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Puthenveetil R, Lee CJ, Banerjee A. Production of Recombinant Transmembrane Proteins from Mammalian Cells for Biochemical and Structural Analyses. ACTA ACUST UNITED AC 2021; 87:e106. [PMID: 32515556 DOI: 10.1002/cpcb.106] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
Eukaryotic integral membrane proteins are key components of various biological processes. Because they are implicated in multiple diseases, it is important to understand their mechanism of action by elucidating their structure and function. Complex technical challenges associated with the generation of recombinant membrane proteins severely impair our ability to understand them using structural and biochemical methods. Here, we provide a detailed procedure to address and mitigate difficulties involved in the large-scale heterologous overexpression and purification of eukaryotic membrane proteins using HEK293S GnTi- cells transduced with baculovirus. Two human proteins, hDHHC15 and hPORCN, are presented as examples, with step-by-step instructions for transient transfection and generation of baculoviruses, followed by overexpression and purification from HEK293S GnTi- cells. © 2020 Wiley Periodicals LLC. Basic Protocol 1: Small-scale protein expression in mammalian HEK293T cells Basic Protocol 2: Generation of baculovirus from Sf9 (insect) cells Alternate Protocol: Enumeration-free method for generating P2 viral stock Support Protocol 1: Small-scale transduction of HEK293T cells with P2 baculovirus Basic Protocol 3: Large-scale viral transduction of HEK293S GnTi- cells Support Protocol 2: Large-scale membrane preparation from HEK293S GnTi- cells Basic Protocol 4: Large-scale purification of membrane proteins from HEK293S GnTi- cells.
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Affiliation(s)
- Robbins Puthenveetil
- Unit on Structural and Chemical Biology of Membrane Proteins, Neurosciences and Cellular and Structural Biology Division (NCSBD), Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD), National Institutes of Health (NIH), Bethesda, Maryland
| | - Chul-Jin Lee
- Unit on Structural and Chemical Biology of Membrane Proteins, Neurosciences and Cellular and Structural Biology Division (NCSBD), Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD), National Institutes of Health (NIH), Bethesda, Maryland
| | - Anirban Banerjee
- Unit on Structural and Chemical Biology of Membrane Proteins, Neurosciences and Cellular and Structural Biology Division (NCSBD), Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD), National Institutes of Health (NIH), Bethesda, Maryland
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2
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Kielkopf CL, Bauer W, Urbatsch IL. Expressing Cloned Genes for Protein Production, Purification, and Analysis. Cold Spring Harb Protoc 2021; 2021:pdb.top102129. [PMID: 33272973 DOI: 10.1101/pdb.top102129] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
Obtaining high quantities of a specific protein directly from native sources is often challenging, particularly when dealing with human proteins. To overcome this obstacle, many researchers take advantage of heterologous expression systems by cloning genes into artificial vectors designed to operate within easily cultured cells, such as Escherichia coli, Pichia pastoris (yeast), and several varieties of insect and mammalian cells. Heterologous expression systems also allow for easy modification of the protein to optimize expression, mutational analysis of specific sites within the protein and facilitate their purification with engineered affinity tags. Some degree of purification of the target protein is usually required for functional analysis. Purification to near homogeneity is essential for characterization of protein structure by X-ray crystallography or nuclear magnetic resonance (NMR) and characterization of the biochemical and biophysical properties of a protein, because contaminating proteins almost always adversely affect the results. Methods for producing and purifying proteins in several different expression platforms and using a variety of vectors are introduced here.
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3
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Kielkopf CL, Bauer W, Urbatsch IL. Expression of Cloned Genes in Pichia pastoris Using the Methanol-Inducible Promoter AOX1. Cold Spring Harb Protoc 2021; 2021:2021/1/pdb.prot102160. [PMID: 33397779 DOI: 10.1101/pdb.prot102160] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
Abstract
Pichia pastoris is a methylotrophic yeast capable of metabolizing methanol as its sole carbon source. Growth in methanol-containing medium results in dramatic induction of genes in the alcohol oxidation pathway including alcohol oxidase (AOX), formaldehyde dehydrogenase (FLD), and dihydroxyacetone synthase (DHAS). These proteins may comprise up to 30% of the biomass. Investigators have exploited these methanol-dependent genes to generate tightly regulated expression vectors. Most Pichia vectors use the strong and tightly regulated AOX1 promoter to drive heterologous protein expression. Obtaining integrated Pichia transformants requires more DNA than transformations into Saccharomyces cerevisiae, where the gene is expressed from episomal plasmids; however, transformants are extremely stable and can be stored for many years.
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Matthies D, Bae C, Toombes GE, Fox T, Bartesaghi A, Subramaniam S, Swartz KJ. Single-particle cryo-EM structure of a voltage-activated potassium channel in lipid nanodiscs. eLife 2018; 7:37558. [PMID: 30109985 PMCID: PMC6093707 DOI: 10.7554/elife.37558] [Citation(s) in RCA: 69] [Impact Index Per Article: 11.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/13/2018] [Accepted: 07/31/2018] [Indexed: 12/17/2022] Open
Abstract
Voltage-activated potassium (Kv) channels open to conduct K+ ions in response to membrane depolarization, and subsequently enter non-conducting states through distinct mechanisms of inactivation. X-ray structures of detergent-solubilized Kv channels appear to have captured an open state even though a non-conducting C-type inactivated state would predominate in membranes in the absence of a transmembrane voltage. However, structures for a voltage-activated ion channel in a lipid bilayer environment have not yet been reported. Here we report the structure of the Kv1.2-2.1 paddle chimera channel reconstituted into lipid nanodiscs using single-particle cryo-electron microscopy. At a resolution of ~3 Å for the cytosolic domain and ~4 Å for the transmembrane domain, the structure determined in nanodiscs is similar to the previously determined X-ray structure. Our findings show that large differences in structure between detergent and lipid bilayer environments are unlikely, and enable us to propose possible structural mechanisms for C-type inactivation.
