
| | - Barry V L Potter
- Drug Discovery & Medicinal Chemistry, Department of Pharmacology, University of Oxford, Mansfield Road, Oxford OX1 3QT, United Kingdom
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8
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Chandran A, Chee X, Prole DL, Rahman T. Exploration of inositol 1,4,5-trisphosphate (IP 3) regulated dynamics of N-terminal domain of IP 3 receptor reveals early phase molecular events during receptor activation. Sci Rep 2019; 9:2454. [PMID: 30792485 PMCID: PMC6385359 DOI: 10.1038/s41598-019-39301-3] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/03/2018] [Accepted: 01/22/2019] [Indexed: 01/12/2023] Open
Abstract
Inositol 1, 4, 5-trisphosphate (IP3) binding at the N-terminus (NT) of IP3 receptor (IP3R) allosterically triggers the opening of a Ca2+-conducting pore located ~100 Å away from the IP3-binding core (IBC). However, the precise mechanism of IP3 binding and correlated domain dynamics in the NT that are central to the IP3R activation, remains unknown. Our all-atom molecular dynamics (MD) simulations recapitulate the characteristic twist motion of the suppressor domain (SD) and reveal correlated ‘clam closure’ dynamics of IBC with IP3-binding, complementing existing suggestions on IP3R activation mechanism. Our study further reveals the existence of inter-domain dynamic correlation in the NT and establishes the SD to be critical for the conformational dynamics of IBC. Also, a tripartite interaction involving Glu283-Arg54-Asp444 at the SD – IBC interface seemed critical for IP3R activation. Intriguingly, during the sub-microsecond long simulation, we observed Arg269 undergoing an SD-dependent flipping of hydrogen bonding between the first and fifth phosphate groups of IP3. This seems to play a major role in determining the IP3 binding affinity of IBC in the presence/absence of the SD. Our study thus provides atomistic details of early molecular events occurring within the NT during and following IP3 binding that lead to channel gating.
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Affiliation(s)
- Aneesh Chandran
- Department of Pharmacology, University of Cambridge, Tennis Court Road, CB2 1PD, Cambridge, UK. .,Molecular Biophysics Unit, Indian Institute of Science, 560 012, Bangalore, India.
| | - Xavier Chee
- Department of Pharmacology, University of Cambridge, Tennis Court Road, CB2 1PD, Cambridge, UK
| | - David L Prole
- Department of Pharmacology, University of Cambridge, Tennis Court Road, CB2 1PD, Cambridge, UK
| | - Taufiq Rahman
- Department of Pharmacology, University of Cambridge, Tennis Court Road, CB2 1PD, Cambridge, UK.
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9
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Cryo-EM reveals ligand induced allostery underlying InsP 3R channel gating. Cell Res 2018; 28:1158-1170. [PMID: 30470765 PMCID: PMC6274648 DOI: 10.1038/s41422-018-0108-5] [Citation(s) in RCA: 42] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/17/2018] [Revised: 09/02/2018] [Accepted: 10/22/2018] [Indexed: 01/06/2023] Open
Abstract
Inositol-1,4,5-trisphosphate receptors (InsP3Rs) are cation channels that mobilize Ca2+ from intracellular stores in response to a wide range of cellular stimuli. The paradigm of InsP3R activation is the coupled interplay between binding of InsP3 and Ca2+ that switches the ion conduction pathway between closed and open states to enable the passage of Ca2+ through the channel. However, the molecular mechanism of how the receptor senses and decodes ligand-binding signals into gating motion remains unknown. Here, we present the electron cryo-microscopy structure of InsP3R1 from rat cerebellum determined to 4.1 Å resolution in the presence of activating concentrations of Ca2+ and adenophostin A (AdA), a structural mimetic of InsP3 and the most potent known agonist of the channel. Comparison with the 3.9 Å-resolution structure of InsP3R1 in the Apo-state, also reported herein, reveals the binding arrangement of AdA in the tetrameric channel assembly and striking ligand-induced conformational rearrangements within cytoplasmic domains coupled to the dilation of a hydrophobic constriction at the gate. Together, our results provide critical insights into the mechanistic principles by which ligand-binding allosterically gates InsP3R channel.
