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This protocol describes an improved SERCA purification method, which includes the disaccharide trehalose in the final centrifugation step. This carbohydrate stabilizes proteins under harsh conditions. The purified SERCA was catalytically active and displayed high purity, making it suitable for structural and functional studies.
Some P-type ATPases, such as sarco/endoplasmic reticulum Ca2+-ATPase (SERCA), are inherently labile membrane proteins that require specific physicochemical conditions during purification to obtain them with high purity and structural quality and in a catalytically active form. The disaccharide trehalose is a compatible solute that is synthesized and accumulated in high concentrations in the yeast cytoplasm to stabilize the membranes and proteins. The use of trehalose as an additive in the protocol for the purification of plasma membrane H+-ATPase results in a high-quality preparation, the hexameric structure of which is shown by biochemical analytical methods. Trehalose can, therefore, be used as a stabilizing additive for the purification of membrane proteins (P-ATPases). This protocol describes the modification of the classical protocol for SERCA purification by subjecting SERCA to centrifugation on a trehalose concentration gradient. The inclusion of this carbohydrate led to the purification of SERCA in a catalytically active form with high purity and, importantly, in a stable form. Partial biochemical characterization of the purified SERCA (SDS-PAGE, enzyme kinetics, FITC labeling, circular dichroism spectroscopy) showed that the enzyme is suitable for functional and structural studies. The use of trehalose in the purification protocol of P-type ATPases and other labile membrane (and cytosolic) proteins is suggested.
Membrane proteins/enzymes are essential biological components of cells as they play critical roles in various processes1,2,3. Some of the functions may include transport of ions and molecules in and out of the cell/internal compartments (either active/passive), cell-cell recognition, intercellular binding, anchorage/attachment, and sensing of the external environment through integration with the signal transduction machinery under normal and harsh physical and chemical conditions (high salt, low water, high temperature, drug resistance, etc.)3 Therefore, the determination of the three-dimensional (3D) structure of membrane proteins and/or enzymes has become of great importance for both basic and applied research4,7,6. Importantly, membrane proteins/enzymes have been extensively used as targets for drug discovery (whether natural or by design)7,8,9. That is, membrane proteins have an inherent importance in health9,10,11.
The hydrophobic character of membrane proteins/enzymes is the most technically challenging physicochemical property for the experimental laboratory12,13,14, even more so when working with oligomeric and/or highly labile integral membrane proteins15,16. The isolation of appropriate amounts of the membrane protein/enzyme with the highest possible quality for functional experimental assays and structural studies is highly desirable17. Membrane proteins, being inherently hydrophobic, are very difficult to purify, and the choice of detergent is usually one of the most important issues to be considered17,18,19,20. In this regard, the laboratory methods used to isolate membrane proteins typically cause some degree of damage to the 3D structural arrangement of the protein21. Some of these methods include the use of (a) sonication (high frequency/energy ultrasonic waves), (b) protein-solubilizing detergents (either harsh, medium, or gentle)22, (c) relatively high pressures in column chromatography and high-speed ultracentrifugation23, (d) precipitating molecules, (e) digestive enzymes, and others21. All these processes can contribute to or be the main cause of protein destabilization during purification21. In this respect, some protocols seem to work relatively well for a given membrane protein. However, optimization is always welcome when using new modern assays or methods that require a higher quality of membrane protein preparation to obtain satisfactory results24. Optimization steps may include, but are not limited to, improving construct design, finding optimal conditions for membrane protein expression, establishing better handling conditions (i.e., pH, temperature, etc.), finding the best compatible detergent, adjusting purification steps such as sonication time, centrifugation speed, reformulating buffer solutions by adding stabilizing agents, etc.25,26,27. Therefore, any change in the purification methodology that leads to an increase in the quality (purity) and activity of the purified membrane protein/enzyme is important.