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Affiliation(s)
- Doreen Matthies
- Laboratory of Cell Biology, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Bethesda, United States
| | - Chanhyung Bae
- Molecular Physiology and Biophysics Section, Porter Neuroscience Research Center, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, United States
| | - Gilman Es Toombes
- Molecular Physiology and Biophysics Section, Porter Neuroscience Research Center, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, United States
| | - Tara Fox
- Center for Molecular Microscopy, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Bethesda, United States.,Cancer Research Technology Program, Frederick National Laboratory for Cancer Research, Frederick, United States
| | - Alberto Bartesaghi
- Laboratory of Cell Biology, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Bethesda, United States
| | - Sriram Subramaniam
- Laboratory of Cell Biology, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Bethesda, United States
| | - Kenton Jon Swartz
- Molecular Physiology and Biophysics Section, Porter Neuroscience Research Center, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, United States
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Shenkarev ZO, Karlova MG, Kulbatskii DS, Kirpichnikov MP, Lyukmanova EN, Sokolova OS. Recombinant Production, Reconstruction in Lipid-Protein Nanodiscs, and Electron Microscopy of Full-Length α-Subunit of Human Potassium Channel Kv7.1. BIOCHEMISTRY (MOSCOW) 2018; 83:562-573. [PMID: 29738690 DOI: 10.1134/s0006297918050097] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
Voltage-gated potassium channel Kv7.1 plays an important role in the excitability of cardiac muscle. The α-subunit of Kv7.1 (KCNQ1) is the main structural element of this channel. Tetramerization of KCNQ1 in the membrane results in formation of an ion channel, which comprises a pore and four voltage-sensing domains. Mutations in the human KCNQ1 gene are one of the major causes of inherited arrhythmias, long QT syndrome in particular. The construct encoding full-length human KCNQ1 protein was synthesized in this work, and an expression system in the Pichia pastoris yeast cells was developed. The membrane fraction of the yeast cells containing the recombinant protein (rKCNQ1) was solubilized with CHAPS detergent. To better mimic the lipid environment of the channel, lipid-protein nanodiscs were formed using solubilized membrane fraction and MSP2N2 protein. The rKCNQ1/nanodisc and rKCNQ1/CHAPS samples were purified using the Rho1D4 tag introduced at the C-terminus of the protein. Protein samples were examined using transmission electron microscopy with negative staining. In both cases, homogeneous rKCNQ1 samples were observed based on image analysis. Statistical analysis of the images of individual protein particles solubilized in the detergent revealed the presence of a tetrameric structure confirming intact subunit assembly. A three-dimensional channel structure reconstructed at 2.5-nm resolution represents a compact density with diameter of the membrane part of ~9 nm and height ~11 nm. Analysis of the images of rKCNQ1 in nanodiscs revealed additional electron density corresponding to the lipid bilayer fragment and the MSP2N2 protein. These results indicate that the nanodiscs facilitate protein isolation, purification, and stabilization in solution and can be used for further structural studies of human Kv7.1.
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Affiliation(s)
- Z O Shenkarev
- Shemyakin-Ovchinnikov Institute of Bioorganic Chemistry, Russian Academy of Sciences, Moscow, 117997, Russia.
| | - M G Karlova
- Shemyakin-Ovchinnikov Institute of Bioorganic Chemistry, Russian Academy of Sciences, Moscow, 117997, Russia.,Lomonosov Moscow State University, Faculty of Biology, Moscow, 119991, Russia
| | - D S Kulbatskii
- Shemyakin-Ovchinnikov Institute of Bioorganic Chemistry, Russian Academy of Sciences, Moscow, 117997, Russia.,Lomonosov Moscow State University, Faculty of Biology, Moscow, 119991, Russia
| | - M P Kirpichnikov
- Shemyakin-Ovchinnikov Institute of Bioorganic Chemistry, Russian Academy of Sciences, Moscow, 117997, Russia.,Lomonosov Moscow State University, Faculty of Biology, Moscow, 119991, Russia
| | - E N Lyukmanova
- Shemyakin-Ovchinnikov Institute of Bioorganic Chemistry, Russian Academy of Sciences, Moscow, 117997, Russia.,Lomonosov Moscow State University, Faculty of Biology, Moscow, 119991, Russia
| | - O S Sokolova
- Lomonosov Moscow State University, Faculty of Biology, Moscow, 119991, Russia.
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Two-Dimensional Crystallization Procedure, from Protein Expression to Sample Preparation. BIOMED RESEARCH INTERNATIONAL 2015; 2015:693869. [PMID: 26413539 PMCID: PMC4564634 DOI: 10.1155/2015/693869] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 05/04/2015] [Accepted: 07/02/2015] [Indexed: 11/18/2022]
Abstract
Membrane proteins play important roles for living cells. Structural studies of membrane proteins provide deeper understanding of their mechanisms and further aid in drug design. As compared to other methods, electron microscopy is uniquely suitable for analysis of a broad range of specimens, from small proteins to large complexes. Of various electron microscopic methods, electron crystallography is particularly well-suited to study membrane proteins which are reconstituted into two-dimensional crystals in lipid environments. In this review, we discuss the steps and parameters for obtaining large and well-ordered two-dimensional crystals. A general description of the principle in each step is provided since this information can also be applied to other biochemical and biophysical methods. The examples are taken from our own studies and published results with related proteins. Our purpose is to give readers a more general idea of electron crystallography and to share our experiences in obtaining suitable crystals for data collection.
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Dhillon MS, Cockcroft CJ, Munsey T, Smith KJ, Powell AJ, Carter P, Wrighton DC, Rong HL, Yusaf SP, Sivaprasadarao A. A functional Kv1.2-hERG chimaeric channel expressed in Pichia pastoris. Sci Rep 2014; 4:4201. [PMID: 24569544 PMCID: PMC3935203 DOI: 10.1038/srep04201] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/09/2013] [Accepted: 02/07/2014] [Indexed: 12/29/2022] Open
Abstract
Members of the six-transmembrane segment family of ion channels share a common structural design. However, there are sequence differences between the members that confer distinct biophysical properties on individual channels. Currently, we do not have 3D structures for all members of the family to help explain the molecular basis for the differences in their biophysical properties and pharmacology. This is due to low-level expression of many members in native or heterologous systems. One exception is rat Kv1.2 which has been overexpressed in Pichia pastoris and crystallised. Here, we tested chimaeras of rat Kv1.2 with the hERG channel for function in Xenopus oocytes and for overexpression in Pichia. Chimaera containing the S1-S6 transmembrane region of HERG showed functional and pharmacological properties similar to hERG and could be overexpressed and purified from Pichia. Our results demonstrate that rat Kv1.2 could serve as a surrogate to express difficult-to-overexpress members of the six-transmembrane segment channel family.