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10
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Vibhute AM, Pushpanandan P, Varghese M, Koniecnzy V, Taylor CW, Sureshan KM. Synthesis of dimeric analogs of adenophostin A that potently evoke Ca 2+ release through IP 3 receptors. RSC Adv 2016; 6:86346-86351. [PMID: 28066549 PMCID: PMC5171214 DOI: 10.1039/c6ra19413c] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/01/2016] [Accepted: 09/05/2016] [Indexed: 11/21/2022] Open
Abstract
Syntheses and Ca2+ release potentials of four dimeric analogs of adenophostin A (AdA) through activation of type 1 IP3R are reported. These analogs are full agonists of IP3R and are equipotent to AdA, the most potent agonist of IP3R.
Inositol 1,4,5-trisphosphate receptors (IP3Rs) are tetrameric intracellular channels through which many extracellular stimuli initiate the Ca2+ signals that regulate diverse cellular responses. There is considerable interest in developing novel ligands of IP3R. Adenophostin A (AdA) is a potent agonist of IP3R and since some dimeric analogs of IP3R ligands are more potent than the corresponding monomer; we considered whether dimeric AdA analogs might provide agonists with increased potency. We previously synthesized traizolophostin, in which a simple triazole replaced the adenine of AdA, and showed it to be equipotent to AdA. Here, we used click chemistry to synthesize four homodimeric analogs of triazolophostin, connected by oligoethylene glycol chains of different lengths. We evaluated the potency of these analogs to release Ca2+ through type 1 IP3R and established that the newly synthesized dimers are equipotent to AdA and triazolophostin.
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Affiliation(s)
- Amol M Vibhute
- School of Chemistry , Indian Institute of Science Education and Research Thiruvananthapuram , Kerala 695016 , India . ; http://kms514.wix.com/kmsgroup
| | - Poornenth Pushpanandan
- School of Chemistry , Indian Institute of Science Education and Research Thiruvananthapuram , Kerala 695016 , India . ; http://kms514.wix.com/kmsgroup
| | - Maria Varghese
- School of Chemistry , Indian Institute of Science Education and Research Thiruvananthapuram , Kerala 695016 , India . ; http://kms514.wix.com/kmsgroup
| | - Vera Koniecnzy
- Department of Pharmacology , University of Cambridge , Tennis Court Road , Cambridge , CB2 1PD , UK
| | - Colin W Taylor
- Department of Pharmacology , University of Cambridge , Tennis Court Road , Cambridge , CB2 1PD , UK
| | - Kana M Sureshan
- School of Chemistry , Indian Institute of Science Education and Research Thiruvananthapuram , Kerala 695016 , India . ; http://kms514.wix.com/kmsgroup
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11
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Vibhute AM, Konieczny V, Taylor CW, Sureshan KM. Triazolophostins: a library of novel and potent agonists of IP3 receptors. Org Biomol Chem 2016; 13:6698-710. [PMID: 25869535 PMCID: PMC4533600 DOI: 10.1039/c5ob00440c] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
IP3R initiate most cellular Ca2+ signaling. AdA is the most potent agonist of IP3R. The structural complexity of AdA makes synthesis of its analogs cumbersome. We report an easy method for generating a library of potent triazole-based analogs of AdA, triazolophostins, which are the most potent AdA analogs devoid of a nucleobase.
IP3 receptors are channels that mediate the release of Ca2+ from the intracellular stores of cells stimulated by hormones or neurotransmitters. Adenophostin A (AdA) is the most potent agonist of IP3 receptors, with the β-anomeric adenine contributing to the increased potency. The potency of AdA and its stability towards the enzymes that degrade IP3 have aroused interest in AdA analogs for biological studies. The complex structure of AdA poses problems that have necessitated optimization of synthetic conditions for each analog. Such lengthy one-at-a-time syntheses limit access to AdA analogs. We have addressed this problem by synthesizing a library of triazole-based AdA analogs, triazolophostins, by employing click chemistry. An advanced intermediate having all the necessary phosphates and a β-azide at the anomeric position was reacted with various alkynes under Cu(i) catalysis to yield triazoles, which upon deprotection gave triazolophostins. All eleven triazolophostins synthesized are more potent than IP3 and some are equipotent with AdA in functional analyses of IP3 receptors. We show that a triazole ring can replace adenine without compromising the potency of AdA and provide facile routes to novel AdA analogs.
