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Cleary SR, Seflova J, Cho EE, Bisht K, Khandelia H, Espinoza-Fonseca LM, Robia SL. Phospholamban inhibits the cardiac calcium pump by interrupting an allosteric activation pathway. J Biol Chem 2024; 300:107267. [PMID: 38583863 PMCID: PMC11098958 DOI: 10.1016/j.jbc.2024.107267] [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: 09/07/2023] [Revised: 03/20/2024] [Accepted: 04/02/2024] [Indexed: 04/09/2024] Open
Abstract
Phospholamban (PLB) is a transmembrane micropeptide that regulates the sarcoplasmic reticulum Ca2+-ATPase (SERCA) in cardiac muscle, but the physical mechanism of this regulation remains poorly understood. PLB reduces the Ca2+ sensitivity of active SERCA, increasing the Ca2+ concentration required for pump cycling. However, PLB does not decrease Ca2+ binding to SERCA when ATP is absent, suggesting PLB does not inhibit SERCA Ca2+ affinity. The prevailing explanation for these seemingly conflicting results is that PLB slows transitions in the SERCA enzymatic cycle associated with Ca2+ binding, altering transport Ca2+ dependence without actually affecting the equilibrium binding affinity of the Ca2+-coordinating sites. Here, we consider another hypothesis, that measurements of Ca2+ binding in the absence of ATP overlook important allosteric effects of nucleotide binding that increase SERCA Ca2+ binding affinity. We speculated that PLB inhibits SERCA by reversing this allostery. To test this, we used a fluorescent SERCA biosensor to quantify the Ca2+ affinity of non-cycling SERCA in the presence and absence of a non-hydrolyzable ATP-analog, AMPPCP. Nucleotide activation increased SERCA Ca2+ affinity, and this effect was reversed by co-expression of PLB. Interestingly, PLB had no effect on Ca2+ affinity in the absence of nucleotide. These results reconcile the previous conflicting observations from ATPase assays versus Ca2+ binding assays. Moreover, structural analysis of SERCA revealed a novel allosteric pathway connecting the ATP- and Ca2+-binding sites. We propose this pathway is disrupted by PLB binding. Thus, PLB reduces the equilibrium Ca2+ affinity of SERCA by interrupting allosteric activation of the pump by ATP.
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Affiliation(s)
- Sean R Cleary
- Department of Cell and Molecular Physiology, Loyola University Chicago, Maywood, Illinois, USA
| | - Jaroslava Seflova
- Department of Cell and Molecular Physiology, Loyola University Chicago, Maywood, Illinois, USA
| | - Ellen E Cho
- Department of Cell and Molecular Physiology, Loyola University Chicago, Maywood, Illinois, USA
| | - Konark Bisht
- Department of Physics, Chemistry, and Pharmacy, PHYLIFE: Physical Life Science, University of Southern Denmark, Odense, Denmark
| | - Himanshu Khandelia
- Department of Physics, Chemistry, and Pharmacy, PHYLIFE: Physical Life Science, University of Southern Denmark, Odense, Denmark
| | - L Michel Espinoza-Fonseca
- Division of Cardiovascular Medicine, Department of Internal Medicine, Center for Arrhythmia Research, University of Michigan, Ann Arbor, Michigan, USA
| | - Seth L Robia
- Department of Cell and Molecular Physiology, Loyola University Chicago, Maywood, Illinois, USA.