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Affiliation(s)
| | | | - Tim Munsey
- School of Biomedical Sciences, Faculty of Biological Sciences
| | - Kathrine J Smith
- GlaxoSmithKline, Gunnels Wood Road, Stevenage, Hertfordshire, SG1 2NY, UK
| | - Andrew J Powell
- GlaxoSmithKline, Gunnels Wood Road, Stevenage, Hertfordshire, SG1 2NY, UK
| | - Paul Carter
- GlaxoSmithKline, Gunnels Wood Road, Stevenage, Hertfordshire, SG1 2NY, UK
| | | | - Hong-lin Rong
- School of Biomedical Sciences, Faculty of Biological Sciences
| | - Shahnaz P Yusaf
- GlaxoSmithKline, Gunnels Wood Road, Stevenage, Hertfordshire, SG1 2NY, UK
| | - Asipu Sivaprasadarao
- 1] School of Biomedical Sciences, Faculty of Biological Sciences [2] Multidisciplinary Cardiovascular Research Centre, University of Leeds, LS2 9JT, Leeds, U.K
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Sengottaiyan P, Ruiz-Pavón L, Persson BL. Functional expression, purification and reconstitution of the recombinant phosphate transporter Pho89 of Saccharomyces cerevisiae. FEBS J 2013; 280:965-75. [PMID: 23216645 PMCID: PMC3633241 DOI: 10.1111/febs.12090] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2012] [Revised: 11/06/2012] [Accepted: 12/05/2012] [Indexed: 11/30/2022]
Abstract
The Saccharomyces cerevisiae high-affinity phosphate transporter Pho89 is a member of the inorganic phosphate (Pi) transporter (PiT) family, and shares significant homology with the type III Na(+)/Pi symporters, hPit1 and hPit2. Currently, detailed biochemical and biophysical analyses of Pho89 to better understand its transport mechanisms are limited, owing to the lack of purified Pho89 in an active form. In the present study, we expressed functional Pho89 in the cell membrane of Pichia pastoris, solubilized it in Triton X-100 and foscholine-12, and purified it by immobilized nickel affinity chromatography combined with size exclusion chromatography. The protein eluted as an oligomer on the gel filtration column, and SDS/PAGE followed by western blotting analysis revealed that the protein appeared as bands of approximately 63, 140 and 520 kDa, corresponding to the monomeric, dimeric and oligomeric masses of the protein, respectively. Proteoliposomes containing purified and reconstituted Pho89 showed Na(+)-dependent Pi transport activity driven by an artificially imposed electrochemical Na(+) gradient. This implies that Pho89 operates as a symporter. Moreover, its activity is sensitive to the Na(+) ionophore monensin. To our knowledge, this study represents the first report on the functional reconstitution of a Pi-coupled PiT family member.
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Barros F, Domínguez P, de la Peña P. Cytoplasmic domains and voltage-dependent potassium channel gating. Front Pharmacol 2012; 3:49. [PMID: 22470342 PMCID: PMC3311039 DOI: 10.3389/fphar.2012.00049] [Citation(s) in RCA: 38] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/24/2011] [Accepted: 03/05/2012] [Indexed: 12/20/2022] Open
Abstract
The basic architecture of the voltage-dependent K+ channels (Kv channels) corresponds to a transmembrane protein core in which the permeation pore, the voltage-sensing components and the gating machinery (cytoplasmic facing gate and sensor–gate coupler) reside. Usually, large protein tails are attached to this core, hanging toward the inside of the cell. These cytoplasmic regions are essential for normal channel function and, due to their accessibility to the cytoplasmic environment, constitute obvious targets for cell-physiological control of channel behavior. Here we review the present knowledge about the molecular organization of these intracellular channel regions and their role in both setting and controlling Kv voltage-dependent gating properties. This includes the influence that they exert on Kv rapid/N-type inactivation and on activation/deactivation gating of Shaker-like and eag-type Kv channels. Some illustrative examples about the relevance of these cytoplasmic domains determining the possibilities for modulation of Kv channel gating by cellular components are also considered.
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Affiliation(s)
- Francisco Barros
- Departamento de Bioquímica y Biología Molecular, Universidad de Oviedo Oviedo, Asturias, Spain
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10
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Bornert O, Alkhalfioui F, Logez C, Wagner R. Overexpression of Membrane Proteins Using
Pichia pastoris. ACTA ACUST UNITED AC 2012; Chapter 29:29.2.1-29.2.24. [DOI: 10.1002/0471140864.ps2902s67] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Affiliation(s)
- Olivier Bornert
- Institut de Recherche de l'Ecole de Biotechnologie de Strasbourg, University of Strasbourg—CNRS Illkirch France
| | - Fatima Alkhalfioui
- Institut de Recherche de l'Ecole de Biotechnologie de Strasbourg, University of Strasbourg—CNRS Illkirch France
| | - Christel Logez
- Institut de Recherche de l'Ecole de Biotechnologie de Strasbourg, University of Strasbourg—CNRS Illkirch France
| | - Renaud Wagner
- Institut de Recherche de l'Ecole de Biotechnologie de Strasbourg, University of Strasbourg—CNRS Illkirch France
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11
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Ramón A, Marín M. Advances in the production of membrane proteins in Pichia pastoris. Biotechnol J 2011; 6:700-6. [DOI: 10.1002/biot.201100146] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/04/2011] [Revised: 03/24/2011] [Accepted: 03/31/2011] [Indexed: 11/07/2022]
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Nordén K, Agemark M, Danielson JÅH, Alexandersson E, Kjellbom P, Johanson U. Increasing gene dosage greatly enhances recombinant expression of aquaporins in Pichia pastoris. BMC Biotechnol 2011; 11:47. [PMID: 21569231 PMCID: PMC3118338 DOI: 10.1186/1472-6750-11-47] [Citation(s) in RCA: 78] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/02/2010] [Accepted: 05/10/2011] [Indexed: 02/03/2023] Open
Abstract
Background When performing functional and structural studies, large quantities of pure protein are desired. Most membrane proteins are however not abundantly expressed in their native tissues, which in general rules out purification from natural sources. Heterologous expression, especially of eukaryotic membrane proteins, has also proven to be challenging. The development of expression systems in insect cells and yeasts has resulted in an increase in successful overexpression of eukaryotic proteins. High yields of membrane protein from such hosts are however not guaranteed and several, to a large extent unexplored, factors may influence recombinant expression levels. In this report we have used four isoforms of aquaporins to systematically investigate parameters that may affect protein yield when overexpressing membrane proteins in the yeast Pichia pastoris. Results By comparing clones carrying a single gene copy, we show a remarkable variation in recombinant protein expression between isoforms and that the poor expression observed for one of the isoforms could only in part be explained by reduced transcript levels. Furthermore, we show that heterologous expression levels of all four aquaporin isoforms strongly respond to an increase in recombinant gene dosage, independent of the amount of protein expressed from a single gene copy. We also demonstrate that the increased expression does not appear to compromise the protein folding and the membrane localisation. Conclusions We report a convenient and robust method based on qPCR to determine recombinant gene dosage. The method is generic for all constructs based on the pPICZ vectors and offers an inexpensive, quick and reliable means of characterising recombinant P. pastoris clones. By using this method we show that: (1) heterologous expression of all aquaporins investigated respond strongly to an increase in recombinant gene dosage (2) expression from a single recombinant gene copy varies in an isoform dependent manner (3) the poor expression observed for AtSIP1;1 is mainly caused by posttranscriptional limitations. The protein folding and membrane localisation seems to be unaffected by increased expression levels. Thus a screen for elevated gene dosage can routinely be performed for identification of P. pastoris clones with high expression levels of aquaporins and other classes of membrane proteins.
