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If that doesn't help, please let us know. Unable to load video. Please check your Internet connection and reload this page. If the problem continues, please let us know and we'll try to help. An unexpected error occurred. Recombinant Tau is isotopically enriched and modified in vitro by a kinase prior to data acquisition and analysis.
Aggregates of the neuronal Tau protein are found inside neurons of Alzheimer's disease patients. Development of the disease is accompanied by increased, abnormal phosphorylation of Tau. In the course of the molecular investigation of Tau functions and dysfunctions in the disease, nuclear magnetic resonance NMR spectroscopy is used to identify the multiple phosphorylations of Tau. We present here detailed protocols of recombinant production of Tau in bacteria, with isotopic enrichment for NMR studies.
Purification steps that take advantage of Tau's heat stability and high isoelectric point are described. The protocol for in vitro phosphorylation of Tau by recombinant activated ERK2 allows for generating multiple phosphorylations. The protein sample is ready for data acquisition at the issue of these steps.
The parameter setup to start recording on the spectrometer is considered next. Finally, the strategy to identify phosphorylation sites of modified Tau, based on NMR data, is explained. The benefit of this methodology compared to other techniques used to identify phosphorylation sites, such as immuno-detection or mass spectrometry MSis discussed. Tau is a microtubule-associated protein that stimulates microtubule MT formation. Tau is equally involved in several neurodegenerative disorders, so-called tauopathies, of which the best known is AD.
In these disorders, Tau self-aggregates in paired helical filaments PHFs and is found modified on many residues by posttranslational modifications PTMs such as phosphorylation 1. of Tau protein is implicated in both regulation of its physiological function of MT stabilization and pathological loss of function that characterizes AD neurons.
Furthermore, Tau protein, when integrated in PHFs in diseased neurons, is invariably hyperphosphorylated 2.
Unlike normal Tau that contains phosphate groups, the hyperphosphorylated Tau in PHFs contains 5 to 9 phosphate groups 3. Hyperphosphorylation of Tau corresponds both to an increase of stoichiometry at some sites and to phosphorylation of additional sites that are called pathological sites of phosphorylation. However, overlap exists between AD and normal adult patterns of phosphorylation, despite quantitative differences in the level 4. How specific phosphorylation events influence function and dysfunction of Tau remains largely unknown.
We aim to decipher Tau regulation by PTMs at the molecular level. To deepen the understanding of the molecular aspects of Tau, we have to address technical challenges. Firstly, Tau is an intrinsically disordered protein IDP when isolated in solution. Such proteins lack well-defined three-dimensional structure under physiological conditions and require particular biophysical methods to study their function s and structural properties.
Tau is a paradigm for the growing class of IDPs, often found associated with pathologies such as neurodegenerative diseases, hence increasing the interest to understand the molecular parameters underlying their functions.
Secondly, characterization of Tau phosphorylation is an analytical challenge, with 80 potential phosphorylation sites along the sequence of the longest amino-acid Tau isoform. A number of antibodies have been developed against phosphorylated epitopes of Tau and are used for detection of pathological Tau in neurons or brain tissue.
Phosphorylation events can take place on at least 20 sites targeted by proline-directed kinases, most of them in close proximity within the Proline-rich region. The qualitative which sites? NMR spectroscopy can be used to investigate disordered proteins that are highly dynamic systems constituted of ensembles of conformers. High-resolution NMR spectroscopy was applied to investigate both structure Svensk seger i f3 em function of the Tau protein. In addition, the complexity of Tau's phosphorylation profile led to the development of molecular tools and new analytical methods using NMR for the identification of phosphorylation sites 6 - 8.
NMR as an analytical method allows for the identification of Tau phosphorylation sites in a global manner, visualization of all the single-site modifications in a single experiment, and of the extent of phosphate incorporation. This point is essential since although phosphorylation studies on Tau abound in the literature, most of them have been performed with antibodies, leaving a large degree of uncertainty over the complete profile of phosphorylation and thus the true impact of individual phosphorylation events.
In addition, Tau mutants that allow for generating specific Tau protein isoforms with well-characterized phosphorylation patterns are used to decipher the phosphorylation code of Tau. NMR spectroscopy is then used to characterize enzymatically modified Tau samples 6 - 8. Indeed, neither the structural impact nor interaction parameters of phosphorylation can always be mimicked by glutamic acids.
Here, the preparation of isotopically labeled Tau for NMR investigations will be described first. Tau protein phosphorylated by ERK2 is modified on numerous sites described as pathological sites of phosphorylation, and thus represents an interesting model of hyperphosphorylated Tau.
A detailed protocol of Tau in vitro phosphorylation by recombinant ERK2 kinase is presented. In addition to the preparation of modified, isotopically-labeled Tau protein, the NMR strategy used for identification of the PTMs is described.
