1
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Dong Y, Li M, Kang L, Wang W, Li Z, Wang Y, Wu Z, Zhu C, Zhu L, Zheng X, Qian D, Dai H, Wu B, Zhao H, Wang J. A new preparation method of covalent annular nanodiscs based on MTGase. Arch Biochem Biophys 2024; 756:109997. [PMID: 38621443 DOI: 10.1016/j.abb.2024.109997] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/04/2023] [Revised: 03/11/2024] [Accepted: 04/12/2024] [Indexed: 04/17/2024]
Abstract
The preservation of the native conformation and functionality of membrane proteins has posed considerable challenges. While detergents and liposome reconstitution have been traditional approaches, nanodiscs (NDs) offer a promising solution by embedding membrane proteins in phospholipids encircled by an amphipathic helical protein MSP belt. Nevertheless, a drawback of commonly used NDs is their limited homogeneity and stability. In this study, we present a novel approach to construct covalent annular nanodiscs (cNDs) by leveraging microbial transglutaminase (MTGase) to catalyze isopeptide bond formation between the side chains of terminal amino acids, specifically Lysine (K) and Glutamine (Q). This methodology significantly enhances the homogeneity and stability of NDs. Characterization of cNDs and the assembly of membrane proteins within them validate the successful reconstitution of membrane proteins with improved homogeneity and stability. Our findings suggest that cNDs represent a more suitable tool for investigating interactions between membrane proteins and lipids, as well as for analyzing membrane protein structures.
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Affiliation(s)
- Yingkui Dong
- Institute of Physical Science and Information Technology, Anhui University, Hefei, Anhui, 230039, China; High Magnetic Field Laboratory, Key Laboratory of High Magnetic Field and Ion Beam Physical Biology, Hefei Institutes of Physical Science, Chinese Academy of Sciences, Hefei, Anhui, 230031, China
| | - Ming Li
- High Magnetic Field Laboratory, Key Laboratory of High Magnetic Field and Ion Beam Physical Biology, Hefei Institutes of Physical Science, Chinese Academy of Sciences, Hefei, Anhui, 230031, China; University of Science and Technology of China, Hefei, Anhui, 230026, China
| | - Li Kang
- Institute of Physical Science and Information Technology, Anhui University, Hefei, Anhui, 230039, China; High Magnetic Field Laboratory, Key Laboratory of High Magnetic Field and Ion Beam Physical Biology, Hefei Institutes of Physical Science, Chinese Academy of Sciences, Hefei, Anhui, 230031, China
| | - Wanxue Wang
- High Magnetic Field Laboratory, Key Laboratory of High Magnetic Field and Ion Beam Physical Biology, Hefei Institutes of Physical Science, Chinese Academy of Sciences, Hefei, Anhui, 230031, China; School of Basic Medical Sciences, Anhui Medical University, Hefei, Anhui, 230032, China
| | - Zehua Li
- High Magnetic Field Laboratory, Key Laboratory of High Magnetic Field and Ion Beam Physical Biology, Hefei Institutes of Physical Science, Chinese Academy of Sciences, Hefei, Anhui, 230031, China; University of Science and Technology of China, Hefei, Anhui, 230026, China
| | - Yizhuo Wang
- High Magnetic Field Laboratory, Key Laboratory of High Magnetic Field and Ion Beam Physical Biology, Hefei Institutes of Physical Science, Chinese Academy of Sciences, Hefei, Anhui, 230031, China; University of Science and Technology of China, Hefei, Anhui, 230026, China
| | - Ziwei Wu
- High Magnetic Field Laboratory, Key Laboratory of High Magnetic Field and Ion Beam Physical Biology, Hefei Institutes of Physical Science, Chinese Academy of Sciences, Hefei, Anhui, 230031, China; University of Science and Technology of China, Hefei, Anhui, 230026, China
| | - Chenchen Zhu
- High Magnetic Field Laboratory, Key Laboratory of High Magnetic Field and Ion Beam Physical Biology, Hefei Institutes of Physical Science, Chinese Academy of Sciences, Hefei, Anhui, 230031, China; University of Science and Technology of China, Hefei, Anhui, 230026, China
| | - Lei Zhu
- High Magnetic Field Laboratory, Key Laboratory of High Magnetic Field and Ion Beam Physical Biology, Hefei Institutes of Physical Science, Chinese Academy of Sciences, Hefei, Anhui, 230031, China
| | - Xinwei Zheng
- High Magnetic Field Laboratory, Key Laboratory of High Magnetic Field and Ion Beam Physical Biology, Hefei Institutes of Physical Science, Chinese Academy of Sciences, Hefei, Anhui, 230031, China
| | - Dongming Qian
- Hefei China Science Longwood Biological Technology Co., Ltd. Hefei, Anhui, 230088, China
| | - Han Dai
- High Magnetic Field Laboratory, Key Laboratory of High Magnetic Field and Ion Beam Physical Biology, Hefei Institutes of Physical Science, Chinese Academy of Sciences, Hefei, Anhui, 230031, China; Hefei China Science Longwood Biological Technology Co., Ltd. Hefei, Anhui, 230088, China
| | - Bo Wu
- High Magnetic Field Laboratory, Key Laboratory of High Magnetic Field and Ion Beam Physical Biology, Hefei Institutes of Physical Science, Chinese Academy of Sciences, Hefei, Anhui, 230031, China.
