1
|
Abstract
In-cell structural biology aims at extracting structural information about proteins or nucleic acids in their native, cellular environment. This emerging field holds great promise and is already providing new facts and outlooks of interest at both fundamental and applied levels. NMR spectroscopy has important contributions on this stage: It brings information on a broad variety of nuclei at the atomic scale, which ensures its great versatility and uniqueness. Here, we detail the methods, the fundamental knowledge, and the applications in biomedical engineering related to in-cell structural biology by NMR. We finally propose a brief overview of the main other techniques in the field (EPR, smFRET, cryo-ET, etc.) to draw some advisable developments for in-cell NMR. In the era of large-scale screenings and deep learning, both accurate and qualitative experimental evidence are as essential as ever to understand the interior life of cells. In-cell structural biology by NMR spectroscopy can generate such a knowledge, and it does so at the atomic scale. This review is meant to deliver comprehensive but accessible information, with advanced technical details and reflections on the methods, the nature of the results, and the future of the field.
Collapse
Affiliation(s)
- Francois-Xavier Theillet
- Université Paris-Saclay, CEA, CNRS, Institute for Integrative Biology of the Cell (I2BC), 91198 Gif-sur-Yvette, France
| |
Collapse
|
2
|
Luchinat E, Cremonini M, Banci L. Radio Signals from Live Cells: The Coming of Age of In-Cell Solution NMR. Chem Rev 2022; 122:9267-9306. [PMID: 35061391 PMCID: PMC9136931 DOI: 10.1021/acs.chemrev.1c00790] [Citation(s) in RCA: 32] [Impact Index Per Article: 16.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
![]()
A detailed knowledge
of the complex processes that make cells and
organisms alive is fundamental in order to understand diseases and
to develop novel drugs and therapeutic treatments. To this aim, biological
macromolecules should ideally be characterized at atomic resolution
directly within the cellular environment. Among the existing structural
techniques, solution NMR stands out as the only one able to investigate
at high resolution the structure and dynamic behavior of macromolecules
directly in living cells. With the advent of more sensitive NMR hardware
and new biotechnological tools, modern in-cell NMR approaches have
been established since the early 2000s. At the coming of age of in-cell
NMR, we provide a detailed overview of its developments and applications
in the 20 years that followed its inception. We review the existing
approaches for cell sample preparation and isotopic labeling, the
application of in-cell NMR to important biological questions, and
the development of NMR bioreactor devices, which greatly increase
the lifetime of the cells allowing real-time monitoring of intracellular
metabolites and proteins. Finally, we share our thoughts on the future
perspectives of the in-cell NMR methodology.
Collapse
Affiliation(s)
- Enrico Luchinat
- Dipartimento di Scienze e Tecnologie Agro-Alimentari, Alma Mater Studiorum−Università di Bologna, Piazza Goidanich 60, 47521 Cesena, Italy
- Magnetic Resonance Center, Università degli Studi di Firenze, Via Luigi Sacconi 6, 50019 Sesto Fiorentino, Italy
| | - Matteo Cremonini
- Magnetic Resonance Center, Università degli Studi di Firenze, Via Luigi Sacconi 6, 50019 Sesto Fiorentino, Italy
| | - Lucia Banci
- Magnetic Resonance Center, Università degli Studi di Firenze, Via Luigi Sacconi 6, 50019 Sesto Fiorentino, Italy
- Consorzio Interuniversitario Risonanze Magnetiche di Metallo Proteine, Via Luigi Sacconi 6, 50019 Sesto Fiorentino, Italy
- Dipartimento di Chimica, Università degli Studi di Firenze, Via della Lastruccia 3, 50019 Sesto Fiorentino, Italy
| |
Collapse
|
3
|
Höfurthner T, Mateos B, Konrat R. On-Cell NMR Contributions to Membrane Receptor Binding Characterization. Chempluschem 2021; 86:938-945. [PMID: 34160899 DOI: 10.1002/cplu.202100134] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/19/2021] [Revised: 05/28/2021] [Indexed: 12/21/2022]
Abstract
NMR spectroscopy has matured into a powerful tool to characterize interactions between biological molecules at atomic resolution, most importantly even under near to native (physiological) conditions. The field of in-cell NMR aims to study proteins and nucleic acids inside living cells. However, cells interrogate their environment and are continuously modulated by external stimuli. Cell signaling processes are often initialized by membrane receptors on the cell surface; therefore, characterizing their interactions at atomic resolution by NMR, hereafter referred as on-cell NMR, can provide valuable mechanistic information. This review aims to summarize recent on-cell NMR tools that give information about the binding site and the affinity of membrane receptors to their ligands together with potential applications to in vivo drug screening systems.
