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Simon MA, Iordanov I, Szollosi A, Csanády L. Estimating the true stability of the prehydrolytic outward-facing state in an ABC protein. eLife 2023; 12:e90736. [PMID: 37782012 PMCID: PMC10569789 DOI: 10.7554/elife.90736] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/06/2023] [Accepted: 10/01/2023] [Indexed: 10/03/2023] Open
Abstract
CFTR, the anion channel mutated in cystic fibrosis patients, is a model ABC protein whose ATP-driven conformational cycle is observable at single-molecule level in patch-clamp recordings. Bursts of CFTR pore openings are coupled to tight dimerization of its two nucleotide-binding domains (NBDs) and in wild-type (WT) channels are mostly terminated by ATP hydrolysis. The slow rate of non-hydrolytic closure - which determines how tightly bursts and ATP hydrolysis are coupled - is unknown, as burst durations of catalytic site mutants span a range of ~200-fold. Here, we show that Walker A mutation K1250A, Walker B mutation D1370N, and catalytic glutamate mutations E1371S and E1371Q all completely disrupt ATP hydrolysis. True non-hydrolytic closing rate of WT CFTR approximates that of K1250A and E1371S. That rate is slowed ~15-fold in E1371Q by a non-native inter-NBD H-bond, and accelerated ~15-fold in D1370N. These findings uncover unique features of the NBD interface in human CFTR.
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Affiliation(s)
- Márton A Simon
- Department of Biochemistry, Semmelweis UniversityBudapestHungary
- HCEMM-SE Molecular Channelopathies Research GroupBudapestHungary
- HUN-REN-SE Ion Channel Research GroupBudapestHungary
| | - Iordan Iordanov
- Department of Biochemistry, Semmelweis UniversityBudapestHungary
- HCEMM-SE Molecular Channelopathies Research GroupBudapestHungary
- HUN-REN-SE Ion Channel Research GroupBudapestHungary
| | - Andras Szollosi
- Department of Biochemistry, Semmelweis UniversityBudapestHungary
- HCEMM-SE Molecular Channelopathies Research GroupBudapestHungary
- HUN-REN-SE Ion Channel Research GroupBudapestHungary
| | - László Csanády
- Department of Biochemistry, Semmelweis UniversityBudapestHungary
- HCEMM-SE Molecular Channelopathies Research GroupBudapestHungary
- HUN-REN-SE Ion Channel Research GroupBudapestHungary
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2
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Szollosi A, Almássy J. Functional characterization of the transient receptor potential melastatin 2 (TRPM2) cation channel from Nematostella vectensis reconstituted into lipid bilayer. Sci Rep 2023; 13:11471. [PMID: 37454209 PMCID: PMC10349829 DOI: 10.1038/s41598-023-38640-6] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/11/2023] [Accepted: 07/12/2023] [Indexed: 07/18/2023] Open
Abstract
Transient receptor potential melastatin 2 (TRPM2) cation channel activity is required for insulin secretion, immune cell activation and body heat control. Channel activation upon oxidative stress is involved in the pathology of stroke and neurodegenerative disorders. Cytosolic Ca2+, ADP-ribose (ADPR) and phosphatidylinositol-4,5-bisphosphate (PIP2) are the obligate activators of the channel. Several TRPM2 cryo-EM structures have been resolved to date, yet functionality of the purified protein has not been tested. Here we reconstituted overexpressed and purified TRPM2 from Nematostella vectensis (nvTRPM2) into lipid bilayers and found that the protein is fully functional. Consistent with the observations in native membranes, nvTRPM2 in lipid bilayers is co-activated by cytosolic Ca2+ and either ADPR or ADPR-2'-phosphate (ADPRP). The physiological metabolite ADPRP has a higher apparent affinity than ADPR. In lipid bilayers nvTRPM2 displays a large linear unitary conductance, its open probability (Po) shows little voltage dependence and is stable over several minutes. Po is high without addition of exogenous PIP2, but is largely blunted by treatment with poly-L-Lysine, a polycation that masks PIP2 headgroups. These results indicate that PIP2 or some other activating phosphoinositol lipid co-purifies with nvTRPM2, suggesting a high PIP2 binding affinity of nvTRPM2 under physiological conditions.
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Affiliation(s)
- Andras Szollosi
- Department of Biochemistry, Semmelweis University, Tuzolto u. 37-47, Budapest, 1094, Hungary.
- ELKH-SE Ion Channel Research Group, Semmelweis University, Tuzolto u. 37-47, Budapest, 1094, Hungary.