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Espinoza-Fonseca LM, Autry JM, Thomas DD. Microsecond molecular dynamics simulations of Mg²⁺- and K⁺-bound E1 intermediate states of the calcium pump. PLoS One 2014; 9:e95979. [PMID: 24760008 PMCID: PMC3997511 DOI: 10.1371/journal.pone.0095979] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/13/2014] [Accepted: 03/31/2014] [Indexed: 12/31/2022] Open
Abstract
We have performed microsecond molecular dynamics (MD) simulations to characterize the structural dynamics of cation-bound E1 intermediate states of the calcium pump (sarcoendoplasmic reticulum Ca²⁺-ATPase, SERCA) in atomic detail, including a lipid bilayer with aqueous solution on both sides. X-ray crystallography with 40 mM Mg²⁺ in the absence of Ca²⁺ has shown that SERCA adopts an E1 structure with transmembrane Ca²⁺-binding sites I and II exposed to the cytosol, stabilized by a single Mg²⁺ bound to a hybrid binding site I'. This Mg²⁺-bound E1 intermediate state, designated E1•Mg²⁺, is proposed to constitute a functional SERCA intermediate that catalyzes the transition from E2 to E1•2Ca²⁺ by facilitating H⁺/Ca²⁺ exchange. To test this hypothesis, we performed two independent MD simulations based on the E1•Mg²⁺ crystal structure, starting in the presence or absence of initially-bound Mg²⁺. Both simulations were performed for 1 µs in a solution containing 100 mM K⁺ and 5 mM Mg²⁺ in the absence of Ca²⁺, mimicking muscle cytosol during relaxation. In the presence of initially-bound Mg²⁺, SERCA site I' maintained Mg²⁺ binding during the entire MD trajectory, and the cytosolic headpiece maintained a semi-open structure. In the absence of initially-bound Mg²⁺, two K⁺ ions rapidly bound to sites I and I' and stayed loosely bound during most of the simulation, while the cytosolic headpiece shifted gradually to a more open structure. Thus MD simulations predict that both E1•Mg²⁺ and E•2K+ intermediate states of SERCA are populated in solution in the absence of Ca²⁺, with the more open 2K+-bound state being more abundant at physiological ion concentrations. We propose that the E1•2K⁺ state acts as a functional intermediate that facilitates the E2 to E1•2Ca²⁺ transition through two mechanisms: by pre-organizing transport sites for Ca²⁺ binding, and by partially opening the cytosolic headpiece prior to Ca²⁺ activation of nucleotide binding.
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Affiliation(s)
- L. Michel Espinoza-Fonseca
- Department of Biochemistry, Molecular Biology, and Biophysics, University of Minnesota, Minneapolis, Minnesota, United States of America
- * E-mail:
| | - Joseph M. Autry
- Department of Biochemistry, Molecular Biology, and Biophysics, University of Minnesota, Minneapolis, Minnesota, United States of America
| | - David D. Thomas
- Department of Biochemistry, Molecular Biology, and Biophysics, University of Minnesota, Minneapolis, Minnesota, United States of America
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Toyoshima C, Cornelius F. New crystal structures of PII-type ATPases: excitement continues. Curr Opin Struct Biol 2013; 23:507-14. [PMID: 23871101 DOI: 10.1016/j.sbi.2013.06.005] [Citation(s) in RCA: 52] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/19/2013] [Revised: 06/11/2013] [Accepted: 06/12/2013] [Indexed: 11/29/2022]
Abstract
P-type ATPases are ATP-powered ion pumps, classified into five subfamilies (PI-PV). Of these, PII-type ATPases, including Ca2+-ATPase, Na+,K+-ATPase and gastric H+,K+-ATPase, among others, have been the most intensively studied. Best understood structurally and biochemically is Ca2+-ATPase from sarcoplasmic reticulum of fast twitch skeletal muscle (sarco(endo)plasmic reticulum Ca2+-ATPase 1a, SERCA1a). Since publication of the first crystal structure in 2000, it has continuously been a source of excitement, as crystal structures for new reaction intermediates always show large structural changes. Crystal structures now exist for most of the reaction intermediates, almost covering the entire reaction cycle. This year the crystal structure of a missing link, the E1·Mg2+ state, finally appeared, bringing another surprise: bound sarcolipin (SLN). The current status of two other important PII-type ATPases, Na+,K+-ATPase and H+,K+-ATPase, is also briefly described.
