1
|
Korn P, Schwieger C, Gruhle K, Garamus VM, Meister A, Ihling C, Drescher S. Azide- and diazirine-modified membrane lipids: Physicochemistry and applicability to study peptide/lipid interactions via cross-linking/mass spectrometry. BIOCHIMICA ET BIOPHYSICA ACTA. BIOMEMBRANES 2022; 1864:184004. [PMID: 35841926 DOI: 10.1016/j.bbamem.2022.184004] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/03/2022] [Revised: 07/06/2022] [Accepted: 07/07/2022] [Indexed: 06/15/2023]
Abstract
Although the incorporation of photo-activatable lipids into membranes potentially opens new avenues for studying interactions with peptides and proteins, the question of whether azide- or diazirine-modified lipids are suitable for such studies remains controversial. We have recently shown that diazirine-modified lipids can indeed form cross-links to membrane peptides after UV activation and that these cross-links can be precisely determined in their position by mass spectrometry (MS). However, we also observed an unexpected backfolding of the lipid's diazirine-containing stearoyl chain to the membrane interface challenging the potential application of this modified lipid for future cross-linking (XL)-MS studies of protein/lipid interactions. In this work, we compared an azide- (AzidoPC) and a diazirine-modified (DiazPC) membrane lipid regarding their self-assembly properties, their mixing behavior with saturated bilayer-forming phospholipids, and their reactivity upon UV activation using differential scanning calorimetry (DSC), dynamic light scattering (DLS), small-angle X-ray scattering (SAXS), transmission electron microscopy (TEM), and MS. Mixtures of both modified lipids with DMPC were further used for photo-chemically induced XL experiments with a transmembrane model peptide (KLAW23) to elucidate similarities and differences between the azide and the diazirine moiety. We showed that both photo-reactive lipids can be used to study lipid/peptide and lipid/protein interactions. The AzidoPC proved easier to handle, whereas the DiazPC had fewer degradation products and a higher cross-linking yield. However, the problem of backfolding occurs in both lipids; thus, it seems to be a general phenomenon.
Collapse
Affiliation(s)
- Patricia Korn
- Institute of Pharmacy-Pharmaceutical Chemistry and Bioanalytics, Charles Tanford Protein Center, Martin Luther University (MLU) Halle-Wittenberg, Kurt-Mothes-Str. 3a, 06120 Halle (Saale), Germany
| | - Christian Schwieger
- Institute of Chemistry, MLU Halle-Wittenberg, Von-Danckelmann-Platz 4, 06120 Halle (Saale), Germany
| | - Kai Gruhle
- Institute of Pharmacy-Pharmaceutical Chemistry and Bioanalytics, Charles Tanford Protein Center, Martin Luther University (MLU) Halle-Wittenberg, Kurt-Mothes-Str. 3a, 06120 Halle (Saale), Germany; Institute of Pharmacy-Biophysical Pharmacy, MLU Halle-Wittenberg, Wolfgang-Langenbeck-Str. 4, 06120 Halle (Saale), Germany
| | - Vasil M Garamus
- Helmholtz-Zentrum Hereon, Max-Planck-Str. 1, 21502 Geesthacht, Germany
| | - Annette Meister
- Interdisciplinary Research Center HALOmem, MLU Halle-Wittenberg, Charles Tanford Protein Center, Kurt-Mothes-Str. 3a, 06120 Halle (Saale), Germany; Institute of Biochemistry and Biotechnology-Physical Biotechnology, Charles Tanford Protein Center, MLU Halle-Wittenberg, Kurt-Mothes-Str. 3a, 06120 Halle (Saale), Germany
| | - Christian Ihling
- Institute of Pharmacy-Pharmaceutical Chemistry and Bioanalytics, Charles Tanford Protein Center, Martin Luther University (MLU) Halle-Wittenberg, Kurt-Mothes-Str. 3a, 06120 Halle (Saale), Germany; Center for Structural Mass Spectrometry, Kurt-Mothes-Str. 3, 06120 Halle (Saale), Germany
| | - Simon Drescher
- Institute of Pharmacy-Biophysical Pharmacy, MLU Halle-Wittenberg, Wolfgang-Langenbeck-Str. 4, 06120 Halle (Saale), Germany; Phospholipid Research Center, Im Neuenheimer Feld 515, 69120 Heidelberg, Germany.
