Name: metabolic labeling of leucine rich repeat kinases 1 and 2 with radioactive phosphate
Uploaded: 2013-09-18T11:00:00
Description: Watch this Scientific Journal Video about Metabolic Labeling of Leucine Rich Repeat Kinases 1 and 2 with Radioactive Phosphate at JoVE.com

We are also grateful to the Michael J. Fox Foundation supporting this study. We thank the Research Foundation - Flanders FWO (FWO project G.0666.09, senior researcher fellowship to JMT), the IWT SBO/80020 project Neuro-TARGET, the KU Leuven (OT/08/052A and IOF-KP/07/ 001) for their support. This research was also supported in part by the Fund Druw&eacute;-Eerdekens managed by the King Baudouin Foundation to JMT.

The present protocol uses radioactive 32P-labeled orthophosphate to follow cellular phosphorylation of LRRK2. It is important to bear in mind that all operations with radioactive reagents should be performed using appropriate protective measures to minimize exposure of radioactive radiation to the operator and the environment. Compounds containing isotopes that emit ionizing radiation can be harmful to human health and strict licensing and regulations at an institutional and national level control their use. T...

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	<li>Hanafusa, H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Leucine-rich+repeat+kinase+LRRK1+regulates+endosomal+trafficking+of+the+EGF+receptor.">Leucine-rich repeat kinase LRRK1 regulates endosomal trafficking of the EGF receptor.</a> Nat Commun. 2, 158 (2011).</li><li>Titz, B., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+proximal+signaling+network+of+the+BCR-ABL1+oncogene+shows+a+modular+organization.">The proximal signaling network of the BCR-ABL1 oncogene shows a modular organization.</a> Oncogene. 29, 5895-5910 (2010).</li><li>Cookson, M. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+role+of+leucine-rich+repeat+kinase+2+(LRRK2)+in+Parkinson's+disease.">The role of leucine-rich repeat kinase 2 (LRRK2) in Parkinson's disease.</a> Nat Rev Neurosci. 11, 791-797 (2010).</li><li>Taymans, J. M., Cookson, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Mechanisms+of+dominant+parkinsonism;+the+toxic+triangle+of+LRRK2,+alpha-synuclein+and+tau.">Mechanisms of dominant parkinsonism; the toxic triangle of LRRK2, alpha-synuclein and tau.</a> Bioessays. 32, 227-235 (2010).</li><li>Lewis, P. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+function+of+ROCO+proteins+in+health+and+disease.">The function of ROCO proteins in health and disease.</a> Biol Cell. 101, 183-191 (2009).</li><li>Marin, I., van Egmond, W. N., van Haastert, P. 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M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Phosphorylation+of+LRRK2:+from+kinase+to+substrate.">Phosphorylation of LRRK2: from kinase to substrate.</a> Biochem Soc Trans. 40, 1102-1110 (2012).</li><li>Gloeckner, C. J., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Phosphopeptide+Analysis+Reveals+Two+Discrete+Clusters+of+Phosphorylation+in+the+N-Terminus+and+the+Roc+Domain+of+the+Parkinson-Disease+Associated+Protein+Kinase+LRRK2.">Phosphopeptide Analysis Reveals Two Discrete Clusters of Phosphorylation in the N-Terminus and the Roc Domain of the Parkinson-Disease Associated Protein Kinase LRRK2.