- HCEMM-SE Molecular Channelopathies Research Group, Semmelweis University, Tuzolto u. 37-47, Budapest, 1094, Hungary.
| | - János Almássy
- Department of Physiology, Semmelweis University, Tuzolto u. 37-47, Budapest, 1094, Hungary
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3
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Szollosi A, Mihalyi C, Iordanov I, Csanady L. Posttranslational modifications of cyclic AMP-dependent protein kinase a affect its binding to the CFTR anion channel. Biophys J 2023; 122:458a. [PMID: 36784349 DOI: 10.1016/j.bpj.2022.11.2464] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/12/2023] Open
Affiliation(s)
- Andras Szollosi
- Medical Biochemistry, Semmelweis University, Budapest, Hungary; Hungarian Centre of Excellence for Molecular Medicine-Semmelweis University Molecular Channelopathies Research Group, Budapest, Hungary
| | - Csaba Mihalyi
- Medical Biochemistry, Semmelweis University, Budapest, Hungary; Hungarian Centre of Excellence for Molecular Medicine-Semmelweis University Molecular Channelopathies Research Group, Budapest, Hungary
| | - Iordan Iordanov
- Medical Biochemistry, Semmelweis University, Budapest, Hungary; Hungarian Centre of Excellence for Molecular Medicine-Semmelweis University Molecular Channelopathies Research Group, Budapest, Hungary
| | - Laszlo Csanady
- Medical Biochemistry, Semmelweis University, Budapest, Hungary; Hungarian Centre of Excellence for Molecular Medicine-Semmelweis University Molecular Channelopathies Research Group, Budapest, Hungary
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4
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Iordanov I, Tóth B, Szollosi A, Csanády L. Enzyme activity and selectivity filter stability of ancient TRPM2 channels were simultaneously lost in early vertebrates. eLife 2019; 8:44556. [PMID: 30938679 PMCID: PMC6461439 DOI: 10.7554/elife.44556] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/19/2018] [Accepted: 04/01/2019] [Indexed: 01/01/2023] Open
Abstract
Transient Receptor Potential Melastatin 2 (TRPM2) is a cation channel important for the immune response, insulin secretion, and body temperature regulation. It is activated by cytosolic ADP ribose (ADPR) and contains a nudix-type motif 9 (NUDT9)-homology (NUDT9-H) domain homologous to ADPR phosphohydrolases (ADPRases). Human TRPM2 (hsTRPM2) is catalytically inactive due to mutations in the conserved Nudix box sequence. Here, we show that TRPM2 Nudix motifs are canonical in all invertebrates but vestigial in vertebrates. Correspondingly, TRPM2 of the cnidarian Nematostella vectensis (nvTRPM2) and the choanoflagellate Salpingoeca rosetta (srTRPM2) are active ADPRases. Disruption of ADPRase activity fails to affect nvTRPM2 channel currents, reporting a catalytic cycle uncoupled from gating. Furthermore, pore sequence substitutions responsible for inactivation of hsTRPM2 also appeared in vertebrates. Correspondingly, zebrafish (Danio rerio) TRPM2 (drTRPM2) and hsTRPM2 channels inactivate, but srTRPM2 and nvTRPM2 currents are stable. Thus, catalysis and pore stability were lost simultaneously in vertebrate TRPM2 channels.
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Affiliation(s)
- Iordan Iordanov
- Department of Medical Biochemistry, Semmelweis University, Budapest, Hungary.,MTA-SE Lendület Ion Channel Research Group, Semmelweis University, Budapest, Hungary
| | - Balázs Tóth
- Department of Medical Biochemistry, Semmelweis University, Budapest, Hungary.,MTA-SE Lendület Ion Channel Research Group, Semmelweis University, Budapest, Hungary
| | - Andras Szollosi
- Department of Medical Biochemistry, Semmelweis University, Budapest, Hungary.,MTA-SE Lendület Ion Channel Research Group, Semmelweis University, Budapest, Hungary
| | - László Csanády
- Department of Medical Biochemistry, Semmelweis University, Budapest, Hungary.,MTA-SE Lendület Ion Channel Research Group, Semmelweis University, Budapest, Hungary
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Zhang Z, Tóth B, Szollosi A, Chen J, Csanády L. Structure of a TRPM2 channel in complex with Ca 2+ explains unique gating regulation. eLife 2018; 7:36409. [PMID: 29745897 PMCID: PMC5976436 DOI: 10.7554/elife.36409] [Citation(s) in RCA: 87] [Impact Index Per Article: 14.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/05/2018] [Accepted: 05/09/2018] [Indexed: 11/18/2022] Open
Abstract
Transient receptor potential melastatin 2 (TRPM2) is a Ca2+-permeable cation channel required for immune cell activation, insulin secretion, and body heat control. TRPM2 is activated by cytosolic Ca2+, phosphatidyl-inositol-4,5-bisphosphate and ADP ribose. Here, we present the ~3 Å resolution electron cryo-microscopic structure of TRPM2 from Nematostella vectensis, 63% similar in sequence to human TRPM2, in the Ca2+-bound closed state. Compared to other TRPM channels, TRPM2 exhibits unique structural features that correlate with its function. The pore is larger and more negatively charged, consistent with its high Ca2+ selectivity and larger conductance. The intracellular Ca2+ binding sites are connected to the pore and cytosol, explaining the unusual dependence of TRPM2 activity on intra- and extracellular Ca2+. In addition, the absence of a post-filter motif is likely the cause of the rapid inactivation of human TRPM2. Together, our cryo-EM and electrophysiology studies provide a molecular understanding of the unique gating mechanism of TRPM2.