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Affiliation(s)
- Chikashi Toyoshima
- Institute of Molecular and Cellular Biosciences, The University of Tokyo, Tokyo 113-0032, Japan.
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4
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Kargacin GJ, Aschar-Sobbi R, Kargacin ME. Inhibition of SERCA2 Ca(2+)-ATPases by Cs(+). Pflugers Arch 2004; 449:356-63. [PMID: 15480749 DOI: 10.1007/s00424-004-1345-7] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/06/2004] [Accepted: 09/06/2004] [Indexed: 10/26/2022]
Abstract
Replacement of K(+) with Cs(+) on the cytoplasmic side of the sarcoplasmic reticulum (SR) membrane reduces the maximum velocity (V(max)) of Ca(2+) uptake into the SR of saponin-permeabilized rat ventricular myocytes. To compare the sensitivity of the cardiac and smooth muscle/non-muscle forms of the sarcoplasmic/endoplasmic reticulum Ca(2+)-ATPase (SERCA2a and -2b respectively) to replacement of K(+) with Cs(+), SERCA2a and SERCA2b were expressed in HEK-293 cells. Ca(2+) uptake into HEK cell microsomes was inhibited by replacement of extravesicular K(+) with Cs(+) (V(max) of SERCA2a-mediated Ca(2+) uptake in CsCl was 80% of that in KCl; V(max) of SERCA2b-mediated uptake was 70% of that in KCl). The Ca(2+) sensitivity of uptake was decreased for both SERCA2a- and SERCA2b-mediated uptake and the Hill coefficients were increased in the presence of CsCl. The effects of Cs(+) on uptake were associated with direct inhibition of the ATPase activity of SERCA2a and SERCA2b. Our results indicate that cation binding sites are present in both SERCA2 isoforms, although the extent to which SERCA2b is inhibited by K(+) replacement is greater than that of SERCA2a or SERCA1. Consideration of these results and the recent molecular modeling work of others suggests that monovalent cations could interact with the Ca(2+) binding region of SERCA.
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Affiliation(s)
- Gary J Kargacin
- Department of Physiology and Biophysics, University of Calgary, 3330 Hospital Drive NW, Calgary, Alberta T2N 4N1, Canada.
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5
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Tadini Buoninsegni F, Bartolommei G, Moncelli MR, Inesi G, Guidelli R. Time-resolved charge translocation by sarcoplasmic reticulum Ca-ATPase measured on a solid supported membrane. Biophys J 2004; 86:3671-86. [PMID: 15189864 PMCID: PMC1304269 DOI: 10.1529/biophysj.103.036608] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/03/2003] [Accepted: 03/01/2004] [Indexed: 11/18/2022] Open
Abstract
Sarcoplasmic reticulum vesicles were adsorbed on an octadecanethiol/phosphatidylcholine mixed bilayer anchored to a gold electrode, and the Ca-ATPase contained in the vesicles was activated by ATP concentration jumps both in the absence and in the presence of K(+) ions and at different pH values. Ca(2+) concentration jumps in the absence of ATP were also carried out. The resulting capacitive current transients were analyzed together with the charge under the transients. The relaxation time constants of the current transients were interpreted on the basis of an equivalent circuit. The current transient after ATP concentration jumps and the charge after Ca(2+) concentration jumps in the absence of ATP exhibit almost the same dependence upon the Ca(2+) concentration, with a half-saturating value of approximately 1.5 microM. The pH dependence of the charge after Ca(2+) translocation demonstrates the occurrence of one H(+) per one Ca(2+) countertransport at pH 7 by direct charge-transfer measurements. The presence of K(+) decreases the magnitude of the current transients without altering their shape; this decrease is explained by K(+) binding to the cytoplasmic side of the pump in the E(1) conformation and being released to the same side during the E(1)-E(2) transition.