</a> J Proteome Res. 9, 1738-1745 (2010).</li><li>Nichols, R. J., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=14-3-3+binding+to+LRRK2+is+disrupted+by+multiple+Parkinson's+disease-associated+mutations+and+regulates+cytoplasmic+localization.">14-3-3 binding to LRRK2 is disrupted by multiple Parkinson's disease-associated mutations and regulates cytoplasmic localization.</a> Biochem J. 430, 393-404 (2010).</li><li>Greggio, E., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Mutations+in+LRRK2/dardarin+associated+with+Parkinson+disease+are+more+toxic+than+equivalent+mutations+in+the+homologous+kinase+LRRK1.">Mutations in LRRK2/dardarin associated with Parkinson disease are more toxic than equivalent mutations in the homologous kinase LRRK1.</a> J.Neurochem. 102, 93-102 (2007).</li><li>Taymans, J. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=LRRK2+Kinase+Activity+Is+Dependent+on+LRRK2+GTP+Binding+Capacity+but+Independent+of+LRRK2+GTP+Binding.">LRRK2 Kinase Activity Is Dependent on LRRK2 GTP Binding Capacity but Independent of LRRK2 GTP Binding.</a> PLoS One. 6, 23207-23 (2011).</li><li>Dani&#235;ls, V. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Insight+into+the+mode+of+action+of+the+LRRK2+Y1699C+pathogenic+mutant.">Insight into the mode of action of the LRRK2 Y1699C pathogenic mutant.</a> J Neurochem. 116, 304-315 (2011).</li><li>Civiero, L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Biochemical+characterization+of+highly+purified+leucine-rich+repeat+kinases+1+and+2+demonstrates+formation+of+homodimers.">Biochemical characterization of highly purified leucine-rich repeat kinases 1 and 2 demonstrates formation of homodimers.</a> PLoS One. 7, e43472 (2012).</li><li>Taymans, J. 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B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Parkinson's+disease-associated+mutations+in+LRRK2+link+enhanced+GTP-binding+and+kinase+activities+to+neuronal+toxicity.">Parkinson's disease-associated mutations in LRRK2 link enhanced GTP-binding and kinase activities to neuronal toxicity.</a> Hum.Mol.Genet. 16, 223-232 (2007).</li><li>Sheng, Z., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Ser1292+autophosphorylation+is+an+indicator+of+LRRK2+kinase+activity+and+contributes+to+the+cellular+effects+of+PD+mutations.">Ser1292 autophosphorylation is an indicator of LRRK2 kinase activity and contributes to the cellular effects of PD mutations.</a> Sci Transl Med. 4, 164ra161 (2012).</li><li>Li, X., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Phosphorylation-dependent+14-3-3+binding+to+LRRK2+is+impaired+by+common+mutations+of+familial+Parkinson's+disease.">Phosphorylation-dependent 14-3-3 binding to LRRK2 is impaired by common mutations of familial Parkinson's disease.</a> PLoS One. 6, e17153 (2011).</li><li>Dzamko, N., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Inhibition+of+LRRK2+kinase+activity+leads+to+dephosphorylation+of+Ser(910)/Ser(935),+disruption+of+14-3-3+binding+and+altered+cytoplasmic+localization.">Inhibition of LRRK2 kinase activity leads to dephosphorylation of Ser(910)/Ser(935), disruption of 14-3-3 binding and altered cytoplasmic localization.</a> Biochem J. 430 (910), 405-413 (2010).</li></ol>