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Affiliation(s)
- Kristina Nordén
- Department of Biochemistry and Structural Biology, Center for Molecular Protein Science, Lund University, PO Box 124, S-221 00 Lund, Sweden.
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Oxidation of NADPH on Kvbeta1 inhibits ball-and-chain type inactivation by restraining the chain. Proc Natl Acad Sci U S A 2011; 108:5885-90. [PMID: 21436029 DOI: 10.1073/pnas.1100316108] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
The Kv1 family voltage-dependent K(+) channels assemble with cytosolic β subunits (Kvβ), which are composed of a flexible N terminus followed by a structured core domain. The N terminus of certain Kvβs inactivates the channel by blocking the ion conduction pore, and the core domain is a functional enzyme that uses NADPH as a cofactor. Oxidation of the Kvβ-bound NADPH inhibits inactivation and potentiates channel current, but the mechanism behind this effect is unknown. Here we show that after oxidation, the core domain binds to part of the N terminus, thus restraining it from blocking the channel. The interaction is partially mediated by two negatively charged residues on the core domain and three positively charged ones on the N terminus. These results provide a molecular basis for the coupling between the cellular redox state and channel activity, and establish Kvβ as a target for pharmacological control of Kv1 channels.
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Functional and structural studies of TRP channels heterologously expressed in budding yeast. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2011; 704:25-40. [PMID: 21290288 DOI: 10.1007/978-94-007-0265-3_2] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
The transient receptor potential (TRP) superfamily is one of the largest families of cation channels. The metazoan TRP family has been subdivided into major branches: TRPC, TRPA, TRPM, TRPP, TRPV, TRPML, and TRPN, while the TRPY family is found in fungi. They are involved in many physiological processes and in the pathogenesis of various disorders. An efficient high-yield expression system for TRP channels is a necessary step towards biophysical and biochemical characterization and structural analysis of these proteins, and the budding yeast, Saccharomyces cerevisiae has proven to be very useful for this purpose. In addition, genetic screens in this organism can be carried out rapidly to identify amino acid residues important for function and to generate useful mutants. Here we present an overview of current developments towards understanding TRP channel function and structure using Saccharomyces cerevisiae as an expression system. In addition, we will summarize recent progress in understanding gating mechanisms of TRP channels using endogenously expressing TRPY channels in S. cerevisiae, and insights gained from genetic screens for mutants in mammalian channels. The discussion will focus particular attention of the use of cryo-electron microscopy (cryo-EM) to determine TRP channel structure, and outlines a "divide and concur" methodology for combining high resolution structures of TRP channel domains determined by X-ray crystallography with lower resolution techniques including cryo-EM and spectroscopy.
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15
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Mio K, Maruyama Y, Ogura T, Kawata M, Moriya T, Mio M, Sato C. Single particle reconstruction of membrane proteins: A tool for understanding the 3D structure of disease-related macromolecules. PROGRESS IN BIOPHYSICS AND MOLECULAR BIOLOGY 2010; 103:122-30. [DOI: 10.1016/j.pbiomolbio.2010.03.001] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/21/2009] [Revised: 02/06/2010] [Accepted: 03/07/2010] [Indexed: 11/28/2022]
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16
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Freigassner M, Pichler H, Glieder A. Tuning microbial hosts for membrane protein production. Microb Cell Fact 2009; 8:69. [PMID: 20040113 PMCID: PMC2807855 DOI: 10.1186/1475-2859-8-69] [Citation(s) in RCA: 63] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/15/2009] [Accepted: 12/29/2009] [Indexed: 12/22/2022] Open
Abstract
The last four years have brought exciting progress in membrane protein research. Finally those many efforts that have been put into expression of eukaryotic membrane proteins are coming to fruition and enable to solve an ever-growing number of high resolution structures. In the past, many skilful optimization steps were required to achieve sufficient expression of functional membrane proteins. Optimization was performed individually for every membrane protein, but provided insight about commonly encountered bottlenecks and, more importantly, general guidelines how to alleviate cellular limitations during microbial membrane protein expression. Lately, system-wide analyses are emerging as powerful means to decipher cellular bottlenecks during heterologous protein production and their use in microbial membrane protein expression has grown in popularity during the past months. This review covers the most prominent solutions and pitfalls in expression of eukaryotic membrane proteins using microbial hosts (prokaryotes, yeasts), highlights skilful applications of our basic understanding to improve membrane protein production. Omics technologies provide new concepts to engineer microbial hosts for membrane protein production.