Collapse
Affiliation(s)
- Theresa Höfurthner
- Department of Structural and Computational Biology, Max Perutz Laboratories, University of Vienna, Vienna Biocenter Campus 5, 1030, Vienna, Austria
| | - Borja Mateos
- Department of Structural and Computational Biology, Max Perutz Laboratories, University of Vienna, Vienna Biocenter Campus 5, 1030, Vienna, Austria
| | - Robert Konrat
- Department of Structural and Computational Biology, Max Perutz Laboratories, University of Vienna, Vienna Biocenter Campus 5, 1030, Vienna, Austria
| |
Collapse
|
4
|
Breindel L, Burz DS, Shekhtman A. Interaction proteomics by using in-cell NMR spectroscopy. J Proteomics 2019; 191:202-211. [PMID: 29427760 PMCID: PMC6082733 DOI: 10.1016/j.jprot.2018.02.006] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/07/2017] [Revised: 01/31/2018] [Accepted: 02/04/2018] [Indexed: 12/17/2022]
Abstract
A synopsis of in-cell NMR spectroscopic approaches to study interaction proteomics in prokaryotic and eukaryotic cells is presented. We describe the use of in-cell NMR spectroscopy to resolve high resolution protein structures, discuss methodologies for determining and analyzing high and low affinity protein-target structural interactions, including intrinsically disordered proteins, and detail important functional interactions that result from these interactions. SIGNIFICANCE: The ultimate goal of structural and biochemical research is to understand how macromolecular interactions give rise to and regulate biological activity in living cells. The challenge is formidable due to the complexity that arises not only from the number of proteins (genes) expressed by the organism, but also from the combinatorial interactions between them. Despite ongoing efforts to decipher the complex nature of protein interactions, new methods for structurally characterizing protein complexes are needed to fully understand molecular networks. With the onset of in-cell NMR spectroscopy, molecular structures and interactions can be studied under physiological conditions shedding light on the structural underpinning of biological activity.
Collapse
Affiliation(s)
- Leonard Breindel
- Department of Chemistry, University at Albany, State University of New York, Albany, NY 12222, USA
| | - David S Burz
- Department of Chemistry, University at Albany, State University of New York, Albany, NY 12222, USA
| | - Alexander Shekhtman
- Department of Chemistry, University at Albany, State University of New York, Albany, NY 12222, USA.
| |
Collapse
|
5
|
Applications of In-Cell NMR in Structural Biology and Drug Discovery. Int J Mol Sci 2019; 20:ijms20010139. [PMID: 30609728 PMCID: PMC6337603 DOI: 10.3390/ijms20010139] [Citation(s) in RCA: 26] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/26/2018] [Revised: 12/24/2018] [Accepted: 12/29/2018] [Indexed: 01/23/2023] Open
Abstract
In-cell nuclear magnetic resonance (NMR) is a method to provide the structural information of a target at an atomic level under physiological conditions and a full view of the conformational changes of a protein caused by ligand binding, post-translational modifications or protein⁻protein interactions in living cells. Previous in-cell NMR studies have focused on proteins that were overexpressed in bacterial cells and isotopically labeled proteins injected into oocytes of Xenopus laevis or delivered into human cells. Applications of in-cell NMR in probing protein modifications, conformational changes and ligand bindings have been carried out in mammalian cells by monitoring isotopically labeled proteins overexpressed in living cells. The available protocols and successful examples encourage wide applications of this technique in different fields such as drug discovery. Despite the challenges in this method, progress has been made in recent years. In this review, applications of in-cell NMR are summarized. The successful applications of this method in mammalian and bacterial cells make it feasible to play important roles in drug discovery, especially in the step of target engagement.
