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Tadini-Buoninsegni F. Protein Adsorption on Solid Supported Membranes: Monitoring the Transport Activity of P-Type ATPases. Molecules 2020; 25:molecules25184167. [PMID: 32933017 PMCID: PMC7570688 DOI: 10.3390/molecules25184167] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/06/2020] [Revised: 09/01/2020] [Accepted: 09/02/2020] [Indexed: 02/07/2023] Open
Abstract
P-type ATPases are a large family of membrane transporters that are found in all forms of life. These enzymes couple ATP hydrolysis to the transport of various ions or phospholipids across cellular membranes, thereby generating and maintaining crucial electrochemical potential gradients. P-type ATPases have been studied by a variety of methods that have provided a wealth of information about the structure, function, and regulation of this class of enzymes. Among the many techniques used to investigate P-type ATPases, the electrical method based on solid supported membranes (SSM) was employed to investigate the transport mechanism of various ion pumps. In particular, the SSM method allows the direct measurement of charge movements generated by the ATPase following adsorption of the membrane-bound enzyme on the SSM surface and chemical activation by a substrate concentration jump. This kind of measurement was useful to identify electrogenic partial reactions and localize ion translocation in the reaction cycle of the membrane transporter. In the present review, we discuss how the SSM method has contributed to investigate some key features of the transport mechanism of P-type ATPases, with a special focus on sarcoplasmic reticulum Ca2+-ATPase, mammalian Cu+-ATPases (ATP7A and ATP7B), and phospholipid flippase ATP8A2.
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2
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Gur M, Golcuk M, Yilmaz SZ, Taka E. Thermodynamic first law efficiency of membrane proteins. J Biomol Struct Dyn 2019; 38:439-449. [PMID: 30727820 DOI: 10.1080/07391102.2019.1577759] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
Proteins are nature's biomolecular machines. Proteins, such as transporters, pumps and motors, have complex function/operating-machinery/mechanisms, comparable to the macro-scaled machines that we encounter in our daily life. These proteins, as it is for their macro-scaled counterparts, convert (part of) other/various forms of energy into work. In this study, we are performing the first law analysis on a set of proteins, including the dopamine transporter, glycine transporters I and II, glutamate transporter, sodium-potassium pump and Ca2+ ATPase. Each of these proteins operates on a thermodynamic/mechanic cycle to perform their function. In each of these cycles, they receive energy from a source, convert part of this energy into work and reject the remaining part of the energy to the environment. Conservation of energy principle was applied to the thermodynamic/mechanic cycle of each protein, and thermodynamic first law efficiency was evaluated for each cycle, which shows how much of the energy input per cycle was converted into useful work. Interestingly, calculations based on experimental data indicate that proteins can operate under a range of efficiencies, which vary based on the extracellular and intracellular ion and substrate concentrations. The lowest observed first law efficiency was 50%, which is a very high value if compared to the efficiency of the macro-scaled heat engines we encounter in our daily lives.Communicated by Ramaswamy H. Sarma.
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Affiliation(s)
- Mert Gur
- Department of Mechanical Engineering, Istanbul Technical University (ITU), Istanbul, Turkey
| | - Mert Golcuk
- Department of Mechanical Engineering, Istanbul Technical University (ITU), Istanbul, Turkey
| | - Sema Zeynep Yilmaz
- Department of Mechanical Engineering, Istanbul Technical University (ITU), Istanbul, Turkey
| | - Elhan Taka
- Department of Mechanical Engineering, Istanbul Technical University (ITU), Istanbul, Turkey
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3
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Rui H, Das A, Nakamoto R, Roux B. Proton Countertransport and Coupled Gating in the Sarcoplasmic Reticulum Calcium Pump. J Mol Biol 2018; 430:5050-5065. [PMID: 30539761 DOI: 10.1016/j.jmb.2018.10.014] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/21/2018] [Revised: 09/25/2018] [Accepted: 10/20/2018] [Indexed: 10/28/2022]
Abstract
The calcium pump of the sarcoplasmic reticulum (SERCA) is an ATP-driven active transporter of Ca2+ ions that functions via an "alternating-access" cycle mechanism. In each cycle, SERCA transports two Ca2+ ions toward the lumen of the sarcoplasmic reticulum and two to three protons to the cytoplasm. How the latter conformational transition is coupled to cytoplasmic release of protons remains poorly understood. The present computational study shows how the mechanism of proton countertransport is coupled to the alternating access gating process in SERCA. Molecular dynamics simulation trajectories are generated starting from a series of configurations taken along the E2 to E1 transition pathway determined by the string method with swarms-of-trajectories. Simulations of different protonation configurations at the binding sites reveal how deprotonation events affect the opening of the cytoplasmic gate. The results show that there is a strong coupling between the chronological order of deprotonation, the entry of water molecules into the TM region, and the opening of the cytoplasmic gate. Deprotonation of E309 and E771 is sequential with E309 being the first to lose the proton. The deprotonation promotes the opening of the cytoplasmic gate but leads to a productive gating transition only if it occurs after the transmembrane domain has reached an intermediate conformation. Deprotonation of E309 and E771 is unproductive when it occurs too early because it causes the re-opening of the luminal gate.
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Affiliation(s)
- Huan Rui
- Department of Biochemistry and Molecular Biology, The University of Chicago, 929 East 57th Street, Chicago, IL 60637, USA
| | - Avisek Das
- Department of Biochemistry and Molecular Biology, The University of Chicago, 929 East 57th Street, Chicago, IL 60637, USA
| | - Robert Nakamoto
- Department of Molecular Physiology and Biological Physics, University of Virginia School of Medicine, PO Box 800886, 480 Ray C. Hunt Drive, Charlottesville, VA 22908, USA
| | - Benoît Roux
- Department of Biochemistry and Molecular Biology, The University of Chicago, 929 East 57th Street, Chicago, IL 60637, USA.
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4
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Mikkelsen SA, Vangheluwe P, Andersen JP. A Darier disease mutation relieves kinetic constraints imposed by the tail of sarco(endo)plasmic reticulum Ca 2+-ATPase 2b. J Biol Chem 2018; 293:3880-3889. [PMID: 29363575 DOI: 10.1074/jbc.ra117.000941] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/13/2017] [Revised: 01/19/2018] [Indexed: 11/06/2022] Open
Abstract
The sarco(endo)plasmic reticulum Ca2+-ATPase (SERCA) 2b isoform possesses an extended C terminus (SERCA2b tail) forming an 11th transmembrane (TM) helix, which slows conformational changes of the Ca2+-pump reaction cycle. Here, we report that a Darier disease (DD) mutation of SERCA2b that changes a glutamate to a lysine in the cytoplasmic loop between TM8 and TM9 (E917K) relieves these kinetic constraints. We analyzed the effects of this mutation on the overall reaction and the individual partial reactions of the Ca2+ pump compared with the corresponding mutations of the SERCA2a and SERCA1a isoforms, lacking the SERCA2b tail. In addition to a reduced affinity for Ca2+, caused by the mutation in all three isoforms examined, we observed a unique enhancing effect on the turnover rates of ATPase activity and Ca2+ transport for the SERCA2b E917K mutation. This relief of kinetic constraints contrasted with inhibitory effects observed for the corresponding SERCA2a and SERCA1a (E918K) mutations. These observations indicated that the E917K/E918K mutations affect the rate-limiting conformational change in isoform-specific ways and that the SERCA2b mutation perturbs the interactions of TM11 with other SERCA2b regions. Mutational analysis of an arginine in TM7 that interacts with the glutamate in SERCA1a crystal structures suggested that in wildtype SERCA2b, the corresponding arginine (Arg-835) may be involved in mediating the conformational restriction by TM11. Moreover, the E917K mutation may disturb TM11 through the cytoplasmic loop between TM10 and TM11. In conclusion, our findings have identified structural elements of importance for the kinetic constraints imposed by TM11.
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Affiliation(s)
- Stine A Mikkelsen
- From the Department of Biomedicine, Aarhus University, DK-8000 Aarhus C, Denmark and
| | - Peter Vangheluwe
- the Department of Cellular and Molecular Medicine, KU Leuven, B-3000 Leuven, Belgium
| | - Jens Peter Andersen
- From the Department of Biomedicine, Aarhus University, DK-8000 Aarhus C, Denmark and
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5
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Yamasaki K, Daiho T, Danko S, Yasuda S, Suzuki H. Nanodisc-based kinetic assays reveal distinct effects of phospholipid headgroups on the phosphoenzyme transition of sarcoplasmic reticulum Ca 2+-ATPase. J Biol Chem 2017; 292:20218-20227. [PMID: 29032359 DOI: 10.1074/jbc.m117.816702] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/07/2017] [Revised: 10/10/2017] [Indexed: 01/08/2023] Open
Abstract
Sarco(endo)plasmic reticulum Ca2+-ATPase catalyzes ATP-driven Ca2+ transport from the cytoplasm to the lumen and is critical for a range of cell functions, including muscle relaxation. Here, we investigated the effects of the headgroups of the 1-palmitoyl-2-oleoyl glycerophospholipids phosphatidylcholine (PC), phosphatidylethanolamine (PE), phosphatidylserine (PS), and phosphatidylglycerol (PG) on sarcoplasmic reticulum (SR) Ca2+-ATPase embedded into a nanodisc, a lipid-bilayer construct harboring the specific lipid. We found that Ca2+-ATPase activity in a PC bilayer is comparable with that of SR vesicles and is suppressed in the other phospholipids, especially in PS. Ca2+ affinity at the high-affinity transport sites in PC was similar to that of SR vesicles, but 2-3-fold reduced in PE and PS. Ca2+ on- and off-rates in the non-phosphorylated ATPase were markedly reduced in PS. Rate-limiting phosphoenzyme (EP) conformational transition in 0.1 m KCl was as rapid in PC as in SR vesicles, but slowed in other phospholipids, especially in PS. Using kinetic plots of the logarithm of rate versus the square of mean activity coefficient of solutes in 0.1-1 m KCl, we noted that PC is optimal for the EP transition, but PG and especially PS had markedly unfavorable electrostatic effects, and PE exhibited a strong non-electrostatic restriction. Thus, the major SR membrane lipid PC is optimal for all steps and, unlike the other headgroups, contributes favorable electrostatics and non-electrostatic elements during the EP transition. Our analyses further revealed that the surface charge of the lipid bilayer directly modulates the transition rate.