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Affiliation(s)
- Maria Freigassner
- Institute of Molecular Biotechnology, Graz University of Technology, Petersgasse 14, 8010 Graz, Austria.
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Korepanova A, Pereda-Lopez A, Solomon LR, Walter KA, Lake MR, Bianchi BR, McDonald HA, Neelands TR, Shen J, Matayoshi ED, Moreland RB, Chiu ML. Expression and purification of human TRPV1 in baculovirus-infected insect cells for structural studies. Protein Expr Purif 2008; 65:38-50. [PMID: 19121396 DOI: 10.1016/j.pep.2008.12.006] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/29/2008] [Revised: 11/11/2008] [Accepted: 12/03/2008] [Indexed: 10/21/2022]
Abstract
TRPV1 is a ligand-gated cation channel that is involved in acute thermal nociception and neurogenic inflammation. By using the GP67 signal peptide, high levels of full-length human TRPV1 was expressed in High Five insect cells using the baculovirus expression system. The functional activity of the expressed TRPV1 was confirmed by whole-cell ligand-gated ion flux recordings in the presence of capsaicin and low pH and via specific ligand binding to the isolated cellular membranes. Efficient solubilization and purification protocols have resulted in milligram amounts of detergent-solubilized channel at 80-90% purity after Ni2+ IMAC chromatography and size exclusion chromatography. Western blot analysis of amino and carboxyl terminal domains and MS of tryptic digestions of purified protein confirmed the presence of the full-length human TRPV1. Specific ligand binding experiments confirmed the protein integrity of the purified human TRPV1.
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Affiliation(s)
- Alla Korepanova
- Department of Structural Biology, R46Y, Abbott Laboratories, Bldg. AP10-LL8, 100 Abbott Park Rd., Abbott Park, IL 60064-6098, USA.
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18
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Pan Y, Weng J, Cao Y, Bhosle RC, Zhou M. Functional coupling between the Kv1.1 channel and aldoketoreductase Kvbeta1. J Biol Chem 2008; 283:8634-42. [PMID: 18222921 DOI: 10.1074/jbc.m709304200] [Citation(s) in RCA: 49] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023] Open
Abstract
The Shaker family voltage-dependent potassium channels (Kv1) assemble with cytosolic beta-subunits (Kvbeta) to form a stable complex. All Kvbeta subunits have a conserved core domain, which in one of them (Kvbeta2) is an aldoketoreductase that utilizes NADPH as a cofactor. In addition to this core, Kvbeta1 has an N terminus that closes the channel by the N-type inactivation mechanism. Point mutations in the putative catalytic site of Kvbeta1 alter the on-rate of inactivation. Whether the core of Kvbeta1 functions as an enzyme and whether its enzymatic activity affects N-type inactivation had not been explored. Here, we show that Kvbeta1 is a functional aldoketoreductase and that oxidation of the Kvbeta1-bound cofactor, either enzymatically by a substrate or non-enzymatically by hydrogen peroxide or NADP(+), induces a large increase in open channel current. The modulation is not affected by deletion of the distal C terminus of the channel, which has been suggested in structural studies to interact with Kvbeta. The rate of increase in current, which reflects NADPH oxidation, is approximately 2-fold faster at 0-mV membrane potential than at -100 mV. Thus, cofactor oxidation by Kvbeta1 is regulated by membrane potential, presumably via voltage-dependent structural changes in Kv1.1 channels.
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Affiliation(s)
- Yaping Pan
- Department of Physiology and Cellular Biophysics, Columbia University College of Physicians and Surgeons, New York, NY 10032, USA
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19
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Abstract
Kv2.1 channels are widely expressed in neuronal and endocrine cells and generate slowly activating K+ currents, which contribute to repolarization in these cells. Kv2.1 is expressed at high levels in the mammalian brain and is a major component of the delayed rectifier current in the hippocampus. In addition, Kv2.1 channels have been implicated in the regulation of membrane repolarization, cytoplasmic calcium levels, and insulin secretion in pancreatic beta-cells. They are therefore an important drug target for the treatment of Type II diabetes mellitus. We used electron microscopy and single particle image analysis to derive a three-dimensional density map of recombinant human Kv2.1. The tetrameric channel is egg-shaped with a diameter of approximately 80 A and a long axis of approximately 120 A. Comparison to known crystal structures of homologous domains allowed us to infer the location of the cytoplasmic and transmembrane assemblies. There is a very good fit of the Kv1.2 crystal structure to the assigned transmembrane assembly of Kv2.1. In other low-resolution maps of K+ channels, the cytoplasmic N-terminal and transmembrane domains form separate rings of density. In contrast, Kv2.1 displays contiguous density that connects the rings, such that there are no large windows between the channel interior and the cytoplasmic space. The crystal structure of KcsA is thought to be in a closed conformation, and the good fit of the KcsA crystal structure to the Kv2.1 map suggests that our preparations of Kv2.1 may also represent a closed conformation. Substantial cytoplasmic density is closely associated with the T1 tetramerization domain and is ascribed to the approximately 184 kDa C-terminal regulatory domains within each tetramer.
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20
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Moncoq K, Kemp G, Li X, Fliegel L, Young HS. Dimeric structure of human Na+/H+ exchanger isoform 1 overproduced in Saccharomyces cerevisiae. J Biol Chem 2007; 283:4145-54. [PMID: 18077454 DOI: 10.1074/jbc.m704844200] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The Na(+)/H(+) exchanger isoform 1 (NHE1) is an integral membrane protein that regulates intracellular pH by extruding an intracellular H(+) in exchange for one extracellular Na(+). The human NHE1 isoform is involved in heart disease and cell growth and proliferation. Although details of NHE1 regulation and transport are being revealed, there is little information available on the structure of the intact protein. In this report, we demonstrate overexpression, purification, and characterization of the human NHE1 (hNHE1) protein in Saccharomyces cerevisiae. Overproduction of the His-tagged protein followed by purification via nickel-nitrilotriacetic acid-agarose chromatography yielded 0.2 mg of pure protein/liter of cell culture. Reconstitution of hNHE1 in proteoliposomes demonstrated that the protein was active and responsive to an NHE1-specific inhibitor. Circular dichroism spectroscopy of purified hNHE1 revealed that the protein contains 41% alpha-helix, 23% beta-sheet, and 36% random coil. Size exclusion chromatography indicated that the protein-detergent micelle was in excess of 200 kDa, consistent with an hNHE1 dimer. Electron microscopy and single particle reconstruction of negatively stained hNHE1 confirmed that the protein was a dimer, with a compact globular domain assigned to the transmembrane region and an apical ridge assigned to the cytoplasmic domain. The transmembrane domain of the hNHE1 reconstruction was clearly dimeric, where each monomer had a size and shape consistent with the predicted 12 membrane-spanning segments for hNHE1.