This paper provides a basic protocol for assaying general phosphorylation level of LRRK1 and LRRK2 in cell lines using metabolic labeling with 32P-orthophosphate. The overall strategy is straightforward. Affinity tagged LRRK proteins are expressed in HEK293T cells which are exposed to medium containing 32P-orthophosphate. The 32P-orthophosphate is assimilated by the cells after only a few hours of incubation and all molecules in the cell containing phosphates are thereby radioactively lab...

Leucine rich repeat kinases 1 and 2 (LRRK1 and LRRK2) are multidomain paralogs which share a similar domain organization. Both proteins encode a GTPase sequence akin to the Ras family of GTPases (Ras of Complex Proteins, or ROC) as well as a C-terminal of ROC domain (COR), effectively classifying both proteins to the ROCO protein family5,6. N-terminal of the ROC-COR domain tandem, both proteins encode a leucine-rich repeat domain as well as an ankyrin-like domain, while only LRRK2 encodes an extra armadillo domein6-8. C-terminal of ROC-COR, both proteins share a serine-threonine kinase domain while only LRRK2 encodes a WD40 domain in the C-terminal region8. The precise cellular roles of LRRK1 and LRRK2 have yet to be elucidated, however LRRK1 has been implicated in tyrosine kinase receptor signaling1,2 , while genetic evidence points to a role for LRRK2 in the pathogenesis of Parkinson's disease3,4 .
The phosphorylation of proteins is a common regulatory mechanism in cells. For example, phosphorylation can be essential for the activation of enzymes or for the recruitment of proteins to a signaling complex. The cellular phosphorylation of LRRK2 has been extensively characterized and phosphosite mapping has shown a majority of cellular phosphorylation sites to occur in a cluster between the ankyrin repeat and leucine rich repeat domains9-11. Although LRRK1 cellular phosphorylation sites have yet to be mapped, evidence from studies using phosphoprotein staining of blots of immunoprecipitated LRRK1 protein from COS7 cells suggests that LRRK1 protein is phosphorylated in cells12.
This paper provides a basic protocol for assaying general phosphorylation level of LRRK1 and LRRK2 in cell lines using metabolic labeling with 32P-orthophosphate. The overall strategy is straightforward. Affinity tagged LRRK proteins are expressed in HEK293T cells which are exposed to medium containing 32P-orthophosphate. The 32P-orthophosphate is assimilated by the cells after only a few hours of incubation and all molecules in the cell containing phosphates are thereby radioactively labeled. The affinity tag (3xflag) is then used to isolate the LRRK proteins from other cellular components by immunoprecipitation. Immunoprecipitates are then separated via SDS-PAGE, blotted to PVDF membranes and analysis of the incorporated phosphates is performed by autoradiography (32P signal) and western detection (protein signal) of the proteins on the blots.

<table border="1">
 <tbody>
 <tr>
 <td>Name of the reagent</td>
 <td>Company</td>
 <td>Catalogue number</td>
 <td>Comments (optional)</td>
 </tr>
 <tr>
 <td>Phosphorus-32 Radionuclide, 1 mCi, buffer disodiumphosphate in 1 ml water</td>
 <td>Perkin Elmer</td>
 <td>NEX011001MC</td>
 <td></td>
 </tr>
 <tr>
 <td>Dulbecco's Modified Eagle Medium (D-MEM) (1X), liquid (high glucose)</td>
 <td>Invitrogen</td>
 <td>11971-025</td>
 <td>This medium contains no phosphates</td>
 </tr>
 <tr>
 <td>Anti Flag M2 affiinty gel</td>
 <td>Sigma</td>
 <td>A2220</td>
 <td>For an equivalent product with red colored gel (useful to more easily visualize the beads), use cat. No. F2426.</td>
 </tr>
 <tr>
 <td>Extra thick blotting filter</td>
 <td>Bio-Rad</td>
 <td>1703965</td>
 <td></td>
 </tr>
 <tr>
 <td>Ponceau S solution</td>
 <td>Sigma</td>
 <td>P7170</td>
 <td></td>
 </tr>
 </tbody>
</table>

metabolic labeling of leucine rich repeat kinases 1 and 2 with radioactive phosphate

Leucine rich repeat kinases 1 and 2 (LRRK1 and LRRK2) are paralogs which share a similar domain organization, including a serine-threonine kinase domain, a Ras of complex proteins domain (ROC), a C-terminal of ROC domain (COR), and leucine-rich and ankyrin-like repeats at the N-terminus. The precise cellular roles of LRRK1 and LRRK2 have yet to be elucidated, however LRRK1 has been implicated in tyrosine kinase receptor signaling1,2, while LRRK2 is implicated in the pathogenesis of Parkinson's disease3,4. In this report, we present a protocol to label the LRRK1 and LRRK2 proteins in cells with 32P orthophosphate, thereby providing a means to measure the overall phosphorylation levels of these 2 proteins in cells. In brief, affinity tagged LRRK proteins are expressed in HEK293T cells which are exposed to medium containing 32P-orthophosphate. The 32P-orthophosphate is assimilated by the cells after only a few hours of incubation and all molecules in the cell containing phosphates are thereby radioactively labeled. Via the affinity tag (3xflag) the LRRK proteins are isolated from other cellular components by immunoprecipitation. Immunoprecipitates are then separated via SDS-PAGE, blotted to PVDF membranes and analysis of the incorporated phosphates is performed by autoradiography (32P signal) and western detection (protein signal) of the proteins on the blots. The protocol can readily be adapted to monitor phosphorylation of any other protein that can be expressed in cells and isolated by immunoprecipitation.