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Abstract
The first high-resolution structure of a P-type ATPase, that of the Ca(2+)-ATPase of skeletal muscle sarcoplasmic reticulum, was published in 2000. This structure has provided many clues to how the Ca(2+)-ATPase might work, but no complete answers. The Ca(2+)-ATPase structure reveals no clear pathway from the cytoplasmic side of the membrane to the pair of high-affinity binding sites for Ca(2+) located in the transmembrane region of the ATPase and no clear pathway from these sites to the lumenal side of the membrane. The ATPase is therefore very unlike an ion channel in its construction. It is unclear from the crystal structure of the Ca(2+)-ATPase exactly how the protein sits within the lipid bilayer that surrounds it in the membrane. The Ca(2+)-ATPase is implicated in thermogenesis in some types of muscle; this could involve processes of slippage and leak modulated by interaction between the Ca(2+)-ATPase and sarcolipin.
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Affiliation(s)
- Anthony G Lee
- Division of Biochemistry and Molecular Biology, School of Biological Sciences, University of Southampton, UK.
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7
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Landeira-Fernandez A. Ca(2+)transport by the sarcoplasmic reticulum Ca(2+)-ATPase in sea cucumber (Ludwigothurea grisea) muscle. J Exp Biol 2001; 204:909-21. [PMID: 11171414 DOI: 10.1242/jeb.204.5.909] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
In muscle cells, the excitation-contraction cycle is triggered by an increase in the concentration of free cytoplasmic Ca(2+). The Ca(2+)-ATPase present in the membrane of the sarcoplasmic reticulum (SR) pumps Ca(2+) from the cytosol into this intracellular compartment, thus promoting muscle relaxation. The microsomal fraction derived from the longitudinal smooth muscle of the body wall from the sea cucumber Ludwigothurea grisea retains a membrane-bound Ca(2+)-ATPase that is able to transport Ca(2+) mediated by ATP hydrolysis. Immunological analyses reveal that monoclonal antibodies against sarco-endoplasmic reticulum Ca(2+)-ATPase (SERCA1 and SERCA2a) cross-react with a 110 kDa band, indicating that the sea cucumber Ca(2+)-ATPase is a SERCA-type ATPase. Like the mammalian Ca(2+)-ATPase isoforms so far described, the enzyme also shows a high affinity for Ca(2+) and ATP, has an optimum pH of approximately 7.0 and is sensitive to thapsigargin and cyclopiazonic acid, specific inhibitors of the SERCA pumps. However, unlike the mammalian SERCA isoforms, concentrations of ATP above 2 mmol l(−1) inhibit Ca(2+) transport, but not ATP hydrolysis, in sea cucumber vesicles, suggesting that high ATP concentrations uncouple the Ca(2+)-ATPase. Another unique feature observed with the sea cucumber Ca(2+)-ATPase is the high dependence of maximal activity on K(+) or Na(+). Similar activation promoted by these cations was observed with various mammalian Ca(2+)-ATPase preparations when they were incubated in the presence of low concentrations of sulphated polysaccharides. In control experiments, K(+) and Na(+) have almost no effect on Ca(2+) transport, but in the presence of heparin or fucosylated chondroitin sulphate, the activity of the different mammalian Ca(2+)-ATPases is inhibited and they are activated by either K(+) or Na(+) in a manner similar to the native sea cucumber ATPase. These results led us to investigate the possible occurrence of a highly sulphated polysaccharide on vesicles from the SR of sea cucumber smooth muscle that could act as an ‘endogenous’ Ca(2+)-ATPase inhibitor. In fact, SR vesicles derived from the sea cucumber, but not from rabbit muscle, contain a highly sulphated polysaccharide. After extraction and purification of these polysaccharide molecules, their effect was tested on vesicles obtained from rabbit muscle. This compound inhibited Ca(2+) uptake in rabbit SR vesicles, at concentrations lower than heparin, and restored the dependence on monovalent cations. These results strongly suggest that the sea cucumber Ca(2+)-ATPase is activated by monovalent cations because of the presence of endogenous sulphated polysaccharides.