In the P-type ATPase family, the yeast plasma membrane H+-ATPase appears to be one of the most labile members28,29. The H+-ATPase loses its ATP hydrolyzing activity upon dehydration (freeze-drying), heat shock, etc.28,29. The use of trehalose as a protein stabilizer was tested in the isolation of the plasma membrane H+-ATPase from the yeast K. lactis30,31; the H+-ATPase preparation obtained was of high purity and catalytically active. Importantly, this allowed the oligomeric state of the enzyme to be resolved by biochemical methods, revealing it to be a hexamer and later confirmed by cryo-electron microscopy31,32,33,34,35. Therefore, it seems likely that the delicate three-dimensional (3D) arrangement of membrane proteins can be lost under relatively harsh conditions during purification36. Biphasic inactivation kinetic is observed for H+-ATPase during heat-mediated inactivation29. In yeast cells, as in many other organisms, the disaccharide trehalose accumulates at high concentrations under environmental stress conditions37,38,39. Trehalose maintains membrane integrity and transport function by stabilizing proteins (both membrane-embedded and cytosolic) and cell membranes40,41. The stabilizing mechanism of trehalose has been extensively studied by several groups and by our laboratory42,43,44,45. Experiments with the H+-ATPase and other enzymes have shown that trehalose is the most effective protein stabilizer among mono- and disaccharides28,29. This led to its inclusion in the H+-ATPase purification protocol30. Recently, trehalose has also been used in the purification of the sarcoplasmic reticulum Ca2+-ATPase (SERCA) from rabbit fast-twitch muscle with good results in protein purity and activity46. Therefore, trehalose seems to be a good and appropriate additive for the purification of P-type ATPases and probably other membrane and cytosolic proteins.
For P-ATPases, the existence of structural cytoplasmic domains is an experimental advantage, especially for substrate/ligand interaction studies47; ATP binding has been studied in highly pure recombinant N-domains47,48,49, thus eliminating the technical considerations for purification of whole membrane enzymes47,48,50, among others51. Unfortunately, some functional (catalytic/energy conversion) and structural (subunit arrangement and interaction with other proteins) studies still require the whole P-ATPase52,53. In this regard, the purification of SERCA has been achieved by several research groups54,55,56,57,58. However, improvements can still be implemented46, for example, increasing the intactness of the purified ATPase59, avoiding protein denaturation/disruption of protein complexes25, increase solubilization without denaturation of the membrane protein (i.e., avoiding formation of macromolecular aggregates)60, lead to better compatibility with assays and other downstream analytical methods61 Furthermore, as new experimental strategies, additives, enzyme inhibitors, etc. appear in the scientific literature61,62,63,64,65,66, they sometimes need to be tested with the whole P-ATPase. This work describes the protocol for the purification of SERCA and the use of trehalose as an additive to stabilize the protein structure and the ATPase activity; i.e., in addition to increasing the enzyme (structural) quality, trehalose helps to prevent the loss of enzyme structure and activity during enzyme isolation and storage, which helps to save biological material and thus reduce the number of enzyme purifications.
All animal procedures were performed in accordance with international and local (NORMA Oficial Mexicana NOM-062-ZOO-1999) guidelines for the handling of animals in experimental laboratories51,67,68. Muscle tissue was obtained from wild-type Oryctolagus cuniculus from a local animal handling unit (INE/CITES/DGVS-ZOO-E0055-SLP-98)46. A veterinarian with expertise in laboratory animal management performed the initial muscle dissection and processing. The details of the reagents and the equipment used in this study are listed in the Table of Materials.
1. Isolation of sarcoplasmic reticulum from fast-twitch rabbit muscle (Timing, 7 - 9 h)
NOTE: For details on the procedure, refer to Champeil et al.69.
2. SERCA purification (Timing, 18 - 20 h)
NOTE: For details on the procedure, refer to Rivera-Morán et al.46.
3. Assay for ATPase activity (Timing, 1 - 2 h)
4. Labeling assay of SERCA with Fluorescein Isothiocyanate (FITC ) (Timing, 30 - 45 min, only for FITC labeling)
NOTE: For details on the procedure, refer to54,75,76.
5. Circular dichroism (CD) spectra (Timing, 30 min)
NOTE: For details on the procedure, refer to11,77.