Collapse
|
6
|
Wall KP, Hough LE. In-Cell NMR within Budding Yeast Reveals Cytoplasmic Masking of Hydrophobic Residues of FG Repeats. Biophys J 2018; 115:1690-1695. [PMID: 30342747 PMCID: PMC6225093 DOI: 10.1016/j.bpj.2018.08.049] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/05/2018] [Revised: 08/26/2018] [Accepted: 08/28/2018] [Indexed: 10/28/2022] Open
Abstract
In-cell NMR spectroscopy is a powerful tool to determine the properties of proteins and nucleic acids within living cells. In-cell NMR can give site-specific measurements of interactions, modifications, and dynamics as well as their modulation by the cellular environment. In-cell NMR requires selective incorporation of heavy isotopes into a protein of interest, either through the introduction of exogenously produced protein to a cell's interior or the selective overexpression of a protein. We developed conditions to allow the use of Saccharomyces cerevisiae, which was chosen because of its genetic tractability, as a eukaryotic expression system for in-cell NMR. We demonstrate this technique using a fragment of S. cerevisiae Nsp1, an FG Nup. FG Nups are intrinsically disordered proteins containing phenylalanine (F)-glycine (G) repeats and form the selective barrier within the nuclear pore complex. Yeast FG Nups have previously been shown to be maintained in a highly dynamic state within living bacteria as measured by in-cell NMR. Interactions thought to stabilize this dynamic state are also present in the protein's native organism, although site specificity of interaction is different between the two cytosols.
Collapse
Affiliation(s)
- Kathryn P Wall
- BioFrontiers Institute, University of Colorado, Boulder, Colorado; Department of Biochemistry, University of Colorado, Boulder, Colorado
| | - Loren E Hough
- BioFrontiers Institute, University of Colorado, Boulder, Colorado; Department of Physics, University of Colorado, Boulder, Colorado.
| |
Collapse
|
7
|
Luchinat E, Banci L. In-Cell NMR in Human Cells: Direct Protein Expression Allows Structural Studies of Protein Folding and Maturation. Acc Chem Res 2018; 51:1550-1557. [PMID: 29869502 DOI: 10.1021/acs.accounts.8b00147] [Citation(s) in RCA: 59] [Impact Index Per Article: 9.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Cellular structural biology methods are needed to characterize biological processes at atomic resolution in the physiological environment of the cell. Toward this goal, solution in-cell NMR is a powerful approach because it provides structural and dynamic data on macromolecules inside living cells. Several approaches have been developed for in-cell NMR in cultured human cells, which are needed to study processes related to human diseases that rely on the delivery of exogenous macromolecules to the cells. Such strategies, however, may not be applicable to proteins that are sensitive to the external environment or prone to aggregate and can introduce artifacts during protein purification or delivery. As a complementary approach, direct protein expression for in-cell NMR in human cells was developed. This strategy is especially useful when studying processes like protein folding, maturation, and post-translational modification, starting right after protein synthesis. Compared with the protein expression techniques in mammalian cells commonly used in cellular biology, the low sensitivity of NMR requires higher protein levels. Among the cell lines used for high-yield protein expression, the HEK293T cell line was chosen, as it can be efficiently transfected with a cost-effective reagent. A vector originally designed for secreted proteins allows high-level cytosolic protein expression. For isotopic labeling, commercially