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Affiliation(s)
- Karine Moncoq
- Department of Biochemistry, University of Alberta, Edmonton, Alberta T6G 2H7, Canada
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21
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Midgett CR, Madden DR. Breaking the bottleneck: Eukaryotic membrane protein expression for high-resolution structural studies. J Struct Biol 2007; 160:265-74. [PMID: 17702603 DOI: 10.1016/j.jsb.2007.07.001] [Citation(s) in RCA: 66] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/01/2007] [Revised: 06/26/2007] [Accepted: 07/06/2007] [Indexed: 10/23/2022]
Abstract
The recombinant expression of eukaryotic membrane proteins has been a major stumbling block in efforts to determine their structures. In the last two years, however, five such proteins have yielded high-resolution X-ray or electron diffraction data, opening the prospect of increased throughput for eukaryotic membrane protein structure determination. Here, we summarize the major expression systems available, and highlight technical advances that should facilitate more systematic screening of expression conditions for this physiologically important class of targets.
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Affiliation(s)
- Charles R Midgett
- Department of Biochemistry, Dartmouth Medical School, 7200 Vail Building, Hanover, NH 03755, USA
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22
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Zeng X, Stahlberg H, Grigorieff N. A maximum likelihood approach to two-dimensional crystals. J Struct Biol 2007; 160:362-74. [PMID: 17964808 PMCID: PMC2147720 DOI: 10.1016/j.jsb.2007.09.013] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/04/2007] [Revised: 09/05/2007] [Accepted: 09/14/2007] [Indexed: 11/24/2022]
Abstract
Maximum likelihood (ML) processing of transmission electron microscopy images of protein particles can produce reconstructions of superior resolution due to a reduced reference bias. We have investigated a ML processing approach to images centered on the unit cells of two-dimensional (2D) crystal images. The implemented software makes use of the predictive lattice node tracking in the MRC software, which is used to window particle stacks. These are then noise-whitened and subjected to ML processing. Resulting ML maps are translated into amplitudes and phases for further processing within the 2dx software package. Compared with ML processing for randomly oriented single particles, the required computational costs are greatly reduced as the 2D crystals restrict the parameter search space. The software was applied to images of negatively stained or frozen hydrated 2D crystals of different crystal order. We find that the ML algorithm is not free from reference bias, even though its sensitivity to noise correlation is lower than for pure cross-correlation alignment. Compared with crystallographic processing, the newly developed software yields better resolution for 2D crystal images of lower crystal quality, and it performs equally well for well-ordered crystal images.
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Affiliation(s)
- Xiangyan Zeng
- Molecular & Cellular Biology, University of California at Davis, 1 Shields Ave., Davis, CA 95616, USA
| | - Henning Stahlberg
- Molecular & Cellular Biology, University of California at Davis, 1 Shields Ave., Davis, CA 95616, USA
| | - Nikolaus Grigorieff
- Howard Hughes Medical Institute and Department of Biochemistry, Rosenstiel Basic Medical Sciences Research Center, Brandeis University, 415 South Street, Waltham, MA 02454-9110, USA
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23
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Nyblom M, Oberg F, Lindkvist-Petersson K, Hallgren K, Findlay H, Wikström J, Karlsson A, Hansson O, Booth PJ, Bill RM, Neutze R, Hedfalk K. Exceptional overproduction of a functional human membrane protein. Protein Expr Purif 2007; 56:110-20. [PMID: 17869538 DOI: 10.1016/j.pep.2007.07.007] [Citation(s) in RCA: 55] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/24/2007] [Revised: 07/02/2007] [Accepted: 07/09/2007] [Indexed: 11/19/2022]
Abstract
Eukaryotic--especially human--membrane protein overproduction remains a major challenge in biochemistry. Heterologously overproduced and purified proteins provide a starting point for further biochemical, biophysical and structural studies, and the lack of sufficient quantities of functional membrane proteins is frequently a bottleneck hindering this. Here, we report exceptionally high production levels of a correctly folded and crystallisable recombinant human integral membrane protein in its active form; human aquaporin 1 (hAQP1) has been heterologously produced in the membranes of the methylotrophic yeast Pichia pastoris. After solubilisation and a two step purification procedure, at least 90 mg hAQP1 per liter of culture is obtained. Water channel activity of this purified hAQP1 was verified by reconstitution into proteoliposomes and performing stopped-flow vesicle shrinkage measurements. Mass spectrometry confirmed the identity of hAQP1 in crude membrane preparations, and also from purified protein reconstituted into proteoliposomes. Furthermore, crystallisation screens yielded diffraction quality crystals of untagged recombinant hAQP1. This study illustrates the power of the yeast P. pastoris as a host to produce exceptionally high yields of a functionally active, human integral membrane protein for subsequent functional and structural characterization.