In order to compare overall phosphorylation levels of LRRK1 and LRRK2 in cells, 3xflag tagged LRRK1 and LRRK2 were expressed in HEK293T cells15. Cells were cultured in 6-well plates and labeled with 32P and analyzed as described above in the protocol text. Figure 1 shows representative results for metabolic labeling of LRRK1 and LRRK2 in HEK293T cells. Radioactive phosphate incorporation is observed for both LRRK1 and LRRK2. Upon quantification of the 32P levels normalize...

Watch this Scientific Journal Video about Metabolic Labeling of Leucine Rich Repeat Kinases 1 and 2 with Radioactive Phosphate at JoVE.com

Metabolic Labeling of Leucine Rich Repeat Kinases 1 and 2 with Radioactive Phosphate

Leucine rich repeat kinases 1 and 2 (LRRK1 and LRRK2) are multidomain proteins which encode both GTPase and kinase domains and which are phosphorylated in cells. Here, we present a protocol to label LRRK1 and LRRK2 in cells with 32P orthophosphate, thereby providing a means to measure their overall cellular phophorylation levels.

Leucine rich repeat kinases 1 and 2 (LRRK1 and LRRK2) are paralogs which share a similar domain organization, including a serine-threonine kinase domain, ...

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Here we describe a metabolic labeling method for following a subpopulation of actively cycling cells through their progression from the DNA replication phase, through to the division and separation of their daughter cells. Coupled with flow cytometry quantification, this protocol enables for measurement of kinetic progression of the cell cycle in the absence of either mechanically- or chemically- induced cellular stresses commonly associated with other cell cycle synchronization methodologies 10. In the following sections we will discuss the methodology, as well as some of its applications in biomedical research.

Tracking subtle changes in the progression and kinetics of cell cycle stages can be accomplished by use of a combination of metabolic labeling of nucleic acids with BrdU and total genomic DNA staining via Propidium Iodide. This method avoids the need of chemical synchronization of cycling cells, thereby preventing the introduction of non-specific DNA damage, which in turn affects cell cycle progression.

Precise control of the initiation and subsequent progression through the various phases of the cell cycle are of paramount importance in proliferating ...

Metabolic Labeling of Newly Transcribed RNA for High Resolution Gene Expression Profiling of RNA Synthesis, Processing and Decay in Cell Culture

The development of whole-transcriptome microarrays and next-generation sequencing has revolutionized our understanding of the complexity of cellular gene expression. Along with a better understanding of the involved molecular mechanisms, precise measurements of the underlying kinetics have become increasingly important. Here, these powerful methodologies face major limitations due to intrinsic properties of the template samples they study, i.e. total cellular RNA. In many cases changes in total cellular RNA occur either too slowly or too quickly to represent the underlying molecular events and their kinetics with sufficient resolution. In addition, the contribution of alterations in RNA synthesis, processing, and decay are not readily differentiated.
We recently developed high-resolution gene expression profiling to overcome these limitations. Our approach is based on metabolic labeling of newly transcribed RNA with 4-thiouridine (thus also referred to as 4sU-tagging) followed by rigorous purification of newly transcribed RNA using thiol-specific biotinylation and streptavidin-coated magnetic beads. It is applicable to a broad range of organisms including vertebrates, Drosophila, and yeast. We successfully applied 4sU-tagging to study real-time kinetics of transcription factor activities, provide precise measurements of RNA half-lives, and obtain novel insights into the kinetics of RNA processing. Finally, computational modeling can be employed to generate an integrated, comprehensive analysis of the underlying molecular mechanisms.

Total cellular RNA provides a poor template for studying short-term changes in RNA synthesis and decay as well as the kinetics of RNA processing. Here, we describe metabolic labeling of newly transcribed RNA with 4-thiouridine followed by thiol-specific biotinylation and purification of newly transcribed RNA allowing to overcome these limitations.

The development of whole-transcriptome microarrays and next-generation sequencing has revolutionized our understanding of the complexity of cellular gene ...