| |
Collapse
|
2
|
Studying membrane proteins with MicroED. Biochem Soc Trans 2022; 50:231-239. [PMID: 35191473 PMCID: PMC9022970 DOI: 10.1042/bst20210911] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/07/2021] [Revised: 01/26/2022] [Accepted: 01/28/2022] [Indexed: 12/27/2022]
Abstract
The structural investigation of biological macromolecules is indispensable in understanding the molecular mechanisms underlying diseases. Several structural biology techniques have been introduced to unravel the structural facets of biomolecules. Among these, the electron cryomicroscopy (cryo-EM) method microcrystal electron diffraction (MicroED) has produced atomic resolution structures of important biological and small molecules. Since its inception in 2013, MicroED established a demonstrated ability for solving structures of difficult samples using vanishingly small crystals. However, membrane proteins remain the next big frontier for MicroED. The intrinsic properties of membrane proteins necessitate improved sample handling and imaging techniques to be developed and optimized for MicroED. Here, we summarize the milestones of electron crystallography of two-dimensional crystals leading to MicroED of three-dimensional crystals. Then, we focus on four different membrane protein families and discuss representatives from each family solved by MicroED.
Collapse
|
3
|
Dorner J, Korn P, Gruhle K, Ramsbeck D, Garamus VM, Lilie H, Meister A, Schwieger C, Ihling C, Sinz A, Drescher S. A Diazirine-Modified Membrane Lipid to Study Peptide/Lipid Interactions - Chances and Challenges. Chemistry 2021; 27:14586-14593. [PMID: 34406694 PMCID: PMC8597076 DOI: 10.1002/chem.202102048] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/10/2021] [Indexed: 01/19/2023]
Abstract
Although incorporation of photo‐activatable lipids into membranes potentially opens up novel avenues for investigating interactions with proteins, the question of whether diazirine‐modified lipids are suitable for such studies, remains under debate. Focusing on the potential for studying lipid/peptide interactions by cross‐linking mass spectrometry (XL‐MS), we developed a diazirine‐modified lipid (DiazPC), and examined its behaviour in membranes incorporating the model α‐helical peptide LAVA20. We observed an unexpected backfolding of the diazirine‐containing stearoyl chain of the lipid. This surprising behaviour challenges the potential application of DiazPC for future XL‐MS studies of peptide and protein/lipid interactions. The observations made for DiazPC most likely represent a general phenomenon for any type of membrane lipids with a polar moiety incorporated into the alkyl chain. Our finding is therefore of importance for future protein/lipid interaction studies relying on modified lipid probes.
Collapse
Affiliation(s)
- Julia Dorner
- Institute of Pharmacy-Pharmaceutical Chemistry and Bioanalytics, Martin Luther University (MLU) Halle-Wittenberg, Kurt-Mothes-Str. 3, 06120, Halle (Saale), Germany
| | - Patricia Korn
- Institute of Pharmacy-Pharmaceutical Chemistry and Bioanalytics, Martin Luther University (MLU) Halle-Wittenberg, Kurt-Mothes-Str. 3, 06120, Halle (Saale), Germany
| | - Kai Gruhle
- Institute of Pharmacy-Pharmaceutical Chemistry and Bioanalytics, Martin Luther University (MLU) Halle-Wittenberg, Kurt-Mothes-Str. 3, 06120, Halle (Saale), Germany.,Institute of Pharmacy-Biophysical Pharmacy, MLU Halle-Wittenberg, Wolfgang-Langenbeck-Str. 4, 06120, Halle (Saale), Germany
| | - Daniel Ramsbeck
- Fraunhofer Institute for Cell Therapy and Immunology IZI, Weinbergweg 22, 06120, Halle (Saale), Germany.,Institute of Pharmacy, University Leipzig, Brüderstr. 34, 04103, Leipzig, Germany