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Affiliation(s)
- Amol M Vibhute
- School of Chemistry, Indian Institute of Science Education and Research, Thiruvananthapuram, Kerala-695016, India.
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12
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Abstract
Synthetic compounds open up new avenues to interrogate and manipulate intracellular Ca2+ signalling pathways. They may ultimately lead to drug-like analogues to intervene in disease. Recent advances in chemical biology tools available to probe Ca2+ signalling are described, with a particular focus on those synthetic analogues from our group that have enhanced biological understanding or represent a step towards more drug-like molecules. Adenophostin (AdA) is the most potent known agonist at the inositol 1,4,5-trisphosphate receptor (IP3R) and synthetic analogues provide a binding model for receptor activation and channel opening. 2-O-Modified inositol 1,4,5-trisphosphate (IP3) derivatives that are partial agonists at the IP3R reveal key conformational changes of the receptor upon ligand binding. Biphenyl polyphosphates illustrate that simple non-inositol surrogates can be engineered to give prototype IP3R agonists or antagonists and act as templates for protein co-crystallization. Cyclic adenosine 5'-diphosphoribose (cADPR) can be selectively modified using total synthesis, generating chemically and biologically stable tools to investigate Ca2+ release via the ryanodine receptor (RyR) and to interfere with cADPR synthesis and degradation. The first neutral analogues with a synthetic pyrophosphate bioisostere surprisingly retain the ability to release Ca2+, suggesting a new route to membrane-permeant tools. Adenosine 5'-diphosphoribose (ADPR) activates the Ca2+-, Na+- and K+-permeable transient receptor potential melastatin 2 (TRPM2) cation channel. Synthetic ADPR analogues provide the first structure-activity relationship (SAR) for this emerging messenger and the first functional antagonists. An analogue based on the nicotinic acid motif of nicotinic acid adenine dinucleotide phosphate (NAADP) antagonizes NAADP-mediated Ca2+ release in vitro and is effective in vivo against induced heart arrhythmia and autoimmune disease, illustrating the therapeutic potential of targeted small molecules.
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13
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Thomas MP, Mills SJ, Potter BVL. The "Other" Inositols and Their Phosphates: Synthesis, Biology, and Medicine (with Recent Advances in myo-Inositol Chemistry). Angew Chem Int Ed Engl 2016; 55:1614-50. [PMID: 26694856 PMCID: PMC5156312 DOI: 10.1002/anie.201502227] [Citation(s) in RCA: 112] [Impact Index Per Article: 14.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/23/2015] [Indexed: 12/24/2022]
Abstract
Cell signaling via inositol phosphates, in particular via the second messenger myo-inositol 1,4,5-trisphosphate, and phosphoinositides comprises a huge field of biology. Of the nine 1,2,3,4,5,6-cyclohexanehexol isomers, myo-inositol is pre-eminent, with "other" inositols (cis-, epi-, allo-, muco-, neo-, L-chiro-, D-chiro-, and scyllo-) and derivatives rarer or thought not to exist in nature. However, neo- and d-chiro-inositol hexakisphosphates were recently revealed in both terrestrial and aquatic ecosystems, thus highlighting the paucity of knowledge of the origins and potential biological functions of such stereoisomers, a prevalent group of environmental organic phosphates, and their parent inositols. Some "other" inositols are medically relevant, for example, scyllo-inositol (neurodegenerative diseases) and d-chiro-inositol (diabetes). It is timely to consider exploration of the roles and applications of the "other" isomers and their derivatives, likely by exploiting techniques now well developed for the myo series.