SDS-PAGE of SERCA at different stages of purification (Figure 1). The Coomassie blue-stained gel shows the enrichment of the SERCA protein band (apparent molecular weight >100 kDa) as the purification protocol progresses. The protein band corresponding to SERCA shows a purity of >90% after centrifugation on a trehalose concentration gradient. Plot of ATP hydrolysis rate versus ATP concentration (Figure 2A). Michaelis-Menten ATPase kinetic (hyper...
Most molecules and ions cannot freely cross the cell membranes, e.g., proton (H+) requires a membrane transporter in the plasma membrane of a variety of organisms and organelles such as mitochondria83,84. Cell membranes are selective, and the molecules and ions that cross the cell membranes are diverse, so several types of membrane proteins can be found in the cell, such as (a) ABC transporters, (b) ion channels, (c) membrane-bound ATPases, (d) SLC tra...
The author declares that he has no competing financial interests.
The author acknowledges the help of Edmundo Mata-Morales in editing the video, VM, Valentín de la Cruz-Torres in purifying the SRVs, Miguel A. Rivera-Moran in SERCA purification and analysis, and Juan C. Gonzalez-Castro, Franco E. Juarez, Alejandra Nevarez, Nicolas Rocha-Vizuet, and Jocelin I. Ramírez-Alonso in video production. No funds, grants, or other support were received to conduct this study.
Name | Company | Catalog Number | Comments |
ATP | Sigma-Aldrich Corp | A2383 | |
Azolectin from soybean | Sigma-Aldrich Corp | 44924 | |
Benchtop UV transilluminator | Cole-Parmer | EW-97623-08 | Dual intensity High setting is ideal for analytical documentation. Low setting reduces photonicking or photobleaching of gel samples while doing preparative work. |
CaCl2 • 2H2O | Sigma-Aldrich Corp | 223506 | |
Coolpix B500 camera | Nikon Corp | S210 | |
Coomassie brilliant blue G-250 | Bio-Rad | 1610406 | |
Dodecyl maltoside | Sigma-Aldrich Corp | D4641 | |
Ethylene glycol-bis(2-aminoethylether)-N,N,N′,N′-tetraacetic acid | Sigma-Aldrich Corp | E4378 | |
Ethylenediaminetetraacetic acid tetrasodium salt dihydrate | Sigma-Aldrich Corp | E6511 | |
Fluorescein isothiocyanate | Sigma-Aldrich Corp | F3651 | |
KCl | JT Baker | 7447-40-7 | |
MgCl2 • 6H2O | Sigma-Aldrich Corp | M9272 | |
MOPS | Sigma-Aldrich Corp | M1254 | |
NADH | Chem-Impex International Inc | 230 | |
N-tetradecyl-N,N- dimethyl-3-ammonium-1-propanesulfonate | Sigma-Aldrich Corp | D0431 | |
Phosphoenolpyruvate (PEP) | Chem-Impex International Inc | 9711 | |
Rabbit muscle lactate dehydrogenase | Roche | 10003557103 | |
Rabbit muscle pyruvate kinase | Sigma-Aldrich Corp | P1506 | |
Sodium deoxycholate | Sigma-Aldrich Corp | D6750 | |
Sodium dodecyl sulfate | Bio-Rad | 1610302 | |
Spectropolarimeter | Jasco Corp. | Jasco J1500 | |
Sucrose | Sigma-Aldrich Corp | 84100 | |
Trehalose | Sigma-Aldrich Corp | T0167 | Dihydrate |
Tris(hydroxymethyl)aminomethane hydrochloride | Sigma-Aldrich Corp | 857645 | |
Ultracentrifuge | Beckman | Optima XPN | |
UV/VIS spectrophotometer | Agilent Technologies | 8453 | The Agilent 8453 UV-Vis Spectrophotometer uses a photodiode array for simultaneous measurement of the complete ultra-violet to visible light spectrum |
WiseStir HS- 30E | Daihan Scientific Co. | DH.WOS01010 | Ideal for all disperging and homogenizing applications, designed for tissue grinders. |
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