| | - Vasil M Garamus
- Helmholtz-Zentrum Hereon, Max-Planck-Str. 1, 21502, Geesthacht, Germany
| | - Hauke Lilie
- Institute for Biochemistry and Biotechnology-Technical Biochemistry, MLU Halle-Wittenberg, Kurt-Mothes-Str. 3, 06120, Halle (Saale), Germany
| | - Annette Meister
- Institute of Biochemistry and Biotechnology-Physical Biotechnology Charles Tanford Protein Center, MLU Halle-Wittenberg, Kurt-Mothes-Str. 3a, 06120, Halle (Saale), Germany.,Interdisciplinary Research Center HALOmem, MLU Halle-Wittenberg Charles Tanford Protein Center, Kurt-Mothes-Str. 3a, 06120, Halle (Saale), Germany
| | - Christian Schwieger
- Interdisciplinary Research Center HALOmem, MLU Halle-Wittenberg Charles Tanford Protein Center, Kurt-Mothes-Str. 3a, 06120, Halle (Saale), Germany
| | - Christian Ihling
- Institute of Pharmacy-Pharmaceutical Chemistry and Bioanalytics, Martin Luther University (MLU) Halle-Wittenberg, Kurt-Mothes-Str. 3, 06120, Halle (Saale), Germany.,Center for Structural Mass Spectrometry, Kurt-Mothes-Str. 3, 06120, Halle (Saale), Germany
| | - Andrea Sinz
- Institute of Pharmacy-Pharmaceutical Chemistry and Bioanalytics, Martin Luther University (MLU) Halle-Wittenberg, Kurt-Mothes-Str. 3, 06120, Halle (Saale), Germany.,Center for Structural Mass Spectrometry, Kurt-Mothes-Str. 3, 06120, Halle (Saale), Germany
| | - Simon Drescher
- Institute of Pharmacy-Biophysical Pharmacy, MLU Halle-Wittenberg, Wolfgang-Langenbeck-Str. 4, 06120, Halle (Saale), Germany.,Phospholipid Research Center, Im Neuenheimer Feld 515, 69120, Heidelberg, Germany
| |
Collapse
|
4
|
Majeed S, Ahmad AB, Sehar U, Georgieva ER. Lipid Membrane Mimetics in Functional and Structural Studies of Integral Membrane Proteins. MEMBRANES 2021; 11:685. [PMID: 34564502 PMCID: PMC8470526 DOI: 10.3390/membranes11090685] [Citation(s) in RCA: 29] [Impact Index Per Article: 9.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 07/27/2021] [Revised: 08/18/2021] [Accepted: 08/30/2021] [Indexed: 12/12/2022]
Abstract
Integral membrane proteins (IMPs) fulfill important physiological functions by providing cell-environment, cell-cell and virus-host communication; nutrients intake; export of toxic compounds out of cells; and more. However, some IMPs have obliterated functions due to polypeptide mutations, modifications in membrane properties and/or other environmental factors-resulting in damaged binding to ligands and the adoption of non-physiological conformations that prevent the protein from returning to its physiological state. Thus, elucidating IMPs' mechanisms of function and malfunction at the molecular level is important for enhancing our understanding of cell and organism physiology. This understanding also helps pharmaceutical developments for restoring or inhibiting protein activity. To this end, in vitro studies provide invaluable information about IMPs' structure and the relation between structural dynamics and function. Typically, these studies are conducted on transferred from native membranes to membrane-mimicking nano-platforms (membrane mimetics) purified IMPs. Here, we review the most widely used membrane mimetics in structural and functional studies of IMPs. These membrane mimetics are detergents, liposomes, bicelles, nanodiscs/Lipodisqs, amphipols, and lipidic cubic phases. We also discuss the protocols for IMPs reconstitution in membrane mimetics as well as the applicability of these membrane mimetic-IMP complexes in studies via a variety of biochemical, biophysical, and structural biology techniques.