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Affiliation(s)
- Mark P Thomas
- Department of Pharmacy & Pharmacology, University of Bath, Claverton Down, Bath, BA2 7AY, UK
| | - Stephen J Mills
- Department of Pharmacy & Pharmacology, University of Bath, Claverton Down, Bath, BA2 7AY, UK
| | - Barry V L Potter
- Department of Pharmacology, University of Oxford, Mansfield Road, Oxford, OX1 3QT, UK.
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Thomas MP, Mills SJ, Potter BVL. Die “anderen” Inositole und ihre Phosphate: Synthese, Biologie und Medizin (sowie jüngste Fortschritte in dermyo-Inositolchemie). Angew Chem Int Ed Engl 2015. [DOI: 10.1002/ange.201502227] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Affiliation(s)
- Mark P. Thomas
- Department of Pharmacy & Pharmacology; University of Bath; Claverton Down Bath BA2 7AY Vereinigtes Königreich
| | - Stephen J. Mills
- Department of Pharmacy & Pharmacology; University of Bath; Claverton Down Bath BA2 7AY Vereinigtes Königreich
| | - Barry V. L. Potter
- Department of Pharmacology; University of Oxford; Mansfield Road Oxford OX1 3QT Vereinigtes Königreich
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15
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Abstract
In the 30 years since IP3 (inositol 1,4,5-trisphosphate) was first shown to release Ca2+ from intracellular stores, the importance of spatially organized interactions within IP3-regulated signalling pathways has been universally recognized. Recent evidence that addresses three different levels of the structural determinants of IP3-evoked Ca2+ signalling is described in the present review. High-resolution structures of the N-terminal region of the IP3R (IP3 receptor) have established that the two essential phosphate groups of IP3 bind to opposite sides of the IP3-binding site, pulling its two domains together. This conformational change is proposed to disrupt an interaction between adjacent subunits within the tetrameric IP3R that normally holds the channel in a closed state. Similar structural changes are thought to allow gating of ryanodine receptors. cAMP increases the sensitivity of IP3Rs and thereby potentiates the Ca2+ signals evoked by receptors that stimulate IP3 formation. We speculate that both IP3 and cAMP are delivered to IP3Rs within signalling junctions, wherein the associated IP3Rs are exposed to a saturating concentration of either messenger. The concentration-dependent effects of extracellular stimuli come from recruitment of junctions rather than from a graded increase in the activity of individual junctions. IP3Rs within 'IP3 junctions' respond directly to receptors that stimulate phospholipase C, whereas extra-junctional IP3Rs are exposed to suboptimal concentrations of IP3 and open only when they are sensitized by cAMP. These results highlight the importance of selective delivery of diffusible messengers to IP3Rs. The spatial organization of IP3Rs also allows them to direct Ca2+ to specific intracellular targets that include other IP3Rs, mitochondria and Ca2+-regulated channels and enzymes. IP3Rs also interact functionally with lysosomes because Ca2+ released by IP3Rs, but not that entering cells via store-operated Ca2+ entry pathways, is selectively accumulated by lysosomes. This Ca2+ uptake shapes the Ca2+ signals evoked by IP3 and it may regulate lysosomal behaviour.
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16
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Saleem H, Tovey SC, Molinski TF, Taylor CW. Interactions of antagonists with subtypes of inositol 1,4,5-trisphosphate (IP3) receptor. Br J Pharmacol 2014; 171:3298-312. [PMID: 24628114 PMCID: PMC4080982 DOI: 10.1111/bph.12685] [Citation(s) in RCA: 88] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/21/2014] [Revised: 02/26/2014] [Accepted: 03/05/2014] [Indexed: 01/26/2023] Open
Abstract
BACKGROUND AND PURPOSE Inositol 1,4,5-trisphosphate receptors (IP3 Rs) are intracellular Ca(2+) channels. Interactions of the commonly used antagonists of IP3Rs with IP3R subtypes are poorly understood. EXPERIMENTAL APPROACH IP3-evoked Ca(2+) release from permeabilized DT40 cells stably expressing single subtypes of mammalian IP3R was measured using a luminal Ca(2+) indicator. The effects of commonly used antagonists on IP3-evoked Ca(2+) release and (3) H-IP3 binding were characterized. KEY RESULTS Functional analyses showed that heparin was a competitive antagonist of all IP3R subtypes with different affinities for each (IP3R3 > IP3R1 ≥ IP3R2). This sequence did not match the affinities for heparin binding to the isolated N-terminal from each IP3R subtype. 2-aminoethoxydiphenyl borate (2-APB) and high concentrations of caffeine selectively inhibited IP3R1 without affecting IP3 binding. Neither Xestospongin C nor Xestospongin D effectively inhibited IP3-evoked Ca(2+) release via any IP3R subtype. CONCLUSIONS AND IMPLICATIONS Heparin competes with IP3, but its access to the IP3-binding core is substantially hindered by additional IP3R residues. These interactions may contribute to its modest selectivity for IP3R3. Practicable concentrations of caffeine and 2-APB inhibit only IP3R1. Xestospongins do not appear to be effective antagonists of IP3Rs.