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Affiliation(s)
- Kazuo Yamasaki
- Department of Biochemistry, Asahikawa Medical University, Midorigaoka-Higashi, Asahikawa 078-8510, Japan.
| | - Takashi Daiho
- Department of Biochemistry, Asahikawa Medical University, Midorigaoka-Higashi, Asahikawa 078-8510, Japan
| | - Stefania Danko
- Department of Biochemistry, Asahikawa Medical University, Midorigaoka-Higashi, Asahikawa 078-8510, Japan
| | - Satoshi Yasuda
- Department of Biochemistry, Asahikawa Medical University, Midorigaoka-Higashi, Asahikawa 078-8510, Japan
| | - Hiroshi Suzuki
- Department of Biochemistry, Asahikawa Medical University, Midorigaoka-Higashi, Asahikawa 078-8510, Japan
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6
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Tadini-Buoninsegni F, Smeazzetto S. Mechanisms of charge transfer in human copper ATPases ATP7A and ATP7B. IUBMB Life 2017; 69:218-225. [PMID: 28164426 DOI: 10.1002/iub.1603] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/21/2016] [Accepted: 12/26/2016] [Indexed: 12/30/2022]
Abstract
ATP7A and ATP7B are Cu+ -transporting ATPases of subclass IB and play a fundamental role in intracellular copper homeostasis. ATP7A/B transfer Cu+ ions across the membrane from delivery to acceptor proteins without establishing a free Cu+ gradient. Transfer of copper across the membrane is coupled to ATP hydrolysis. Current measurements on solid supported membranes (SSM) were performed to investigate the mechanism of copper-related charge transfer across ATP7A and ATP7B. SSM measurements demonstrated that electrogenic copper displacement occurs within ATP7A/B following addition of ATP and formation of the phosphorylated intermediate. Comparison of the time constants for cation displacement in ATP7A/B and sarcoplasmic reticulum Ca2+ -ATPase is consistent with the slower phosphoenzyme formation in copper ATPases. Moreover, ATP-dependent copper transfer in ATP7A/B is not affected by varying the pH, suggesting that net proton counter-transport may not occur in copper ATPases. Platinum anticancer drugs activate ATP7A/B and are subjected to ATP-dependent vectorial displacement with a mechanism analogous to that of copper. © 2016 IUBMB Life, 69(4):218-225, 2017.
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Affiliation(s)
| | - Serena Smeazzetto
- Department of Chemistry "Ugo Schiff,", University of Florence, Sesto Fiorentino, Italy
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7
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Tadini-Buoninsegni F, Moncelli MR, Peruzzi N, Ninham BW, Dei L, Nostro PL. Hofmeister effect of anions on calcium translocation by sarcoplasmic reticulum Ca(2+)-ATPase. Sci Rep 2015; 5:14282. [PMID: 26435197 PMCID: PMC4593048 DOI: 10.1038/srep14282] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/20/2015] [Accepted: 07/24/2015] [Indexed: 11/18/2022] Open
Abstract
The occurrence of Hofmeister (specific ion) effects in various membrane-related physiological processes is well documented. For example the effect of anions on the transport activity of the ion pump Na+, K+-ATPase has been investigated. Here we report on specific anion effects on the ATP-dependent Ca2+ translocation by the sarcoplasmic reticulum Ca2+-ATPase (SERCA). Current measurements following ATP concentration jumps on SERCA-containing vesicles adsorbed on solid supported membranes were carried out in the presence of different potassium salts. We found that monovalent anions strongly interfere with ATP-induced Ca2+ translocation by SERCA, according to their increasing chaotropicity in the Hofmeister series. On the contrary, a significant increase in Ca2+ translocation was observed in the presence of sulphate. We suggest that the anions can affect the conformational transition between the phosphorylated intermediates E1P and E2P of the SERCA cycle. In particular, the stabilization of the E1P conformation by chaotropic anions seems to be related to their adsorption at the enzyme/water and/or at the membrane/water interface, while the more kosmotropic species affect SERCA conformation and functionality by modifying the hydration layers of the enzyme.
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Affiliation(s)
| | - Maria Rosa Moncelli
- Department of Chemistry "Ugo Schiff", University of Florence, 50019 Sesto Fiorentino (Firenze), Italy
| | - Niccolò Peruzzi
- Department of Chemistry "Ugo Schiff", University of Florence, 50019 Sesto Fiorentino (Firenze), Italy.,CSGI, University of Florence, 50019 Sesto Fiorentino (Firenze), Italy
| | - Barry W Ninham
- Research School of Physical Sciences and Engineering, Australian National University, Canberra, Australia 0200
| | - Luigi Dei
- Department of Chemistry "Ugo Schiff", University of Florence, 50019 Sesto Fiorentino (Firenze), Italy.,CSGI, University of Florence, 50019 Sesto Fiorentino (Firenze), Italy
| | - Pierandrea Lo Nostro
- Department of Chemistry "Ugo Schiff", University of Florence, 50019 Sesto Fiorentino (Firenze), Italy.,CSGI, University of Florence, 50019 Sesto Fiorentino (Firenze), Italy
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8
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Ca(2+)/H (+) exchange, lumenal Ca(2+) release and Ca (2+)/ATP coupling ratios in the sarcoplasmic reticulum ATPase. J Cell Commun Signal 2013; 8:5-11. [PMID: 24302441 PMCID: PMC3972395 DOI: 10.1007/s12079-013-0213-7] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/04/2013] [Accepted: 11/01/2013] [Indexed: 12/29/2022] Open
Abstract
The Ca2+ transport ATPase (SERCA) of sarcoplasmic reticulum (SR) plays an important role in muscle cytosolic signaling, as it stores Ca2+ in intracellular membrane bound compartments, thereby lowering cytosolic Ca2+ to induce relaxation. The stored Ca2+ is in turn released upon membrane excitation to trigger muscle contraction. SERCA is activated by high affinity binding of cytosolic Ca2+, whereupon ATP is utilized by formation of a phosphoenzyme intermediate, which undergoes protein conformational transitions yielding reduced affinity and vectorial translocation of bound Ca2+. We review here biochemical and biophysical evidence demonstrating that release of bound Ca2+ into the lumen of SR requires Ca2+/H+ exchange at the low affinity Ca2+ sites. Rise of lumenal Ca2+ above its dissociation constant from low affinity sites, or reduction of the H+ concentration by high pH, prevent Ca2+/H+ exchange. Under these conditions Ca2+ release into the lumen of SR is bypassed, and hydrolytic cleavage of phosphoenzyme may yield uncoupled ATPase cycles. We clarify how such Ca2+pump slippage does not occur within the time length of muscle twitches, but under special conditions and in special cells may contribute to thermogenesis.
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9
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Lewis D, Pilankatta R, Inesi G, Bartolommei G, Moncelli MR, Tadini-Buoninsegni F. Distinctive features of catalytic and transport mechanisms in mammalian sarco-endoplasmic reticulum Ca2+ ATPase (SERCA) and Cu+ (ATP7A/B) ATPases. J Biol Chem 2012; 287:32717-27. [PMID: 22854969 DOI: 10.1074/jbc.m112.373472] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023] Open
Abstract
Ca(2+) (sarco-endoplasmic reticulum Ca(2+) ATPase (SERCA)) and Cu(+) (ATP7A/B) ATPases utilize ATP through formation of a phosphoenzyme intermediate (E-P) whereby phosphorylation potential affects affinity and orientation of bound cation. SERCA E-P formation is rate-limited by enzyme activation by Ca(2+), demonstrated by the addition of ATP and Ca(2+) to SERCA deprived of Ca(2+) (E2) as compared with ATP to Ca(2+)-activated enzyme (E1·2Ca(2+)). Activation by Ca(2+) is slower at low pH (2H(+)·E2 to E1·2Ca(2+)) and little sensitive to temperature-dependent activation energy. On the other hand, subsequent (forward or reverse) phosphoenzyme processing is sensitive to activation energy, which relieves conformational constraints limiting Ca(2+) translocation. A "H(+)-gated pathway," demonstrated by experiments on pH variations, charge transfer, and Glu-309 mutation allows luminal Ca(2+) release by H(+)/Ca(2+) exchange. As compared with SERCA, initial utilization of ATP by ATP7A/B is much slower and highly sensitive to temperature-dependent activation energy, suggesting conformational constraints of the headpiece domains. Contrary to SERCA, ATP7B phosphoenzyme cleavage shows much lower temperature dependence than EP formation. ATP-dependent charge transfer in ATP7A and -B is observed, with no variation of net charge upon pH changes and no evidence of Cu(+)/H(+) exchange. As opposed to SERCA after Ca(2+) chelation, ATP7A/B does not undergo reverse phosphorylation with P(i) after copper chelation unless a large N-metal binding extension segment is deleted. This is attributed to the inactivating interaction of the copper-deprived N-metal binding extension with the headpiece domains. We conclude that in addition to common (P-type) phosphoenzyme intermediate formation, SERCA and ATP7A/B possess distinctive features of catalytic and transport mechanisms.