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Affiliation(s)
- Maria Nyblom
- Department of Chemical and Biological Engineering, Chalmers University of Technology, SE-405 30 Göteborg, Sweden
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24
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Schäfer E, Dencher NA, Vonck J, Parcej DN. Three-Dimensional Structure of the Respiratory Chain Supercomplex I1III2IV1 from Bovine Heart Mitochondria,. Biochemistry 2007; 46:12579-85. [DOI: 10.1021/bi700983h] [Citation(s) in RCA: 131] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Eva Schäfer
- Physical Biochemistry, Department of Chemistry, Petersenstrasse 22, Darmstadt University of Technology, D-64287 Darmstadt, and Department of Structural Biology, Max-Planck-Institute of Biophysics, Max-von-Laue-Strasse 3, D-60438 Frankfurt am Main, Germany
| | - Norbert A. Dencher
- Physical Biochemistry, Department of Chemistry, Petersenstrasse 22, Darmstadt University of Technology, D-64287 Darmstadt, and Department of Structural Biology, Max-Planck-Institute of Biophysics, Max-von-Laue-Strasse 3, D-60438 Frankfurt am Main, Germany
| | - Janet Vonck
- Physical Biochemistry, Department of Chemistry, Petersenstrasse 22, Darmstadt University of Technology, D-64287 Darmstadt, and Department of Structural Biology, Max-Planck-Institute of Biophysics, Max-von-Laue-Strasse 3, D-60438 Frankfurt am Main, Germany
| | - David N. Parcej
- Physical Biochemistry, Department of Chemistry, Petersenstrasse 22, Darmstadt University of Technology, D-64287 Darmstadt, and Department of Structural Biology, Max-Planck-Institute of Biophysics, Max-von-Laue-Strasse 3, D-60438 Frankfurt am Main, Germany
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25
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Mancia F, Hendrickson WA. Expression of recombinant G-protein coupled receptors for structural biology. MOLECULAR BIOSYSTEMS 2007; 3:723-34. [PMID: 17882334 DOI: 10.1039/b713558k] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Affiliation(s)
- Filippo Mancia
- Howard Hughes Medical Institute and Department of Biochemistry and Molecular Biophysics, Columbia University, New York, NY 10032, USA
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26
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Abstract
Structure determination has already proven useful for lead optimization and direct drug design. The number of high-resolution structures available in public databases today exceeds 30,000 and will definitely aid in structure-based drug design. Structural genomics approaches covering whole genomes, topologically similar proteins or gene families are great assets for further progress in the development of new drugs. However, membrane proteins representing 70% of current drug targets are poorly characterized structurally. The problems have been related to difficulties in obtaining large amount of recombinant membrane proteins as well as their purification and structure determination. Structural genomics has proven successful in developing new methods in areas from expression to structure determination by studying a large number of target proteins in parallel.
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Affiliation(s)
- K Lundstrom
- Flamel Technologies, 33 Avenue du Dr. Georges Lévy, 69693 Vénissieux, France.
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27
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Standfuss J, Xie G, Edwards PC, Burghammer M, Oprian DD, Schertler GFX. Crystal structure of a thermally stable rhodopsin mutant. J Mol Biol 2007; 372:1179-88. [PMID: 17825322 PMCID: PMC2258155 DOI: 10.1016/j.jmb.2007.03.007] [Citation(s) in RCA: 186] [Impact Index Per Article: 10.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/05/2007] [Revised: 02/28/2007] [Accepted: 03/06/2007] [Indexed: 11/16/2022]
Abstract
We determined the structure of the rhodopsin mutant N2C/D282C expressed in mammalian cells; the first structure of a recombinantly produced G protein-coupled receptor (GPCR). The mutant was designed to form a disulfide bond between the N terminus and loop E3, which allows handling of opsin in detergent solution and increases thermal stability of rhodopsin by 10 deg.C. It allowed us to crystallize a fully deglycosylated rhodopsin (N2C/N15D/D282C). N15 mutations are normally misfolding and cause retinitis pigmentosa in humans. Microcrystallographic techniques and a 5 microm X-ray beam were used to collect data along a single needle measuring 5 microm x 5 microm x 90 microm. The disulfide introduces only minor changes but fixes the N-terminal cap over the beta-sheet lid covering the ligand-binding site, a likely explanation for the increased stability. This work allows structural investigation of rhodopsin mutants and shows the problems encountered during structure determination of GPCRs and other mammalian membrane proteins.
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Affiliation(s)
- Jörg Standfuss
- MRC Laboratory of Molecular Biology, Structural Studies, Hills Road, Cambridge CB2 2QH, UK
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28
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Pagliuca C, Goetze TA, Wagner R, Thiel G, Moroni A, Parcej D. Molecular Properties of Kcv, a Virus Encoded K+ Channel. Biochemistry 2007; 46:1079-90. [PMID: 17240991 DOI: 10.1021/bi061530w] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The miniature viral K+ channel Kcv represents the pore module of all K+ channels. A synthetic gene of Kcv with an elevated GC content compared to that of the wild-type gene was expressed heterologously in Pichia pastoris, and the purified protein was functionally reconstituted into liposomes. Biochemical assays reveal a remarkable cation selective stability of the channel tetramer via SDS-PAGE. Only cations, which permeate Kcv, were able to protect the oligomer against disassembly into monomers at high temperatures. Electrophysiological characterization of the single Kcv channel reveals a saturating conductance (lambda(max)) of 360 pS; the single-channel current-voltage relation was strongly rectifying with a negative slope conductance at extreme voltages. The channel was highly selective for K+ and was blocked by Ba2+ and in a side specific manner by Na+ and Cs+ also. The channel conducted Rb+, but as a consequence, the channel was shifted into a hyperactive state. We conclude that specific binding interactions of cations in the conductive pathway are an important determinant of channel stability and function.
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Affiliation(s)
- Cinzia Pagliuca
- Dipartimento di Biologia e IBF-CNR, Universitá degli Studi di Milano, Via Celoria 26, 20133 Milano, Italy
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29
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Structural Genomics. CELL ENGINEERING 2007. [PMCID: PMC7122701 DOI: 10.1007/1-4020-5252-9_1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Subscribe] [Scholar Register] [Indexed: 12/04/2022]
Abstract
Drug discovery based on structural knowledge has proven useful as several structure-based medicines are already on the market. Structural genomics aims at studying a large number of gene products including whole genomes, topologically similar proteins, protein families and protein subtypes in parallel. Particularly, therapeutically relevant targets have been selected for structural genomics initiatives. In this context, integral membrane proteins, which represent 60–70% of the current drug targets, have been of major interest. Paradoxically, membrane proteins present the last frontier to conquer in structural biology as some 100 high resolution structures among the 30,000 entries in public structural databases are available. The modest success rate on membrane proteins relates to the difficulties in their expression, purification and crystallography. To facilitate technology development large networks providing expertise in molecular biology, protein biochemistry and structural biology have been established. The privately funded MePNet program has studied 100 G protein-coupled receptors, which resulted in high level expression of a large number of receptors at structural biology compatible levels. Currently, selected GPCRs have been purified and subjected to crystallization attempts
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30
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Wagner S, Bader ML, Drew D, de Gier JW. Rationalizing membrane protein overexpression. Trends Biotechnol 2006; 24:364-71. [PMID: 16820235 DOI: 10.1016/j.tibtech.2006.06.008] [Citation(s) in RCA: 199] [Impact Index Per Article: 11.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/10/2006] [Revised: 04/20/2006] [Accepted: 06/16/2006] [Indexed: 11/27/2022]
Abstract
Functional and structural studies of membrane proteins usually require overexpression of the proteins in question. Often, however, the 'trial and error' approaches that are mainly used to produce membrane proteins are not successful. Our rapidly increasing understanding of membrane protein insertion, folding and degradation means that membrane protein overexpression can be more rationalized, both at the level of the overexpression host and the overexpressed membrane protein. This change of mindset is likely to have a significant impact on membrane protein research.