Collapse
Affiliation(s)
- Saman Majeed
- Department of Chemistry and Biochemistry, Texas Tech University, Lubbock, TX 79409, USA
| | - Akram Bani Ahmad
- Department of Chemistry and Biochemistry, Texas Tech University, Lubbock, TX 79409, USA
| | - Ujala Sehar
- Department of Chemistry and Biochemistry, Texas Tech University, Lubbock, TX 79409, USA
| | - Elka R Georgieva
- Department of Chemistry and Biochemistry, Texas Tech University, Lubbock, TX 79409, USA
- Department of Cell Physiology and Molecular Biophysics, Texas Tech University Health Science Center, Lubbock, TX 79409, USA
| |
Collapse
|
5
|
Lindner S, Gruhle K, Schmidt R, Garamus VM, Ramsbeck D, Hause G, Meister A, Sinz A, Drescher S. Azide-Modified Membrane Lipids: Synthesis, Properties, and Reactivity. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2017; 33:4960-4973. [PMID: 28457130 DOI: 10.1021/acs.langmuir.7b00228] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
In the present work, we describe the synthesis and the temperature-dependent behavior of photoreactive membrane lipids as well as their capability to study peptide/lipid interactions. The modified phospholipids contain an azide group either in the middle part or at the end of an alkyl chain and also differ in the linkage (ester vs ether) of the second alkyl chain. The temperature-dependent aggregation behavior of the azidolipids was studied using differential scanning calorimetry (DSC), Fourier-transform infrared (FTIR) spectroscopy, and small-angle X-ray scattering (SAXS). Aggregate structures were visualized by stain and cryo transmission electron microscopy (TEM) and were further characterized by dynamic light scattering (DLS). We show that the position of the azide group and the type of linkage of the alkyl chain at the sn-2 position of the glycerol influences the type of aggregates formed as well as their long-term stability: P10AzSPC and r12AzSHPC show the formation of extrudable liposomes, which are stable in size during storage. In contrast, azidolipids that carry a terminal azido moiety either form extrudable liposomes, which show time-dependent vesicle fusion (P15AzPdPC), or self-assemble in large sheet-like, nonextrudable aggregates (r15AzPdHPC) where the lipid molecules are arranged in an interdigitated orientation at temperatures below Tm (LβI phase). Finally, a P10AzSPC:DMPC mixture was used for photochemically induced cross-linking experiments with a transmembrane peptide (WAL-peptide) to demonstrate the applicability of the azidolipids for the analysis of peptide/lipid interactions. The efficiency of photo-cross-linking was monitored by attenuated total reflection infrared (ATR-IR) spectroscopy and mass spectrometry (MS).
Collapse
Affiliation(s)
- Sindy Lindner
- Institute of Pharmacy - Pharmaceutical Chemistry and Bioanalytics, Martin Luther University (MLU) Halle-Wittenberg , Wolfgang-Langenbeck-Strasse 4, 06120 Halle (Saale), Germany
- Institute of Pharmacy - Biophysical Pharmacy, MLU Halle-Wittenberg , Wolfgang-Langenbeck-Strasse 4, 06120 Halle (Saale), Germany
| | - Kai Gruhle
- Institute of Pharmacy - Biophysical Pharmacy, MLU Halle-Wittenberg , Wolfgang-Langenbeck-Strasse 4, 06120 Halle (Saale), Germany
| | - Rico Schmidt
- Institute of Pharmacy - Pharmaceutical Chemistry and Bioanalytics, Martin Luther University (MLU) Halle-Wittenberg , Wolfgang-Langenbeck-Strasse 4, 06120 Halle (Saale), Germany
| | - Vasil M Garamus
- Helmholtz-Zentrum Geesthacht: Zentrum für Material und Küstenforschung GmbH (HZG), Max-Planck-Strasse 1, 21502 Geesthacht, Germany
| | - Daniel Ramsbeck
- Fraunhofer Institute for Cell Therapy and Immunology IZI , Weinbergweg 22, 06120 Halle (Saale), Germany
| | - Gerd Hause
- Biocenter, MLU Halle-Wittenberg , Weinbergweg 22, 06120 Halle (Saale), Germany
| | - Annette Meister
- Institute of Chemistry and Institute of Biochemistry and Biotechnology, MLU Halle-Wittenberg , von-Danckelmann-Platz 4, 06120 Halle (Saale), Germany
| | - Andrea Sinz
- Institute of Pharmacy - Pharmaceutical Chemistry and Bioanalytics, Martin Luther University (MLU) Halle-Wittenberg , Wolfgang-Langenbeck-Strasse 4, 06120 Halle (Saale), Germany
| | - Simon Drescher
- Institute of Pharmacy - Biophysical Pharmacy, MLU Halle-Wittenberg , Wolfgang-Langenbeck-Strasse 4, 06120 Halle (Saale), Germany
| |
Collapse
|
6
|
Stahlberg H, Biyani N, Engel A. 3D reconstruction of two-dimensional crystals. Arch Biochem Biophys 2015; 581:68-77. [PMID: 26093179 DOI: 10.1016/j.abb.2015.06.006] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/24/2015] [Revised: 06/08/2015] [Accepted: 06/11/2015] [Indexed: 02/02/2023]
Abstract
Electron crystallography of two-dimensional (2D) crystals determines the structure of membrane proteins in the lipid bilayer by imaging with cryo-electron microscopy and image processing. Membrane proteins can be packed in regular 2D arrays by their reconstitution in the presence of lipids at low lipid to protein weight-to-weight ratio. The crystal quality depends on the protein purity and homogeneity, its stability, and on the crystallization conditions. A 2D crystal presents the membrane protein in a functional and fully lipidated state. Electron crystallography determines the 3D structure even of small membrane proteins up to atomic resolution, but 3D density maps have a better resolution in the membrane plane than in the vertical direction. This problem can be partly eliminated by applying an iterative algorithm that exploits additional known constraints about the 2D crystal. 2D electron crystallography is particularly attractive for the structural analysis of membrane proteins that are too small for single particle analyses and too unstable to form 3D crystals. With the recent introduction of direct electron detector cameras, the routine determination of the atomic 3D structure of membrane-embedded membrane proteins is in reach.