available or homemade labeled media are employed. Uniform or amino acid type-selective labeling strategies are possible. Protein expression can be targeted to specific organelles (e.g., mitochondria), allowing for in organello NMR applications. A variant of the approach was developed that allows the sequential expression of two or more proteins, with only one selectively labeled. Protein expression in HEK293T cells was applied to recapitulate the maturation steps of intracellular superoxide dismutase 1 (SOD1) and to study the effect of mutations linked to familial amyotrophic lateral sclerosis (fALS) by in-cell NMR. Intracellular wild-type SOD1 spontaneously binds zinc, while it needs the copper chaperone for superoxide dismutase (CCS) for copper delivery and disulfide bond formation. Some fALS-linked mutations impair zinc binding and cause SOD1 to irreversibly unfold, likely forming the precursor of cytotoxic aggregates. The SOD-like domain of CCS acts as a molecular chaperone toward mutant SOD1, stabilizing its folding and allowing zinc binding and correct maturation. Changes in protein redox state distributions can also be investigated by in-cell NMR. Mitochondrial proteins require the redox-regulating partners glutaredoxin 1 (Grx1) and thioredoxin (Trx) to remain in the reduced, import-competent state in the cytosol, whereas SOD1 requires CCS for disulfide bond formation. In both cases, the proteins do not equilibrate with the cytosolic redox pool. Cysteine oxidation in response to oxidative stress can also be monitored. In the near future, in-cell NMR in human cells will likely benefit from technological advancements in NMR hardware, the development of bioreactor systems for increased sample lifetime, the application of paramagnetic NMR to obtain structural restraints, and advanced tools for genome engineering and should be increasingly integrated with advanced cellular imaging techniques.
Collapse
Affiliation(s)
- Enrico Luchinat
- Magnetic Resonance Center - CERM, University of Florence, 50019 Sesto Fiorentino, Italy
- Department of Experimental and Clinical Biomedical Sciences “Mario Serio”, University of Florence, 50134 Florence, Italy
| | - Lucia Banci
- Magnetic Resonance Center - CERM, University of Florence, 50019 Sesto Fiorentino, Italy
- Department of Chemistry, University of Florence, 50019 Sesto Fiorentino, Italy
| |
Collapse
|
8
|
iNEXT: a European facility network to stimulate translational structural biology. FEBS Lett 2018; 592:1909-1917. [DOI: 10.1002/1873-3468.13062] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
|
9
|
DeMott CM, Girardin R, Cobbert J, Reverdatto S, Burz DS, McDonough K, Shekhtman A. Potent Inhibitors of Mycobacterium tuberculosis Growth Identified by Using in-Cell NMR-based Screening. ACS Chem Biol 2018; 13:733-741. [PMID: 29359908 DOI: 10.1021/acschembio.7b00879] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
In-cell NMR spectroscopy was used to screen for drugs that disrupt the interaction between prokaryotic ubiquitin like protein, Pup, and mycobacterial proteasome ATPase, Mpa. This interaction is critical for Mycobacterium tuberculosis resistance against nitric oxide (NO) stress; interruption of this process was proposed as a mechanism to control latent infection. Three compounds isolated from the NCI Diversity set III library rescued the physiological proteasome substrate from degradation suggesting that the proteasome degradation pathway was selectively targeted. Two of the compounds bind to Mpa with sub-micromolar to nanomolar affinity, and all three exhibit potency toward mycobacteria comparable to antibiotics currently available on the market, inhibiting growth in the low micromolar range.
