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Xiao P, Drewniak P, Dingwell DA, Brown LS, Ladizhansky V. Probing the energy barriers and stages of membrane protein unfolding using solid-state NMR spectroscopy. SCIENCE ADVANCES 2024; 10:eadm7907. [PMID: 38758787 DOI: 10.1126/sciadv.adm7907] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/06/2023] [Accepted: 04/15/2024] [Indexed: 05/19/2024]
Abstract
Understanding how the amino acid sequence dictates protein structure and defines its stability is a fundamental problem in molecular biology. It is especially challenging for membrane proteins that reside in the complex environment of a lipid bilayer. Here, we obtain an atomic-level picture of the thermally induced unfolding of a membrane-embedded α-helical protein, human aquaporin 1, using solid-state nuclear magnetic resonance spectroscopy. Our data reveal the hierarchical two-step pathway that begins with unfolding of a structured extracellular loop and proceeds to an intermediate state with a native-like helical packing. In the second step, the transmembrane domain unravels as a single unit, resulting in a heterogeneous misfolded state with high helical content but with nonnative helical packing. Our results show the importance of loops for the kinetic stabilization of the whole membrane protein structure and support the three-stage membrane protein folding model.
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Affiliation(s)
- Peng Xiao
- Department of Physics and Biophysics Interdepartmental Group, University of Guelph, Guelph, ON N1G2W1, Canada
| | - Philip Drewniak
- Department of Physics and Biophysics Interdepartmental Group, University of Guelph, Guelph, ON N1G2W1, Canada
| | - Dylan Archer Dingwell
- Department of Physics and Biophysics Interdepartmental Group, University of Guelph, Guelph, ON N1G2W1, Canada
| | - Leonid S Brown
- Department of Physics and Biophysics Interdepartmental Group, University of Guelph, Guelph, ON N1G2W1, Canada
| | - Vladimir Ladizhansky
- Department of Physics and Biophysics Interdepartmental Group, University of Guelph, Guelph, ON N1G2W1, Canada
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2
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Zerbetto De Palma G, Recoulat Angelini AA, Vitali V, González Flecha FL, Alleva K. Cooperativity in regulation of membrane protein function: phenomenological analysis of the effects of pH and phospholipids. Biophys Rev 2023; 15:721-731. [PMID: 37681089 PMCID: PMC10480370 DOI: 10.1007/s12551-023-01095-0] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/03/2023] [Accepted: 07/01/2023] [Indexed: 09/09/2023] Open
Abstract
Interaction between membrane proteins and ligands plays a key role in governing a wide spectrum of cellular processes. These interactions can provide a cooperative-type regulation of protein function. A wide variety of proteins, including enzymes, channels, transporters, and receptors, displays cooperative behavior in their interactions with ligands. Moreover, the ligands involved encompass a vast diversity and include specific molecules or ions that bind to specific binding sites. In this review, our particular focus is on the interaction between integral membrane proteins and ligands that can present multiple "binding sites", such as protons or membrane phospholipids. The study of the interaction that protons or lipids have with membrane proteins often presents challenges for classical mechanistic modeling approaches. In this regard, we show that, like Hill's pioneering work on hemoglobin regulation, phenomenological modeling constitutes a powerful tool for capturing essential features of these systems.
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Affiliation(s)
- Gerardo Zerbetto De Palma
- Facultad de Farmacia y Bioquímica, Departamento de Fisicomatemática, Universidad de Buenos Aires, Buenos Aires, Argentina
- Instituto de Biotecnología, Universidad Nacional de Hurlingham, Villa Tesei, Buenos Aires, Argentina
- Instituto de Química y Fisicoquímica Biológica (IQUIFIB), CONICET, Universidad de Buenos Aires, Buenos Aires, Argentina
| | - Alvaro A. Recoulat Angelini
- Instituto de Química y Fisicoquímica Biológica (IQUIFIB), CONICET, Universidad de Buenos Aires, Buenos Aires, Argentina
| | - Victoria Vitali
- Facultad de Farmacia y Bioquímica, Departamento de Fisicomatemática, Universidad de Buenos Aires, Buenos Aires, Argentina
- Instituto de Química y Fisicoquímica Biológica (IQUIFIB), CONICET, Universidad de Buenos Aires, Buenos Aires, Argentina
| | - F. Luis. González Flecha
- Instituto de Química y Fisicoquímica Biológica (IQUIFIB), CONICET, Universidad de Buenos Aires, Buenos Aires, Argentina
| | - Karina Alleva
- Facultad de Farmacia y Bioquímica, Departamento de Fisicomatemática, Universidad de Buenos Aires, Buenos Aires, Argentina
- Instituto de Química y Fisicoquímica Biológica (IQUIFIB), CONICET, Universidad de Buenos Aires, Buenos Aires, Argentina
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3
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Adams WR, Gautam R, Locke A, Masson LE, Borrachero-Conejo AI, Dollinger B, Throckmorton GA, Duvall C, Jansen ED, Mahadevan-Jansen A. Visualizing Lipid Dynamics Role in Infrared Neural Stimulation using Stimulated Raman Scattering. Biophys J 2022; 121:1525-1540. [PMID: 35276133 PMCID: PMC9072573 DOI: 10.1016/j.bpj.2022.03.006] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/10/2021] [Revised: 10/14/2021] [Accepted: 03/04/2022] [Indexed: 11/02/2022] Open
Abstract
Infrared neural stimulation, or INS, uses pulsed infrared light to yield label-free neural stimulation with broad experimental and translational utility. Despite its robust demonstration, INS's mechanistic and biophysical underpinnings have been the subject of debate for more than a decade. The role of lipid membrane thermodynamics appears to play an important role in how fast IR-mediated heating nonspecifically drives action potential generation. Direct observation of lipid membrane dynamics during INS remains to be shown in a live neural model system. We used hyperspectral stimulated Raman scattering (hsSRS) microscopy to study biochemical signatures of high-speed vibrational dynamics underlying INS in a live neural cell culture model. Findings suggest that lipid bilayer structural changes are occurring during INS in vitro in NG108-15 neuroglioma cells. Lipid-specific signatures of cell SRS spectra varied with stimulation energy and radiant exposure. Spectroscopic observations agree with high-speed ratiometric fluorescence imaging of a conventional lipophilic membrane structure reporter, di-4-ANNEPS. Overall, the presented findings support the hypothesis that INS causes changes in the lipid membrane of neural cells by changing lipid membrane packing order. Furthermore, this work highlights the potential of hsSRS as a method to study biophysical and biochemical dynamics safely in live cells.