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Affiliation(s)
- David Lewis
- California Pacific Medical Center Research Institute, San Francisco, California 94107, USA
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10
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Musgaard M, Thøgersen L, Schiøtt B. Protonation states of important acidic residues in the central Ca²⁺ ion binding sites of the Ca²⁺-ATPase: a molecular modeling study. Biochemistry 2011; 50:11109-20. [PMID: 22082179 DOI: 10.1021/bi201164b] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The P-type ATPases are responsible for the transport of cations across cell membranes. The sarco(endo)plasmic reticulum Ca²⁺-ATPase (SERCA) transports two Ca²⁺ ions from the cytoplasm to the lumen of the sarco(endo)plasmic reticulum and countertransports two or three protons per catalytic cycle. Two binding sites for Ca²⁺ ions have been located via protein crystallography, including four acidic amino acid residues that are essential to the ion coordination. In this study, we present molecular dynamics (MD) simulations examining the protonation states of these amino acid residues in a Ca²⁺-free conformation of SERCA. Such knowledge will be important for an improved understanding of atomistic details of the transport mechanism of protons and Ca²⁺ ions. Eight combinations of the protonation of four central acidic residues, Glu309, Glu771, Asp800, and Glu908, are tested from 10 ns MD simulations with respect to protein stability and ability to maintain a structure similar to the crystal structure. The trajectories for the most prospective combinations of protonation states were elongated to 50 ns and subjected to more detailed analysis, including prediction of pK(a) values of the four acidic residues over the trajectories. From the simulations we find that the combination leaving only Asp800 as charged is most likely. The results are compared to available experimental data and explain the observed destabilization upon full deprotonation, resulting in the entry of cytoplasmic K⁺ ions into the Ca²⁺ binding sites during the simulation in which Ca²⁺ ions are absent. Furthermore, a hypothesis for the exchange of protons from the central binding cavity is proposed.
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Affiliation(s)
- Maria Musgaard
- Department of Chemistry, Aarhus University, Langelandsgade 140, DK-8000 Aarhus C, Denmark
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11
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Fibich A, Apell HJ. Kinetics of luminal proton binding to the SR Ca-ATPase. Biophys J 2011; 101:1896-904. [PMID: 22004743 DOI: 10.1016/j.bpj.2011.09.014] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/21/2011] [Revised: 08/23/2011] [Accepted: 09/13/2011] [Indexed: 10/16/2022] Open
Abstract
An open membrane preparation containing SR Ca-ATPase was prepared from sarcoplasmic-reticulum vesicles to study the ion binding kinetics in the P-E(2) conformation. Because Ca(2+) and H(+) binding are electrogenic reactions, fluorescent styryl dyes could be used to determine changes in the binding site occupation in equilibrium titration experiments and time-resolved relaxation processes triggered by a pH jump. By photo release from caged proton the pH of the electrolyte could be decreased in a step of 0.1 pH units by a single ultraviolet-laser flash. Analysis of the pH-jump induced relaxation process in the P-E(2) conformation showed that three Ca-ATPase-specific processes could be identified, fast H(+) binding (τ < 100 μs) and pH-insensitive conformational relaxations after the release of the Ca(2+) ion (τ ∼160 ms), and a slow process (τ ∼3.4 s) whose origin could not be unambiguously revealed. The Ca(2+)-binding affinity in the P-E(2) conformation was reduced with increasing pH, a behavior that can be explained by a reversible transition of the empty P-E(2) state to an inactivated state of the ion pump. All findings are interpreted in the framework of the Post-Albers pump cycle introduced previously, supplemented by an additional transition to an inhibited state of the ion pump.
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Affiliation(s)
- Andreas Fibich
- Department of Biology, University of Konstanz, Konstanz, Germany
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12
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Bartolommei G, Moncelli MR, Rispoli G, Kelety B, Tadini-Buoninsegni F. Electrogenic ion pumps investigated on a solid supported membrane: comparison of current and voltage measurements. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2009; 25:10925-10931. [PMID: 19518101 DOI: 10.1021/la901469n] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/27/2023]
Abstract
Current and voltage measurements were performed on Na,K-ATPase and sarcoplasmic reticulum (SR) Ca-ATPase. Measurements of current transients under short-circuit conditions and of voltage transients under open-circuit conditions were carried out by employing a solid supported membrane (SSM). Purified membrane fragments containing Na,K-ATPase or native SR vesicles were adsorbed on a SSM and were activated by performing substrate concentration jumps. Current and voltage transients were recorded in the external circuit. They are related to pump activity and can be attributed to electrogenic events in the reaction cycles of the two enzymes. While current transients of very small amplitude are difficult to detect, the corresponding voltage transients can be measured with higher accuracy because of a much more favorable signal-to-noise ratio. Therefore, voltage measurements are preferable for the investigation of slow processes generating low current signals, e.g., for the analysis of low turnover transporters.
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Affiliation(s)
- G Bartolommei
- Department of Chemistry, University of Florence, Via della Lastruccia 3, 50019 Sesto Fiorentino, Italy
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13
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Liu Y, Pilankatta R, Lewis D, Inesi G, Tadini-Buoninsegni F, Bartolommei G, Moncelli MR. High-yield heterologous expression of wild type and mutant Ca(2+) ATPase: Characterization of Ca(2+) binding sites by charge transfer. J Mol Biol 2009; 391:858-71. [PMID: 19559032 PMCID: PMC2928698 DOI: 10.1016/j.jmb.2009.06.044] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/24/2009] [Revised: 06/04/2009] [Accepted: 06/17/2009] [Indexed: 11/16/2022]
Abstract
High-yield heterologous SERCA1 (Ca(2+) ATPase) expression was obtained in COS-1 cells infected with recombinant adenovirus vector (rAdSERCA). Higher transcription and expression were obtained in the presence of a His(6) tag at the amino terminus, as compared with a His(6) tag at the carboxyl SERCA terminus, or no tag. The expressed protein was targeted extensively to intracellular membranes. Optimal yield of functional Ca(2+) ATPase corresponded to 10% of total protein, with phosphoenzyme levels, catalytic turnover and Ca(2+) transport identical with those of native SERCA1. This recombinant membrane-bound (detergent-free) enzyme was used for characterization of Ca(2+) binding at the two specific transmembrane sites (ATP-free) by measurements of net charge transfer upon Ca(2+) binding to the protein, yielding cooperative isotherms (K(1)=5.9+/-0.5x10(5) M(-1) and K(2)=5.7+/-0.3x10(6) M(-1)). Non-cooperative binding of only one Ca(2+), and loss of ATPase activation, were observed following E309 mutation at site II. On the other hand, as a consequence of the site II mutation, the affinity of site I for Ca(2+) was increased (K=4.4+/-0.2x10(6) M(-1)). This change was due to a pK(a) shift of site I acidic residues, and to contributions of oxygen functions from empty site II to Ca(2+) binding at site I. No charge movement was observed following E771Q mutation at site I, indicating no Ca(2+) binding to either site. Therefore, calcium occupancy of site I is required to trigger cooperative binding to site II and catalytic activation. In the presence of millimolar Mg(2+), the charge movement upon addition of Ca(2+) to WT ATPase was reduced by 50%, while it was reduced by 90% when Ca(2+) was added to the E309Q/A mutants, demonstrating that competitive Mg(2+) binding can occur at site I but not at site II.
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Affiliation(s)
- Yueyong Liu
- California Pacific Medical Center Research Institute, San Francisco, CA 94107, USA
| | - Rajendra Pilankatta
- California Pacific Medical Center Research Institute, San Francisco, CA 94107, USA
| | - David Lewis
- California Pacific Medical Center Research Institute, San Francisco, CA 94107, USA
| | - Giuseppe Inesi
- California Pacific Medical Center Research Institute, San Francisco, CA 94107, USA
| | | | | | - Maria Rosa Moncelli
- Department of Chemistry, University of Florence, 50019 Sesto Fiorentino, Italy
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14
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Vangheluwe P, Sepúlveda MR, Missiaen L, Raeymaekers L, Wuytack F, Vanoevelen J. Intracellular Ca2+- and Mn2+-Transport ATPases. Chem Rev 2009; 109:4733-59. [DOI: 10.1021/cr900013m] [Citation(s) in RCA: 71] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Affiliation(s)
- Peter Vangheluwe
- Laboratory of Ca2+-transport ATPases and Laboratory of Molecular and Cellular Signaling, Department of Molecular Cell Biology, Katholieke Universiteit Leuven, Leuven, Belgium
| | - M. Rosario Sepúlveda
- Laboratory of Ca2+-transport ATPases and Laboratory of Molecular and Cellular Signaling, Department of Molecular Cell Biology, Katholieke Universiteit Leuven, Leuven, Belgium
| | - Ludwig Missiaen
- Laboratory of Ca2+-transport ATPases and Laboratory of Molecular and Cellular Signaling, Department of Molecular Cell Biology, Katholieke Universiteit Leuven, Leuven, Belgium
| | - Luc Raeymaekers
- Laboratory of Ca2+-transport ATPases and Laboratory of Molecular and Cellular Signaling, Department of Molecular Cell Biology, Katholieke Universiteit Leuven, Leuven, Belgium
| | - Frank Wuytack
- Laboratory of Ca2+-transport ATPases and Laboratory of Molecular and Cellular Signaling, Department of Molecular Cell Biology, Katholieke Universiteit Leuven, Leuven, Belgium
| | - Jo Vanoevelen
- Laboratory of Ca2+-transport ATPases and Laboratory of Molecular and Cellular Signaling, Department of Molecular Cell Biology, Katholieke Universiteit Leuven, Leuven, Belgium
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15
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Ion transport and energy transduction of P-type ATPases: Implications from electrostatic calculations. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2009; 1787:721-9. [DOI: 10.1016/j.bbabio.2009.02.015] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/09/2008] [Revised: 02/13/2009] [Accepted: 02/17/2009] [Indexed: 12/12/2022]
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16
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A thermodynamic model of the cardiac sarcoplasmic/endoplasmic Ca(2+) (SERCA) pump. Biophys J 2009; 96:2029-42. [PMID: 19254563 DOI: 10.1016/j.bpj.2008.11.045] [Citation(s) in RCA: 64] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/10/2008] [Accepted: 11/05/2008] [Indexed: 11/20/2022] Open
Abstract
We present a biophysically based kinetic model of the cardiac SERCA pump that consolidates a range of experimental data into a consistent and thermodynamically constrained framework. The SERCA model consists of a number of sub-states with partial reactions that are sensitive to Ca(2+) and pH, and to the metabolites MgATP, MgADP, and Pi. Optimization of model parameters to fit experimental data favors a fully cooperative Ca(2+)-binding mechanism and predicts a Ca(2+)/H(+) counter-transport stoichiometry of 2. Moreover, the order of binding of the partial reactions, particularly the binding of MgATP, proves to be a strong determinant of the ability of the model to fit the data. A thermodynamic investigation of the model indicates that the binding of MgATP has a large inhibitory effect on the maximal reverse rate of the pump. The model is suitable for integrating into whole-cell models of cardiac electrophysiology and Ca(2+) dynamics to simulate the effects on the cell of compromised metabolism arising in ischemia and hypoxia.