Collapse
Affiliation(s)
- Christopher M. DeMott
- Department of Chemistry, University at Albany, State University of New York, Albany, New York 12222, United States
| | - Roxie Girardin
- Wadsworth Center, New York Department of Health, Albany, New York 12208, United States
| | - Jacqueline Cobbert
- Department of Chemistry, University at Albany, State University of New York, Albany, New York 12222, United States
| | - Sergey Reverdatto
- Department of Chemistry, University at Albany, State University of New York, Albany, New York 12222, United States
| | - David S. Burz
- Department of Chemistry, University at Albany, State University of New York, Albany, New York 12222, United States
| | - Kathleen McDonough
- Wadsworth Center, New York Department of Health, Albany, New York 12208, United States
- Department of Biomedical Sciences, University at Albany, State University of New York, Albany, New York 12222, United States
| | - Alexander Shekhtman
- Department of Chemistry, University at Albany, State University of New York, Albany, New York 12222, United States
| |
Collapse
|
10
|
Lippens G, Cahoreau E, Millard P, Charlier C, Lopez J, Hanoulle X, Portais JC. In-cell NMR: from metabolites to macromolecules. Analyst 2018; 143:620-629. [PMID: 29333554 DOI: 10.1039/c7an01635b] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
In-cell NMR of macromolecules has gained momentum over the last ten years as an approach that might bridge the branches of cell biology and structural biology. In this review, we put it in the context of earlier efforts that aimed to characterize by NMR the cellular environment of live cells and their intracellular metabolites. Although technical aspects distinguish these earlier in vivo NMR studies and the more recent in cell NMR efforts to characterize macromolecules in a cellular environment, we believe that both share major concerns ranging from sensitivity and line broadening to cell viability. Approaches to overcome the limitations in one subfield thereby can serve the other one and vice versa. The relevance in biomedical sciences might stretch from the direct following of drug metabolism in the cell to the observation of target binding, and thereby encompasses in-cell NMR both of metabolites and macromolecules. We underline the efforts of the field to move to novel biological insights by some selected examples.
Collapse
Affiliation(s)
- G Lippens
- LISBP, Université de Toulouse, CNRS, INRA, INSA, Toulouse, France.
| | - E Cahoreau
- LISBP, Université de Toulouse, CNRS, INRA, INSA, Toulouse, France.
| | - P Millard
- LISBP, Université de Toulouse, CNRS, INRA, INSA, Toulouse, France.
| | - C Charlier
- Laboratory of Chemical Physics, NIDDK, National Institutes of Health, Bethesda, Maryland 20892-0520, USA
| | - J Lopez
- CERMN, Seccion Quimica, Departemento de Ciencias, Pontificia Universidad Catolica del Peru, Lima 32, Peru
| | - X Hanoulle
- Unité de Glycobiologie Structurale et Fonctionnelle (UGSF), University of Lille, CNRS UMR8576, Lille, France
| | - J C Portais
- LISBP, Université de Toulouse, CNRS, INRA, INSA, Toulouse, France.
| |
Collapse
|
11
|
Luchinat E, Banci L. In-cell NMR: a topical review. IUCRJ 2017; 4:108-118. [PMID: 28250949 PMCID: PMC5330521 DOI: 10.1107/s2052252516020625] [Citation(s) in RCA: 89] [Impact Index Per Article: 12.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/21/2016] [Accepted: 12/29/2016] [Indexed: 05/18/2023]
Abstract
Classical structural biology approaches allow structural characterization of biological macromolecules in vitro, far from their physiological context. Nowadays, thanks to the wealth of structural data available and to technological and methodological advances, the interest of the research community is gradually shifting from pure structural determination towards the study of functional aspects of biomolecules. Therefore, a cellular structural approach is ideally needed to characterize biological molecules, such as proteins, in their native cellular environment and the functional processes that they are involved in. In-cell NMR is a new application of high-resolution nuclear magnetic resonance spectroscopy that allows structural and dynamical features of proteins and other macromolecules to be analyzed directly in living cells. Owing to its challenging nature, this methodology has shown slow, but steady, development over the past 15 years. To date, several in-cell NMR approaches have been successfully applied to both bacterial and eukaryotic cells, including several human cell lines, and important structural and functional aspects have been elucidated. In this topical review, the major advances of in-cell NMR are summarized, with a special focus on recent developments in eukaryotic and mammalian cells.