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Affiliation(s)
- Zhe Zhang
- Laboratory of Membrane Biophysics and Biology, The Rockefeller University, New York, United States.,Howard Hughes Medical Institute, Chevy Chase, United States
| | - Balázs Tóth
- Department of Medical Biochemistry, Semmelweis University, Budapest, Hungary.,MTA-SE Ion Channel Research Group, Semmelweis University, Budapest, Hungary
| | - Andras Szollosi
- Department of Medical Biochemistry, Semmelweis University, Budapest, Hungary.,MTA-SE Ion Channel Research Group, Semmelweis University, Budapest, Hungary
| | - Jue Chen
- Laboratory of Membrane Biophysics and Biology, The Rockefeller University, New York, United States.,Howard Hughes Medical Institute, Chevy Chase, United States
| | - László Csanády
- Department of Medical Biochemistry, Semmelweis University, Budapest, Hungary.,MTA-SE Ion Channel Research Group, Semmelweis University, Budapest, Hungary
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6
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Demeter G, Pajkossy P, Szollosi A, Lukács A, Valálik I, Racsmány M. The effect of subthalamic deep brain stimulation on executive and memory functions in Parkinson's disease. Brain Stimul 2017. [DOI: 10.1016/j.brs.2017.01.173] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022] Open
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7
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Bouwmeester S, Verkoeijen PPJL, Aczel B, Barbosa F, Bègue L, Brañas-Garza P, Chmura TGH, Cornelissen G, Døssing FS, Espín AM, Evans AM, Ferreira-Santos F, Fiedler S, Flegr J, Ghaffari M, Glöckner A, Goeschl T, Guo L, Hauser OP, Hernan-Gonzalez R, Herrero A, Horne Z, Houdek P, Johannesson M, Koppel L, Kujal P, Laine T, Lohse J, Martins EC, Mauro C, Mischkowski D, Mukherjee S, Myrseth KOR, Navarro-Martínez D, Neal TMS, Novakova J, Pagà R, Paiva TO, Palfi B, Piovesan M, Rahal RM, Salomon E, Srinivasan N, Srivastava A, Szaszi B, Szollosi A, Thor KØ, Tinghög G, Trueblood JS, Van Bavel JJ, van 't Veer AE, Västfjäll D, Warner M, Wengström E, Wills J, Wollbrant CE. Registered Replication Report: Rand, Greene, and Nowak (2012). Perspect Psychol Sci 2017; 12:527-542. [PMID: 28475467 PMCID: PMC5453400 DOI: 10.1177/1745691617693624] [Citation(s) in RCA: 82] [Impact Index Per Article: 11.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
In an anonymous 4-person economic game, participants contributed more money to a common project (i.e., cooperated) when required to decide quickly than when forced to delay their decision (Rand, Greene & Nowak, 2012), a pattern consistent with the social heuristics hypothesis proposed by Rand and colleagues. The results of studies using time pressure have been mixed, with some replication attempts observing similar patterns (e.g., Rand et al., 2014) and others observing null effects (e.g., Tinghög et al., 2013; Verkoeijen & Bouwmeester, 2014). This Registered Replication Report (RRR) assessed the size and variability of the effect of time pressure on cooperative decisions by combining 21 separate, preregistered replications of the critical conditions from Study 7 of the original article (Rand et al., 2012). The primary planned analysis used data from all participants who were randomly assigned to conditions and who met the protocol inclusion criteria (an intent-to-treat approach that included the 65.9% of participants in the time-pressure condition and 7.5% in the forced-delay condition who did not adhere to the time constraints), and we observed a difference in contributions of -0.37 percentage points compared with an 8.6 percentage point difference calculated from the original data. Analyzing the data as the original article did, including data only for participants who complied with the time constraints, the RRR observed a 10.37 percentage point difference in contributions compared with a 15.31 percentage point difference in the original study. In combination, the results of the intent-to-treat analysis and the compliant-only analysis are consistent with the presence of selection biases and the absence of a causal effect of time pressure on cooperation.