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Affiliation(s)
- Huma Saleem
- Department of Pharmacology, University of CambridgeCambridge, UK
| | - Stephen C Tovey
- Department of Pharmacology, University of CambridgeCambridge, UK
| | | | - Colin W Taylor
- Department of Pharmacology, University of CambridgeCambridge, UK
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17
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Rossi AM, Taylor CW. High-throughput fluorescence polarization assay of ligand binding to IP3 receptors. Cold Spring Harb Protoc 2013; 2013:938-946. [PMID: 24086050 DOI: 10.1101/pdb.prot073080] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
Fluorescence polarization (FP) allows quantification of the binding of a small fluorescent ligand to a larger protein because the free ligand rotates more rapidly than the bound form. This protocol describes an FP assay for the binding of fluorescein-labeled inositol 1,4,5-trisphosphate (IP3) to amino-terminal fragments of the IP3 receptor at different temperatures and in the presence of competing ligands. The method requires fluorescein-labeled IP3 and a plate-reader capable of FP measurements. The assay can measure low-affinity interactions in real time, it avoids use of radioactive materials, is nondestructive, and can resolve changes in Gibbs free energy (ΔG°), enthalpy (ΔH°), and entropy (ΔS°) that occur with ligand binding. It is applicable to any purified protein for which a fluorescent ligand is available. After optimization, the procedure can be completed in 1-6 h.
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Affiliation(s)
- Ana M Rossi
- Department of Pharmacology, University of Cambridge, Cambridge CB2 1PD, United Kingdom
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18
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A fluorescence-based method for evaluating inositol 1,4,5-trisphosphate receptor ligands: Determination of subtype selectivity and partial agonist effects. J Biotechnol 2013; 167:248-54. [DOI: 10.1016/j.jbiotec.2013.06.012] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/05/2013] [Revised: 05/19/2013] [Accepted: 06/23/2013] [Indexed: 11/22/2022]
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Saleem H, Tovey SC, Riley AM, Potter BVL, Taylor CW. Stimulation of inositol 1,4,5-trisphosphate (IP3) receptor subtypes by adenophostin A and its analogues. PLoS One 2013; 8:e58027. [PMID: 23469136 PMCID: PMC3585173 DOI: 10.1371/journal.pone.0058027] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/21/2012] [Accepted: 01/30/2013] [Indexed: 11/25/2022] Open
Abstract
Inositol 1,4,5-trisphosphate receptors (IP3R) are intracellular Ca(2+) channels. Most animal cells express mixtures of the three IP3R subtypes encoded by vertebrate genomes. Adenophostin A (AdA) is the most potent naturally occurring agonist of IP3R and it shares with IP3 the essential features of all IP3R agonists, namely structures equivalent to the 4,5-bisphosphate and 6-hydroxyl of IP3. The two essential phosphate groups contribute to closure of the clam-like IP3-binding core (IBC), and thereby IP3R activation, by binding to each of its sides (the α- and β-domains). Regulation of the three subtypes of IP3R by AdA and its analogues has not been examined in cells expressing defined homogenous populations of IP3R. We measured Ca(2+) release evoked by synthetic adenophostin A (AdA) and its analogues in permeabilized DT40 cells devoid of native IP3R and stably expressing single subtypes of mammalian IP3R. The determinants of high-affinity binding of AdA and its analogues were indistinguishable for each IP3R subtype. The results are consistent with a cation-π interaction between the adenine of AdA and a conserved arginine within the IBC α-domain contributing to closure of the IBC. The two complementary contacts between AdA and the α-domain (cation-π interaction and 3″-phosphate) allow activation of IP3R by an analogue of AdA (3″-dephospho-AdA) that lacks a phosphate group equivalent to the essential 5-phosphate of IP3. These data provide the first structure-activity analyses of key AdA analogues using homogenous populations of all mammalian IP3R subtypes. They demonstrate that differences in the Ca(2+) signals evoked by AdA analogues are unlikely to be due to selective regulation of IP3R subtypes.