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Affiliation(s)
- Wilson R Adams
- Dept. of Biomedical Engineering, Vanderbilt University, Nashville, TN, USA
| | - Rekha Gautam
- Dept. of Biomedical Engineering, Vanderbilt University, Nashville, TN, USA
| | - Andrea Locke
- Dept. of Biomedical Engineering, Vanderbilt University, Nashville, TN, USA
| | - Laura E Masson
- Dept. of Biomedical Engineering, Vanderbilt University, Nashville, TN, USA
| | | | - Bryan Dollinger
- Dept. of Biomedical Engineering, Vanderbilt University, Nashville, TN, USA
| | | | - Craig Duvall
- Dept. of Biomedical Engineering, Vanderbilt University, Nashville, TN, USA
| | - E Duco Jansen
- Dept. of Biomedical Engineering, Vanderbilt University, Nashville, TN, USA; Dept. of Neurosurgery, Vanderbilt University Medical Center, Nashville, TN, USA
| | - Anita Mahadevan-Jansen
- Dept. of Biomedical Engineering, Vanderbilt University, Nashville, TN, USA; Dept. of Neurosurgery, Vanderbilt University Medical Center, Nashville, TN, USA.
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4
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Placenti MA, Roman EA, González Flecha FL, González-Lebrero RM. Functional characterization of Legionella pneumophila Cu + transport ATPase. The activation by Cu + and ATP. BIOCHIMICA ET BIOPHYSICA ACTA. BIOMEMBRANES 2022; 1864:183822. [PMID: 34826402 DOI: 10.1016/j.bbamem.2021.183822] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/04/2021] [Revised: 11/08/2021] [Accepted: 11/17/2021] [Indexed: 06/13/2023]
Abstract
Cu+-ATPases are integral membrane proteins belonging to the IB subfamily of the P-type ATPases that couple Cu+ transport to the hydrolysis of ATP. As some structural and functional particularities arise for Cu+-ATPases, several authors suggest that some of the reaction steps of the Albers-Post model postulated for other P-ATPases may be different. In this work we describe a functional characterization of Legionella pneumophila Cu+-ATPase (LpCopA), the first PIB-ATPase whose structure was determined by X-ray crystallography. Cu+-ATPase activity of the enzyme presents a maximum at ∼37 °C and pH 6.6-6.8. Phospholipids enhance LpCopA Cu+-ATPase activity in a non-essential mode where optimal activity is achieved at an asolectin molar fraction of 0.15 and an amphiphile-protein ratio of ~30,000. As described for other P-ATPases, Mg2+ acts as an essential activator. Furthermore, Cu+-ATPase activity dependence on [Cu+] and [ATP] can both be described by a sum of two hyperbolic functions. Based on that, and the [Cu+] and [ATP] dependencies of the best fitting parameters of the hyperbolae pointed above, we propose a minimal reaction scheme for the catalytic mechanism that shares the basic reaction steps of the Albers-Post model for P-type ATPases. The reaction scheme postulated contemplates two different binding affinities for a single ATP (apparent affinities of 0.66 and 550 μM at [Cu+] → ∞) and binding of at least 2 Cu+ with different affinities as well (apparent affinities of 1.4 and 102.5 μM at [ATP] → ∞).
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Affiliation(s)
- M Agueda Placenti
- Universidad de Buenos Aires, Facultad de Farmacia y Bioquímica, Departamento de Química Biológica, Buenos Aires, Argentina; Consejo Nacional de Investigaciones Científicas y Técnicas, Instituto de Química y Fisicoquímica Biológicas, Buenos Aires, Argentina
| | - Ernesto A Roman
- Consejo Nacional de Investigaciones Científicas y Técnicas, Instituto de Química y Fisicoquímica Biológicas, Buenos Aires, Argentina; Universidad de Buenos Aires, Facultad de Ciencias Exactas y Naturales, Departamento de Química Biológica, Buenos Aires, Argentina
| | - F Luis González Flecha
- Universidad de Buenos Aires, Facultad de Farmacia y Bioquímica, Departamento de Química Biológica, Buenos Aires, Argentina; Consejo Nacional de Investigaciones Científicas y Técnicas, Instituto de Química y Fisicoquímica Biológicas, Buenos Aires, Argentina.
| | - Rodolfo M González-Lebrero
- Universidad de Buenos Aires, Facultad de Farmacia y Bioquímica, Departamento de Química Biológica, Buenos Aires, Argentina; Consejo Nacional de Investigaciones Científicas y Técnicas, Instituto de Química y Fisicoquímica Biológicas, Buenos Aires, Argentina.
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5
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Conrard L, Tyteca D. Regulation of Membrane Calcium Transport Proteins by the Surrounding Lipid Environment. Biomolecules 2019; 9:E513. [PMID: 31547139 PMCID: PMC6843150 DOI: 10.3390/biom9100513] [Citation(s) in RCA: 24] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/08/2019] [Revised: 09/09/2019] [Accepted: 09/10/2019] [Indexed: 12/11/2022] Open
Abstract
Calcium ions (Ca2+) are major messengers in cell signaling, impacting nearly every aspect of cellular life. Those signals are generated within a wide spatial and temporal range through a large variety of Ca2+ channels, pumps, and exchangers. More and more evidences suggest that Ca2+ exchanges are regulated by their surrounding lipid environment. In this review, we point out the technical challenges that are currently being overcome and those that still need to be defeated to analyze the Ca2+ transport protein-lipid interactions. We then provide evidences for the modulation of Ca2+ transport proteins by lipids, including cholesterol, acidic phospholipids, sphingolipids, and their metabolites. We also integrate documented mechanisms involved in the regulation of Ca2+ transport proteins by the lipid environment. Those include: (i) Direct interaction inside the protein with non-annular lipids; (ii) close interaction with the first shell of annular lipids; (iii) regulation of membrane biophysical properties (e.g., membrane lipid packing, thickness, and curvature) directly around the protein through annular lipids; and (iv) gathering and downstream signaling of several proteins inside lipid domains. We finally discuss recent reports supporting the related alteration of Ca2+ and lipids in different pathophysiological events and the possibility to target lipids in Ca2+-related diseases.
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Affiliation(s)
- Louise Conrard
- CELL Unit, de Duve Institute and Université catholique de Louvain, UCL B1.75.05, avenue Hippocrate, 75, B-1200 Brussels, Belgium
| | - Donatienne Tyteca
- CELL Unit, de Duve Institute and Université catholique de Louvain, UCL B1.75.05, avenue Hippocrate, 75, B-1200 Brussels, Belgium.
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6
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Corradi V, Sejdiu BI, Mesa-Galloso H, Abdizadeh H, Noskov SY, Marrink SJ, Tieleman DP. Emerging Diversity in Lipid-Protein Interactions. Chem Rev 2019; 119:5775-5848. [PMID: 30758191 PMCID: PMC6509647 DOI: 10.1021/acs.chemrev.8b00451] [Citation(s) in RCA: 245] [Impact Index Per Article: 49.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
![]()
Membrane
lipids interact with proteins in a variety of ways, ranging
from providing a stable membrane environment for proteins to being
embedded in to detailed roles in complicated and well-regulated protein
functions. Experimental and computational advances are converging
in a rapidly expanding research area of lipid–protein interactions.