Collapse
Affiliation(s)
- Enrico Luchinat
- Magnetic Resonance Center – CERM, University of Florence, Via Luigi Sacconi 6, 50019 Sesto Fiorentino, Florence, Italy
- Department of Biomedical, Clinical and Experimental Sciences, University of Florence, Viale Morgagni 50, 50134 Florence, Italy
| | - Lucia Banci
- Magnetic Resonance Center – CERM, University of Florence, Via Luigi Sacconi 6, 50019 Sesto Fiorentino, Florence, Italy
- Department of Chemistry, University of Florence, Via della Lastruccia 3, 50019 Sesto Fiorentino, Florence, Italy
| |
Collapse
|
12
|
Towards understanding cellular structure biology: In-cell NMR. BIOCHIMICA ET BIOPHYSICA ACTA-PROTEINS AND PROTEOMICS 2017; 1865:547-557. [PMID: 28257994 DOI: 10.1016/j.bbapap.2017.02.018] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/01/2016] [Revised: 02/22/2017] [Accepted: 02/27/2017] [Indexed: 12/20/2022]
Abstract
To watch biological macromolecules perform their functions inside the living cells is the dream of any biologists. In-cell nuclear magnetic resonance is a branch of biomolecular NMR spectroscopy that can be used to observe the structures, interactions and dynamics of these molecules in the living cells at atomic level. In principle, in-cell NMR can be applied to different cellular systems to achieve biologically relevant structural and functional information. In this review, we summarize the existing approaches in this field and discuss its applications in protein interactions, folding, stability and post-translational modifications. We hope this review will emphasize the effectiveness of in-cell NMR for studies of intricate biological processes and for structural analysis in cellular environments.
Collapse
|
13
|
Pastore A, Temussi PA. The Emperor's new clothes: Myths and truths of in-cell NMR. Arch Biochem Biophys 2017; 628:114-122. [PMID: 28259514 DOI: 10.1016/j.abb.2017.02.008] [Citation(s) in RCA: 31] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/02/2017] [Revised: 02/24/2017] [Accepted: 02/27/2017] [Indexed: 11/25/2022]
Abstract
In-cell NMR is a technique developed to study the structure and dynamical behavior of biological macromolecules in their natural environment, circumventing all isolation and purification steps. In principle, the potentialities of the technique are enormous, not only for the possibility of bypassing all purification steps but, even more importantly, for the wealth of information that can be gained from directly monitoring interactions among biological macromolecules in a natural cell. Here, we review critically the promises, successes and limits of this technique as it stands now. Interestingly, many of the problems of NMR in bacterial cells stem from the artificially high concentration of the protein under study whose overexpression is anyway necessary to select it from the background. This has, as a consequence, that when overexpressed, most globular proteins, do not show an NMR spectrum, limiting the applicability of the technique to intrinsically unfolded or specifically behaving proteins. The outlook for in-cell NMR of eukaryotic cells is more promising and is possibly the most attracting aspect for the future.
Collapse
Affiliation(s)
- Annalisa Pastore
- The Wohl Institute, King's College London, 5 Cutcombe Rd, London SE5 9RT, UK; University of Pavia, Department of Molecular Medicine, Pavia, Italy.
| | - Piero Andrea Temussi
- The Wohl Institute, King's College London, 5 Cutcombe Rd, London SE5 9RT, UK; University of Naples "Federico II", Department of Chemical Sciences, Naples, Italy
| |
Collapse
|
14
|
Abstract
In-cell NMR spectroscopy is a unique tool for characterizing biological macromolecules in their physiological environment at atomic resolution. Recent progress in NMR instruments and sample preparation methods allows functional processes, such as metal uptake, disulfide-bond formation and protein folding, to be analyzed by NMR in living, cultured human cells. This protocol describes the necessary steps to overexpress one or more proteins of interest inside human embryonic kidney 293T (HEK293T) cells, and it explains how to set up in-cell NMR experiments. The cDNA is transiently transfected as a complex with a cationic polymer (DNA:PEI (polyethylenimine)), and protein expression is carried on for 2-3 d, after which the NMR sample is prepared. (1)H and (1)H-(15)N correlation NMR experiments (for example, using band-selective optimized flip-angle short-transient heteronuclear multiple quantum coherence (SOFAST-HMQC)) can be carried out in <2 h, ensuring cell viability. Uniform (15)N labeling and amino-acid-specific (e.g., cysteine, methionine) labeling schemes are possible. The entire procedure takes 4 d from cell culture seeding to NMR data collection.
Collapse
|