| | - Hongxin Zhao
- High Magnetic Field Laboratory, Key Laboratory of High Magnetic Field and Ion Beam Physical Biology, Hefei Institutes of Physical Science, Chinese Academy of Sciences, Hefei, Anhui, 230031, China; Hefei China Science Longwood Biological Technology Co., Ltd. Hefei, Anhui, 230088, China.
| | - Junfeng Wang
- Institute of Physical Science and Information Technology, Anhui University, Hefei, Anhui, 230039, China; High Magnetic Field Laboratory, Key Laboratory of High Magnetic Field and Ion Beam Physical Biology, Hefei Institutes of Physical Science, Chinese Academy of Sciences, Hefei, Anhui, 230031, China; University of Science and Technology of China, Hefei, Anhui, 230026, China.
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2
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Zhao C. Limitations in membrane protein structure determination by lipid nanodiscs. Trends Biochem Sci 2024; 49:475-476. [PMID: 38538407 DOI: 10.1016/j.tibs.2024.03.010] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/10/2024] [Revised: 03/18/2024] [Accepted: 03/19/2024] [Indexed: 06/09/2024]
Abstract
Lipid nanodiscs are popular mimetics of biological membranes for determining membrane protein structures. However, a recent study revealed that the choice of nanodisc scaffold directly influenced the structure of an ion channel. This finding prompts us to be cautious and calls for improved membrane mimetics for structure determination.
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Affiliation(s)
- Chen Zhao
- Department of Biochemistry and Molecular Biology, University of Florida, College of Medicine, Gainesville, FL 32611, USA.
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3
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Scheyer MW, Campbell C, William PL, Hussain M, Begum A, Fonseca SE, Asare IK, Dabney P, Dabney-Smith C, Lorigan GA, Sahu ID. Electron paramagnetic resonance spectroscopic characterization of the human KCNE3 protein in lipodisq nanoparticles for structural dynamics of membrane proteins. Biophys Chem 2023; 301:107080. [PMID: 37531799 DOI: 10.1016/j.bpc.2023.107080] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/25/2023] [Revised: 07/07/2023] [Accepted: 07/24/2023] [Indexed: 08/04/2023]
Abstract
One of the major challenges in solubilization of membrane proteins is to find the optimal physiological environment for their biophysical studies. EPR spectroscopy is a powerful biophysical technique for studying the structural and dynamic properties of macromolecules. However, the challenges in the membrane protein sample preparation and flexible motion of the spin label limit the utilization of EPR spectroscopy to a majority of membrane protein systems in a physiological membrane-bound state. Recently, lipodisq nanoparticles or styrene-maleic acid copolymer-lipid nanoparticles (SMALPs) have emerged as a membrane mimetic system for investigating the structural studies of membrane proteins. However, its detail characterization for membrane protein studies is still poorly understood. Recently, we characterized the potassium channel membrane protein KCNQ1 voltage sensing domain (KCNQ1-VSD) and KCNE1 reconstituted into lipodisq nanoparticles using EPR spectroscopy. In this study, the potassium channel accessory protein KCNE3 containing flexible N- and C-termini was encapsulated into proteoliposomes and lipodisq nanoparticles and characterized for studying its structural and dynamic properties using nitroxide based site-directed spin labeling EPR spectroscopy. CW-EPR lineshape analysis data indicated an increase in spectral line broadenings with the addition of the styrene-maleic acid (SMA) polymer which approaches close to the rigid limit providing a homogeneous stabilization of the protein-lipid complex. Similarly, EPR DEER measurements indicated an enhanced quality of distance measurements with an increase in the phase memory time (Tm) values upon incorporation of the sample into lipodisq nanoparticles, when compared to proteoliposomes. These results agree with the solution NMR structural structure of the KCNE3 and EPR studies of other membrane proteins in lipodisq nanoparticles. This study along with our earlier studies will provide the reference characterization data that will provide benefit to the membrane protein researchers for studying structural dynamics of challenging membrane proteins.