Experimentally, the database of high-resolution membrane protein structures
is growing, as are capabilities to identify the complex lipid composition
of different membranes, to probe the challenging time and length scales
of lipid–protein interactions, and to link lipid–protein
interactions to protein function in a variety of proteins. Computationally,
more accurate membrane models and more powerful computers now enable
a detailed look at lipid–protein interactions and increasing
overlap with experimental observations for validation and joint interpretation
of simulation and experiment. Here we review papers that use computational
approaches to study detailed lipid–protein interactions, together
with brief experimental and physiological contexts, aiming at comprehensive
coverage of simulation papers in the last five years. Overall, a complex
picture of lipid–protein interactions emerges, through a range
of mechanisms including modulation of the physical properties of the
lipid environment, detailed chemical interactions between lipids and
proteins, and key functional roles of very specific lipids binding
to well-defined binding sites on proteins. Computationally, despite
important limitations, molecular dynamics simulations with current
computer power and theoretical models are now in an excellent position
to answer detailed questions about lipid–protein interactions.
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Affiliation(s)
- Valentina Corradi
- Centre for Molecular Simulation and Department of Biological Sciences , University of Calgary , 2500 University Drive NW , Calgary , Alberta T2N 1N4 , Canada
| | - Besian I Sejdiu
- Centre for Molecular Simulation and Department of Biological Sciences , University of Calgary , 2500 University Drive NW , Calgary , Alberta T2N 1N4 , Canada
| | - Haydee Mesa-Galloso
- Centre for Molecular Simulation and Department of Biological Sciences , University of Calgary , 2500 University Drive NW , Calgary , Alberta T2N 1N4 , Canada
| | - Haleh Abdizadeh
- Groningen Biomolecular Sciences and Biotechnology Institute and Zernike Institute for Advanced Materials , University of Groningen , Nijenborgh 7 , 9747 AG Groningen , The Netherlands
| | - Sergei Yu Noskov
- Centre for Molecular Simulation and Department of Biological Sciences , University of Calgary , 2500 University Drive NW , Calgary , Alberta T2N 1N4 , Canada
| | - Siewert J Marrink
- Groningen Biomolecular Sciences and Biotechnology Institute and Zernike Institute for Advanced Materials , University of Groningen , Nijenborgh 7 , 9747 AG Groningen , The Netherlands
| | - D Peter Tieleman
- Centre for Molecular Simulation and Department of Biological Sciences , University of Calgary , 2500 University Drive NW , Calgary , Alberta T2N 1N4 , Canada
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7
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González Flecha FL. Kinetic stability of membrane proteins. Biophys Rev 2017; 9:563-572. [PMID: 28921106 DOI: 10.1007/s12551-017-0324-0] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2017] [Accepted: 08/29/2017] [Indexed: 12/25/2022] Open
Abstract
Although membrane proteins constitute an important class of biomolecules involved in key cellular processes, study of the thermodynamic and kinetic stability of their structures is far behind that of soluble proteins. It is known that many membrane proteins become unstable when removed by detergent extraction from the lipid environment. In addition, most of them undergo irreversible denaturation, even under mild experimental conditions. This process was found to be associated with partial unfolding of the polypeptide chain exposing hydrophobic regions to water, and it was proposed that the formation of kinetically trapped conformations could be involved. In this review, we will describe some of the efforts toward understanding the irreversible inactivation of membrane proteins. Furthermore, its modulation by phospholipids, ligands, and temperature will be herein discussed.
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Affiliation(s)
- F Luis González Flecha
- Universidad de Buenos Aires, CONICET, Laboratorio de Biofísica Molecular, Instituto de Química y Fisicoquímica Biológicas, Buenos Aires, Argentina.
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8
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Placenti MA, Kaufman SB, González Flecha FL, González Lebrero RM. Unexpected Effects of K + and Adenosine Triphosphate on the Thermal Stability of Na +,K +-ATPase. J Phys Chem B 2017; 121:4949-4957. [PMID: 28441865 DOI: 10.1021/acs.jpcb.7b00629] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Na+,K+-ATPase is an integral membrane protein which couples ATP hydrolysis to the transport of three Na+ out and two K+ into the cell. The aim of this work is to characterize the effect of K+, ATP, and Mg2+ (essential activator) on the Na+,K+-ATPase thermal stability. Under all conditions tested, thermal inactivation of the enzyme is concomitant with a structural change involving the ATP binding site and membrane-associated regions. Both ligands exert a clear stabilizing effect due to both enthalpic and entropic contributions. Competition experiments between ATP and K+ showed that, when ATP is present, the inactivation rate coefficient exhibits a biphasic dependence on K+ concentration. At low [K+], destabilization of the enzyme is observed, while stabilization occurred at larger cation concentrations. This is not expected for a simple competition between the enzyme and two ligands that individually protect the enzyme. A model that includes enzyme species with none, one, or two K+ and/or one molecule of ATP bound explains the experimental data. We concluded that, despite both ligands stabilizing the enzyme, the species with one K+ and one ATP simultaneously bound is unstable.
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Affiliation(s)
- M Agueda Placenti
- Instituto de Química y Fisicoquímica Biológicas and Departamento de Química Biológica, Facultad de Farmacia y Bioquímica, Universidad de Buenos Aires - CONICET , Buenos Aires, Argentina
| | - Sergio B Kaufman
- Instituto de Química y Fisicoquímica Biológicas and Departamento de Química Biológica, Facultad de Farmacia y Bioquímica, Universidad de Buenos Aires - CONICET , Buenos Aires, Argentina
| | - F Luis González Flecha
- Instituto de Química y Fisicoquímica Biológicas and Departamento de Química Biológica, Facultad de Farmacia y Bioquímica, Universidad de Buenos Aires - CONICET , Buenos Aires, Argentina
| | - Rodolfo M González Lebrero
- Instituto de Química y Fisicoquímica Biológicas and Departamento de Química Biológica, Facultad de Farmacia y Bioquímica, Universidad de Buenos Aires - CONICET , Buenos Aires, Argentina
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9
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Bredeston LM, González Flecha FL. The promiscuous phosphomonoestearase activity of Archaeoglobus fulgidus CopA, a thermophilic Cu+ transport ATPase. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2016; 1858:1471-8. [PMID: 27086711 DOI: 10.1016/j.bbamem.2016.04.006] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Subscribe] [Scholar Register] [Received: 11/16/2015] [Revised: 04/01/2016] [Accepted: 04/13/2016] [Indexed: 11/19/2022]
Abstract
Membrane transport P-type ATPases display two characteristic enzymatic activities: a principal ATPase activity provides the driving force for ion transport across biological membranes, whereas a promiscuous secondary activity catalyzes the hydrolysis of phosphate monoesters. This last activity is usually denoted as the phosphatase activity of P-ATPases. In the present study, we characterize the phosphatase activity of the Cu(+)-transport ATPase from Archaeglobus fulgidus (Af-CopA) and compare it with the principal ATPase activity. Our results show that the phosphatase turnover number was 20 times higher than that corresponding to the ATPase activity, but it is compensated by a high value of Km, producing a less efficient catalysis for pNPP. This secondary activity is enhanced by Mg(2+) (essential activator) and phospholipids (non-essential activator), and inhibited by salts and Cu(+). Transition state analysis of the catalyzed and noncatalyzed hydrolysis of pNPP indicates that Af-CopA enhances the reaction rates by a factor of 10(5) (ΔΔG(‡)=38 kJ/mol) mainly by reducing the enthalpy of activation (ΔΔH(‡)=30 kJ/mol), whereas the entropy of activation is less negative on the enzyme than in solution. For the ATPase activity, the decrease in the enthalpic component of the barrier is higher (ΔΔH(‡)=39 kJ/mol) and the entropic component is small on both the enzyme and in solution. These results suggest that different mechanisms are involved in the transference of the phosphoryl group of p-nitrophenyl phosphate and ATP.
