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Opdensteinen P, Sperl LE, Mohamadi M, Kündgen‐Redding N, Hagn F, Buyel JF. The transient expression of recombinant proteins in plant cell packs facilitates stable isotope labelling for NMR spectroscopy. PLANT BIOTECHNOLOGY JOURNAL 2022; 20:1928-1939. [PMID: 35702941 PMCID: PMC9491462 DOI: 10.1111/pbi.13873] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 11/03/2021] [Revised: 04/05/2022] [Accepted: 06/03/2022] [Indexed: 06/15/2023]
Abstract
Nuclear magnetic resonance (NMR) spectroscopy can be used to determine the structure, dynamics and interactions of proteins. However, protein NMR requires stable isotope labelling for signal detection. The cells used for the production of recombinant proteins must therefore be grown in medium containing isotopically labelled substrates. Stable isotope labelling is well established in Escherichia coli, but bacteria are only suitable for the production of simple proteins without post-translational modifications. More complex proteins require eukaryotic production hosts, but their growth can be impaired by labelled media, thus reducing product yields and increasing costs. To address this limitation, we used media supplemented with isotope-labelled substrates to cultivate the tobacco-derived cell line BY-2, which was then cast into plant cell packs (PCPs) for the transient expression of a labelled version of the model protein GB1. Mass spectrometry confirmed the feasibility of isotope labelling with 15 N and 2 H using this approach. The resulting NMR spectrum featured a signal dispersion comparable to recombinant GB1 produced in E. coli. PCPs therefore offer a rapid and cost-efficient alternative for the production of isotope-labelled proteins for NMR analysis, especially suitable for complex proteins that cannot be produced in microbial systems.
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Affiliation(s)
- Patrick Opdensteinen
- Fraunhofer Institute for Molecular Biology and Applied Ecology IMEAachenGermany
- Institute for Molecular BiotechnologyRWTH Aachen UniversityAachenGermany
| | - Laura E. Sperl
- Bavarian NMR Center (BNMRZ) at the Department of ChemistryTechnical University of MunichGarchingGermany
- Institute of Structural BiologyHelmholtz Zentrum MünchenNeuherbergGermany
| | - Mariam Mohamadi
- Bavarian NMR Center (BNMRZ) at the Department of ChemistryTechnical University of MunichGarchingGermany
- Institute of Structural BiologyHelmholtz Zentrum MünchenNeuherbergGermany
| | | | - Franz Hagn
- Bavarian NMR Center (BNMRZ) at the Department of ChemistryTechnical University of MunichGarchingGermany
- Institute of Structural BiologyHelmholtz Zentrum MünchenNeuherbergGermany
| | - Johannes Felix Buyel
- Fraunhofer Institute for Molecular Biology and Applied Ecology IMEAachenGermany
- Institute for Molecular BiotechnologyRWTH Aachen UniversityAachenGermany
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Rogals MJ, Yang JY, Williams RV, Moremen KW, Amster IJ, Prestegard JH. Sparse isotope labeling for nuclear magnetic resonance (NMR) of glycoproteins using 13C-glucose. Glycobiology 2021; 31:425-435. [PMID: 32902634 PMCID: PMC8091466 DOI: 10.1093/glycob/cwaa071] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/06/2020] [Revised: 07/22/2020] [Accepted: 07/24/2020] [Indexed: 01/02/2023] Open
Abstract
Preparation of samples for nuclear magnetic resonance (NMR) characterization of larger proteins requires enrichment with less abundant, NMR-active, isotopes such as 13C and 15N. This is routine for proteins that can be expressed in bacterial culture where low-cost isotopically enriched metabolic substrates can be used. However, it can be expensive for glycosylated proteins expressed in mammalian culture where more costly isotopically enriched amino acids are usually used. We describe a simple, relatively inexpensive procedure in which standard commercial media is supplemented with 13C-enriched glucose to achieve labeling of all glycans plus all alanines of the N-terminal domain of the highly glycosylated protein, CEACAM1. We demonstrate an ability to detect partially occupied N-glycan sites, sites less susceptible to processing by an endoglycosidase, and some unexpected truncation of the amino acid sequence. The labeling of both the protein (through alanines) and the glycans in a single culture requiring no additional technical expertise past standard mammalian expression requirements is anticipated to have several applications, including structural and functional screening of the many glycosylated proteins important to human health.