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Affiliation(s)
- Huma Saleem
- Department of Pharmacology, Cambridge, United Kingdom
| | | | - Andrew M. Riley
- Wolfson Laboratory of Medicinal Chemistry, Department of Pharmacy and Pharmacology, University of Bath, Bath, United Kingdom
| | - Barry V. L. Potter
- Wolfson Laboratory of Medicinal Chemistry, Department of Pharmacy and Pharmacology, University of Bath, Bath, United Kingdom
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Saleem H, Tovey SC, Rahman T, Riley AM, Potter BVL, Taylor CW. Stimulation of inositol 1,4,5-trisphosphate (IP3) receptor subtypes by analogues of IP3. PLoS One 2013; 8:e54877. [PMID: 23372785 PMCID: PMC3556037 DOI: 10.1371/journal.pone.0054877] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/19/2012] [Accepted: 12/17/2012] [Indexed: 11/19/2022] Open
Abstract
Most animal cells express mixtures of the three subtypes of inositol 1,4,5-trisphosphate receptor (IP(3)R) encoded by vertebrate genomes. Activation of each subtype by different agonists has not hitherto been examined in cells expressing defined homogenous populations of IP(3)R. Here we measure Ca(2+) release evoked by synthetic analogues of IP(3) using a Ca(2+) indicator within the lumen of the endoplasmic reticulum of permeabilized DT40 cells stably expressing single subtypes of mammalian IP(3)R. Phosphorylation of (1,4,5)IP(3) to (1,3,4,5)IP(4) reduced potency by ~100-fold. Relative to (1,4,5)IP(3), the potencies of IP(3) analogues modified at the 1-position (malachite green (1,4,5)IP(3)), 2-position (2-deoxy(1,4,5)IP(3)) or 3-position (3-deoxy(1,4,5)IP(3), (1,3,4,5)IP(4)) were similar for each IP(3)R subtype. The potency of an analogue, (1,4,6)IP(3), in which the orientations of the 2- and 3-hydroxyl groups were inverted, was also reduced similarly for all three IP(3)R subtypes. Most analogues of IP(3) interact similarly with the three IP(3)R subtypes, but the decrease in potency accompanying removal of the 1-phosphate from (1,4,5)IP(3) was least for IP(3)R3. Addition of a large chromophore (malachite green) to the 1-phosphate of (1,4,5)IP(3) only modestly reduced potency suggesting that similar analogues could be used to measure (1,4,5)IP(3) binding optically. These data provide the first structure-activity analyses of key IP(3) analogues using homogenous populations of each mammalian IP(3)R subtype. They demonstrate broadly similar structure-activity relationships for all mammalian IP(3)R subtypes and establish the potential utility of (1,4,5)IP(3) analogues with chromophores attached to the 1-position.