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Affiliation(s)
- Luis M Bredeston
- Laboratorio de Biofísica Molecular, Instituto de Química y Fisicoquímica Biológicas, Departamento de Química Biológica, Facultad de Farmacia y Bioquímica, Universidad de Buenos Aires - CONICET, Buenos Aires, Argentina
| | - F Luis González Flecha
- Laboratorio de Biofísica Molecular, Instituto de Química y Fisicoquímica Biológicas, Departamento de Química Biológica, Facultad de Farmacia y Bioquímica, Universidad de Buenos Aires - CONICET, Buenos Aires, Argentina.
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10
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Thermal Stability of Dopamine Transporters. J Membr Biol 2015; 248:775-81. [DOI: 10.1007/s00232-015-9794-9] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/24/2014] [Accepted: 03/16/2015] [Indexed: 11/25/2022]
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11
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Pignataro MF, Dodes-Traian MM, González-Flecha FL, Sica M, Mangialavori IC, Rossi JPFC. Modulation of plasma membrane Ca2+-ATPase by neutral phospholipids: effect of the micelle-vesicle transition and the bilayer thickness. J Biol Chem 2015; 290:6179-90. [PMID: 25605721 PMCID: PMC4358257 DOI: 10.1074/jbc.m114.585828] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/30/2014] [Revised: 10/29/2014] [Indexed: 11/06/2022] Open
Abstract
The effects of lipids on membrane proteins are likely to be complex and unique for each membrane protein. Here we studied different detergent/phosphatidylcholine reconstitution media and tested their effects on plasma membrane Ca(2+) pump (PMCA). We found that Ca(2+)-ATPase activity shows a biphasic behavior with respect to the detergent/phosphatidylcholine ratio. Moreover, the maximal Ca(2+)-ATPase activity largely depends on the length and the unsaturation degree of the hydrocarbon chain. Using static light scattering and fluorescence correlation spectroscopy, we monitored the changes in hydrodynamic radius of detergent/phosphatidylcholine particles during the micelle-vesicle transition. We found that, when PMCA is reconstituted in mixed micelles, neutral phospholipids increase the enzyme turnover. The biophysical changes associated with the transition from mixed micelles to bicelles increase the time of residence of the phosphorylated intermediate (EP), decreasing the enzyme turnover. Molecular dynamics simulations analysis of the interactions between PMCA and the phospholipid bilayer in which it is embedded show that in the 1,2-dioleoyl-sn-glycero-3-phosphocholine bilayer, charged residues of the protein are trapped in the hydrophobic core. Conversely, in the 1,2-dimyristoyl-sn-glycero-3-phosphocholine bilayer, the overall hydrophobic-hydrophilic requirements of the protein surface are fulfilled the best, reducing the thermodynamic cost of exposing charged residues to the hydrophobic core. The apparent mismatch produced by a 1,2-dioleoyl-sn-glycero-3-phosphocholine thicker bilayer could be a structural foundation to explain its functional effect on PMCA.
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Affiliation(s)
- María Florencia Pignataro
- From the Instituto de Química y Fisicoquímica Biológicas, Facultad de Farmacia y Bioquímica, Universidad de Buenos Aires, CONICET, Junín 956 (1113) Buenos Aires, Argentina and
| | - Martín M Dodes-Traian
- From the Instituto de Química y Fisicoquímica Biológicas, Facultad de Farmacia y Bioquímica, Universidad de Buenos Aires, CONICET, Junín 956 (1113) Buenos Aires, Argentina and
| | - F Luis González-Flecha
- From the Instituto de Química y Fisicoquímica Biológicas, Facultad de Farmacia y Bioquímica, Universidad de Buenos Aires, CONICET, Junín 956 (1113) Buenos Aires, Argentina and
| | - Mauricio Sica
- the Laboratorio de Bioenergías, IEDS, CONICET Centro Atómico Bariloche, E. Bustillo 9,500 (8400), San Carlos de Bariloche, Río Negro, Argentina
| | - Irene C Mangialavori
- From the Instituto de Química y Fisicoquímica Biológicas, Facultad de Farmacia y Bioquímica, Universidad de Buenos Aires, CONICET, Junín 956 (1113) Buenos Aires, Argentina and
| | - Juan Pablo F C Rossi
- From the Instituto de Química y Fisicoquímica Biológicas, Facultad de Farmacia y Bioquímica, Universidad de Buenos Aires, CONICET, Junín 956 (1113) Buenos Aires, Argentina and
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12
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Yoneda JS, Rigos CF, de Lourenço TFA, Sebinelli HG, Ciancaglini P. Na,K-ATPase reconstituted in ternary liposome: the presence of cholesterol affects protein activity and thermal stability. Arch Biochem Biophys 2014; 564:136-41. [PMID: 25286376 DOI: 10.1016/j.abb.2014.09.015] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/01/2014] [Revised: 09/12/2014] [Accepted: 09/26/2014] [Indexed: 01/27/2023]
Abstract
Differential scanning calorimetry (DSC) was applied to investigate the effect of cholesterol on the thermotropic properties of the lipid membrane (DPPC and DPPE). The thermostability and unfolding of solubilized and reconstituted Na,K-ATPase in DPPC:DPPE:cholesterol-liposomes was also studied to gain insight into the role of cholesterol in the Na,K-ATPase modulation of enzyme function and activity. The tertiary system (DPPC:DPPE:cholesterol) (molar ratio DPPC:DPPE equal 1:1) when cholesterol content was increased from 0% up to 40% results in a slight decrease in the temperature of transition and enthalpy, and an increase in width. We observed that, without heating treatment, at 37°C, the activity was higher for 20mol% cholesterol. However, thermal inactivation experiments showed that the enzyme activity loss time depends on the cholesterol membrane content. The unfolding of the enzyme incorporated to liposomes of DPPC:DPPE (1:1mol) with different cholesterol contents, ranging from 0% to 40% mol was also studied by DSC. Some differences between the thermograms indicate that the presence of lipids promotes a conformational change in protein structure and this change is enough to change the way Na,K-ATPase thermally unfolds.