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Affiliation(s)
- Monique J Rogals
- Complex Carbohydrate Research Center, University of Georgia, 315 Riverbend Rd., Athens, GA 30602, USA
| | - Jeong-Yeh Yang
- Complex Carbohydrate Research Center, University of Georgia, 315 Riverbend Rd., Athens, GA 30602, USA
| | - Robert V Williams
- Complex Carbohydrate Research Center, University of Georgia, 315 Riverbend Rd., Athens, GA 30602, USA
- Department of Chemistry
| | - Kelley W Moremen
- Complex Carbohydrate Research Center, University of Georgia, 315 Riverbend Rd., Athens, GA 30602, USA
- Department of Biochemistry and Molecular Biology
| | | | - James H Prestegard
- Complex Carbohydrate Research Center, University of Georgia, 315 Riverbend Rd., Athens, GA 30602, USA
- Department of Chemistry
- Department of Biochemistry and Molecular Biology
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Shahzad-Ul-Hussan S, Sastry M, Lemmin T, Soto C, Loesgen S, Scott DA, Davison JR, Lohith K, O'Connor R, Kwong PD, Bewley CA. Insights from NMR Spectroscopy into the Conformational Properties of Man-9 and Its Recognition by Two HIV Binding Proteins. Chembiochem 2017; 18:764-771. [PMID: 28166380 PMCID: PMC5557091 DOI: 10.1002/cbic.201600665] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/10/2016] [Indexed: 12/12/2022]
Abstract
Man9 GlcNAc2 (Man-9) present at the surface of HIV makes up the binding sites of several HIV-neutralizing agents and the mammalian lectin DC-SIGN, which is involved in cellular immunity and trans-infections. We describe the conformational properties of Man-9 in its free state and when bound by the HIV entry-inhibitor protein microvirin (MVN), and define the minimum epitopes of both MVN and DC-SIGN by using NMR spectroscopy. To facilitate the implementation of 3D 13 C-edited spectra to deconvolute spectral overlap and to determine the solution structure of Man-9, we developed a robust expression system for the production of 13 C,15 N-labeled glycans in mammalian cells. The studies reveal that Man-9 interacts with HIV-binding proteins through distinct epitopes and adopts diverse conformations in the bound state. In combination with molecular dynamics simulations we observed receptor-bound conformations to be sampled by Man-9 in the free state, thus suggesting a conformational selection mechanism for diverse recognition.
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Affiliation(s)
- Syed Shahzad-Ul-Hussan
- Laboratory of Bioorganic Chemistry, National Institute of Diabetes and Digestive and Kidney Diseases, 8 Center Drive, Bethesda, MD, 20892, USA
- Structural Biology Section, Vaccine Research Center, National Institute of Allergy and Infectious Diseases, 40 Convent Drive, Bethesda, MD, 20892, USA
- Present address: Department of Biology, SBA School of Science and Engineering, Lahore University of Management Sciences, Lahore, 54792, Pakistan
| | - Mallika Sastry
- Structural Biology Section, Vaccine Research Center, National Institute of Allergy and Infectious Diseases, 40 Convent Drive, Bethesda, MD, 20892, USA
| | - Thomas Lemmin
- Structural Biology Section, Vaccine Research Center, National Institute of Allergy and Infectious Diseases, 40 Convent Drive, Bethesda, MD, 20892, USA
- Structural Bioinformatics Core Section, Vaccine Research Center, National Institute of Allergy and Infectious Diseases, 40 Convent Drive, Bethesda, MD, 20892, USA
| | - Cinque Soto
- Structural Biology Section, Vaccine Research Center, National Institute of Allergy and Infectious Diseases, 40 Convent Drive, Bethesda, MD, 20892, USA