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17
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Mahaney JE, Thomas DD, Farrance IK, Froehlich JP. Intermolecular interactions in the mechanism of skeletal muscle sarcoplasmic reticulum Ca(2+)-ATPase (SERCA1): evidence for a triprotomer. Biochemistry 2009; 47:13711-25. [PMID: 19046074 DOI: 10.1021/bi801024a] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Native membrane sarcoplasmic reticulum (SR) Ca(2+)-ATPase isolated from skeletal muscle (SERCA1) exhibits oligomeric kinetic behavior [Mahaney, J. E., Thomas, D. D., and Froehlich, J. P. (2004) Biochemistry 43, 4400-4416]. In the present study we used quenched-flow mixing, electron paramagnetic resonance (EPR), and chemical cross-linking to probe for intermolecular interactions at physiological (0.1 M) and high (0.4 M) KCl. Exposure of SR membranes to water- and lipid-soluble cross-linking reagents revealed a mixture of SERCA1 oligomeric species consisting mainly of dimers and trimers. Titration of iodoacetamide spin-labeled SERCA1 with AMPPCP in the presence of 10 microM Ca(2+) and 0.1 M KCl revealed high- (K(D) = 45 microM) and low-affinity (K(D) = 315 microM) nucleotide binding sites in a 2:1 ratio, respectively. Raising the [KCl] to 0.4 M increased the fraction of weak binding sites and lowered the K(D) of the high-affinity component (20 microM). Phosphorylation by 10 microM ATP at 21 degrees C and 0.1 M KCl produced an early burst of P(i) production without a corresponding decline in the steady-state phosphoenzyme (EP) level. The steady-state EP level was twice as large as the P(i) burst and received equal contributions from E1P and E2P. Chasing the phosphoenzyme at 0.4 M KCl and 2 degrees C with ADP revealed a biphasic time course of E1P formation with a slow phase that matched the kinetics of the transient EPR signal from the spin-labeled Ca(2+)-ATPase. The absence of a fast component in the EPR signal excludes E1P as its source. Instead, it arises from a slow, KCl-dependent transformation at the start of the cycle which controls the formation of downstream intermediates with an increased mole fraction of rotationally restricted probes. We modeled this behavior with a SERCA1 trimer in which the formation of E1P/E2/E2P from E1ATP/E2P/E1P results from concerted transformations in the subunits coupling phosphorylation (E1ATP --> E1P + ADP) to dephosphorylation (E2P --> E2 + P(i)) and the conversion of E1P to E2P.
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Affiliation(s)
- James E Mahaney
- Edward Via Virginia College of Osteopathic Medicine, Blacksburg, Virginia 24060, USA
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18
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Niggli V, Sigel E. Anticipating antiport in P-type ATPases. Trends Biochem Sci 2008; 33:156-60. [PMID: 18343670 DOI: 10.1016/j.tibs.2007.12.005] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/13/2007] [Revised: 12/03/2007] [Accepted: 12/07/2007] [Indexed: 11/20/2022]
Abstract
Cation-transporting P-type ATPases show a high degree of structural and functional homology. Nevertheless, for many members of this large family, the molecular mechanism of transport is unclear; namely, whether transport is electrogenic or not and if countertransport is involved remains to be established. In a few well-studied cases such as the Na(+)-K(+)-ATPase, plasma membrane Ca(2+) ATPase (PMCA) and sarcoplasmic reticulum Ca(2+) ATPase (SERCA) countertransport has been clearly demonstrated. New data based on the crystal structure of SERCA now strongly indicate that countertransport could be mandatory for all P-type ATPases. This concept should be verified for other known and for all newly characterized P-type ATPases.
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Affiliation(s)
- Verena Niggli
- Institute of Pathology, University of Bern, Murtenstrasse 31, Bern, Switzerland.
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19
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Tadini-Buoninsegni F, Bartolommei G, Moncelli MR, Fendler K. Charge transfer in P-type ATPases investigated on planar membranes. Arch Biochem Biophys 2008; 476:75-86. [PMID: 18328799 DOI: 10.1016/j.abb.2008.02.031] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/23/2008] [Revised: 02/19/2008] [Accepted: 02/20/2008] [Indexed: 11/18/2022]
Abstract
Planar lipid bilayers, e.g., black lipid membranes (BLM) and solid supported membranes (SSM), have been employed to investigate charge movements during the reaction cycle of P-type ATPases. The BLM/SSM method allows a direct measurement of the electrical currents generated by the cation transporter following chemical activation by a substrate concentration jump. The electrical current transients provides information about the reaction mechanism of the enzyme. In particular, the BLM/SSM technique allows identification of electrogenic steps which in turn may be used to localize ion translocation during the reaction cycle of the pump. In addition, using the high time resolution of the technique, especially when rapid activation via caged ATP is employed, rate constants of electrogenic and electroneutral steps can be determined. In the present review, we will discuss the main results obtained by the BLM and SSM methods and how they have contributed to unravel the transport mechanism of P-type ATPases.
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20
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Side-chain protonation and mobility in the sarcoplasmic reticulum Ca2+-ATPase: implications for proton countertransport and Ca2+ release. Biophys J 2007; 93:3259-70. [PMID: 17938423 DOI: 10.1529/biophysj.107.109363] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Protonation of acidic residues in the sarcoplasmic reticulum Ca(2+)-ATPase (SERCA 1a) was studied by multiconformation continuum electrostatic calculations in the Ca(2+)-bound state Ca(2)E1, in the Ca(2+)-free state E2(TG) with bound thapsigargin, and in the E2P (ADP-insensitive phosphoenzyme) analog state with MgF(4)(2-) E2(TG+MgF(4)(2-)). Around physiological pH, all acidic Ca(2+) ligands (Glu(309), Glu(771), Asp(800), and Glu(908)) were unprotonated in Ca(2)E1; in E2(TG) and E2(TG+MgF(4)(2-)) Glu(771), Asp(800), and Glu(908) were protonated. Glu(771) and Glu(908) had calculated pK(a) values larger than 14 in E2(TG) and E2(TG+MgF(4)(2-)), whereas Asp(800) titrated with calculated pK(a) values near 7.5. Glu(309) had very different pK(a) values in the Ca(2+)-free states: 8.4 in E2(TG+MgF(4)(2-)) and 4.7 in E2(TG) because of a different local backbone conformation. This indicates that Glu(309) can switch between a high and a low pK(a) mode, depending on the local backbone conformation. Protonated Glu(309) occupied predominantly two main, very differently orientated side-chain conformations in E2(TG+MgF(4)(2-)): one oriented inward toward the other Ca(2+) ligands and one oriented outward toward a protein channel that seems to be in contact with the cytoplasm. Upon deprotonation, Glu(309) adopted completely the outwardly orientated side-chain conformation. The contact of Glu(309) with the cytoplasm in E2(TG+MgF(4)(2-)) makes this residue unlikely to bind lumenal protons. Instead it might serve as a proton shuttle between Ca(2+)-binding site I and the cytoplasm. Glu(771), Asp(800), and Glu(908) are proposed to take part in proton countertransport.
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21
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Ai H, Zhang C, Li Y, Zhang L, Li F. Dependence of Positive Binding Energies on Side ChainsA Theoretical Prediction on the Origin of Regular Ordering for the Amino Acid Residues in the Selectivity Filter. J Phys Chem B 2007; 111:13786-96. [DOI: 10.1021/jp074198m] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Affiliation(s)
- Hongqi Ai
- School of Chemistry and Chemical Engineering, University of Jinan, Jinan, 250022, People's Republic of China, Department of Chemistry and Technology, Liaocheng University, Liaocheng, 252059, People's Republic of China, and Institute of Theoretical Chemistry, Shandong University, Jinan, 250100, People's Republic of China
| | - Chong Zhang
- School of Chemistry and Chemical Engineering, University of Jinan, Jinan, 250022, People's Republic of China, Department of Chemistry and Technology, Liaocheng University, Liaocheng, 252059, People's Republic of China, and Institute of Theoretical Chemistry, Shandong University, Jinan, 250100, People's Republic of China
| | - Yun Li
- School of Chemistry and Chemical Engineering, University of Jinan, Jinan, 250022, People's Republic of China, Department of Chemistry and Technology, Liaocheng University, Liaocheng, 252059, People's Republic of China, and Institute of Theoretical Chemistry, Shandong University, Jinan, 250100, People's Republic of China
| | - Liang Zhang
- School of Chemistry and Chemical Engineering, University of Jinan, Jinan, 250022, People's Republic of China, Department of Chemistry and Technology, Liaocheng University, Liaocheng, 252059, People's Republic of China, and Institute of Theoretical Chemistry, Shandong University, Jinan, 250100, People's Republic of China
| | - Fang Li
- School of Chemistry and Chemical Engineering, University of Jinan, Jinan, 250022, People's Republic of China, Department of Chemistry and Technology, Liaocheng University, Liaocheng, 252059, People's Republic of China, and Institute of Theoretical Chemistry, Shandong University, Jinan, 250100, People's Republic of China
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22
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Andersson J, Hauser K, Karjalainen EL, Barth A. Protonation and hydrogen bonding of Ca2+ site residues in the E2P phosphoenzyme intermediate of sarcoplasmic reticulum Ca2+-ATPase studied by a combination of infrared spectroscopy and electrostatic calculations. Biophys J 2007; 94:600-11. [PMID: 17890386 PMCID: PMC2157260 DOI: 10.1529/biophysj.107.114033] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Protonation of the Ca(2+) ligands of the SR Ca(2+)-ATPase (SERCA1a) was studied by a combination of rapid scan FTIR spectroscopy and electrostatic calculations. With FTIR spectroscopy, we investigated the pH dependence of C=O bands of the Ca(2+)-free phosphoenzyme (E2P) and obtained direct experimental evidence for the protonation of carboxyl groups upon Ca(2+) release. At least three of the infrared signals from protonated carboxyl groups of E2P are pH dependent with pK(a) values near 8.3: a band at 1758 cm(-1) characteristic of nonhydrogen-bonded carbonyl groups, a shoulder at 1720 cm(-1), and part of a band at 1710 cm(-1), both characteristic of hydrogen-bonded carbonyl groups. The bands are thus assigned to H(+) binding residues, some of which are involved in H(+) countertransport. At pH 9, bands at 1743 and 1710 cm(-1) remain which we do not attribute to Ca(2+)/H(+) exchange. We also obtained evidence for a pH-dependent conformational change in beta-sheet or turn structures of the ATPase. With MCCE on the E2P analog E2(TG+MgF(4)(2-)), we assigned infrared bands to specific residues and analyzed whether or not the carbonyl groups of the acidic Ca(2+) ligands are hydrogen bonded. The carbonyl groups of Glu(771), Asp(800), and Glu(908) were found to be hydrogen bonded and will thus contribute to the lower wave number bands. The carbonyl group of some side-chain conformations of Asp(800) is left without a hydrogen-bonding partner; they will therefore contribute to the higher wave number band.