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Affiliation(s)
- B. Szaszi
- Doctoral School of Psychology, Eötvös Lorand University, Budapest, Hungary
- Institute of Psychology, Eötvös Loránd University, Budapest, Hungary
| | - A. Szollosi
- Institute of Psychology, Eötvös Loránd University, Budapest, Hungary
- School of Psychology, The University of New South Wales, Sydney, Australia
| | - B. Palfi
- Institute of Psychology, Eötvös Loránd University, Budapest, Hungary
| | - B. Aczel
- Institute of Psychology, Eötvös Loránd University, Budapest, Hungary
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9
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Szollosi A, Vieira-Pires RS, Teixeira-Duarte CM, Rocha R, Morais-Cabral JH. Dissecting the Molecular Mechanism of Nucleotide-Dependent Activation of the KtrAB K+ Transporter. PLoS Biol 2016; 14:e1002356. [PMID: 26771197 PMCID: PMC4714889 DOI: 10.1371/journal.pbio.1002356] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/04/2015] [Accepted: 12/10/2015] [Indexed: 11/18/2022] Open
Abstract
KtrAB belongs to the Trk/Ktr/HKT superfamily of monovalent cation (K+ and Na+) transport proteins that closely resemble K+ channels. These proteins underlie a plethora of cellular functions that are crucial for environmental adaptation in plants, fungi, archaea, and bacteria. The activation mechanism of the Trk/Ktr/HKT proteins remains unknown. It has been shown that ATP stimulates the activity of KtrAB while ADP does not. Here, we present X-ray structural information on the KtrAB complex with bound ADP. A comparison with the KtrAB-ATP structure reveals conformational changes in the ring and in the membrane protein. In combination with a biochemical and functional analysis, we uncover how ligand-dependent changes in the KtrA ring are propagated to the KtrB membrane protein and conclude that, despite their structural similarity, the activation mechanism of KtrAB is markedly different from the activation mechanism of K+ channels. This study reveals how structural changes triggered by the exchange of bound ADP for ATP activate KtrAB, a potassium ion transporter involved in osmotic adaption in bacteria. Animals have organs that regulate the balance of water and ions in the fluids bathing their cells. In contrast, the cells of plants, bacteria, and fungi have little or no control over those fluids and, thus, they have to cope with changes in the local environment. These cells have therefore evolved specific molecular systems that are crucial for environmental adaptation. We study the molecular properties of the membrane protein KtrAB—a member of the Trk/Ktr/HKT superfamily of transport proteins that shuffle K+ and Na+ ions across the plasma membrane, closely resemble K+ channels, and underlie environmental adaptation of cells of plants, fungi, bacteria, and archaea. KtrAB is formed by the KtrB membrane protein and the KtrA cytosolic ring protein. KtrA binds to both ADP and ATP, resulting in a low-activity ADP-bound state and a high-activity ATP-bound state, respectively. We determined a low resolution structure of a low-activity form of the transport protein. A comparison of this structure with the structure of ATP-bound KtrAB reveals changes in both the KtrA ring and the KtrB membrane protein. We uncover how changes in the KtrA ring are propagated to KtrB and conclude that, despite their structural similarity, the activation mechanism of KtrAB is markedly different from the activation mechanism of K+ channels.
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Affiliation(s)
- Andras Szollosi
- IBMC, Instituto de Biologia Molecular e Celular, Universidade do Porto, Porto, Portugal
| | | | - Celso M. Teixeira-Duarte
- IBMC, Instituto de Biologia Molecular e Celular, Universidade do Porto, Porto, Portugal
- Instituto de Investigação e Inovação em Saúde, Universidade do Porto, Porto, Portugal
| | - Rita Rocha
- IBMC, Instituto de Biologia Molecular e Celular, Universidade do Porto, Porto, Portugal
- Instituto de Investigação e Inovação em Saúde, Universidade do Porto, Porto, Portugal
| | - João H. Morais-Cabral
- IBMC, Instituto de Biologia Molecular e Celular, Universidade do Porto, Porto, Portugal
- Instituto de Investigação e Inovação em Saúde, Universidade do Porto, Porto, Portugal
- * E-mail:
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Szendi I, Demeter G, Szollosi A, Janacsek K, Domján N, Greminger N, Németh D, Racsmány M. Double Dissociation of Explicit and Implicit Learning Performances in Neurocognitive Subgroups of Schizophrenia. Eur Psychiatry 2015. [DOI: 10.1016/s0924-9338(15)30712-4] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
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Csanády L, Mihályi C, Szollosi A, Töröcsik B, Vergani P. Conformational changes in the catalytically inactive nucleotide-binding site of CFTR. ACTA ACUST UNITED AC 2013; 142:61-73. [PMID: 23752332 PMCID: PMC3691448 DOI: 10.1085/jgp.201210954] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
A central step in the gating of the cystic fibrosis transmembrane conductance regulator (CFTR) chloride channel is the association of its two cytosolic nucleotide-binding domains (NBDs) into a head-to-tail dimer, with two nucleotides bound at the interface. Channel opening and closing, respectively, are coupled to formation and disruption of this tight NBD dimer. CFTR is an asymmetric adenosine triphosphate (ATP)-binding cassette protein in which the two interfacial-binding sites (composite sites 1 and 2) are functionally different. During gating, the canonical, catalytically active nucleotide-binding site (site 2) cycles between dimerized prehydrolytic (state O1), dimerized post-hydrolytic (state O2), and dissociated (state C) forms in a preferential C→O1→O2→C sequence. In contrast, the catalytically inactive nucleotide-binding site (site 1) is believed to remain associated, ATP-bound, for several gating cycles. Here, we have examined the possibility of conformational changes in site 1 during gating, by studying gating effects of perturbations in site 1. Previous work showed that channel closure is slowed, both under hydrolytic and nonhydrolytic conditions, by occupancy of site 1 by N6-(2-phenylethyl)-ATP (P-ATP) as well as by the site-1 mutation H1348A (NBD2 signature sequence). Here, we found that P-ATP prolongs wild-type (WT) CFTR burst durations by selectively slowing (>2×) transition O1→O2 and decreases the nonhydrolytic closing rate (transition O1→C) of CFTR mutants K1250A (∼4×) and E1371S (∼3×). Mutation H1348A also slowed (∼3×) the O1→O2 transition in the WT background and decreased the nonhydrolytic closing rate of both K1250A (∼3×) and E1371S (∼3×) background mutants. Neither P-ATP nor the H1348A mutation affected the 1:1 stoichiometry between ATP occlusion and channel burst events characteristic to WT CFTR gating in ATP. The marked effect that different structural perturbations at site 1 have on both steps O1→C and O1→O2 suggests that the overall conformational changes that CFTR undergoes upon opening and coincident with hydrolysis at the active site 2 include significant structural rearrangement at site 1.