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Affiliation(s)
- Samuel Wagner
- Department of Biochemistry and Biophysics, Stockholm University, SE-106 91 Stockholm, Sweden
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31
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Licata L, Haase W, Eckhardt-Strelau L, Parcej DN. Over-expression of a mammalian small conductance calcium-activated K+ channel in Pichia pastoris: effects of trafficking signals and subunit fusions. Protein Expr Purif 2005; 47:171-8. [PMID: 16290007 DOI: 10.1016/j.pep.2005.10.010] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2005] [Revised: 09/30/2005] [Accepted: 10/05/2005] [Indexed: 11/15/2022]
Abstract
Mammalian SK proteins are Ca2+-activated K+ channels, which show a sub-20 pS conductance. We have expressed the SK2 variant gene in Pichia pastoris and found protein to be produced at considerably higher levels than in brain tissue. The channel was correctly folded as evidenced by its high affinity interaction with apamin, a specific ligand from bee venom. However, the protein was largely unable to reach the plasma membrane, its normal destination, instead remaining in the endoplasmic reticulum. Adding a putative translocation sequence altered the intracellular distribution significantly with enhanced trafficking out of the endoplamic reticulum. Fusion of SK2 with the associated protein calmodulin also altered the channel localisation but in a different manner with channels now found mainly in transit between endoplasmic reticulum and Golgi compartments.
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Affiliation(s)
- Luana Licata
- Department of Structural Biology, Max Planck Institute for Biophysics, Frankfurt am Main, Germany
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32
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Long SB, Campbell EB, Mackinnon R. Crystal Structure of a Mammalian Voltage-Dependent Shaker Family K+ Channel. Science 2005; 309:897-903. [PMID: 16002581 DOI: 10.1126/science.1116269] [Citation(s) in RCA: 1683] [Impact Index Per Article: 88.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
Voltage-dependent potassium ion (K+) channels (Kv channels) conduct K+ ions across the cell membrane in response to changes in the membrane voltage, thereby regulating neuronal excitability by modulating the shape and frequency of action potentials. Here we report the crystal structure, at a resolution of 2.9 angstroms, of a mammalian Kv channel, Kv1.2, which is a member of the Shaker K+ channel family. This structure is in complex with an oxido-reductase beta subunit of the kind that can regulate mammalian Kv channels in their native cell environment. The activation gate of the pore is open. Large side portals communicate between the pore and the cytoplasm. Electrostatic properties of the side portals and positions of the T1 domain and beta subunit are consistent with electrophysiological studies of inactivation gating and with the possibility of K+ channel regulation by the beta subunit.
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Affiliation(s)
- Stephen B Long
- Howard Hughes Medical Institute, Laboratory of Molecular Neurobiology and Biophysics, Rockefeller University, 1230 York Avenue, New York, NY 10021, USA
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33
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Orlova EV, Saibil HR. Structure determination of macromolecular assemblies by single-particle analysis of cryo-electron micrographs. Curr Opin Struct Biol 2004; 14:584-90. [PMID: 15465319 DOI: 10.1016/j.sbi.2004.08.004] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
A new generation of electron microscopes equipped with field emission gun electron sources and the ability to image molecules in their native environment at liquid nitrogen or helium temperatures has enabled the analysis of macromolecular structures at medium resolution (approximately 10 angstroms) and in different conformational states. The amalgamation of electron microscopy and X-ray crystallographic approaches makes it possible to solve structures in the 100-1000 angstroms size range, advancing our understanding of the function of complex assemblies. Many new structures have been solved during the past two years, including one of the smallest complexes to be determined by single-particle cryo-electron microscopy, the transferrin receptor-transferrin complex. Other notable results include the near atomic level resolution structure of the nicotinic acetylcholine receptor in helical arrays and an icosahedral virus structure with an asymmetric polymerase resolved.
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Affiliation(s)
- Elena V Orlova
- School of Crystallography, Birkbeck College, University of London, Malet Street, London WC1E 7HX, UK
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34
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Sokolova O. Structure of cation channels, revealed by single particle electron microscopy. FEBS Lett 2004; 564:251-6. [PMID: 15111105 DOI: 10.1016/s0014-5793(04)00254-6] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/05/2003] [Accepted: 02/23/2004] [Indexed: 11/18/2022]
Abstract
A large barrier in the way to obtaining high-resolution structures of eukaryotic ion channels remains the expression and purification of sufficient amounts of channel protein to carry out crystallization trials. In the absence of crystals, the main available source of structural information has been electron microscopy (EM), which is well suited to the visualization of isolated macromolecular complexes and their conformational changes. The recently published EM structures outline native conformations of eukaryotic cation channels that until now have eluded crystallization. According to these results, homo-tetrameric K(+) channels have a distinct two-layer architecture with connectors conjoining the two layers, while the pseudo-tetrameric Ca(2+) or Na(+) channels are more globular and have flexible surface loops, which makes the identification of subunits complicated. Subunits can be identified using atomic structure docking into the EM maps, labeling, or deletion studies.
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Affiliation(s)
- Olga Sokolova
- Howard Hughes Medical Institute, Department of Biochemistry, Brandeis University, 415 South Street, Waltham, MA 02454-9110, USA.
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