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Affiliation(s)
- Julia Andersson
- Department of Biochemistry and Biophysics, Stockholm University, Stockholm, Sweden
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23
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Karjalainen EL, Hauser K, Barth A. Proton paths in the sarcoplasmic reticulum Ca(2+) -ATPase. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2007; 1767:1310-8. [PMID: 17904096 DOI: 10.1016/j.bbabio.2007.07.010] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/05/2007] [Revised: 07/23/2007] [Accepted: 07/27/2007] [Indexed: 10/22/2022]
Abstract
The sarcoplasmic reticulum Ca(2+)-ATPase (SERCA1a) pumps Ca(2+) and countertransport protons. Proton pathways in the Ca(2+) bound and Ca(2+)-free states are suggested based on an analysis of crystal structures to which water molecules were added. The pathways are indicated by chains of water molecules that interact favorably with the protein. In the Ca(2+) bound state Ca(2)E1, one of the proposed Ca(2+) entry paths is suggested to operate additionally or alternatively as proton pathway. In analogs of the ADP-insensitive phosphoenzyme E2P and in the Ca(2+)-free state E2, the proton path leads between transmembrane helices M5 to M8 from the lumenal side of the protein to the Ca(2+) binding residues Glu-771, Asp-800 and Glu-908. The proton path is different from suggested Ca(2+) dissociation pathways. We suggest that separate proton and Ca(2+) pathways enable rapid (partial) neutralization of the empty cation binding sites. For this reason, transient protonation of empty cation binding sites and separate pathways for different ions are advantageous for P-type ATPases in general.
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Affiliation(s)
- Eeva-Liisa Karjalainen
- Department of Biochemistry and Biophysics, Stockholm University, Arrhenius Laboratories for Natural Sciences, Svante Arrhenius väg 12, SE-106 91, Stockholm, Sweden
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24
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Tadini-Buoninsegni F, Bartolommei G, Moncelli MR, Guidelli R, Inesi G. Pre-steady state electrogenic events of Ca2+/H+ exchange and transport by the Ca2+-ATPase. J Biol Chem 2006; 281:37720-7. [PMID: 17032645 DOI: 10.1074/jbc.m606040200] [Citation(s) in RCA: 69] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Native or recombinant SERCA (sarco(endo)plasmic reticulum Ca(2+) ATPase) was adsorbed on a solid supported membrane and then activated with Ca(2+) and ATP concentration jumps through rapid solution exchange. The resulting electrogenic events were recorded as electrical currents flowing along the external circuit. Current transients were observed following Ca(2+) jumps in the absence of ATP and following ATP jumps in the presence of Ca(2+). The related charge movements are attributed to Ca(2+) reaching its binding sites in the ground state of the enzyme (E(1)) and to its vectorial release from the enzyme phosphorylated by ATP (E(2)P). The Ca(2+) concentration and pH dependence as well as the time frames of the observed current transients are consistent with equilibrium and pre-steady state biochemical measurements of sequential steps within a single enzymatic cycle. Numerical integration of the current transients recorded at various pH values reveal partial charge compensation by H(+) in exchange for Ca(2+) at acidic (but not at alkaline) pH. Most interestingly, charge movements induced by Ca(2+) and ATP vary over different pH ranges, as the protonation probability of residues involved in Ca(2+)/H(+) exchange is lower in the E(1) than in the E(2)P state. Our single cycle measurements demonstrate that this difference contributes directly to the reduction of Ca(2+) affinity produced by ATP utilization and results in the countertransport of two Ca(2+) and two H(+) within each ATPase cycle at pH 7.0. The effects of site-directed mutations indicate that Glu-771 and Asp-800, within the Ca(2+) binding domain, are involved in the observed Ca(2+)/H(+) exchange.
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25
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Ai H, Li Q. Concerted transfer and transfer direction of three protons in the protonated amino-acid dimers. Chem Phys 2006. [DOI: 10.1016/j.chemphys.2006.06.031] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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26
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Møller JV, Olesen C, Jensen AML, Nissen P. The structural basis for coupling of Ca2+ transport to ATP hydrolysis by the sarcoplasmic reticulum Ca2+-ATPase. J Bioenerg Biomembr 2006; 37:359-64. [PMID: 16691465 DOI: 10.1007/s10863-005-9471-2] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2022]
Abstract
Recently, a series of structure determinations has nearly completed a structural description of the transport cycle of the sarcoplasmic reticulum Ca(2+)-ATPase, especially those steps concerned with the phosphorylation by ATP and the dephosphorylation reaction. From these structures Ca(2+)-ATPase emerges as a molecular machine, where globular cytosolic domains and transmembrane helices work in concert like a mechanical pump, as can be vividly demonstrated in animated versions of the pump cycle. The structures show that both ATP phosphorylation and dephosphorylation at Asp351 take place as nucleophilic SN2 reactions, which are associated with Ca(2+) and H(+) occluded states, respectively. These transitory steps ensure efficient coupling between Ca(2+) transport and ATP hydrolysis.
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Affiliation(s)
- Jesper Vuust Møller
- Department of Biophysics, Institute of Physiology and Biophysics, University of Aarhus, DK-8000, Aarhus C, Denmark.
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27
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Hauser K. Electrostatic calculations for assignment of infrared difference bands to carboxyl groups getting protonated during protein reactions. Biopolymers 2006; 82:430-4. [PMID: 16283666 DOI: 10.1002/bip.20410] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Fourier transform infrared (FTIR) difference spectroscopy is predestined to monitor the protonation of carboxyl groups during protein reactions, making glutamic and aspartic amino acids unique to follow proton pathways. The absorption of the corresponding vibrations are clearly distinguishable from the absorption of other amino acids. However, the assignment to specific groups within the protein needs additional information, e.g., from induced spectral changes due to isotopic labeling or mutation. Here, the capability of electrostatic calculations to assign IR difference bands to specific carboxyl groups getting protonated is demonstrated by the ion pump mechanism of the sarcoplasmic reticulum Ca(2+)-ATPase. Active Ca(2+) transport is coupled to the hydrolysis of ATP. Two Ca(2+) ions are transported per ATP hydrolysed and two or three H(+) ions are countertransported. FTIR difference spectra show that during the Ca(2+) release step, carboxyl groups become protonated. Multiconformation continuum electrostatic calculations (MCCE) have been carried out to determine the equilibrium distribution of residue ionization and side chain conformation in dependence of pH. Available structural X-ray data from the calcium-bound and the calcium-free state allows us to simulate the transition between the two states monitored in the IR difference spectra. Exemplarily for Asp 800, ligand of both calcium ions, it is shown that MCCE calculations can identify this specific Asp to contribute to the IR bands and therefore to take part in the proton countertransport of the Ca(2+)-ATPase. In addition, an energy analysis can be performed to understand what interactions shift the pK(a).
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Affiliation(s)
- Karin Hauser
- Institut für Biophysik, Johann Wolfgang Goethe-Universität Frankfurt, Max-von-Laue-Strasse 1, 60438 Frankfurt am Main, Germany.
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28
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Abstract
The time-resolved kinetics of Ca2+ binding to the SR Ca-ATPase in the E1 state was investigated by Ca(2+)-concentration jump experiments. Ca2+ was released by an ultraviolet-light flash from caged calcium, and charge movements in the membrane domain of the ion pumps were detected by the fluorescent styryl dye 2BITC. The partial reaction (H3E1 <-->) E1 <--> CaE1 <--> Ca2E1 can be characterized by two time constants, tau1 and tau2, both of which are not significantly Ca(2+)-concentration-dependent and only weakly pH-dependent at pH < 7.5. Both time constants differ by a factor of approximately 50 (4.7 vs. 200 ms). The weak substrate-dependence indicates that the rate-limiting process is not related to Ca2+ migration through the access channel and ion binding to the binding sites but to conformational rearrangements preceding the ion movements. The high activation energy obtained for both processes, 42.3 kJ mol(-1) and 60.3 kJ mol(-1) at pH 7.2, support this concept. Transient binding of Ca ions to the loop L67 and a movement of the Ca-loaded loop are discussed as a mechanism that facilitates the entrance of both Ca ions into the access channel to the ion-binding sites.