Please recommend JoVE to your librarian. Figure 3A shows a major absorption peak at nm observed during the elution gradient. This peak corresponds to purified Tau protein as seen on the acrylamide gel above the chromatogram.
Figure 3B shows a well separated absorption peak at nm and peak of conductivity, ensuring that desalting of the protein is efficient. Figure 4 shows protein gel-shift observed by SDS-PAGE analysis 16 characteristic of multiple protein phosphorylation compare lanes 2 and 3. The frequency of the residual signal is used to define the o1p parameter frequency offset for 1 H.
Figure 7C shows a 1D 1 H spectrum with good signal to noise ratio, indicating that the basic acquisition parameters were correctly set and a signal from the protein sample can be detected. Figure 9B at MHz, shows appearance of additional peaks in the spectrum corresponding to phosphorylated residues red box.
Figure 9C at MHz, shows peaks in the spectrum corresponding to phosphorylated residues red box. Resolution is better than in Figure 9B. Figure 10B shows a 1 H- 13 C plane extracted from the 1 H- 15 N- 13 C 3D spectrum with good signal intensity allowing to detect 13 C signals from both i and i-1 residues.
Scheme of the main steps of recombinant protein production and isotopic labeling. Steps from bacteria transformation to recombinant protein production are outlined as described in paragraph 1 of the protocol.
Please click here to view a larger version of this figure. Scheme of the main steps of Svensk seger i f3 em Tau protein purification.
Steps from bacterial cells lysis to recombinant protein purification are outlined as described paragraph 2 of the protocol. Liquid chromatography steps of protocol. A Cation exchange chromatography fractionation of the heated bacterial extract. The absorbance at nm, nm and the conductivity correspond respectively to solid and dashed black lines and dotted red line.
B Desalting of the Tau protein into a buffer suitable for lyophilization. Steps from NMR sample preparation to data acquisition and processing are outlined as described in paragraph 4 of the protocol. Set-up of the p1 parameter Svensk seger i f3 em NMR data acquisition.
This parameter differs between samples and is mainly dependent on salt concentration. Single-scan spectra with a recycle delay of 30 sec were collected and plotted horizontally. A Free induction signal decay in the time domain. A good quality Tau sample B Tau sample showing degradation as revealed by the appearance of additional resonances in a particular region of the spectrum high field 1 H, low field 15 Nhere boxed in blue.
This last sample was prepared without protease inhibitors. Additional resonances in a particular region of Svensk seger i f3 em spectrum, here boxed in red, are observed in phosphorylated Tau spectra. These resonances, which correspond to proton amide 1 H- 15 N correlations of pSer and pThr residues, are easily visualized in the region around 8. A and B correspond to spectra acquired at MHz, 2, and data points at spectral widths of 14 and 25 ppm were recorded in the 1 H F2 and 15 N F1 dimensions, respectively.
Spectral widths are 14, 25, and 61 ppm, centered on 4. Duration of the acquisition using 16 scans is 4 days and 6 hr. Data processing and representation were done using NMR acquisition and processing software. A zoom on the right centered on the 1 H chemical shift of 9.
The 13 CB resonance is aliased due to the width of the spectral window. Graphical representation and peak picking were performed using NMR analysis software. We have used NMR spectroscopy to characterize enzymatically modified Tau samples. The recombinant expression and purification described here for the full-length human Tau protein can similarly be used to produce mutant Tau or Tau domains.
Isotopically enriched protein is needed for NMR spectroscopy, necessitating recombinant expression. Identification of phosphorylation sites requires resonance assignment and a 15 N, 13 C doubly labeled protein.
Given the cost of isotopes, good yield is required in the recombinant expression step. Glucose is the limiting factor for the bacterial growth in the M9 medium therefore the amount of 13 C 6 -glucose can be increased to 4 g per liter of growth medium to improve yield. Addition of complete medium and MEM vitamins are not compulsory but help to stimulate growth and improve yield.
Given the high cost of the complete labeled medium, this product is only used as a growth medium supplement. Bacterial growth is slow in M9 medium.
An OD of 1. Expected yield of recombinant Tau protein is about 15 mg per liter of bacterial culture. The use of a programmable incubator allows to conveniently schedule protein production, collection of the bacterial pellet and analytical control of protein production during working day hours.
Sample concentration is important to obtain a good quality spectrum. Access to a high-field spectrometer, such as the MHz instrument used in this study will provide better signal-to-noise and reduce constraints on sample concentration Figure 8. Given that Tau is a large disordered protein, its NMR spectra are characterized by considerable signal "Svensk seger i f3 em," and a high-field NMR spectrometer will also be the best choice in terms of resolution Figure 8.
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