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Affiliation(s)
- Matthew W Scheyer
- Natural Science Division, Campbellsville University, Campbellsville, KY 42718, USA
| | - Conner Campbell
- Natural Science Division, Campbellsville University, Campbellsville, KY 42718, USA
| | - Patrick L William
- Natural Science Division, Campbellsville University, Campbellsville, KY 42718, USA
| | - Mustakim Hussain
- Natural Science Division, Campbellsville University, Campbellsville, KY 42718, USA
| | - Afsana Begum
- Natural Science Division, Campbellsville University, Campbellsville, KY 42718, USA
| | | | - Isaac K Asare
- Natural Science Division, Campbellsville University, Campbellsville, KY 42718, USA
| | - Peyton Dabney
- Natural Science Division, Campbellsville University, Campbellsville, KY 42718, USA
| | - Carole Dabney-Smith
- Department of Chemistry and Biochemistry, Miami University, Oxford, OH 45056, USA
| | - Gary A Lorigan
- Department of Chemistry and Biochemistry, Miami University, Oxford, OH 45056, USA
| | - Indra D Sahu
- Natural Science Division, Campbellsville University, Campbellsville, KY 42718, USA; Department of Chemistry and Biochemistry, Miami University, Oxford, OH 45056, USA.
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4
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Role of membrane mimetics on biophysical EPR studies of membrane proteins. BIOCHIMICA ET BIOPHYSICA ACTA. BIOMEMBRANES 2023; 1865:184138. [PMID: 36764474 DOI: 10.1016/j.bbamem.2023.184138] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/06/2022] [Revised: 02/01/2023] [Accepted: 02/03/2023] [Indexed: 02/11/2023]
Abstract
Biological membranes are essential in providing the stability of membrane proteins in a functional state. Functionally stable homogeneous sample is required for biophysical electron paramagnetic resonance (EPR) studies of membrane proteins for obtaining pertinent structural dynamics of the protein. Significant progresses have been made for the optimization of the suitable membrane environments required for biophysical EPR measurements. However, no universal membrane mimetic system is available that can solubilize all membrane proteins suitable for biophysical EPR studies while maintaining the functional integrity. Great efforts are needed to optimize the sample condition to obtain better EPR data quality of membrane proteins that can provide meaningful information on structural dynamics. In this mini-review, we will discuss important aspects of membrane mimetics for biophysical EPR measurements and current progress with some of the recent examples.
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5
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Johansen NT, Tidemand FG, Pedersen MC, Arleth L. Travel light: Essential packing for membrane proteins with an active lifestyle. Biochimie 2023; 205:3-26. [PMID: 35963461 DOI: 10.1016/j.biochi.2022.07.014] [Citation(s) in RCA: 5] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/06/2022] [Revised: 06/29/2022] [Accepted: 07/23/2022] [Indexed: 11/02/2022]
Abstract
We review the considerable progress during the recent decade in the endeavours of designing, optimising, and utilising carrier particle systems for structural and functional studies of membrane proteins in near-native environments. New and improved systems are constantly emerging, novel studies push the perceived limits of a given carrier system, and specific carrier systems consolidate and entrench themselves as the system of choice for particular classes of target membrane protein systems. This review covers the most frequently used carrier systems for such studies and emphasises similarities and differences between these systems as well as current trends and future directions for the field. Particular interest is devoted to the biophysical properties and membrane mimicking ability of each system and the manner in which this may impact an embedded membrane protein and an eventual structural or functional study.