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Affiliation(s)
- László Csanády
- Department of Medical Biochemistry, Semmelweis University, Budapest H-1094, Hungary.
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Mihalyi C, Szollosi A, Vergani P, Csanady L. Conformational Changes in the Catalytically Inactive Nucleotide Binding Site of CFTR. Biophys J 2013. [DOI: 10.1016/j.bpj.2012.11.3463] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022] Open
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13
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Szollosi A, Muallem DR, Csanády L, Vergani P. Mutant cycles at CFTR's non-canonical ATP-binding site support little interface separation during gating. ACTA ACUST UNITED AC 2011; 137:549-62. [PMID: 21576373 PMCID: PMC3105517 DOI: 10.1085/jgp.201110608] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
Cystic fibrosis transmembrane conductance regulator (CFTR) is a chloride channel belonging to the adenosine triphosphate (ATP)-binding cassette (ABC) superfamily. ABC proteins share a common molecular mechanism that couples ATP binding and hydrolysis at two nucleotide-binding domains (NBDs) to diverse functions. This involves formation of NBD dimers, with ATP bound at two composite interfacial sites. In CFTR, intramolecular NBD dimerization is coupled to channel opening. Channel closing is triggered by hydrolysis of the ATP molecule bound at composite site 2. Site 1, which is non-canonical, binds nucleotide tightly but is not hydrolytic. Recently, based on kinetic arguments, it was suggested that this site remains closed for several gating cycles. To investigate movements at site 1 by an independent technique, we studied changes in thermodynamic coupling between pairs of residues on opposite sides of this site. The chosen targets are likely to interact based on both phylogenetic analysis and closeness on structural models. First, we mutated T460 in NBD1 and L1353 in NBD2 (the corresponding site-2 residues become energetically coupled as channels open). Mutation T460S accelerated closure in hydrolytic conditions and in the nonhydrolytic K1250R background; mutation L1353M did not affect these rates. Analysis of the double mutant showed additive effects of mutations, suggesting that energetic coupling between the two residues remains unchanged during the gating cycle. We next investigated pairs 460–1348 and 460–1375. Although both mutations H1348A and H1375A produced dramatic changes in hydrolytic and nonhydrolytic channel closing rates, in the corresponding double mutants these changes proved mostly additive with those caused by mutation T460S, suggesting little change in energetic coupling between either positions 460–1348 or positions 460–1375 during gating. These results provide independent support for a gating model in which ATP-bound composite site 1 remains closed throughout the gating cycle.
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Affiliation(s)
- Andras Szollosi
- Department of Medical Biochemistry, Semmelweis University, Budapest, Hungary
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Szollosi A, Muallem DR, Vergani P, Csanády L. Studies on Correlated Pairs at the NBD-NBD and NBD-TMD Interfaces in CFTR. Biophys J 2011. [DOI: 10.1016/j.bpj.2010.12.1653] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022] Open
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15
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Szollosi A, Vergani P, Csanády L. Involvement of F1296 and N1303 of CFTR in induced-fit conformational change in response to ATP binding at NBD2. ACTA ACUST UNITED AC 2011; 136:407-23. [PMID: 20876359 PMCID: PMC2947058 DOI: 10.1085/jgp.201010434] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
The chloride ion channel cystic fibrosis transmembrane conductance regulator (CFTR) displays a typical adenosine trisphosphate (ATP)-binding cassette (ABC) protein architecture comprising two transmembrane domains, two intracellular nucleotide-binding domains (NBDs), and a unique intracellular regulatory domain. Once phosphorylated in the regulatory domain, CFTR channels can open and close when supplied with cytosolic ATP. Despite the general agreement that formation of a head-to-tail NBD dimer drives the opening of the chloride ion pore, little is known about how ATP binding to individual NBDs promotes subsequent formation of this stable dimer. Structural studies on isolated NBDs suggest that ATP binding induces an intra-domain conformational change termed “induced fit,” which is required for subsequent dimerization. We investigated the allosteric interaction between three residues within NBD2 of CFTR, F1296, N1303, and R1358, because statistical coupling analysis suggests coevolution of these positions, and because in crystal structures of ABC domains, interactions between these positions appear to be modulated by ATP binding. We expressed wild-type as well as F1296S, N1303Q, and R1358A mutant CFTR in Xenopus oocytes and studied these channels using macroscopic inside-out patch recordings. Thermodynamic mutant cycles were built on several kinetic parameters that characterize individual steps in the gating cycle, such as apparent affinities for ATP, open probabilities in the absence of ATP, open probabilities in saturating ATP in a mutant background (K1250R), which precludes ATP hydrolysis, as well as the rates of nonhydrolytic closure. Our results suggest state-dependent changes in coupling between two of the three positions (1296 and 1303) and are consistent with a model that assumes a toggle switch–like interaction pattern during the intra-NBD2 induced fit in response to ATP binding. Stabilizing interactions of F1296 and N1303 present before ATP binding are replaced by a single F1296-N1303 contact in ATP-bound states, with similar interaction partner toggling occurring during the much rarer ATP-independent spontaneous openings.