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Affiliation(s)
- A Landeira-Fernandez
- Instituto de Ciências Biomédicas, Departamento de Bioquímica Médica, Universidade Federal do Rio de Janeiro, UFRJ, Cidade Universitária, RJ, Rio de Janeiro, Brasil 21941-590.
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8
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Landeira-Fernandez AM, Galina A, Jennings P, Montero-Lomeli M, de Meis L. Sarcoplasmic reticulum Ca(2+)-ATPase of sea cucumber smooth muscle: regulation by K(+) and ATP. Comp Biochem Physiol A Mol Integr Physiol 2000; 126:263-74. [PMID: 10936766 DOI: 10.1016/s1095-6433(00)00197-5] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Abstract
Although several Ca(2+)-ATPase isoforms have been described in vertebrates, little is known about Ca(2+)-transport in the muscle of invertebrates. In the microsomal fraction obtained from the sea cucumber (Ludwigothurea grisea) longitudinal body wall smooth muscle, we identified a Ca(2+)-transport ATPase that is able to transport Ca(2+) at the expense of ATP hydrolysis. This enzyme has a high affinity for both Ca(2+) and ATP, an optimum pH around 7.0, and - different from the vertebrate sarcoplasmic reticulum Ca(2+)-ATPases isoforms so far described - is activated 3- to 5-fold by K(+) but not by Li(+), at all temperatures, Ca(2+) and ATP concentrations tested. Calcium accumulation by the sea cucumber microsomes is inhibited by Mg/ATP concentrations >1 mM and the accumulated Ca(2+) is released to the medium when the ATP concentration is raised from 0.1 to 4.0 mM.
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Affiliation(s)
- A M Landeira-Fernandez
- Departamento de Bioquímica Médica, Instituto de Ciências Biomédicas, Universidade Federal do Rio de Janeiro, Cidade Universitária, 21941-590, Rio de Janeiro, Brazil
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9
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Champeil P, Henao F, de Foresta B. Dissociation of Ca2+ from sarcoplasmic reticulum Ca2+-ATPase and changes in fluorescence of optically selected Trp residues. Effects of KCl and NaCl and implications for substeps in Ca2+ dissociation. Biochemistry 1997; 36:12383-93. [PMID: 9315879 DOI: 10.1021/bi9709699] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
Sequential dissociation of the two Ca2+ ions bound to non-phosphorylated sarcoplasmic reticulum Ca2+-ATPase was triggered by addition, in a stopped-flow experiment, of quin2, which acted both as a high-affinity chelator and as a Ca2+-sensitive fluorescent probe. The kinetics of Ca2+ dissociation were deduced from the observed changes in quin2 fluorescence in the visible region (with lambdaex = 313 nm), while fluorescence detection in the UV region (with lambdaex = 290 nm) made it possible to monitor the tryptophan fluorescence changes accompanying this dissociation under the same ionic conditions. In the absence of KCl or NaCl, at pH 6 or 7, the observed changes in quin2 fluorescence were monoexponential, with rate constants very close to those of the changes in ATPase tryptophan fluorescence, which also appeared monophasic. In the presence of 100 mM KCl, quin2 fluorescence changes, although still monoexponential, were faster than in the absence of the monovalent ions but distinctly slower than the changes in tryptophan fluorescence, which were accelerated to a larger extent. In addition, the apparent kinetics of the Trp fluorescence changes depended on the excitation wavelength. Using an excitation wavelength of 296 nm, the Trp fluorescence drop was still faster than with an excitation wavelength of 290 nm, and in the presence of NaCl it even displayed a clear undershoot. We conclude that in the presence of KCl or NaCl and with an excitation wavelength of 290 nm, the rapid drop in tryptophan fluorescence mainly monitors the dissociation of the first of the two Ca2+ ions to be released from Ca2+-ATPase, while excitation at 296 nm optically selects a subpopulation of Trp residues whose fluorescence level is lower in the ATPase species with one Ca2+ ion bound than in the Ca2+-deprived ATPase species. The latter conditions result in an initial drop in Trp fluorescence whose apparent rate constant (in single-exponential analysis) is faster than the true rate of dissociation of the first Ca2+ ion and in a subsequent slower rise related to dissociation of the second Ca2+ ion. The difference between results obtained in the absence and in the presence of K+ or Na+ is due to an antagonizing effect of these cations on proton-induced conformational rearrangement of Ca2+-free ATPase, a conformational rearrangement which changes the ATPase Trp fluorescence level and significantly affects the cooperativity of Ca2+ binding at equilibrium.