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29
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Takara D, Sánchez GA, Toma AF, Bonazzola P, Alonso GL. Effect of carticaine on the sarcoplasmic reticulum Ca2+-adenosine triphosphatase. II. Cations dependence. Naunyn Schmiedebergs Arch Pharmacol 2005; 371:375-82. [PMID: 15997393 DOI: 10.1007/s00210-005-1061-7] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/13/2004] [Accepted: 03/29/2005] [Indexed: 11/29/2022]
Abstract
Ca2+-ATPase is a major intrinsic protein in the sarcoplasmic reticulum (SR) from skeletal muscles. It actively transports Ca2+ from the cytoplasm to the SR lumen, reducing cytoplasmic [Ca2+] to promote muscle relaxation. Carticaine is a local anesthetic widely used in operative dentistry. We previously showed that carticaine inhibits SR Ca2+-ATPase activity and the coupled Ca(2+) uptake by isolated SR vesicles, and increases the rate of Ca2+ efflux from preloaded vesicles. We also found that these effects were antagonized by divalent cations, and concluded that they were mainly due to the direct interaction of carticaine with the Ca2+-ATPase protein. Here we present additional results on the modulation of the above effects of carticaine by Ca2+ and Mg2+. The activating effect of Ca2+ on the ATPase activity is competitively inhibited by carticaine, indicating a decreased Ca2+ binding to the high affinity Ca2+ transport sites. The activating effect of Mg2+ on the phosphorylation of Ca2+-ATPase by orthophosphate is also inhibited by carticaine. The anesthetic does not affect the reaction mechanism of the cations acting as cofactors of ATP in the catalytic site. On the basis of the present and our previous results, we propose a model that describes the effect of carticaine on the Ca2+-ATPase cycle.
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Affiliation(s)
- Delia Takara
- Cátedra de Biofísica, Facultad de Odontología, Universidad de Buenos Aires, 1122AAH Buenos Aires, Argentina.
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30
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Olesen C, Sørensen TLM, Nielsen RC, Møller JV, Nissen P. Dephosphorylation of the calcium pump coupled to counterion occlusion. Science 2005; 306:2251-5. [PMID: 15618517 DOI: 10.1126/science.1106289] [Citation(s) in RCA: 230] [Impact Index Per Article: 12.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
P-type ATPases extract energy by hydrolysis of adenosine triphosphate (ATP) in two steps, formation and breakdown of a covalent phosphoenzyme intermediate. This process drives active transport and countertransport of the cation pumps. We have determined the crystal structure of rabbit sarcoplasmic reticulum Ca2+ adenosine triphosphatase in complex with aluminum fluoride, which mimics the transition state of hydrolysis of the counterion-bound (protonated) phosphoenzyme. On the basis of structural analysis and biochemical data, we find this form to represent an occluded state of the proton counterions. Hydrolysis is catalyzed by the conserved Thr-Gly-Glu-Ser motif, and it exploits an associative nucleophilic reaction mechanism of the same type as phosphoryl transfer from ATP. On this basis, we propose a general mechanism of occluded transition states of Ca2+ transport and H+ countertransport coupled to phosphorylation and dephosphorylation, respectively.
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Affiliation(s)
- Claus Olesen
- Centre for Structural Biology, Department of Molecular Biology, University of Aarhus, Gustav Wieds Vej 10C, DK-8000 Aarhus C, Denmark
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31
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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: 1.8] [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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32
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Apell HJ. Structure-function relationship in P-type ATPases--a biophysical approach. Rev Physiol Biochem Pharmacol 2004; 150:1-35. [PMID: 12811587 DOI: 10.1007/s10254-003-0018-9] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
P-type ATPases are a large family of membrane proteins that perform active ion transport across biological membranes. In these proteins the energy-providing ATP hydrolysis is coupled to ion-transport that builds up or maintains the electrochemical potential gradients of one or two ion species across the membrane. P-type ATPases are found in virtually all eukaryotic cells and also in bacteria, and they are transporters of a broad variety of ions. So far, a crystal structure with atomic resolution is available only for one species, the SR Ca-ATPase. However, biochemical and biophysical studies provide an abundance of details on the function of this class of ion pumps. The aim of this review is to summarize the results of preferentially biophysical investigations of the three best-studied ion pumps, the Na,K-ATPase, the gastric H,K-ATPase, and the SR Ca-ATPase, and to compare functional properties to recent structural insights with the aim of contributing to the understanding of their structure-function relationship.
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Affiliation(s)
- H-J Apell
- Department of Biology, University of Konstanz, Fach M635, 78457 Konstanz, Germany.
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Grewer C, Watzke N, Rauen T, Bicho A. Is the glutamate residue Glu-373 the proton acceptor of the excitatory amino acid carrier 1? J Biol Chem 2003; 278:2585-92. [PMID: 12419818 DOI: 10.1074/jbc.m207956200] [Citation(s) in RCA: 51] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Glutamate transport by the neuronal excitatory amino acid carrier (EAAC1) is accompanied by the coupled movement of one proton across the membrane. We have demonstrated previously that the cotransported proton binds to the carrier in the absence of glutamate and, thus, modulates the EAAC1 affinity for glutamate. Here, we used site-directed mutagenesis together with a rapid kinetic technique that allows one to generate sub-millisecond glutamate concentration jumps to locate possible binding sites of the glutamate transporter for the cotransported proton. One candidate for this binding site, the highly conserved glutamic acid residue Glu-373 of EAAC1, was mutated to glutamine. Our results demonstrate that the mutant transporter does not catalyze net transport of glutamate, whereas Na(+)/glutamate homoexchange is unimpaired. Furthermore, the voltage dependence of the rates of Na(+) binding and glutamate translocation are unchanged compared with the wild-type. In contrast to the wild-type, however, homoexchange of the E373Q transporter is completely pH-independent. In line with these findings the transport kinetics of the mutant EAAC1 show no deuterium isotope effect. Thus, we suggest a new transport mechanism, in which Glu-373 forms part of the binding site of EAAC1 for the cotransported proton. In this model, protonation of Glu-373 is required for Na(+)/glutamate translocation, whereas the relocation of the carrier is only possible when Glu-373 is negatively charged. Interestingly, the Glu-373-homologous amino acid residue is glutamine in the related neutral amino acid transporter alanine-serine-cysteine transporter. The function of alanine-serine-cysteine transporter is neither potassium- nor proton-dependent. Consequently, our results emphasize the general importance of glutamate and aspartate residues for proton transport across membranes.
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Affiliation(s)
- Christof Grewer
- Max-Planck-Institut für Biophysik, Kennedyallee 70, Frankfurt D-60596, Germany.
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34
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Dode L, Vilsen B, Van Baelen K, Wuytack F, Clausen JD, Andersen JP. Dissection of the functional differences between sarco(endo)plasmic reticulum Ca2+-ATPase (SERCA) 1 and 3 isoforms by steady-state and transient kinetic analyses. J Biol Chem 2002; 277:45579-91. [PMID: 12207029 DOI: 10.1074/jbc.m207778200] [Citation(s) in RCA: 75] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Steady-state and transient-kinetic studies were conducted to characterize the overall and partial reactions of the Ca(2+)-transport cycle mediated by the human sarco(endo)plasmic reticulum Ca(2+)-ATPase 3 (SERCA3) isoforms: SERCA3a, SERCA3b, and SERCA3c. Relative to SERCA1a, all three human SERCA3 enzymes displayed a reduced apparent affinity for cytosolic Ca(2+) in activation of the overall reaction due to a decreased E(2) to E(1)Ca(2) transition rate and an increased rate of Ca(2+) dissociation from E(1)Ca(2). At neutral pH, the ATPase activity of the SERCA3 enzymes was not significantly enhanced upon permeabilization of the microsomal vesicles with calcium ionophore, indicating a difference from SERCA1a with respect to regulation of the lumenal Ca(2+) level (either an enhanced efflux of lumenal Ca(2+) through the pump in E(2) form or insensitivity to inhibition by lumenal Ca(2+)). Other differences from SERCA1a with respect to the overall ATPase reaction were an alkaline shift of the pH optimum, increased catalytic turnover rate at pH optimum (highest for SERCA3b, the isoform with the longest C terminus), and an increased sensitivity to inhibition by vanadate that disappeared under equilibrium conditions in the absence of Ca(2+) and ATP. The transient-kinetic analysis traced several of the differences from SERCA1a to an enhancement of the rate of dephosphorylation of the E(2)P phosphoenzyme intermediate, which was most pronounced at alkaline pH and increased with the length of the alternatively spliced C terminus.
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Affiliation(s)
- Leonard Dode
- Wellcome Trust Centre for Human Genetics, University of Oxford, Roosevelt Drive, Oxford OX3 7BN, United Kingdom
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35
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Dulhunty AF, Lavert DR. A Ca2+-activated anion channel in the sarcoplasmic reticulum of skeletal muscle. CURRENT TOPICS IN MEMBRANES 2002. [DOI: 10.1016/s1063-5823(02)53028-3] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
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36
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Peinelt C, Apell HJ. Kinetics of the Ca(2+), H(+), and Mg(2+) interaction with the ion-binding sites of the SR Ca-ATPase. Biophys J 2002; 82:170-81. [PMID: 11751306 PMCID: PMC1302459 DOI: 10.1016/s0006-3495(02)75384-8] [Citation(s) in RCA: 57] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Electrochromic styryl dyes were used to investigate mutually antagonistic effects of Ca(2+) and H(+) on binding of the other ion in the E(1) and P-E(2) states of the SR Ca-ATPase. On the cytoplasmic side of the protein in the absence of Mg(2+) a strictly competitive binding sequence, H(2)E(1) <==> HE(1) <==> E(1) <==> CaE(1) <==> Ca(2)E(1), was found with two Ca(2+) ions bound cooperatively. The apparent equilibrium dissociation constants were in the order of K(1/2)(2 Ca) = 34 nM, K(1/2)(H) = 1 nM and K(1/2)(H(2)) = 1.32 microM. Up to 2 Mg(2+) ions were also able to enter the binding sites electrogenically and to compete with the transported substrate ions (K(1/2)(Mg) = 165 microM, K(1/2)(Mg(2)) = 7.4 mM). In the P-E(2) state, with binding sites facing the lumen of the sarcoplasmatic reticulum, the measured concentration dependence of Ca(2+) and H(+) binding could be described satisfactorily only with a branched reaction scheme in which a mixed state, P-E(2)CaH, exists. From numerical simulations, equilibrium dissociation constants could be determined for Ca(2+) (0.4 mM and 25 mM) and H(+) (2 microM and 10 microM). These simulations reproduced all observed antagonistic concentration dependences. The comparison of the dielectric ion binding in the E(1) and P-E(2) conformations indicates that the transition between both conformations is accompanied by a shift of their (dielectric) position.