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Affiliation(s)
- Andras Szollosi
- Department of Medical Biochemistry, Semmelweis University, Budapest, Hungary
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Szollosi A, Nenquin M, Henquin JC. Pharmacological stimulation and inhibition of insulin secretion in mouse islets lacking ATP-sensitive K+ channels. Br J Pharmacol 2010; 159:669-77. [PMID: 20128805 DOI: 10.1111/j.1476-5381.2009.00588.x] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
BACKGROUND AND PURPOSE ATP-sensitive potassium channels (K(ATP) channels) in beta cells are a major target for insulinotropic drugs. Here, we studied the effects of selected stimulatory and inhibitory pharmacological agents in islets lacking K(ATP) channels. EXPERIMENTAL APPROACH We compared insulin secretion (IS) and cytosolic calcium ([Ca(2+)](c)) changes in islets isolated from control mice and mice lacking sulphonylurea receptor1 (SUR1), and thus K(ATP) channels in their beta cells (Sur1KO). KEY RESULTS While similarly increasing [Ca(2+)](c) and IS in controls, agents binding to site A (tolbutamide) or site B (meglitinide) of SUR1 were ineffective in Sur1KO islets. Of two non-selective blockers of potassium channels, quinine was inactive, whereas tetraethylammonium was more active in Sur1KO compared with control islets. Phentolamine, efaroxan and alinidine, three imidazolines binding to K(IR)6.2 (pore of K(ATP) channels), stimulated control islets, but only phentolamine retained weaker stimulatory effects on [Ca(2+)](c) and IS in Sur1KO islets. Neither K(ATP) channel opener (diazoxide, pinacidil) inhibited Sur1KO islets. Calcium channel blockers (nimodipine, verapamil) or diphenylhydantoin decreased [Ca(2+)](c) and IS in both types of islets, verapamil and diphenylhydantoin being more efficient in Sur1KO islets. Activation of alpha(2)-adrenoceptors or dopamine receptors strongly inhibited IS while partially (clonidine > dopamine) lowering [Ca(2+)](c) (control > Sur1KO islets). CONCLUSIONS AND IMPLICATIONS Those drugs retaining effects on IS in islets lacking K(ATP) channels, also affected [Ca(2+)](c), indicating actions on other ionic channels. The greater effects of some inhibitors in Sur1KO than in control islets might be relevant to medical treatment of congenital hyperinsulinism caused by inactivating mutations of K(ATP) channels.
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Affiliation(s)
- A Szollosi
- Unité d'Endocrinologie et Métabolisme, Faculty of Medicine, University of Louvain, Brussels, Belgium
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Abstract
Glucose-induced insulin secretion by pancreatic beta-cells is generally schematized by a 'consensus model' that involves the following sequence of events: acceleration of glucose metabolism, closure of ATP-sensitive potassium channels (K(ATP) channels) in the plasma membrane, depolarization, influx of Ca(2+) through voltage-dependent calcium channels and a rise in cytosolic-free Ca(2+) concentration that induces exocytosis of insulin-containing granules. This model adequately depicts the essential triggering pathway but is incomplete. In this article, we first make a case for a model of dual regulation in which a metabolic amplifying pathway is also activated by glucose and augments the secretory response to the triggering Ca(2+) signal under physiological conditions. We next discuss experimental evidence, largely but not exclusively obtained from beta-cells lacking K(ATP) channels, which indicates that these channels are not the only possible transducers of glucose effects on the triggering Ca(2+)signal. We finally address the identity of the widely neglected background inward current (Cl(-) efflux vs. Na(+) or Ca(2+) influx through voltage-independent channels) that is necessary to cause beta-cell depolarization when glucose closes K(ATP) channels. More attention should be paid to the possibility that some components of this background current are influenced by glucose metabolism and have their place in a model of glucose-induced insulin secretion.