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Affiliation(s)
- P Champeil
- Département de Biologie Cellulaire et Moléculaire, Commissariat à l'Energie Atomique, Gif-sur-Yvette, France
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Takara D, Alonso GL. Effect of haloperidol on the sarcoplasmic reticulum Ca-dependent adenosine triphosphatase. BIOCHIMICA ET BIOPHYSICA ACTA 1996; 1314:57-65. [PMID: 8972718 DOI: 10.1016/s0167-4889(96)00076-6] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
Several effects of the neuroleptic agent haloperidol on the sarcoplasmic reticulum (SR) Ca-dependent adenosine triphosphatase (Ca-ATPase) and Ca transport are described. Haloperidol inhibits the Ca-ATPase activity in the presence of calcimycin. The effect depends on the conditions of preexposure of the membranes to the drug: the inhibition increases with the preincubation time; Ca and Mg protect the enzyme against the effect of the drug. The inhibitory effect of haloperidol decreases upon increasing [Ca2+], at constant [Mg], and disappears at 20 mM [Mg] for any [Ca2+], and at 0.5 mM [Ca2+] for any [Mg2+]. Haloperidol also inhibits phosphorylation of the enzyme by Pi, and ATP-dependent Ca2+ uptake, in both cases with apparent Ki = 0.10-0.15 mM, and increases the rate of Ca efflux from preloaded vesicles in this concentration range. The results suggest that haloperidol interacts with the catalytic site, interfering with the effect of the divalent catalytic cation, but not at other steps of the enzymatic cycle, where Mg2+ and Ca2+ are also activators. They are consistent with a reaction model where haloperidol interacts with the E2 conformers of the enzyme, with lower affinity for the phosphoenzyme than for the dephospho species. The inhibition of Ca uptake by SR vesicles is ascribed to an increased Ca2+ permeability rather than to the inhibition of the Ca-ATPase, which requires higher concentrations of the drug.
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Affiliation(s)
- D Takara
- Cátedra de Biofísica, Facultad de Odontología, Universidad de Buenos Aires, Argentina
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11
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Canet D, Forge V, Guillain F, Mintz E. Ca2+ translocation across sarcoplasmic reticulum ATPase randomizes the two transported ions. J Biol Chem 1996; 271:20566-72. [PMID: 8702801 DOI: 10.1074/jbc.271.34.20566] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023] Open
Abstract
Cytoplasmic Ca2+ dissociation is sequential, and the Ca2+ ions bound to the nonphosphorylated ATPase are commonly represented as superimposed on each other, so that the superficial Ca2+ is freely exchangeable from the cytoplasm, whereas the deeper Ca2+ is not. Under conditions where ADP-sensitive phosphoenzyme accumulates (leaky vesicles, 5 degrees C, pH 8, 300 mM K+), luminal Ca2+ dissociation is sequential as well, so that the representation of two superimposed Ca2+ ions still holds on the phosphoenzyme, with the superficial Ca2+ facing the lumen freely exchangeable and the deeper Ca2+ blocked by the superficial Ca2+. Under the same conditions, we have investigated whether a prebuilt Ca2+ order is maintained during membrane translocation. Starting from a prebuilt order on the cytoplasmic side, we showed that the Ca2+ ions cannot be identified after translocation to the luminal side. The same result was obtained starting from a prebuilt order on the luminal side and following the luminal to cytoplasmic translocation. We conclude that the two Ca2+ ions are mixed during ATP-induced phosphorylation as well as during ADP-induced dephosphorylation.