- Structural Bioinformatics Core Section, Vaccine Research Center, National Institute of Allergy and Infectious Diseases, 40 Convent Drive, Bethesda, MD, 20892, USA
| | - Sandra Loesgen
- Laboratory of Bioorganic Chemistry, National Institute of Diabetes and Digestive and Kidney Diseases, 8 Center Drive, Bethesda, MD, 20892, USA
| | - Danielle A Scott
- Laboratory of Bioorganic Chemistry, National Institute of Diabetes and Digestive and Kidney Diseases, 8 Center Drive, Bethesda, MD, 20892, USA
| | - Jack R Davison
- Laboratory of Bioorganic Chemistry, National Institute of Diabetes and Digestive and Kidney Diseases, 8 Center Drive, Bethesda, MD, 20892, USA
| | - Katheryn Lohith
- Laboratory of Bioorganic Chemistry, National Institute of Diabetes and Digestive and Kidney Diseases, 8 Center Drive, Bethesda, MD, 20892, USA
| | - Robert O'Connor
- Laboratory of Bioorganic Chemistry, National Institute of Diabetes and Digestive and Kidney Diseases, 8 Center Drive, Bethesda, MD, 20892, USA
| | - Peter D Kwong
- Structural Biology Section, Vaccine Research Center, National Institute of Allergy and Infectious Diseases, 40 Convent Drive, Bethesda, MD, 20892, USA
- Structural Bioinformatics Core Section, Vaccine Research Center, National Institute of Allergy and Infectious Diseases, 40 Convent Drive, Bethesda, MD, 20892, USA
| | - Carole A Bewley
- Laboratory of Bioorganic Chemistry, National Institute of Diabetes and Digestive and Kidney Diseases, 8 Center Drive, Bethesda, MD, 20892, USA
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Takeuchi K, Arthanari H, Shimada I, Wagner G. Nitrogen detected TROSY at high field yields high resolution and sensitivity for protein NMR. JOURNAL OF BIOMOLECULAR NMR 2015; 63:323-331. [PMID: 26497830 PMCID: PMC4749451 DOI: 10.1007/s10858-015-9991-y] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/12/2015] [Accepted: 10/01/2015] [Indexed: 05/18/2023]
Abstract
Detection of (15)N in multidimensional NMR experiments of proteins has sparsely been utilized because of the low gyromagnetic ratio (γ) of nitrogen and the presumed low sensitivity of such experiments. Here we show that selecting the TROSY components of proton-attached (15)N nuclei (TROSY (15)NH) yields high quality spectra in high field magnets (>600 MHz) by taking advantage of the slow (15)N transverse relaxation and compensating for the inherently low (15)N sensitivity. The (15)N TROSY transverse relaxation rates increase modestly with molecular weight but the TROSY gain in peak heights depends strongly on the magnetic field strength. Theoretical simulations predict that the narrowest line width for the TROSY (15)NH component can be obtained at 900 MHz, but sensitivity reaches its maximum around 1.2 GHz. Based on these considerations, a (15)N-detected 2D (1)H-(15)N TROSY-HSQC ((15)N-detected TROSY-HSQC) experiment was developed and high-quality 2D spectra were recorded at 800 MHz in 2 h for 1 mM maltose-binding protein at 278 K (τc ~ 40 ns). Unlike for (1)H detected TROSY, deuteration is not mandatory to benefit (15)N detected TROSY due to reduced dipolar broadening, which facilitates studies of proteins that cannot be deuterated, especially in cases where production requires eukaryotic expression systems. The option of recording (15)N TROSY of proteins expressed in H2O media also alleviates the problem of incomplete amide proton back exchange, which often hampers the detection of amide groups in the core of large molecular weight proteins that are expressed in D2O culture media and cannot be refolded for amide back exchange. These results illustrate the potential of (15)NH-detected TROSY experiments as a means to exploit the high resolution offered by high field magnets near and above 1 GHz.