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Henquin JC, Nenquin M, Szollosi A, Kubosaki A, Notkins AL. Insulin secretion in islets from mice with a double knockout for the dense core vesicle proteins islet antigen-2 (IA-2) and IA-2beta. J Endocrinol 2008; 196:573-81. [PMID: 18310453 DOI: 10.1677/joe-07-0496] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
Islet antigen-2 (IA-2 or ICA 512) and IA-2beta (or phogrin) are major autoantigens in type 1 diabetes. They are located in dense core secretory vesicles including insulin granules, but their role in beta-cell function is unclear. Targeted disruption of either IA-2 or IA-2beta, or both, impaired glucose tolerance, an effect attributed to diminution of insulin secretion. In this study, we therefore characterized the dynamic changes in cytosolic Ca2+([Ca2+](c)) and insulin secretion in islets from IA-2/IA-2beta double knockout (KO) mice. High glucose (15 mM) induced biphasic insulin secretion in IA-2/IA-2beta KO islets, with a similar first phase and smaller second phase compared with controls. Since the insulin content of IA-2/IA-2beta KO islets was approximately 45% less than that of controls, fractional insulin secretion (relative to content) was thus increased during first phase and unaffected during second phase. This peculiar response occurred in spite of a slightly smaller rise in [Ca2+](c), could not be attributed to an alteration of glucose metabolism (NADPH fluorescence) and also was observed with tolbutamide. The dual control of insulin secretion via the K(ATP) channel-dependent triggering pathway and K(ATP) channel-independent amplifying pathway was unaltered in IA-2/IA-2beta KO islets, and so were the potentiations by acetylcholine or cAMP (forskolin). Intriguingly, amino acids, in particular the cationic arginine and lysine, induced larger fractional insulin secretion in IA-2/IA-2beta KO than control islets. In conclusion, IA-2 and IA-2beta are dispensable for exocytosis of insulin granules, but are probably more important for cargo loading and/or stability of dense core vesicles.
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Affiliation(s)
- Jean-Claude Henquin
- Unit of Endocrinology and Metabolism, Faculty of Medicine, University of Louvain, UCL 55.30, Avenue Hippocrate 55, B-1200 Brussels, Belgium
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Szollosi A, Nenquin M, Henquin JC. Overnight culture unmasks glucose-induced insulin secretion in mouse islets lacking ATP-sensitive K+ channels by improving the triggering Ca2+ signal. J Biol Chem 2007; 282:14768-76. [PMID: 17389589 DOI: 10.1074/jbc.m701382200] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
A current model ascribes glucose-induced insulin secretion to the interaction of a triggering pathway (K(ATP) channel-dependent Ca(2+) influx and rise in cytosolic [Ca(2+)](c)) and an amplifying pathway (K(ATP) channel-independent augmentation of secretion without further increase of [Ca(2+)](c)). However, several studies of sulfonylurea receptor 1 null mice (Sur1KO) failed to measure significant effects of glucose in their islets lacking K(ATP) channels. We addressed this issue that challenges the model. Compared with controls, fresh Sur1KO islets showed slightly elevated basal [Ca(2+)](c) and insulin secretion. In 15 mm glucose, the absolute rate of secretion was approximately 3-fold lower in Sur1KO than control islets, with only poor increase above base line. Overnight culture of Sur1KO islets in 10 mm glucose (not in 5 mm) augmented basal insulin secretion and considerably improved the response to 15 mm glucose, which reached higher values than in control islets, in which culture had little impact. Glucose stimulation during KCl depolarization showed that the amplifying pathway is functional in fresh and cultured Sur1KO islets. The differences in insulin secretion between fresh and cultured Sur1KO islets and between Sur1KO and control islets were not attributable to differences in insulin content, glucose oxidation rate, or synchronization of [Ca(2+)](c) oscillations. The unmasking of glucose-induced insulin secretion in beta-cells lacking K(ATP) channels is paradoxically due to improvement in the production of a triggering signal (elevated [Ca(2+)](c)). The results show that K(ATP) channels are not the only transducer of glucose effects on [Ca(2+)](c) in beta-cells. They explain controversies in the literature and refute arguments raised against the model implicating an amplifying pathway in glucose-induced insulin secretion.