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MESH Headings
- Amino Acid Sequence
- Animals
- Calcium/metabolism
- Cell Line
- Gene Expression
- Inositol 1,4,5-Trisphosphate/chemistry
- Inositol 1,4,5-Trisphosphate/metabolism
- Inositol 1,4,5-Trisphosphate Receptors/chemistry
- Inositol 1,4,5-Trisphosphate Receptors/genetics
- Inositol 1,4,5-Trisphosphate Receptors/metabolism
- Kinetics
- Ligands
- Mice
- Models, Molecular
- Molecular Docking Simulation
- Molecular Sequence Data
- Molecular Structure
- Protein Binding
- Rats
- Recombinant Proteins/chemistry
- Recombinant Proteins/genetics
- Recombinant Proteins/metabolism
- Structure-Activity Relationship
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Affiliation(s)
- Huma Saleem
- Department of Pharmacology, University of Cambridge, Cambridge, United Kingdom
| | - Stephen C. Tovey
- Department of Pharmacology, University of Cambridge, Cambridge, United Kingdom
| | - Taufiq Rahman
- Department of Pharmacology, University of Cambridge, Cambridge, United Kingdom
| | - Andrew M. Riley
- Wolfson Laboratory of Medicinal Chemistry, Department of Pharmacy and Pharmacology, University of Bath, Bath, United Kingdom
| | - Barry V. L. Potter
- Wolfson Laboratory of Medicinal Chemistry, Department of Pharmacy and Pharmacology, University of Bath, Bath, United Kingdom
| | - Colin W. Taylor
- Department of Pharmacology, University of Cambridge, Cambridge, United Kingdom
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Sureshan KM, Riley AM, Thomas MP, Tovey SC, Taylor CW, Potter BVL. Contribution of phosphates and adenine to the potency of adenophostins at the IP₃ receptor: synthesis of all possible bisphosphates of adenophostin A. J Med Chem 2012; 55:1706-20. [PMID: 22248345 PMCID: PMC3285137 DOI: 10.1021/jm201571p] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
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Although adenophostin A (AdA), the most potent agonist
of d-myo-inositol 1,4,5-trisphosphate receptors
(IP3R), is thought to mimic IP3, the relative
roles
of the different phosphate groups and the adenosine motif have not
been established. We synthesized all three possible bisphosphate analogues
of AdA and glucose 3,4-bisphosphate (7, AdA lacking the
2′-AMP). 2′-Dephospho-AdA (6) was prepared
via a novel regioselective dephosphorylation strategy. Assessment
of the abilities of these bisphosphates to stimulate intracellular
Ca2+ release using recombinant rat type 1 IP3R (IP3R1) revealed that 6, a mimic of Ins(4,5)P2, is only 4-fold less potent than IP3, while 7 is some 400-fold weaker and even 3″-dephospho-AdA
(5) is measurably active, despite missing one of the
vicinal bisphosphate groups normally thought to be crucial for IP3-like activity. Compound 6 is the most potent
bisphosphate yet discovered with activity at IP3R. Thus,
adenosine has a direct role independent of the 2′-phosphate
group in contributing toward the potency of adenophostins, the vicinal
bisphosphate motif is not essential for activity at the IP3R, as always thought, and it is possible to design potent agonists
with just two of the three phosphates. A model with a possible adenine–R504
interaction supports the activity of 5 and 6 and also allows a reappraisal of the unexpected activity previously
reported for the AdA regioisomer 2″-phospho-3″-dephospho-AdA 40.
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Affiliation(s)
- Kana M Sureshan
- Wolfson Laboratory of Medicinal Chemistry, Department of Pharmacy and Pharmacology, University of Bath, Claverton Down, Bath BA2 7AY, United Kingdom
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22
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Parys JB, De Smedt H. Inositol 1,4,5-trisphosphate and its receptors. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2012; 740:255-79. [PMID: 22453946 DOI: 10.1007/978-94-007-2888-2_11] [Citation(s) in RCA: 86] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Activation of cells by many extracellular agonists leads to the production of inositol 1,4,5-trisphosphate (IP₃). IP₃ is a global messenger that easily diffuses in the cytosol. Its receptor (IP₃R) is a Ca(2+)-release channel located on intracellular membranes, especially the endoplasmic reticulum (ER). The IP₃R has an affinity for IP(3) in the low nanomolar range. A prime regulator of the IP₃R is the Ca(2+) ion itself. Cytosolic Ca(2+) is considered as a co-agonist of the IP₃R, as it strongly increases IP(3)R activity at concentrations up to about 300 nM. In contrast, at higher concentrations, cytosolic Ca(2+) inhibits the IP₃R. Also the luminal Ca(2+) sensitizes the IP₃R. In higher organisms three genes encode for an IP₃R and additional diversity exists as a result of alternative splicing mechanisms and the formation of homo- and heterotetramers. The various IP₃R isoforms have a similar structure and a similar function, but due to differences in their affinity for IP₃, their variable sensitivity to regulatory parameters, their differential interaction with associated proteins, and the variation in their subcellular localization, they participate differently in the formation of intracellular Ca(2+) signals and this affects therefore the physiological consequences of these signals.