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Affiliation(s)
- Nicolai Tidemand Johansen
- Section for Transport Biology, Department of Plant and Environmental Sciences, University of Copenhagen, Thorvaldsensvej 40, Frederiksberg C, 1871, Denmark.
| | - Frederik Grønbæk Tidemand
- Section for Transport Biology, Department of Plant and Environmental Sciences, University of Copenhagen, Thorvaldsensvej 40, Frederiksberg C, 1871, Denmark
| | - Martin Cramer Pedersen
- Condensed Matter Physics, Niels Bohr Institute, University of Copenhagen, Universitetsparken 5, Copenhagen E, 2100, Denmark
| | - Lise Arleth
- Condensed Matter Physics, Niels Bohr Institute, University of Copenhagen, Universitetsparken 5, Copenhagen E, 2100, Denmark
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6
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Dallo S, Shin J, Zhang S, Ren Q, Bao H. Designer Nanodiscs to Probe and Reprogram Membrane Biology in Synapses. J Mol Biol 2023; 435:167757. [PMID: 35872069 PMCID: PMC9805492 DOI: 10.1016/j.jmb.2022.167757] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/01/2022] [Revised: 07/17/2022] [Accepted: 07/18/2022] [Indexed: 02/04/2023]
Abstract
Signal transduction at the synapse is mediated by a variety of protein-lipid interactions, which are vital for the spatial and temporal regulation of synaptic vesicle biogenesis, neurotransmitter release, and postsynaptic receptor activation. Therefore, our understanding of synaptic transmission cannot be completed until the elucidation of these critical protein-lipid interactions. On this front, recent advances in nanodiscs have vastly expanded our ability to probe and reprogram membrane biology in synapses. Here, we summarize the progress of the nanodisc toolbox and discuss future directions in this exciting field.
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Affiliation(s)
- Sarah Dallo
- Department of Molecular Medicine, UF Scripps Biomedical Research, 130 Scripps Way, Jupiter 33458, FL, USA
| | - Jeehae Shin
- Department of Molecular Medicine, UF Scripps Biomedical Research, 130 Scripps Way, Jupiter 33458, FL, USA
| | - Shanwen Zhang
- Department of Molecular Medicine, UF Scripps Biomedical Research, 130 Scripps Way, Jupiter 33458, FL, USA
| | - Qian Ren
- Department of Molecular Medicine, UF Scripps Biomedical Research, 130 Scripps Way, Jupiter 33458, FL, USA
| | - Huan Bao
- Department of Molecular Medicine, UF Scripps Biomedical Research, 130 Scripps Way, Jupiter 33458, FL, USA.
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7
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Catania R, Machin J, Rappolt M, Muench SP, Beales PA, Jeuken LJC. Detergent-Free Functionalization of Hybrid Vesicles with Membrane Proteins Using SMALPs. Macromolecules 2022; 55:3415-3422. [PMID: 35571225 PMCID: PMC9097535 DOI: 10.1021/acs.macromol.2c00326] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/14/2022] [Revised: 04/08/2022] [Indexed: 11/28/2022]
Abstract
![]()
Hybrid
vesicles (HVs) that consist of mixtures of block copolymers
and lipids are robust biomimetics of liposomes, providing a valuable
building block in bionanotechnology, catalysis, and synthetic biology.
However, functionalization of HVs with membrane proteins remains laborious
and expensive, creating a significant current challenge in the field.
Here, using a new approach of extraction with styrene-maleic acid
(SMA), we show that a membrane protein (cytochrome bo3) directly transfers into HVs with an efficiency of 73.9
± 13.5% without the requirement of detergent, long incubation
times, or mechanical disruption. Direct transfer of membrane proteins
using this approach was not possible into liposomes, suggesting that
HVs are more amenable than liposomes to membrane protein incorporation
from a SMA lipid particle system. Finally, we show that this transfer
method is not limited to cytochrome bo3 and can also be performed with complex membrane protein mixtures.