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Affiliation(s)
- Andras Szollosi
- Unit of Endocrinology and Metabolism, University of Louvain Faculty of Medicine, UCL55.30, B-1200 Brussels, Belgium
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Szollosi A, Nenquin M, Aguilar-Bryan L, Bryan J, Henquin JC. Glucose stimulates Ca2+ influx and insulin secretion in 2-week-old beta-cells lacking ATP-sensitive K+ channels. J Biol Chem 2006; 282:1747-56. [PMID: 17138557 DOI: 10.1074/jbc.m609875200] [Citation(s) in RCA: 60] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
In adult beta-cells glucose-induced insulin secretion involves two mechanisms (a) a K(ATP) channel-dependent Ca(2+) influx and rise of cytosolic [Ca(2+)](c) and (b) a K(ATP) channel-independent amplification of secretion without further increase of [Ca(2+)](c). Mice lacking the high affinity sulfonylurea receptor (Sur1KO), and thus K(ATP) channels, have been developed as a model of congenital hyperinsulinism. Here, we compared [Ca(2+)](c) and insulin secretion in overnight cultured islets from 2-week-old normal and Sur1KO mice. Control islets proved functionally mature: the magnitude and biphasic kinetics of [Ca(2+)](c) and insulin secretion changes induced by glucose, and operation of the amplifying pathway, were similar to adult islets. Sur1KO islets perifused with 1 mm glucose showed elevation of both basal [Ca(2+)](c) and insulin secretion. Stimulation with 15 mm glucose produced a transient drop of [Ca(2+)](c) followed by an overshoot and a sustained elevation, accompanied by a monophasic, 6-fold increase in insulin secretion. Glucose also increased insulin secretion when [Ca(2+)](c) was clamped by KCl. When Sur1KO islets were cultured in 5 instead of 10 mm glucose, [Ca(2+)](c) and insulin secretion were unexpectedly low in 1 mm glucose and increased following a biphasic time course upon stimulation by 15 mm glucose. This K(ATP) channel-independent first phase [Ca(2+)](c) rise was attributed to a Na(+)-, Cl(-)-, and Na(+)-pump-independent depolarization of beta-cells, leading to Ca(2+) influx through voltage-dependent calcium channels. Glucose indeed depolarized Sur1KO islets under these conditions. It is suggested that unidentified potassium channels are sensitive to glucose and subserve the acute and long-term metabolic control of [Ca(2+)](c) in beta-cells without functional K(ATP) channels.
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Affiliation(s)
- Andras Szollosi
- Unit of Endocrinology and Metabolism, University of Louvain Faculty of Medicine, UCL 55.30, Avenue Hippocrate 55, B-1200 Brussels, Belgium
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Nenquin M, Szollosi A, Aguilar-Bryan L, Bryan J, Henquin JC. Both triggering and amplifying pathways contribute to fuel-induced insulin secretion in the absence of sulfonylurea receptor-1 in pancreatic beta-cells. J Biol Chem 2004; 279:32316-24. [PMID: 15175349 DOI: 10.1074/jbc.m402076200] [Citation(s) in RCA: 87] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
In normal beta-cells glucose induces insulin secretion by activating both a triggering pathway (closure of K(ATP) channels, depolarization, and rise in cytosolic [Ca(2+)](i)) and an amplifying pathway (augmentation of Ca(2+) efficacy on exocytosis). It is unclear if and how nutrients can regulate insulin secretion by beta-cells lacking K(ATP) channels (Sur1 knockout mice). We compared glucose- and amino acid-induced insulin secretion and [Ca(2+)](i) changes in control and Sur1KO islets. In 1 mm glucose (non-stimulatory for controls), the triggering signal [Ca(2+)](i) was high (loss of regulation) and insulin secretion was stimulated in Sur1KO islets. This "basal" secretion was decreased or increased by imposed changes in [Ca(2+)](i) and was dependent on ATP production, indicating that both triggering and amplifying signals are involved. High glucose stimulated insulin secretion in Sur1KO islets, by an unsuspected, transient increase in [Ca(2+)](i) and a sustained activation of the amplifying pathway. Unlike controls, Sur1KO islets were insensitive to diazoxide and tolbutamide, which rules out effects of either drug at sites other than K(ATP) channels. Amino acids potently increased insulin secretion by Sur1KO islets through both a further electrogenic rise in [Ca(2+)](i) and a metabolism-dependent activation of the amplifying pathway. After sulfonylurea blockade of their K(ATP) channels, control islets qualitatively behaved like Sur1KO islets, but their insulin secretion rate was consistently lower for a similar or even higher [Ca(2+)](i). In conclusion, fuel secretagogues can control insulin secretion in beta-cells without K(ATP) channels, partly by an unsuspected influence on the triggering [Ca(2+)](i) signal and mainly by the modulation of a very effective amplifying pathway.
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Affiliation(s)
- Myriam Nenquin
- Unité d'Endocrinologie et Métabolisme, University of Louvain Faculty of Medicine UCL 55.30, Ave. Hippocrate 55, B-1200 Brussels, Belgium
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Marcaillou C, Szollosi A, Porcheron P, Dray F. Uptake of horseradish peroxydase by the testis of locusta migratoria during the last larval instar; relation with variations of ecdysteroid levels in haemolymph. Cell Tissue Res 1978; 188:63-74. [PMID: 639097 DOI: 10.1007/bf00220514] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
By using horseradish peroxydase (HRP) as a tracer, it is shown that the gonial region of the locust testis is an "open" compartment which is almost always freely penetrated by the tracer. During the last larval instar, however, the penetration of HRP decreases and ceases at the time when high levels of ecdysteroids are detected in the haemolymph by radioimmunoassay. A cause and effect relationship between tracer uptake and hormonal level could not be demonstrated by the experiments carried out up to now. From ultrastructural observations of the testis, it is concluded that the temporary isolation of the gonial compartment is not based upon any morphological structure which could act as a barrier. Penetration of the macromolecule is considered as the expression of an active uptake by the testis and the short period of nonpenetrability as a state of inertia whose significance remains to be discovered.
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