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Affiliation(s)
- Koh Takeuchi
- Molecular Profiling Research Center for Drug Discovery, National Institute for Advanced Industrial Science and Technology, Tokyo, 135-0063, Japan
- PRESTO, JST, Tokyo, 135-0063, Japan
| | - Haribabu Arthanari
- Department of Biochemistry and Molecular Pharmacology, Harvard Medical School, 240 Longwood Avenue, Boston, MA, 02115, USA
| | - Ichio Shimada
- Molecular Profiling Research Center for Drug Discovery, National Institute for Advanced Industrial Science and Technology, Tokyo, 135-0063, Japan.
- Graduate Schools of Pharmaceutical Sciences, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, 113-0033, Japan.
| | - Gerhard Wagner
- Department of Biochemistry and Molecular Pharmacology, Harvard Medical School, 240 Longwood Avenue, Boston, MA, 02115, USA.
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Abstract
Isotope labeling of biologically interesting proteins is a prerequisite for structural and dynamics studies by NMR spectroscopy. Many of these proteins require mammalian cofactors, chaperons, or posttranslational modifications such as myristoylation, glypiation, disulfide bond formation, or N- or O-linked glycosylation; and mammalian cells have the necessary machinery to produce them in their functional forms. Here, we describe recent advances in mammalian expression, including an efficient adenoviral vector-based system, for the production of isotopically labeled proteins. This system enables expression of mammalian proteins and their complexes, including proteins that require posttranslational modifications. We describe a roadmap to produce isotopically labeled (15)N and (13)C posttranslationally modified proteins, such as the outer domain of HIV-1 gp120, which has four disulfide bonds and 15 potential sites of N-linked glycosylation. These methods should allow NMR spectroscopic analysis of the structure and function of posttranslationally modified and secreted, cytoplasmic, or membrane-bound proteins.
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Affiliation(s)
- Mallika Sastry
- Vaccine Research Center, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, Maryland, USA.
| | - Carole A Bewley
- Laboratory of Bioorganic Chemistry, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, Maryland, USA.
| | - Peter D Kwong
- Vaccine Research Center, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, Maryland, USA.
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Robust and low cost uniform 15N-labeling of proteins expressed in Drosophila S2 cells and Spodoptera frugiperda Sf9 cells for NMR applications. J Struct Biol 2014; 188:71-8. [DOI: 10.1016/j.jsb.2014.08.002] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/21/2014] [Revised: 06/15/2014] [Accepted: 08/15/2014] [Indexed: 12/11/2022]
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Moseri A, Schnur E, Noah E, Zherdev Y, Kessler N, Singhal Sinha E, Abayev M, Naider F, Scherf T, Anglister J. NMR observation of HIV-1 gp120 conformational flexibility resulting from V3 truncation. FEBS J 2014; 281:3019-31. [PMID: 24819826 DOI: 10.1111/febs.12839] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/25/2014] [Revised: 05/08/2014] [Accepted: 05/09/2014] [Indexed: 11/30/2022]
Abstract
The envelope spike of HIV-1, which consists of three external gp120 and three transmembrane gp41 glycoproteins, recognizes its target cells by successively binding to its primary CD4 receptor and a coreceptor molecule. Until recently, atomic-resolution structures were available primarily for monomeric HIV-1 gp120, in which the V1, V2 and V3 variable loops were omitted (gp120core ), in complex with soluble CD4 (sCD4). Differences between the structure of HIV gp120core in complex with sCD4 and the structure of unliganded simian immunodeficiency virus gp120core led to the hypothesis that gp120 undergoes a major conformational change upon sCD4 binding. To investigate the conformational flexibility of gp120, we generated two forms of mutated gp120 amenable for NMR studies: one with V1, V2 and V3 omitted ((mut) gp120core ) and the other containing the V3 region [(mut) gp120core (+V3)]. The TROSY-(1)H-(15)N-HSQC spectra of [(2)H, (13)C, (15)N]Arg-labeled and [(2)H, (13)C, (15)N]Ile-labeled unliganded (mut) gp120core showed many fewer crosspeaks than the expected number, and also many fewer crosspeaks in comparison with the labeled (mut) gp120core bound to the CD4-mimic peptide, CD4M33. This finding suggests that in the unliganded form, (mut) gp120core shows considerable flexibility and motions on the millisecond time scale. In contrast, most of the expected crosspeaks were observed for the unliganded (mut) gp120core (+V3), and only a few changes in chemical shift were observed upon CD4M33 binding. These results indicate that (mut) gp120core (+V3) does not show any significant conformational flexibility in its unliganded form and does not undergo any significant conformational change upon CD4M33 binding, underlining the importance of V3 in stabilizing the gp120core conformation.