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Affiliation(s)
- Juliana Sakamoto Yoneda
- Faculdade de Filosofia Ciências e Letras de Ribeirão Preto - FFCLRP-USP, Depto. Química, 14040-901 Ribeirão Preto, SP, Brazil
| | - Carolina Fortes Rigos
- Faculdade de Filosofia Ciências e Letras de Ribeirão Preto - FFCLRP-USP, Depto. Química, 14040-901 Ribeirão Preto, SP, Brazil
| | | | - Heitor Gobbi Sebinelli
- Faculdade de Filosofia Ciências e Letras de Ribeirão Preto - FFCLRP-USP, Depto. Química, 14040-901 Ribeirão Preto, SP, Brazil
| | - Pietro Ciancaglini
- Faculdade de Filosofia Ciências e Letras de Ribeirão Preto - FFCLRP-USP, Depto. Química, 14040-901 Ribeirão Preto, SP, Brazil.
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13
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Amphipols and Photosynthetic Light-Harvesting Pigment-Protein Complexes. J Membr Biol 2014; 247:1031-41. [DOI: 10.1007/s00232-014-9712-6] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/10/2014] [Accepted: 07/23/2014] [Indexed: 10/24/2022]
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14
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Roman EA, González Flecha FL. Kinetics and thermodynamics of membrane protein folding. Biomolecules 2014; 4:354-73. [PMID: 24970219 PMCID: PMC4030980 DOI: 10.3390/biom4010354] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/31/2013] [Revised: 02/19/2014] [Accepted: 02/23/2014] [Indexed: 02/06/2023] Open
Abstract
Understanding protein folding has been one of the great challenges in biochemistry and molecular biophysics. Over the past 50 years, many thermodynamic and kinetic studies have been performed addressing the stability of globular proteins. In comparison, advances in the membrane protein folding field lag far behind. Although membrane proteins constitute about a third of the proteins encoded in known genomes, stability studies on membrane proteins have been impaired due to experimental limitations. Furthermore, no systematic experimental strategies are available for folding these biomolecules in vitro. Common denaturing agents such as chaotropes usually do not work on helical membrane proteins, and ionic detergents have been successful denaturants only in few cases. Refolding a membrane protein seems to be a craftsman work, which is relatively straightforward for transmembrane β-barrel proteins but challenging for α-helical membrane proteins. Additional complexities emerge in multidomain membrane proteins, data interpretation being one of the most critical. In this review, we will describe some recent efforts in understanding the folding mechanism of membrane proteins that have been reversibly refolded allowing both thermodynamic and kinetic analysis. This information will be discussed in the context of current paradigms in the protein folding field.
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Affiliation(s)
- Ernesto A Roman
- Laboratory of Molecular Biophysics, Institute of Biochemistry and Biophysical Chemistry, University of Buenos Aires-CONICET, Buenos Aires 1113, Argentina.
| | - F Luis González Flecha
- Laboratory of Molecular Biophysics, Institute of Biochemistry and Biophysical Chemistry, University of Buenos Aires-CONICET, Buenos Aires 1113, Argentina.
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15
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Addition of subunit γ, K+ ions, and lipid restores the thermal stability of solubilized Na,K-ATPase. Arch Biochem Biophys 2013; 530:93-100. [DOI: 10.1016/j.abb.2012.12.022] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/22/2012] [Revised: 12/21/2012] [Accepted: 12/23/2012] [Indexed: 11/19/2022]
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16
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Dodes Traian MM, Cattoni DI, Levi V, González Flecha FL. A two-stage model for lipid modulation of the activity of integral membrane proteins. PLoS One 2012; 7:e39255. [PMID: 22723977 PMCID: PMC3378530 DOI: 10.1371/journal.pone.0039255] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/27/2012] [Accepted: 05/22/2012] [Indexed: 01/23/2023] Open
Abstract
Lipid-protein interactions play an essential role in the regulation of biological function of integral membrane proteins; however, the underlying molecular mechanisms are not fully understood. Here we explore the modulation by phospholipids of the enzymatic activity of the plasma membrane calcium pump reconstituted in detergent-phospholipid mixed micelles of variable composition. The presence of increasing quantities of phospholipids in the micelles produced a cooperative increase in the ATPase activity of the enzyme. This activation effect was reversible and depended on the phospholipid/detergent ratio and not on the total lipid concentration. Enzyme activation was accompanied by a small structural change at the transmembrane domain reported by 1-aniline-8-naphtalenesulfonate fluorescence. In addition, the composition of the amphipilic environment sensed by the protein was evaluated by measuring the relative affinity of the assayed phospholipid for the transmembrane surface of the protein. The obtained results allow us to postulate a two-stage mechanistic model explaining the modulation of protein activity based on the exchange among non-structural amphiphiles at the hydrophobic transmembrane surface, and a lipid-induced conformational change. The model allowed to obtain a cooperativity coefficient reporting on the efficiency of the transduction step between lipid adsorption and catalytic site activation. This model can be easily applied to other phospholipid/detergent mixtures as well to other membrane proteins. The systematic quantitative evaluation of these systems could contribute to gain insight into the structure-activity relationships between proteins and lipids in biological membranes.