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Affiliation(s)
- D Canet
- Commissariat à l'Energie Atomique and Unité de Recherche 2096 Associée au Centre National de la Recherche Scientifique, Section de Biophysique des Protéines et des Membranes, Département de Biologie Cellulaire et Moléculaire, Centre d'
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12
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Ferreira ST, Coelho-Sampaio T. Intrinsic fluorescence as a probe of structure-function relationships in Ca(2+)-transport ATPases. Biosci Rep 1996; 16:87-106. [PMID: 8790915 DOI: 10.1007/bf01206199] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023] Open
Abstract
Applications of intrinsic fluorescence measurements in the study of Ca(2+)-transport ATPases are reviewed. Since the initial reports showing that the fluorescence emission was sensitive to Ca2+ binding, a substantial amount of work has focused on the use of both steady-state and time-resolved fluorescence spectroscopy to investigate structure-function relationships in sarcoplasmic reticulum and plasma membrane Ca(2+)-ATPases. These studies have revealed ligand-induced conformational changes, as well as provided information on protein-protein, protein-solvent and/or protein-lipid interactions in different functional states of these proteins. The main results of these studies, as well as possible future prospects are discussed.
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Affiliation(s)
- S T Ferreira
- Departamento de Bioquímica Médica, Universidade Federal do Rio de Janeiro, Brazil
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13
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Two types of proton-modulated calcium binding in the sarcoplasmic reticulum Ca(2+)-ATPase. I. A model of two different conformations of chemically equivalent ATPase molecules. J Biol Chem 1994. [DOI: 10.1016/s0021-9258(18)47354-1] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022] Open
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14
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Kalabokis VN, Hardwicke PM. Effect of the biochemical state of the Ca-ATPase protein of scallop sarcoplasmic reticulum on its interaction with trans-parinaric acid. BIOCHIMICA ET BIOPHYSICA ACTA 1993; 1147:35-41. [PMID: 8466929 DOI: 10.1016/0005-2736(93)90313-o] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
The polyene fluorescent probe trans-parinaric acid (tPA) was used to compare lipid-protein interactions in the scallop fragmented sarcoplasmic reticulum (FSR) between biochemical states where the Ca-ATPase molecules were arranged differently in the membrane and had different tertiary conformations. The state of the bulk lipid phase was examined over the temperature range -3 to +32 degrees C by exciting the tPA directly at 320 nm. The state of the system close to the Ca-ATPase protein was followed over the same temperature range by indirectly exciting the tPA through resonance energy transfer from the Ca-ATPase protein, with approximately one twenty-fifth the quantum yield of the directly excited probe. Raising the tPA/lipid ratio in the membrane to high levels (approx. 1:9), caused the quantum yield of indirectly excited tPA to reach a maximum, which may reflect saturation of the annular lipid phase with the probe, or contribution to the fluorescence from indirectly excited tPA bound directly to the protein. In the presence of 0.1 M KCl, a thermal perturbation was observed at approx. 7 degrees C using indirect excitation when the Ca(2+)-binding sites on the Ca-ATPase were occupied, and the subunits were disorganized. This transition was not detected in the presence of 0.1 M KCl and EGTA, when the Ca(2+)-binding sites were empty, and the Ca-ATPase subunits were organized in dimeric arrays. The transition seen with the E1(Ca2+)2 form of the membrane may involve an event at the protein/lipid interface, or a change in the environment of tPA bound to the Ca-ATPase. The temperature at which the perturbation occurs is close to that of a discontinuity in the Arrhenius plot of the Ca-ATPase enzyme activity determined in the presence of 0.1 M KCl (Kalabokis, V.N. and Hardwicke, P.M.D. (1988) J. Biol. Chem. 263, 15184-15188). No perturbation was observed in the bulk properties of the lipid component of the membrane in either the E1(Ca2+)2 or E2 states.