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Affiliation(s)
- Rosa Catania
- Astbury Centre of Structural Molecular Biology, University of Leeds, Leeds LS2 9JT, U.K
- School of Biomedical Sciences, University of Leeds, Leeds LS2 9JT, U.K
| | - Jonathan Machin
- Astbury Centre of Structural Molecular Biology, University of Leeds, Leeds LS2 9JT, U.K
- School of Biomedical Sciences, University of Leeds, Leeds LS2 9JT, U.K
| | - Michael Rappolt
- School of Food Science and Nutrition, University of Leeds, Leeds LS2 9JT, U.K
| | - Stephen P. Muench
- Astbury Centre of Structural Molecular Biology, University of Leeds, Leeds LS2 9JT, U.K
- School of Biomedical Sciences, University of Leeds, Leeds LS2 9JT, U.K
| | - Paul A. Beales
- Astbury Centre of Structural Molecular Biology, University of Leeds, Leeds LS2 9JT, U.K
- School of Chemistry, University of Leeds, Leeds LS2 9JT, U.K
| | - Lars J. C. Jeuken
- Astbury Centre of Structural Molecular Biology, University of Leeds, Leeds LS2 9JT, U.K
- School of Biomedical Sciences, University of Leeds, Leeds LS2 9JT, U.K
- Leiden Institute of Chemistry, University Leiden, Leiden 2300RA, The Netherlands
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8
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Ravula T, Ramamoorthy A. Measurement of Residual Dipolar Couplings Using Magnetically Aligned and Flipped Nanodiscs. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2022; 38:244-252. [PMID: 34965145 PMCID: PMC9575995 DOI: 10.1021/acs.langmuir.1c02449] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/19/2023]
Abstract
Recent developments in lipid nanodisc technology have successfully overcome the major challenges in the structural and functional studies of membrane proteins and drug delivery. Among the different types of nanodiscs, the use of synthetic amphiphilic polymers created new directions including the applications of solution and solid-state NMR spectroscopy. The ability to magnetically align large-size (>20 nm diameter) polymer nanodiscs and flip them using paramagnetic lanthanide ions has enabled high-resolution studies on membrane proteins using solid-state NMR techniques. The use of polymer-based macro-nanodiscs (>20 nm diameter) as an alignment medium to measure residual dipolar couplings (RDCs) and residual quadrupole couplings by NMR experiments has also been demonstrated. In this study, we demonstrate the use of magnetically aligned and 90°-flipped polymer nanodiscs as alignment media for structural studies on proteins by solution NMR spectroscopy. These macro-nanodiscs, composed of negatively charged SMA-EA polymers and 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) lipids, were used to measure residual 1H-15N dipolar couplings (RDCs) from the water-soluble ∼21 kDa uniformly 15N-labeled flavin mononucleotide binding domain (FBD) of cytochrome-P450 reductase. The experimentally measured 1H-15N RDC values are compared with the values calculated from the crystal structures of cytochrome-P450 reductase that lacks the transmembrane domain. The N-H RDCs measured using aligned and 90°-flipped nanodiscs show a modulation by the function (3 cos2 θ - 1), where θ is the angle between the N-H bond vector and the applied magnetic field direction. This successful demonstration of the use of two orthogonally oriented alignment media should enable structural studies on a variety of systems including small molecules, DNA, and RNA.
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Affiliation(s)
- Thirupathi Ravula
- Biophysics and Department of Chemistry, Biomedical Engineering, Macromolecular Science and Engineering, The University of Michigan, Ann Arbor, MI 48109-1055, USA
- National Magnetic Resonance Facility at Madison, Department of Biochemistry, University of Wisconsin, Madison, WI 53706-1544, USA
| | - Ayyalusamy Ramamoorthy
- Biophysics and Department of Chemistry, Biomedical Engineering, Macromolecular Science and Engineering, The University of Michigan, Ann Arbor, MI 48109-1055, USA
- Corresponding author’s
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9
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Guo Y. Detergent-free systems for structural studies of membrane proteins. Biochem Soc Trans 2021; 49:1361-1374. [PMID: 34110369 PMCID: PMC8276625 DOI: 10.1042/bst20201080] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/03/2021] [Revised: 05/03/2021] [Accepted: 05/17/2021] [Indexed: 11/17/2022]
Abstract
Membrane proteins play vital roles in living organisms, serving as targets for most currently prescribed drugs. Membrane protein structural biology aims to provide accurate structural information to understand their mechanisms of action. The advance of membrane protein structural biology has primarily relied on detergent-based methods over the past several decades. However, detergent-based approaches have significant drawbacks because detergents often damage the native protein-lipid interactions, which are often crucial for maintaining the natural structure and function of membrane proteins. Detergent-free methods recently have emerged as alternatives with a great promise, e.g. for high-resolution structure determinations of membrane proteins in their native cell membrane lipid environments. This minireview critically examines the current status of detergent-free methods by a comparative analysis of five groups of membrane protein structures determined using detergent-free and detergent-based methods. This analysis reveals that current detergent-free systems, such as the styrene-maleic acid lipid particles (SMALP), the diisobutyl maleic acid lipid particles (DIBMALP), and the cycloalkane-modified amphiphile polymer (CyclAPol) technologies are not better than detergent-based approaches in terms of maintenance of native cell membrane lipids on the transmembrane domain and high-resolution structure determination. However, another detergent-free technology, the native cell membrane nanoparticles (NCMN) system, demonstrated improved maintenance of native cell membrane lipids with the studied membrane proteins, and produced particles that were suitable for high-resolution structural analysis. The ongoing development of new membrane-active polymers and their optimization will facilitate the maturation of these new detergent-free systems.