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Affiliation(s)
- Martín M Dodes Traian
- Laboratorio de Biofísica Molecular - Instituto de Química y Fisicoquímica Biológicas, Universidad de Buenos Aires - CONICET, Buenos Aires, Argentina
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17
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Kaufman SB, González-Flecha FL, González-Lebrero RM. Opposing Effects of Na+ and K+ on the Thermal Stability of Na+,K+-ATPase. J Phys Chem B 2012; 116:3421-9. [DOI: 10.1021/jp2124108] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Affiliation(s)
- Sergio B. Kaufman
- Instituto
de Química y Fisicoquímica
Biológicas and Departamento de Química Biológica,
Facultad de Farmacia y Bioquímica, Universidad de Buenos Aires, Buenos Aires, Argentina
| | - F. Luis González-Flecha
- Instituto
de Química y Fisicoquímica
Biológicas and Departamento de Química Biológica,
Facultad de Farmacia y Bioquímica, Universidad de Buenos Aires, Buenos Aires, Argentina
| | - Rodolfo M. González-Lebrero
- Instituto
de Química y Fisicoquímica
Biológicas and Departamento de Química Biológica,
Facultad de Farmacia y Bioquímica, Universidad de Buenos Aires, Buenos Aires, Argentina
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18
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Loura LMS, Prieto M. FRET in Membrane Biophysics: An Overview. Front Physiol 2011; 2:82. [PMID: 22110442 PMCID: PMC3216123 DOI: 10.3389/fphys.2011.00082] [Citation(s) in RCA: 81] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/10/2011] [Accepted: 10/26/2011] [Indexed: 12/31/2022] Open
Abstract
Förster resonance energy transfer (FRET), in most applications used as a “spectroscopic ruler,” allows an easy determination of the donor-acceptor intermolecular distance. However, the situation becomes complex in membranes, since around each donor there is an ensemble of acceptors at non-correlated distances. In this review, state-of-the-art methodologies for this situation are presented, usually involving time-resolved data and model fitting. This powerful approach can be used to study the occurrence of phase separation (“rafts” or other type of domains), allowing their detection as well as size evaluation. Formalisms for studying lipid–protein and protein–protein interactions according to specific topologies are also addressed. The advantages and added complexity of a specific type of FRET (energy homotransfer or energy migration) are described, as well as applications of FRET under the microscope.
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Affiliation(s)
- Luís M S Loura
- Faculdade de Farmácia, Universidade de Coimbra Coimbra, Portugal
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19
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Garber Cohen IP, Castello PR, González Flecha FL. Ice-induced partial unfolding and aggregation of an integral membrane protein. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2010; 1798:2040-7. [PMID: 20691147 DOI: 10.1016/j.bbamem.2010.07.035] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/10/2010] [Revised: 07/10/2010] [Accepted: 07/28/2010] [Indexed: 11/27/2022]
Abstract
Although the deleterious effects of ice on water-soluble proteins are well established, little is known about the freeze stability of membrane proteins. Here we explore this issue through a combined kinetic and spectroscopic approach using micellar-purified plasma membrane calcium pump as a model. The ATPase activity of this protein significantly diminished after freezing using a slow-cooling procedure, with the decrease in the activity being an exponential function of the storage time at 253K, with t(½)=3.9±0.6h. On the contrary, no significant changes on enzyme activity were detected when a fast cooling procedure was performed. Regardless of the cooling rate, successive freeze-thaw cycles produced an exponential decrease in the Ca(2+)-ATPase activity, with the number of cycles at which the activity was reduced to half being 9.2±0.3 (fast cooling) and 3.7±0.2 (slow cooling). PAGE analysis showed that neither degradation nor formation of SDS-stable aggregates of the protein takes place during protein inactivation. Instead, the inactivation process was found to be associated with the irreversible partial unfolding of the polypeptide chain, as assessed by Trp fluorescence, far UV circular dichroism, and 1-anilino-naphtalene-8-sulfonate binding. This inactive protein undergoes, in a later stage, a further irreversible transformation leading to large aggregates.
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20
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Loura LMS, Prieto M, Fernandes F. Quantification of protein-lipid selectivity using FRET. EUROPEAN BIOPHYSICS JOURNAL : EBJ 2010; 39:565-78. [PMID: 20238256 PMCID: PMC2841278 DOI: 10.1007/s00249-009-0532-z] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 05/15/2009] [Revised: 07/30/2009] [Accepted: 08/04/2009] [Indexed: 12/11/2022]
Abstract
Membrane proteins exhibit different affinities for different lipid species, and protein-lipid selectivity regulates the membrane composition in close proximity to the protein, playing an important role in the formation of nanoscale membrane heterogeneities. The sensitivity of Förster resonance energy transfer (FRET) for distances of 10 A up to 100 A is particularly useful to retrieve information on the relative distribution of proteins and lipids in the range over which protein-lipid selectivity is expected to influence membrane composition. Several FRET-based methods applied to the quantification of protein-lipid selectivity are described herein, and different formalisms applied to the analysis of FRET data for particular geometries of donor-acceptor distribution are critically assessed.
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Affiliation(s)
- Luís M. S. Loura
- Faculdade de Farmácia, Universidade de Coimbra, Pólo das Ciências da Saúde, Azinhaga de Santa Comba, 3000-548 Coimbra, Portugal
- Centro de Química de Évora, Rua Romão Ramalho, 59, 7000-671 Evora, Portugal
| | - Manuel Prieto
- Centro de Química Física Molecular and Institute of Nanosciences and Nanotechnologies, Complexo I, Instituto Superior Técnico, Av. Rovisco Pais, 1049-001 Lisbon, Portugal
| | - Fábio Fernandes
- Department of Membrane Biophysics, Max-Planck Institute for Biophysical Chemistry, Am Fassberg 11, 37077 Göttingen, Germany
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21
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Toth SI, Smith LA, Ahmed SA. Extreme sensitivity of botulinum neurotoxin domains towards mild agitation. J Pharm Sci 2009; 98:3302-11. [PMID: 19226630 DOI: 10.1002/jps.21676] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
Botulinum neurotoxins (BoNTs) and their fragments are targets of therapeutic developments and are increasingly used as therapeutic, prophylactic, and research reagents. However, published data on their properties vary widely. In order to gain a better understanding of these variations, we initiated a systematic investigation of the stability parameters of catalytic light chains (Lc) as well as of cell surface binding domains (Hc) of the neurotoxin. When followed by CD spectroscopy, we noticed that the recombinant light chains of serotypes A (LcA), B, D, E, and G rapidly lost their secondary structures by mild stirring. Denaturation of LcA increased with stirring speed and temperature resulting in a catalytically inactive precipitate. Reducing agents or an anaerobic environment were ineffective in the denaturation. Under identical conditions, bovine serum albumin, ovalbumin, carboxypeptidase B, and of thermolysin, a structural and functional analogue of LcA, remained unchanged. Hc domains of serotype A, B, C, E, and F were also denatured by mild stirring. Adding the nonionic detergent Tween-20 to LcA completely prevented the denaturation. We speculate that the BoNT domains undergo surface denaturation due to rapid exposure of hydrophobic residues by mechanical agitation. This study has important implications for handling BoNT proteins used in therapeutic development.