Collapse
Affiliation(s)
- Henning Stahlberg
- Center for Cellular Imaging and NanoAnalytics, Biozentrum, University of Basel, Mattenstrasse 26, 4058 Basel, Switzerland
| | - Nikhil Biyani
- Center for Cellular Imaging and NanoAnalytics, Biozentrum, University of Basel, Mattenstrasse 26, 4058 Basel, Switzerland
| | - Andreas Engel
- Department of BioNanoscience, Delft University of Technology, Van der Waalsweg 8, 2628 CH Delft, The Netherlands; Department of Pharmacology, Case Western Reserve University, 10900 Euclid Avenue, Wood Bldg 321D, Cleveland, OH 44106-4965, USA.
| |
Collapse
|
7
|
Uddin YM, Schmidt-Krey I. Inducing two-dimensional crystallization of membrane proteins by dialysis for electron crystallography. Methods Enzymol 2015; 557:351-62. [PMID: 25950973 DOI: 10.1016/bs.mie.2014.12.022] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Electron crystallography is an electron cryo-microscopy (cryo-EM) method that is particularly suitable for structure-function studies of small membrane proteins, which are crystallized in two-dimensional (2D) arrays for subsequent cryo-EM data collection and image processing. This approach allows for structural analysis of membrane proteins in a close-to-native, phospholipid bilayer environment. The process of growing 2D crystals from purified membrane proteins by dialysis detergent removal is described in this chapter. A short section covers screening for and identifying 2D crystals by transmission electron microscopy, and in the last section, optimization of the purification to obtain crystals of higher quality is discussed.
Collapse
Affiliation(s)
- Yusuf M Uddin
- School of Biology, Georgia Institute of Technology, Atlanta, Georgia, USA
| | - Ingeborg Schmidt-Krey
- School of Biology, Georgia Institute of Technology, Atlanta, Georgia, USA; School of Chemistry and Biochemistry, Georgia Institute of Technology, Atlanta, Georgia, USA.
| |
Collapse
|
8
|
Lasala R, Coudray N, Abdine A, Zhang Z, Lopez-Redondo M, Kirshenbaum R, Alexopoulos J, Zolnai Z, Stokes DL, Ubarretxena-Belandia I. Sparse and incomplete factorial matrices to screen membrane protein 2D crystallization. J Struct Biol 2014; 189:123-34. [PMID: 25478971 DOI: 10.1016/j.jsb.2014.11.008] [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: 06/06/2014] [Revised: 11/18/2014] [Accepted: 11/24/2014] [Indexed: 01/09/2023]
Abstract
Electron crystallography is well suited for studying the structure of membrane proteins in their native lipid bilayer environment. This technique relies on electron cryomicroscopy of two-dimensional (2D) crystals, grown generally by reconstitution of purified membrane proteins into proteoliposomes under conditions favoring the formation of well-ordered lattices. Growing these crystals presents one of the major hurdles in the application of this technique. To identify conditions favoring crystallization a wide range of factors that can lead to a vast matrix of possible reagent combinations must be screened. However, in 2D crystallization these factors have traditionally been surveyed in a relatively limited fashion. To address this problem we carried out a detailed analysis of published 2D crystallization conditions for 12 β-barrel and 138 α-helical membrane proteins. From this analysis we identified the most successful conditions and applied them in the design of new sparse and incomplete factorial matrices to screen membrane protein 2D crystallization. Using these matrices we have run 19 crystallization screens for 16 different membrane proteins totaling over 1300 individual crystallization conditions. Six membrane proteins have yielded diffracting 2D crystals suitable for structure determination, indicating that these new matrices show promise to accelerate the success rate of membrane protein 2D crystallization.