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Affiliation(s)
- Youzhong Guo
- Department of Medicinal Chemistry and Institute for Structural Biology, Drug Discovery and Development, Virginia Commonwealth University, Richmond, VA 23298-0540, USA
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10
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Ravula T, Dai X, Ramamoorthy A. Solid-State NMR Study to Probe the Effects of Divalent Metal Ions (Ca 2+ and Mg 2+) on the Magnetic Alignment of Polymer-Based Lipid Nanodiscs. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2021; 37:7780-7788. [PMID: 34129342 PMCID: PMC8587631 DOI: 10.1021/acs.langmuir.1c01018] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/29/2023]
Abstract
Divalent cations, especially Ca2+ and Mg2+, play a vital role in the function of biomolecules and making them important to be constituents in samples for in vitro biophysical and biochemical characterizations. Although lipid nanodiscs are becoming valuable tools for structural biology studies on membrane proteins and for drug delivery, most types of nanodiscs used in these studies are unstable in the presence of divalent metal ions. To avoid the interaction of divalent metal ions with the belt of the nanodiscs, synthetic polymers have been designed and demonstrated to form stable lipid nanodiscs under such unstable conditions. Such polymer-based nanodiscs have been shown to provide an ideal platform for structural studies using both solid-state and solution NMR spectroscopies because of the near-native cell-membrane environment they provide and the unique magnetic-alignment behavior of large-size nanodiscs. In this study, we report an investigation probing the effects of Ca2+ and Mg2+ ions on the formation of polymer-based lipid nanodiscs and the magnetic-alignment properties using a synthetic polymer, styrene maleimide quaternary ammonium (SMA-QA), and 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) lipids. Phosphorus-31 NMR experiments were used to evaluate the stability of the magnetic-alignment behavior of the nanodiscs for varying concentrations of Ca2+ or Mg2+ at different temperatures. It is remarkable that the interaction of divalent cations with lipid headgroups promotes the stacking up of nanodiscs that results in the enhanced magnetic alignment of nanodiscs. Interestingly, the reported results show that both the temperature and the concentration of divalent metal ions can be optimized to achieve the optimal alignment of nanodiscs in the presence of an applied magnetic field. We expect the reported results to be useful in the design of nanodisc-based nanoparticles for various applications in addition to atomic-resolution structural and dynamics studies using NMR and other biophysical techniques.
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Affiliation(s)
- Thirupathi Ravula
- Biophysics Program and Department of Chemistry, Biomedical Engineering, and Macromolecular Science and Engineering, The University of Michigan, Ann Arbor, MI 48109-1055, USA
| | - Xiaofeng Dai
- Biophysics Program and Department of Chemistry, Biomedical Engineering, and Macromolecular Science and Engineering, The University of Michigan, Ann Arbor, MI 48109-1055, USA
- Xiaofeng Dai was a visiting student from the College of Chemistry, Nankai University, Tianjin 300071, China
| | - Ayyalusamy Ramamoorthy
- Biophysics Program and Department of Chemistry, Biomedical Engineering, and Macromolecular Science and Engineering, The University of Michigan, Ann Arbor, MI 48109-1055, USA
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