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Affiliation(s)
- Adi Moseri
- Department of Structural Biology, Weizmann Institute of Science, Rehovot, Israel
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Miyazawa-Onami M, Takeuchi K, Takano T, Sugiki T, Shimada I, Takahashi H. Perdeuteration and methyl-selective (1)H, (13)C-labeling by using a Kluyveromyces lactis expression system. JOURNAL OF BIOMOLECULAR NMR 2013; 57:297-304. [PMID: 24146206 DOI: 10.1007/s10858-013-9789-8] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/02/2013] [Accepted: 10/07/2013] [Indexed: 06/02/2023]
Abstract
The production of stable isotope-labeled proteins is critical in structural analyses of large molecular weight proteins using NMR. Although prokaryotic expression systems using Escherichia coli have been widely used for this purpose, yeast strains have also been useful for the expression of functional eukaryotic proteins. Recently, we reported a cost-effective stable isotope-labeled protein expression using the hemiascomycete yeast Kluyveromyces lactis (K. lactis), which allow us to express exogenous proteins at costs comparable to prokaryotic expression systems. Here, we report the successful production of highly deuterated (>90 %) protein in the K. lactis system. We also examined the methyl-selective (1)H, (13)C-labeling of Ile, Leu, and Val residues using commonly used amino acid precursors. The efficiency of (1)H-(13)C-incorporation varied significantly based on the amino acid. Although a high level of (1)H-(13)C-incorporation was observed for the Ile δ1 position, (1)H, (13)C-labeling rates of Val and Leu methyl groups were limited due to the mitochondrial localization of enzymes involved in amino acid biosynthesis and the lack of transporters for α-ketoisovalerate in the mitochondrial membrane. In line with this notion, the co-expression with branched-chain-amino-acid aminotransferase in the cytosol significantly improved the incorporation rates of amino acid precursors. Although it would be less cost-effective, addition of (13)C-labeled valine can circumvent problems associated with precursors and achieve high level (1)H, (13)C-labeling of Val and Leu. Taken together, the K. lactis system would be a good alternative for expressing large eukaryotic proteins that need deuteration and/or the methyl-selective (1)H, (13)C-labeling for the sensitive detection of NMR resonances.
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Affiliation(s)
- Mayumi Miyazawa-Onami
- Research and Development Department, Japan Biological Informatics Consortium, Tokyo, Japan
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Hiroaki H. Recent applications of isotopic labeling for protein NMR in drug discovery. Expert Opin Drug Discov 2013; 8:523-36. [PMID: 23480844 DOI: 10.1517/17460441.2013.779665] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Abstract
INTRODUCTION Nuclear magnetic resonance (NMR) applications in drug discovery are classified into two categories: ligand-based methods and protein-based methods. The latter is based on the observation of the (1)H-(15)N HSQC spectra of a protein with and without lead compounds. However, in order to take this strategy, isotopic labeling is an absolute necessity. Given that each (1)H-(15)N HSQC signal corresponds to a residue of the target protein, signal changes provide specific information on whether a compound will fit into a pocket. Thus, this protein-based method is particularly suitable for fragment-based approaches, such as "SAR-by-NMR" and "fragment-growing." Alternatively, the information from a protein interface may be used to develop inhibitors for protein-protein interactions. AREAS COVERED This review discusses at the experimental procedures for preparing isotopically labeled protein and introduces selected topics on atom-specific and residue-selective isotope labeling, which may facilitate the development of PPI/PA inhibitors. Furthermore, the author reviews the recent applications of "in-cell" NMR spectroscopy, which is now considered as an important tool in drug delivery research. EXPERT OPINION Many recent advances in labeling methods have succeeded in expanding NMR's potential for drug discovery. In addition to those methods, another new technique called "in-cell NMR" allows the observation of protein-ligand interactions inside living cells. In other words, "in-cell NMR" may become a pharmaceutical NMR technique for drug delivery.