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Affiliation(s)
- Stephen I Toth
- Department Molecular Biology, Integrated Toxicology Division, United States Army Medical Research Institute of Infectious Diseases, Fort Detrick, Maryland 21702, USA
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22
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Effects of phosphatidylethanolamine glycation on lipid-protein interactions and membrane protein thermal stability. Biochem J 2008; 416:145-52. [PMID: 18564061 DOI: 10.1042/bj20080618] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
Non-enzymatic glycation of biomolecules has been implicated in the pathophysiology of aging and diabetes. Among the potential targets for glycation are biological membranes, characterized by a complex organization of lipids and proteins interacting and forming domains of different size and stability. In the present study, we analyse the effects of glycation on the interactions between membrane proteins and lipids. The phospholipid affinity for the transmembrane surface of the PMCA (plasma-membrane Ca(2+)-ATPase) was determined after incubating the protein or the phospholipids with glucose. Results show that the affinity between PMCA and the surrounding phospholipids decreases significantly after phosphospholipid glycation, but remains unmodified after glycation of the protein. Furthermore, phosphatidylethanolamine glycation decreases by approximately 30% the stability of PMCA against thermal denaturation, suggesting that glycated aminophospholipids induce a structural rearrangement in the protein that makes it more sensitive to thermal unfolding. We also verified that lipid glycation decreases the affinity of lipids for two other membrane proteins, suggesting that this effect might be common to membrane proteins. Extending these results to the in vivo situation, we can hypothesize that, under hyperglycaemic conditions, glycation of membrane lipids may cause a significant change in the structure and stability of membrane proteins, which may affect the normal functioning of membranes and therefore of cells.
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23
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Cura CI, Corradi GR, Rinaldi DE, Adamo HP. High sensibility to reactivation by acidic lipids of the recombinant human plasma membrane Ca2+-ATPase isoform 4xb purified from Saccharomyces cerevisiae. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2008; 1778:2757-64. [PMID: 18822268 DOI: 10.1016/j.bbamem.2008.08.020] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/25/2008] [Revised: 08/25/2008] [Accepted: 08/26/2008] [Indexed: 11/17/2022]
Abstract
The human plasma membrane Ca2+ pump (isoform 4xb) was expressed in Saccharomyces cerevisiae and purified by calmodulin-affinity chromatography. Under optimal conditions the recombinant enzyme (yPMCA) hydrolyzed ATP in a Ca2+ dependent manner at a rate of 15 micromol/mg/min. The properties of yPMCA were compared to those of the PMCA purified from human red cells (ePMCA). The mobility of yPMCA in SDS-PAGE was the expected for the hPMCA4xb protein but slightly lower than that of ePMCA. Both enzymes achieved maximal activity when supplemented with acidic phospholipids. However, while ePMCA in mixed micelles of phosphatidylcholine-detergent had 30% of its maximal activity, the yPMCA enzyme was nearly inactive. Increasing the phosphatidylcholine content of the micelles did not increase the activity of yPMCA but the activity in the presence of phosphatidylcholine improved by partially removing the detergent. The reactivation of the detergent solubilized yPMCA required specifically acidic lipids and, as judged by the increase in the level of phosphoenzyme, it involved the increase in the amount of active enzyme. These results indicate that the function of yPMCA is highly sensitive to delipidation and the restitution of acidic lipids is needed for a functional enzyme.
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Affiliation(s)
- Carolina I Cura
- Instituto de Química y Fisicoquímica Biológicas (IQUIFIB)-Facultad de Farmacia y Bioquímica, Universidad de Buenos Aires, Junín 956, 1113 Ciudad de Buenos Aires, Argentina.
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24
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Thermal stability of CopA, a polytopic membrane protein from the hyperthermophile Archaeoglobus fulgidus. Arch Biochem Biophys 2008; 471:198-206. [DOI: 10.1016/j.abb.2007.12.013] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/24/2007] [Revised: 12/19/2007] [Accepted: 12/20/2007] [Indexed: 11/21/2022]
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25
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Despa F, Orgill DP, Neuwalder J, Lee RC. The relative thermal stability of tissue macromolecules and cellular structure in burn injury. Burns 2005; 31:568-77. [PMID: 15993302 DOI: 10.1016/j.burns.2005.01.015] [Citation(s) in RCA: 62] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
Abstract
When tissue is subjected to higher than physiological temperatures, protein and cell organelle structures can be altered resulting in cell death and subsequent tissue necrosis. A burn injury can be stratified into three main zones, coagulation, stasis and edema, which correlate with the extent of heat exposure and thermal properties of the tissue. While there has been considerable effort to characterize the time-temperature dependence of the injury, relatively little attention has been paid to the other important variable, the thermal susceptibility of the tissue. In the present study, we employ a standard physical chemistry approach to predict the level of denaturation at supraphysiological temperatures of 12 vital proteins as well as RNA, DNA and cell membrane components. Melting temperatures and unfolding enthalpies of the cellular components are used as input experimental parameters. This approach allows us to establish a relation between the level of denaturation of critical cellular components and clinical manifestations of the burn through the characteristic zones of the injury. Specifically, we evaluate the degree of molecular alteration for characteristic temperature profiles at two different depths (Mid-Dermis and Dermis-Fat interface) of 80 degrees C; 20s contact burn. The results of this investigation suggest that the thermal alteration of the plasma membrane is likely the most significant cause of the tissue necrosis. The lipid bilayer and membrane-bound ATPases show a high probability of thermal damage (almost 100% for the former and 85% for the latter) for short heat exposure times. These results suggest that strategies to minimize the damage in a burn injury might focus on the stabilization of the cellular membrane and membrane-bound ATPases. Further work will be required to validate these predictions in an in vivo model.
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Affiliation(s)
- F Despa
- Department of Surgery, MC6035, The University of Chicago, Chicago, IL 60637, USA
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26
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Filomatori CV, Rega AF. On the mechanism of activation of the plasma membrane Ca2+-ATPase by ATP and acidic phospholipids. J Biol Chem 2003; 278:22265-71. [PMID: 12660230 DOI: 10.1074/jbc.m302657200] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The activation of purified and phospholipid-depleted plasma membrane Ca2+-ATPase by phospholipids and ATP was studied. Enzyme activity increased with [ATP] along biphasic curves representing the sum of two Michaelis-Menten equations. Acidic phospholipids (phosphatidylinositol (PI) and phosphatidylserine (PS)) increased Vmax without affecting apparent affinities of the ATP sites. In the presence of 20 microm ATP, phosphorylation of the enzyme preincubated with Ca2+ (CaE1) was very fast (kapp congruent with 400 s-1). vo of phosphorylation of CaE1 increased with [ATP] along a Michaelis-Menten curve (Km of 15 microm) and was phospholipid-independent. Without Ca2+ preincubation (E1 + E2), vo of phosphorylation was also phospholipid-independent, but was slower and increased with [ATP] along biphasic curves. The high affinity component reflected rapid phosphorylation of CaE1, the low affinity component the E2 --> E1 shift, which accelerated to a rate higher than that of the ATPase activity when ATP was bound to the regulatory site. Dephosphorylation of EP did not occur without ATP. Dephosphorylation increased along a biphasic curve with increasing [ATP], showing that ATP accelerated dephosphorylation independently of phospholipid. PI, but not phosphatidylethanolamine (PE), accelerated dephosphorylation even in the absence of ATP. kapp for dephosphorylation was 57 s-1 at 0 microM ATP; that rate was further increased by ATP. Steady-state [EP] x kapp for dephosphorylation varied with [ATP], and matched the Ca2+-ATPase activity measured under the same conditions. Apparently, the catalytic cycle is rate-limited by dephosphorylation. Acidic phospholipids stimulate Ca2+-ATPase activity by accelerating dephosphorylation, while ATP accelerates both dephosphorylation and the conformational change from E2 to E1, further stimulating the ATPase activity.