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Affiliation(s)
- V N Kalabokis
- Department of Medical Biochemistry, Southern Illinois University, Carbondale
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15
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Cataldi de Flombaum MA, Stoppani AO. High-affinity calcium-stimulated, magnesium-dependent adenosine triphosphatase in Trypanosoma cruzi. COMPARATIVE BIOCHEMISTRY AND PHYSIOLOGY. B, COMPARATIVE BIOCHEMISTRY 1992; 103:933-7. [PMID: 1478071 DOI: 10.1016/0305-0491(92)90218-g] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
1. A high-affinity (Ca2+ + Mg2+)-ATPase and a low-affinity Mg(2+)-ATPase were identified in the 105,000 g fraction from epimastigote forms of Trypanosoma cruzi, the agent of Chagas' disease (Tulahuen strain). 2. Activities were conserved after enzyme solubilization with deoxycholate. 3. The Ca(2+)-stimulated ATPase activity was (a) lower than that of the Mg(2+)-ATPase; (b) inhibited by p-chloromercurobenzoate and orthovanadate and (c) insensitive to oligomycin. 4. Optimal stimulation by Ca2+ was observed at pH 6.5-6.8 in the presence of 1 mM MgCl2 and 0.1 M KCl. 5. The Mg(2+)-ATPase was insensitive to p-chloromercurobenzoate and orthovanadate and did not require KCl for activity. 6. Kinetic analysis of the (Ca2+ + Mg2+)-ATPase yielded a half-maximal stimulating concentration of 1.1 microM for Ca2+ and a Km of 66 microM for ATP. 7. The (Ca2+ + Mg2+)-ATPase clearly differed from the Ca(2+)- or Mg(2+)-ATPases previously characterized in the same strain of T. cruzi (Frasch et al., 1978; Comp. Biochem. Physiol. 60B, 271-275).
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Girardet JL, Dupont Y. Ellipticity changes of the sarcoplasmic reticulum Ca(2+)-ATPase induced by cation binding and phosphorylation. FEBS Lett 1992; 296:103-6. [PMID: 1530922 DOI: 10.1016/0014-5793(92)80413-b] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
The sarcoplasmic reticulum (SR) Ca(2+)-ATPase is a member of the 'P-type' class of cation transport ATPases which form a covalent phosphorylated intermediate. It has been proposed that during ion transport, these proteins cyclically adopt two major enzymatic states E1 and E2, that are related to two essential conformations of the protein. By the use of especially sensitive circular dichroism (CD) instrumentation it is shown here that Ca2+ addition induces 5% or 2.5% increases in Ca(2+)-ATPase ellipticity at 225 nm in the absence or in the presence of Mg2+, respectively. Furthermore, a 2% change in the same direction was observed when the enzyme was phosphorylated with Pi in the absence of Ca2+. These results suggest that the E1----E2 transition and the E2-P formation are associated with structural changes of the polypeptide backbone structure of the calcium pump protein.
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Affiliation(s)
- J L Girardet
- Département de Biologie Moléculaire et Structurale, Centre d'Etudes Nucléaires de Grenoble URA CNRS 520, France
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Kalabokis V, Bozzola J, Castellani L, Hardwicke P. A possible role for the dimer ribbon state of scallop sarcoplasmic reticulum. Dimmer ribbons are associated with stabilization of the Ca(2+)-free Ca-ATPase. J Biol Chem 1991. [DOI: 10.1016/s0021-9258(18)54742-6] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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