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Affiliation(s)
- Hidekazu Hiroaki
- Nagoya University, Graduate School of Pharmaceutical Sciences, Furocho, Chikusa-kum, Koto-kenkyu-kan, Nagoya, 464-8601, Japan.
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Wiktor M, Morin S, Sass HJ, Kebbel F, Grzesiek S. Biophysical and structural investigation of bacterially expressed and engineered CCR5, a G protein-coupled receptor. JOURNAL OF BIOMOLECULAR NMR 2013; 55:79-95. [PMID: 23229639 DOI: 10.1007/s10858-012-9688-4] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/10/2012] [Accepted: 11/22/2012] [Indexed: 06/01/2023]
Abstract
The chemokine receptor CCR5 belongs to the class of G protein-coupled receptors. Besides its role in leukocyte trafficking, it is also the major HIV-1 coreceptor and hence a target for HIV-1 entry inhibitors. Here, we report Escherichia coli expression and a broad range of biophysical studies on E. coli-produced CCR5. After systematic screening and optimization, we obtained 10 mg of purified, detergent-solubilized, folded CCR5 from 1L culture in a triply isotope-labeled ((2)H/(15)N/(13)C) minimal medium. Thus the material is suitable for NMR spectroscopic studies. The expected α-helical secondary structure content is confirmed by circular dichroism spectroscopy. The solubilized CCR5 is monodisperse and homogeneous as judged by transmission electron microscopy. Interactions of CCR5 with its ligands, RANTES and MIP-1β were assessed by surface plasmon resonance yielding K(D) values in the nanomolar range. Using size exclusion chromatography, stable monomeric CCR5 could be isolated. We show that cysteine residues affect both the yield and oligomer distribution of CCR5. HSQC spectra suggest that the transmembrane domains of CCR5 are in equilibrium between several conformations. In addition we present a model of CCR5 based on the crystal structure of CXCR4 as a starting point for protein engineering.
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Affiliation(s)
- Maciej Wiktor
- Focal Area Structural Biology and Biophysics, Biozentrum, University of Basel, Klingelbergstrasse 50/70, 4056 Basel, Switzerland
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Sastry M, Bewley CA, Kwong PD. Mammalian expression of isotopically labeled proteins for NMR spectroscopy. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2012; 992:197-211. [PMID: 23076586 DOI: 10.1007/978-94-007-4954-2_11] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
NMR spectroscopic characterization of biologically interesting proteins generally requires the incorporation of (15)N/(13)C and/or (2)H stable isotopes. While prokaryotic incorporation systems are regularly used, mammalian ones are not: of the nearly 9,000 NMR macromolecular structures currently deposited in the Protein Data Bank, only a handful (<0.5%) were solved with proteins expressed in mammalian systems. This low number of structures is largely a reflection of the difficulty in producing uniformly labeled, mammalian-expressed proteins. This is unfortunate, as many interesting proteins require mammalian cofactors, chaperons, or post-translational modifications such as N-linked glycosylation, and mammalian cells have the necessary machinery to produce them correctly. Here we describe recent advances in mammalian expression, including an efficient adenoviral vector-based system, for the production of isotopically enriched proteins. This system allows for the expression of mammalian proteins and their complexes, including proteins that require post-translational modifications. We describe how this system can produce isotopically labeled (15)N and (13)C post-translationally modified proteins, such as the outer domain of HIV-1 gp120, which has 15 sites of N-linked glycosylation. Selective amino-acid labeling is also described. These developments should reduce barriers to the determination of NMR structures with isotopically labeled proteins from mammalian expression systems.
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Affiliation(s)
- Mallika Sastry
- National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, MD 20892-3027, USA.
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