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Affiliation(s)
- Claudia V Filomatori
- Instituto de Química y Fisicoquímica Biológicas, Facultad de Farmacia y Bioquímica, Junín 956, 1113 Buenos Aires, Argentina
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27
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Levi V, Rossi JPFC, Castello PR, González Flecha FL. Quantitative analysis of membrane protein-amphiphile interactions using resonance energy transfer. Anal Biochem 2003; 317:171-9. [PMID: 12758255 DOI: 10.1016/s0003-2697(03)00132-5] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Abstract
This work describes a simple method for determining the association constant of amphiphiles to membrane proteins. The method uses a fluorescent phospholipid probe, which senses the competition among unlabeled amphiphiles for positions on the transmembrane surface of the protein. The contact between the probe and the protein surface is detected through resonance energy transfer. We have analyzed theoretically this process deriving a general equation for the dependence of the energy transfer efficiency on the composition of the micelles/bilayers in which the protein is inserted. This equation includes an exchange constant for each amphiphile, which gives a measure of its affinity for the protein with respect to that of an amphiphile set as the reference. We applied this method to determine the exchange constant of different phospholipids for the plasma membrane calcium pump.
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Affiliation(s)
- Valeria Levi
- Instituto de Química y Fisicoquímica Biológicas, Departamento de Química Biológica, Facultad de Farmacia y Bioquímica, Universidad de Buenos Aires, Junín 956, Buenos Aires C1113AAD, Argentina
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28
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Levi V, Rossi JPFC, Giraldo AMV, Castello PR, González Flecha FL. An improved method to measure the interactions of p-type ATPases with the lipidic environment. Ann N Y Acad Sci 2003; 986:283-6. [PMID: 12763823 DOI: 10.1111/j.1749-6632.2003.tb07187.x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Valeria Levi
- Instituto de Química y Fisicoquímica Biológicas, Departamento de Química Biológica, Facultad de Farmacia y Bioquímica, Universidad de Buenos Aires, Argentina
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29
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Abstract
For large-scale production, as required in structural biology, membrane proteins can be expressed in an insoluble form as inclusion bodies and be refolded in vitro. This requires refolding conditions where the native form is thermodynamically stable and where nonproductive pathways leading to aggregation are avoided. Examples of successful refolding are reviewed and general guidelines to establish refolding protocols of membrane proteins are presented.
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Affiliation(s)
- Hans Kiefer
- m-phasys GmbH, Vor dem Kreuzberg 17, D-72070 Tübingen, Germany.
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30
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Abstract
Pyrene is one of the most frequently used lipid-linked fluorophores. Its most characteristic features are a long excited state lifetime and (local) concentration-dependent formation of excimers. Pyrene is also hydrophobic and thus does not significantly distort the conformation of the labeled lipid molecule. These characteristics make pyrene lipids well-suited for studies on a variety of biophysical phenomena like lateral diffusion, inter- or transbilayer movement of lipids and lateral organization of membranes. Pyrene lipids have also been widely employed to determine protein binding to membranes, lipid conformation and the activity of lipolytic enzymes. In cell biology, pyrene lipids are promising tools for studies on lipid trafficking and metabolism, as well as for microscopic mapping of membrane properties. The main disadvantage of pyrene lipids is the relatively large size of the fluorophore. Another disadvantage is that they require UV-excitation, which is not feasible with all microscopes.
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Affiliation(s)
- Pentti Somerharju
- Institute of Biomedicine, Biomedicum, Room C205b, Haartmaninkatu 8, P.O. Box 63, University of Helsinki, 00014 Helsinki, Finland.
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31
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Levi V, Rossi JPFC, Castello PR, González Flecha FL. Structural significance of the plasma membrane calcium pump oligomerization. Biophys J 2002; 82:437-46. [PMID: 11751330 PMCID: PMC1302483 DOI: 10.1016/s0006-3495(02)75408-8] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
Abstract
The oligomerization of the plasma membrane calcium pump (PMCA) in phospholipid/detergent micelles was evaluated using a combined spectroscopic and kinetic approach and related to the enzyme stability. Energy transfer between fluorescein-5'-isothiocyanate and eosin-5'-isothiocyanate attached to different PMCA molecules was used to determine the dissociation constant of dimeric PMCA (140 +/- 50 nM at 25 degrees C) and characterize the time course of dimerization. The enzyme thermal stability at different dimer/monomer ratios was evaluated, quantifying the kinetic coefficient of thermal inactivation. This coefficient decreases with PMCA concentration, becoming approximately constant beyond 300 nM. Thermal treatment leads to the formation of inactive monomers that associate only with native monomers. These mixed dimers are formed with a kinetic coefficient that is half that determined for the native dimers. We proposed a model for PMCA thermal inactivation that considers the equilibria among dimers, monomers, and mixed dimers, and the inactivation of the last two species through irreversible steps. The numerical resolution of the differential equations describing this model fitted to the experimental data allowed the determination of the model coefficients. This analysis shows that thermal inactivation occurs through the denaturation of the monomer, which lifetime is 25 min at 44 degrees C. The obtained results suggest that PMCA dimerization constitutes a mechanism of self protection against spontaneous denaturation.
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Affiliation(s)
- Valeria Levi
- Departamento de Química Biológica, Instituto de Quimica y Fisicoquimica Biologicas, Facultad de Farmacia y Bioquímica, Universidad de Buenos Aires, 1113 Buenos Aires, Argentina
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32
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Levi V, Rossi JP, Castello PR, González Flecha FL. Oligomerization of the plasma membrane calcium pump involves two regions with different thermal stability. FEBS Lett 2000; 483:99-103. [PMID: 11042261 DOI: 10.1016/s0014-5793(00)02093-7] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/17/2022]
Abstract
Ca(2+) pump dimerization was studied by using a combined approach of thermal denaturation and fluorescence resonance energy transfer. The measurement of calcium pump ability to dimerize after the unfolding of individual functional domains of the enzyme demonstrated the existence of two different regions involved in the self-association process. One of these regions is highly susceptible to thermal unfolding and was identified as the calmodulin (CaM)-binding domain. The other region whose thermal stability is higher than those of the catalytic and CaM-binding domains could be related with the previously found C28W-binding regions.
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Affiliation(s)
- V Levi
- Departamento de Química Biológica-IQUIFIB, Facultad de Farmacia y Bioquímica, Universidad de Buenos Aires, Junín 956, 1113 Buenos Aires, Argentina
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