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Affiliation(s)
- Jan B Parys
- Laboratory of Molecular and Cellular Signaling, Department of Cellular and Molecular Medicine, KU Leuven, Campus Gasthuisberg O/N1 - Bus 802, Herestraat 49, Belgium.
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Rossi AM, Tovey SC, Rahman T, Prole DL, Taylor CW. Analysis of IP3 receptors in and out of cells. Biochim Biophys Acta Gen Subj 2011; 1820:1214-27. [PMID: 22033379 DOI: 10.1016/j.bbagen.2011.10.004] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/07/2011] [Revised: 10/07/2011] [Accepted: 10/08/2011] [Indexed: 10/16/2022]
Abstract
BACKGROUND Inositol 1,4,5-trisphosphate receptors (IP3R) are expressed in almost all animal cells. Three mammalian genes encode closely related IP3R subunits, which assemble into homo- or hetero-tetramers to form intracellular Ca2+ channels. SCOPE OF THE REVIEW In this brief review, we first consider a variety of complementary methods that allow the links between IP3 binding and channel gating to be defined. How does IP3 binding to the IP3-binding core in each IP3R subunit cause opening of a cation-selective pore formed by residues towards the C-terminal? We then describe methods that allow IP3, Ca2+ signals and IP3R mobility to be examined in intact cells. A final section briefly considers genetic analyses of IP3R signalling. MAJOR CONCLUSIONS All IP3R are regulated by both IP3 and Ca2+. This allows them to initiate and regeneratively propagate intracellular Ca2+ signals. The elementary Ca2+ release events evoked by IP3 in intact cells are mediated by very small numbers of active IP3R and the Ca2+-mediated interactions between them. The spatial organization of these Ca2+ signals and their stochastic dependence on so few IP3Rs highlight the need for methods that allow the spatial organization of IP3R signalling to be addressed with single-molecule resolution. GENERAL SIGNIFICANCE A variety of complementary methods provide insight into the structural basis of IP3R activation and the contributions of IP3-evoked Ca2+ signals to cellular physiology. This article is part of a Special Issue entitled Biochemical, biophysical and genetic approaches to intracellular calcium signaling.
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Abstract
Quantification of the associations between biomolecules is required both to predict and understand the interactions that underpin all biological activity. Fluorescence polarization (FP) provides a nondisruptive means of measuring the association of a fluorescent ligand with a larger molecule. We describe an FP assay in which binding of fluorescein-labeled inositol 1,4,5-trisphosphate (IP(3)) to N-terminal fragments of IP(3) receptors can be characterized at different temperatures and in competition with other ligands. The assay allows the standard Gibbs free energy (ΔG°), enthalpy (ΔH°) and entropy (ΔS°) changes of ligand binding to be determined. The method is applicable to any purified ligand-binding site for which an appropriate fluorescent ligand is available. FP can be used to measure low-affinity interactions in real time without the use of radioactive materials, it is nondestructive and, with appropriate care, it can resolve ΔH° and ΔS°. The first part of the protocol, protein preparation, may take several weeks, whereas the FP measurements, once they have been optimized, would normally take 1-6 h.
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Affiliation(s)
- Ana M Rossi
- Department of Pharmacology, University of Cambridge, Cambridge, UK
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Rossi AM, Riley AM, Potter BV, Taylor CW. Adenophostins. CURRENT TOPICS IN MEMBRANES 2010; 66:209-33. [DOI: 10.1016/s1063-5823(10)66010-3] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 03/04/2023]
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