Collapse
Affiliation(s)
- R Lasala
- New York Structural Biology Center, 89 Convent Avenue, New York, NY 10027, USA
| | - N Coudray
- New York Structural Biology Center, 89 Convent Avenue, New York, NY 10027, USA
| | - A Abdine
- Department of Structural and Chemical Biology, Icahn School of Medicine at Mount Sinai, 1425 Madison Avenue, New York, NY 10029, USA
| | - Z Zhang
- New York Structural Biology Center, 89 Convent Avenue, New York, NY 10027, USA
| | - M Lopez-Redondo
- Skirball Institute of Biomolecular Medicine and Department of Cell Biology, New York University School of Medicine, 540 First Avenue, New York, NY 10016, USA
| | - R Kirshenbaum
- Department of Structural and Chemical Biology, Icahn School of Medicine at Mount Sinai, 1425 Madison Avenue, New York, NY 10029, USA
| | - J Alexopoulos
- Skirball Institute of Biomolecular Medicine and Department of Cell Biology, New York University School of Medicine, 540 First Avenue, New York, NY 10016, USA
| | - Z Zolnai
- Department of Biochemistry, University of Wisconsin-Madison, 433 Babcock Drive, Madison, WI 53706, USA
| | - D L Stokes
- New York Structural Biology Center, 89 Convent Avenue, New York, NY 10027, USA; Skirball Institute of Biomolecular Medicine and Department of Cell Biology, New York University School of Medicine, 540 First Avenue, New York, NY 10016, USA
| | - I Ubarretxena-Belandia
- New York Structural Biology Center, 89 Convent Avenue, New York, NY 10027, USA; Department of Structural and Chemical Biology, Icahn School of Medicine at Mount Sinai, 1425 Madison Avenue, New York, NY 10029, USA.
| |
Collapse
|
9
|
Johnson MC, Schmidt-Krey I. Two-dimensional crystallization by dialysis for structural studies of membrane proteins by the cryo-EM method electron crystallography. Methods Cell Biol 2013; 113:325-37. [PMID: 23317909 DOI: 10.1016/b978-0-12-407239-8.00015-x] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/12/2023]
Abstract
Two-dimensional (2D) crystals of integral membrane proteins, comprising ordered protein reconstituted into a synthetic lipid bilayer, can be induced to form from detergent solubilized and purified membrane protein sources via the addition of exogenous lipid and the subsequent removal of the solubilizing detergent. This is most commonly accomplished by dialysis of a small volume of ternary protein-detergent-lipid mixture against a large volume of buffer, and can be carried out using common, easily available materials. Following successful crystallization, electron crystallographic data obtained by electron cryo-microscopy (cryo-EM) of vitrified 2D crystals can be used to determine the structure of the lipid bilayer-embedded integral membrane protein.
Collapse
Affiliation(s)
- Matthew C Johnson
- Georgia Institute of Technology, School of Biology, Atlanta, GA, USA
| | | |
Collapse
|
10
|
Abstract
Membrane proteins play a tremendously important role in cell physiology and serve as a target for an increasing number of drugs. Structural information is key to understanding their function and for developing new strategies for combating disease. However, the complex physical chemistry associated with membrane proteins has made them more difficult to study than their soluble cousins. Electron crystallography has historically been a successful method for solving membrane protein structures and has the advantage of providing a native lipid environment for these proteins. Specifically, when membrane proteins form two-dimensional arrays within a lipid bilayer, electron microscopy can be used to collect images and diffraction and the corresponding data can be combined to produce a three-dimensional reconstruction, which under favorable conditions can extend to atomic resolution. Like X-ray crystallography, the quality of the structures are very much dependent on the order and size of the crystals. However, unlike X-ray crystallography, high-throughput methods for screening crystallization trials for electron crystallography are not in general use. In this chapter, we describe two alternative methods for high-throughput screening of membrane protein crystallization within the lipid bilayer. The first method relies on the conventional use of dialysis for removing detergent and thus reconstituting the bilayer; an array of dialysis wells in the standard 96-well format allows the use of a liquid-handling robot and greatly increases throughput. The second method relies on titration of cyclodextrin as a chelating agent for detergent; a specialized pipetting robot has been designed not only to add cyclodextrin in a systematic way, but to use light scattering to monitor the reconstitution process. In addition, the use of liquid-handling robots for making negatively stained grids and methods for automatically imaging samples in the electron microscope are described.
Collapse
|