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Affiliation(s)
- Christine Peinelt
- Department of Biology, University of Konstanz, 78457 Konstanz, Germany
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37
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Salvador JM, Inesi G, Rigaud JL, Mata AM. Ca2+ transport by reconstituted synaptosomal ATPase is associated with H+ countertransport and net charge displacement. J Biol Chem 1998; 273:18230-4. [PMID: 9660785 DOI: 10.1074/jbc.273.29.18230] [Citation(s) in RCA: 58] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The synaptosomal plasma membrane Ca2+-ATPase (PMCA) purified from pig brain was reconstituted with liposomes prepared by reverse phase evaporation at a lipid to protein ratio of 150/1 (w/w). ATP-dependent Ca2+ uptake and H+ ejection by the reconstituted proteoliposomes were demonstrated by following light absorption and fluorescence changes undergone by arsenazo III and 8-hydroxy-1,3, 6-pyrene trisulfonate, respectively. Ca2+ uptake was increased up to 2-3-fold by the H+ ionophore carbonyl cyanide p-trifluoromethoxyphenylhydrazone, consistent with relief of an inhibitory transmembrane pH gradient (i.e. lumenal alkalinization) generated by H+ countertransport. The stoichiometric ratio of Ca2+/H+ countertransport was 1.0/0.6, and the ATP/Ca2+ coupling stoichiometry was 1/1 at 25 degrees C. The electrogenic character of the Ca2+/H+ countertransport was demonstrated by measuring light absorption changes undergone by oxonol VI. It was shown that a 20 mV steady state potential (positive on the lumenal side) was formed as a consequence of net charge transfer associated with the 1/1 Ca2+/H+ countertransport. Calmodulin stimulated ATPase activity, Ca2+ uptake, and H+ ejection, demonstrating that these parameters are linked by the same mechanism of PMCA regulation.
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Affiliation(s)
- J M Salvador
- Departamento de Bioquímica y Biología Molecular y Genética, Facultad de Ciencias, Universidad de Extremadura, 06071 Badajoz, Spain
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38
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Kourie JI. Chloride channels in the sarcoplasmic reticulum of muscle. PROGRESS IN BIOPHYSICS AND MOLECULAR BIOLOGY 1998; 68:263-300. [PMID: 9652173 DOI: 10.1016/s0079-6107(97)00029-1] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- J I Kourie
- Department of Chemistry, Australian National University, Canberra City, Australia
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39
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Ahern GP, Laver DR. ATP inhibition and rectification of a Ca2+-activated anion channel in sarcoplasmic reticulum of skeletal muscle. Biophys J 1998; 74:2335-51. [PMID: 9591661 PMCID: PMC1299577 DOI: 10.1016/s0006-3495(98)77943-3] [Citation(s) in RCA: 23] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
Abstract
We describe ATP-dependent inhibition of the 75-105-pS (in 250 mM Cl-) anion channel (SCl) from the sarcoplasmic reticulum (SR) of rabbit skeletal muscle. In addition to activation by Ca2+ and voltage, inhibition by ATP provides a further mechanism for regulating SCl channel activity in vivo. Inhibition by the nonhydrolyzable ATP analog 5'-adenylylimidodiphosphate (AMP-PNP) ruled out a phosphorylation mechanism. Cytoplasmic ATP (approximately 1 mM) inhibited only when Cl- flowed from cytoplasm to lumen, regardless of membrane voltage. Flux in the opposite direction was not inhibited by 9 mM ATP. Thus ATP causes true, current rectification in SCl channels. Inhibition by cytoplasmic ATP was also voltage dependent, having a K(I) of 0.4-1 mM at -40 mV (Hill coefficient approximately 2), which increased at more negative potentials. Luminal ATP inhibited with a K(I) of approximately 2 mM at +40 mV, and showed no block at negative voltages. Hidden Markov model analysis revealed that ATP inhibition 1) reduced mean open times without altering the maximum channel amplitude, 2) was mediated by a novel, single, voltage-independent closed state (approximately 1 ms), and 3) was much less potent on lower conductance substates than the higher conductance states. Therefore, the SCl channel is unlikely to pass Cl- from cytoplasm to SR lumen in vivo, and balance electrogenic Ca2+ uptake as previously suggested. Possible roles for the SCl channel in the transport of other anions are discussed.
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Affiliation(s)
- G P Ahern
- John Curtin School of Medical Research, Australian National University, Canberra ACT.
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40
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41
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Inesi G, Lewis D, Sumbilla C, Nandi A, Kirtley M, Ordahl CP. ATPase gene transfer and mutational analysis of the cation translocation mechanism. Ann N Y Acad Sci 1997; 834:207-20. [PMID: 9405809 DOI: 10.1111/j.1749-6632.1997.tb52252.x] [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: 02/05/2023]
Abstract
The peptide segment interposed between cation binding and phosphorylation domains retains a high degree of homology in all cation transport ATPases. Mutational analysis and chimeric replacements of Ca2+ ATPase components with corresponding Na+,K(+)-ATPase components indicate that this segment is utilized by various cation ATPases as a common structural device for a long-range functional linkage of enzyme phosphorylation and cation transport. Vectorial displacement of bound cation is rendered possible by a transmembrane channel formed by four clustered helices (M4, M5, M6, and M8). Originating from the four helices, the oxygen functions of Glu309, Glu771, Thr799, Asp800, and Glu908 form a duplex Ca2+ binding site in the middle of the channel, while Lys297 seals the luminal end of the channel with its positively charged side chain. The perturbation triggered by enzyme phosphorylation is apparently transmitted through the linkage segment to produce rotational displacement of the M4 helix with minimal change of secondary structure. The cation binding site is thereby disrupted and the Lys297 side chain removed, permitting Ca2+ to dissociate in exchange for H+ and to flow through the luminal end of the channel.
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Affiliation(s)
- G Inesi
- Department of Biochemistry and Molecular Biology, University of Maryland, Baltimore 21201, USA
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42
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Barth A, Kreutz W, Mäntele W. Ca2+ release from the phosphorylated and the unphosphorylated sarcoplasmic reticulum Ca2+ ATPase results in parallel structural changes. An infrared spectroscopic study. J Biol Chem 1997; 272:25507-10. [PMID: 9325264 DOI: 10.1074/jbc.272.41.25507] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
Structural changes of the sarcoplasmic reticulum Ca2+-ATPase occurring in the reaction step involving phosphoenzyme conversion and Ca2+ release (Ca2E1-P --> E2-P) were followed using time-resolved infrared spectroscopy in H2O and 2H2O. The difference spectra measured between 1800 and 1500 cm-1 were almost identical to those of Ca2+ release from the unphosphorylated ATPase (Ca2E1 --> E), implying that parallel structural changes occur in both steps. This suggests that characteristic structural features of the high affinity Ca2+ binding sites of Ca2E1 are still present in the ADP-sensitive phosphoenzyme Ca2E1-P. In both Ca2+ release steps at least two carboxyl groups become protonated, each of them experiencing the same strength of hydrogen bonding irrespective of whether or not the Ca2+ free ATPase is phosphorylated. This suggests that the same amino acid residues are involved and that they are most likely those that participate in high affinity Ca2+ binding and H+ countertransport. We propose that during Ca2+ release from the phosphoenzyme protons from the lumenal side have access to these residues. Our results are consistent with only one pair of Ca2+ binding sites on the ATPase that serves both Ca2+ translocation and H+ countertransport.
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Affiliation(s)
- A Barth
- Institut für Biophysik und Strahlenbiologie der Universität Freiburg, Albertstrasse 23, D-79104 Freiburg, Germany.
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43
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Møller JV, Juul B, le Maire M. Structural organization, ion transport, and energy transduction of P-type ATPases. BIOCHIMICA ET BIOPHYSICA ACTA 1996; 1286:1-51. [PMID: 8634322 DOI: 10.1016/0304-4157(95)00017-8] [Citation(s) in RCA: 563] [Impact Index Per Article: 20.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Affiliation(s)
- J V Møller
- Department of Biophysics, University of Aarhus, Denmark
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44
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Chen L, Sumbilla C, Lewis D, Zhong L, Strock C, Kirtley ME, Inesi G. Short and long range functions of amino acids in the transmembrane region of the sarcoplasmic reticulum ATPase. A mutational study. J Biol Chem 1996; 271:10745-52. [PMID: 8631884 DOI: 10.1074/jbc.271.18.10745] [Citation(s) in RCA: 38] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023] Open
Abstract
Mutational analysis of several amino acids in the transmembrane region of the sarcoplasmic reticulum ATPase was performed by expressing wild type ATPase and 32 site-directed mutants in COS-1 cells followed by functional characterization of the microsomal fraction. Four different phenotype characteristics were observed in the mutants: (a) functions similar to those sustained by the wild type ATPase; (b) Ca2+ transport inhibited to a greater extent than ATPase hydrolytic activity; (c) inhibition of transport and hydrolytic activity in the presence of high levels of phosphorylated enzyme intermediate; and (d) total inhibition of ATP utilization by the enzyme while retaining the ability to form phosphoenzyme by utilization of P(i). Analysis of experimental observations and molecular models revealed short and long range functions of several amino acids within the transmembrane region. Short range functions include: (a) direct involvement of five amino acids in Ca2+ binding within a channel formed by clustered transmembrane helices M4, M5, M6, and M8; (b) roles of several amino acids in structural stabilization of the helical cluster for optimal channel function; and (c) a specific role of Lys297 in sealing the distal end of the channel, suggesting that the M4 helix rotates to allow vectorial flux of Ca2+ upon enzyme phosphorylation. Long range functions are related to the influence of several transmembrane amino acids on phosphorylation reactions with ATP or P(i), transmitted to the extramembranous region of the ATPase in the presence or in the absence of Ca2+.
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Affiliation(s)
- L Chen
- Department of Biochemistry and Molecular Biology, University of Maryland School of Medicine, Baltimore 21201, USA
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45
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Bode H, Himmen A, Göke B. Evidence for vacuolar-type proton pumps in nonmitochondrial and inositol 1,4,5-trisphosphate-sensitive calcium stores of insulin-secreting cells. Pflugers Arch 1996; 432:97-104. [PMID: 8662273 DOI: 10.1007/s004240050110] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
This study examines whether acidic, vacuolar-type, proton-pump-carrying organelles of insulin-secreting cells (clonal endocrine pancreatic cell line INS-1) function as rapidly exchanging, inositol 1,4,5-trisphosphate-sensitive calcium stores. Calcium uptake into calcium stores will be modulated by the proton concentration within the stores, since calcium pumps in general appear to mediate a countertransport of calcium with protons. We therefore tested for sensitivity of calcium sequestration by nonmitochondrial stores (inhibition of mitochondrial calcium uptake by 2 microM ruthenium red) in saponin-permeabilized cells to proton-conducting ionophores and proton pump inhibition, using this as a marker for involvement of acidic organelles. Calcium sequestration was partially inhibited by the protonophores nigericin (10-50 microM) and carbonylcyanide m-chlorophenylhydrazone (CCCP; 20-50 microM), as well as by inclusion of 30 mM NH4Cl. Bafilomycin A1, a potent and selective inhibitor of vacuolar-type proton pumps, alone (1 - 500 nM) had no effect on calcium sequestration. however, it induced an inhibitory effect in the presence of nigericin or CCCP, even at low concentrations (5 microM) of these ionophores, lacking itself an inhibitory action on calcium sequestration. Bafilomycin A1 then was already maximally active at a concentration as low as 10 nM. Corres ponding to inhibition of total nonmitochondrial calcium sequestration, filling of inositol 1,4,5-trisphosphate-sensitive stores was decreased or even abolished by the protonophores alone or the protonophores combined with bafilomycin A1. We conclude that vacuolar-type proton pumps are present in at least a part of nonmitochondrial and inositol 1,4,5-trisphosphate-sensitive calcium stores in INS-1 cells. This assigns these stores to organelles such as secretory granules, the trans Golgi network, or endosomes. Luminal acidity of these stores will stimulate calcium sequestration by providing more protons for countertransport of calcium by calcium pumps. High concentrations of protonophores may be required for inhibitory effects because otherwise the proton pumps may be able to compensate sufficiently for ionophore-mediated proton loss. The lack of effect of bafilomycin A1 without protonophores may be due to a sufficient luminal buffering capacity or to preceding inhibition of the pump by an inside-positive transmembrane potential.
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Affiliation(s)
- H Bode
- Department of Pharmacology, Philipps-University, Karl-von-Frisch-Strasse, D-35033 Marburg, Germany
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46
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Tamarappoo BK, McDonald KK, Kilberg MS. Expressed human hippocampal ASCT1 amino acid transporter exhibits a pH-dependent change in substrate specificity. BIOCHIMICA ET BIOPHYSICA ACTA 1996; 1279:131-6. [PMID: 8603078 DOI: 10.1016/0005-2736(95)00259-6] [Citation(s) in RCA: 26] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
In mammalian cells, the basal Na+-dependent uptake for many of the neutral amino acids is mediated by a transport activity designated System ASC. A cloned human brain cDNA sequence, ASCT1, encodes a Na+-dependent neutral amino acid transport activity that exhibits a substrate specificity similar to that commonly associated with System ASC. However, the characteristics of ASC activity varies significantly between cell types and not all tissues contain detectable levels of ASCT1 mRNA. A unique property of System ASC activity is an altered substrate selectivity such that at pH values below 7.4 anionic amino acids function as inhibitors and substrates. The experiments in this report were designed to determine if the cloned ASCT1 transporter exhibited this pH-dependent anionic transport. Following transfection of HeLa cells with the ASCT1 cDNA, transport strongly favored neutral zwitterionic) amino acids when uptake was measured at a physiologic pH value of 7.5. However, lowering the assay pH to 5.5 significantly enhanced the interaction of the ASCT1 carrier with anionic amino acids such as cysteate, in a pH-dependent manner. The apparent pK for the titratable group was in the range of 6.5-7.0. These results provide evidence that the human brain ASCT1 transporter exhibits the most distinguishing characteristic known for System ASC and provides a model system to investigate the molecular basis for this shift in substrate acceptance.
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Affiliation(s)
- B K Tamarappoo
- Department of Biochemistry and Molecular Biology, University of Florida College of Medicine, Gainesville, 32610, USA
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47
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Desrosiers MG, Gately LJ, Gambel AM, Menick DR. Purification and characterization of the Ca2+-ATPase of Flavobacterium odoratum. J Biol Chem 1996; 271:3945-51. [PMID: 8632017 DOI: 10.1074/jbc.271.7.3945] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023] Open
Abstract
The P-type Ca2+-ATPase from Flavobacterium odoratum has been purified to homogeneity and characterized. Inside-out membrane vesicles were extracted with C12E8, followed by ammonium sulfate fractionation, centrifugation through two successive 32-48% glycerol gradients, and DE52 ion exchange chromatography. The purified Ca2+-ATPase consists of a single polypeptide. It migrates electrophoretically with an apparent molecular mass of 60,000 Da, consistent with the phosphorylation pattern originally reported in membrane vesicles. This single polypeptide is functional and capable of calcium-dependent vanadate-sensitive ATP hydrolysis and of forward and reverse phosphorylation. Maximum hydrolysis activity occurs at pH 8.0, with a specific activity of approximately 75 micromol of ATP hydrolyzed min-1 mg-1 protein. The purified Ca2+-ATPase has an apparent Km for calcium of 1.5 microM and for ATP of 90 microM. Vanadate strongly inhibits the activity with an IC50 of 0.6 microM. The prokaryotic Ca2+-ATPase is insensitive to the SR Ca2+-ATPase inhibitors fluorescein isothiocyanate, thapsigargin, and cyclopiazonic acid. It is rapidly phosphorylated by [gamma-32P]ATP in a calcium-dependent vanadate-inhibited manner and can be phosphorylated by Pi in both the presence and absence of calcium.
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Affiliation(s)
- M G Desrosiers
- Cardiology Division, Department of Medicine, Medical University of South Carolina, Charleston, 29425-2221, USA
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48
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Rigaud JL, Pitard B, Levy D. Reconstitution of membrane proteins into liposomes: application to energy-transducing membrane proteins. BIOCHIMICA ET BIOPHYSICA ACTA 1995; 1231:223-46. [PMID: 7578213 DOI: 10.1016/0005-2728(95)00091-v] [Citation(s) in RCA: 338] [Impact Index Per Article: 11.7] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Affiliation(s)
- J L Rigaud
- Section de Bióenergétique, DBCM, CEA-Saclay, Gif sur Yvette, France
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49
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Andersen JP. Dissection of the functional domains of the sarcoplasmic reticulum Ca(2+)-ATPase by site-directed mutagenesis. Biosci Rep 1995; 15:243-61. [PMID: 8825028 DOI: 10.1007/bf01788358] [Citation(s) in RCA: 111] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023] Open
Abstract
The results of site-directed mutagenesis studies of the sarcoplasmic reticulum Ca(2+)-ATPase are reviewed. More than 250 different point mutants have been expressed in cell culture and analysed by a panel of functional assays. Thereby, 40-50 important amino acid residues have been pinpointed, and the mutants have been assigned to functional classes: the Ca(2+)-affinity mutants, the phosphorylation-negative mutants, the ATP-affinity mutants, the E1P mutants, the E2P mutants, and the uncoupled mutants. Moreover, regions important to the specific inhibition by thapsigargin have been identified by analysis of Ca(2+)-ATPase/Na+,K(+)-ATPase chimeric constructs.
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Affiliation(s)
- J P Andersen
- Department of Physiology, University of Aarhus, Denmark
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50
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Inesi G, Chen L, Sumbilla C, Lewis D, Kirtley ME. Ca2+ binding and translocation by the sarcoplasmic reticulum ATPase: functional and structural considerations. Biosci Rep 1995; 15:327-39. [PMID: 8825035 DOI: 10.1007/bf01788365] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023] Open
Abstract
Three experimental systems are described including sarcoplasmic reticulum (SR) vesicles, reconstituted proteoliposomes, and recombinant protein obtained by gene transfer and expression in foreign cells. It is shown that the Ca(2+) ATPase of sarcoplasmic reticulum (SR) includes an extramembranous globular head which is connected through a stalk to a membrane bound region. Cooperative binding of two calcium ions occurs sequentially, within a channel formed by four clustered helices within the membrane bound region. Destabilization of the helical cluster is produced following enzyme phosphorylation by ATP at the catalytic site in the extramembranous region. The affinity and orientation of the Ca2+ binding site are thereby changed, permitting vectorial dissociation of bound Ca2+ against a concentration gradient. A long range linkage between phosphorylation and Ca2+ binding sites is provided by an intervening peptide segment that retains high homology in cation transport ATPases, and whose function is highly sensitive to mutational perturbations.
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Affiliation(s)
- G Inesi
- Department of Biological Chemistry, University of Maryland School of Medicine, Baltimore, Maryland 21201, USA
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