Metabolic Labeling and Membrane Fractionation for Comparative Proteomic Analysis of Arabidopsis thaliana Suspension Cell Cultures

Plasma membrane microdomains are features based on the physical properties of the lipid and sterol environment and have particular roles in signaling processes. Extracting sterol-enriched membrane microdomains from plant cells for proteomic analysis is a difficult task mainly due to multiple preparation steps and sources for contaminations from other cellular compartments. The plasma membrane constitutes only about 5-20% of all the membranes in a plant cell, and therefore isolation of highly purified plasma membrane fraction is challenging. A frequently used method involves aqueous two-phase partitioning in polyethylene glycol and dextran, which yields plasma membrane vesicles with a purity of 95% 1. Sterol-rich membrane microdomains within the plasma membrane are insoluble upon treatment with cold nonionic detergents at alkaline pH. This detergent-resistant membrane fraction can be separated from the bulk plasma membrane by ultracentrifugation in a sucrose gradient 2. Subsequently, proteins can be extracted from the low density band of the sucrose gradient by methanol/chloroform precipitation. Extracted protein will then be trypsin digested, desalted and finally analyzed by LC-MS/MS. Our extraction protocol for sterol-rich microdomains is optimized for the preparation of clean detergent-resistant membrane fractions from Arabidopsis thaliana cell cultures.
We use full metabolic labeling of Arabidopsis thaliana suspension cell cultures with K15NO3 as the only nitrogen source for quantitative comparative proteomic studies following biological treatment of interest 3. By mixing equal ratios of labeled and unlabeled cell cultures for joint protein extraction the influence of preparation steps on final quantitative result is kept at a minimum. Also loss of material during extraction will affect both control and treatment samples in the same way, and therefore the ratio of light and heave peptide will remain constant. In the proposed method either labeled or unlabeled cell culture undergoes a biological treatment, while the other serves as control 4.

Metabolic Labeling and Membrane Fractionation for Comparative Proteomic Analysis of Arabidopsis thaliana Suspension Cell Cultures

Here we describe a robust method for the fractionation of plant plasma membranes into detergent resistant and detergent soluble membranes based on a mixture of unlabeled and in vivo fully 15N labeled Arabidopsis thaliana cell cultures. The procedure is applied for comparative proteomic studies to understand signaling processes.

Plasma membrane microdomains are features based on the physical properties of the lipid and sterol environment and have particular roles in signaling ...

A New Approach for the Comparative Analysis of Multiprotein Complexes Based on 15N Metabolic Labeling and Quantitative Mass Spectrometry

The introduced protocol provides a tool for the analysis of multiprotein complexes in the thylakoid membrane, by revealing insights into complex composition under different conditions. In this protocol the approach is demonstrated by comparing the composition of the protein complex responsible for cyclic electron flow (CEF) in Chlamydomonas reinhardtii, isolated from genetically different strains. The procedure comprises the isolation of thylakoid membranes, followed by their separation into multiprotein complexes by sucrose density gradient centrifugation, SDS-PAGE, immunodetection and comparative, quantitative mass spectrometry (MS) based on differential metabolic labeling (14N/15N) of the analyzed strains. Detergent solubilized thylakoid membranes are loaded on sucrose density gradients at equal chlorophyll concentration. After ultracentrifugation, the gradients are separated into fractions, which are analyzed by mass-spectrometry based on equal volume. This approach allows the investigation of the composition within the gradient fractions and moreover to analyze the migration behavior of different proteins, especially focusing on ANR1, CAS, and PGRL1. Furthermore, this method is demonstrated by confirming the results with immunoblotting and additionally by supporting the findings from previous studies (the identification and PSI-dependent migration of proteins that were previously described to be part of the CEF-supercomplex such as PGRL1, FNR, and cyt f). Notably, this approach is applicable to address a broad range of questions for which this protocol can be adopted and e.g. used for comparative analyses of multiprotein complex composition isolated from distinct environmental conditions.

A New Approach for the Comparative Analysis of Multiprotein Complexes Based on 15N Metabolic Labeling and Quantitative Mass Spectrometry

The described comparative, quantitative proteomic approach aims at obtaining insights into the composition of multiprotein complexes&#160;under different conditions and is demonstrated by comparing genetically different strains. For quantitative analysis equal volumes of different fractions from a sucrose density gradient are mixed and analyzed by mass spectrometry.

The introduced protocol provides a tool for the analysis of multiprotein complexes in the thylakoid membrane, by revealing insights into complex ...

Sequence-specific Labeling of Nucleic Acids and Proteins with Methyltransferases and Cofactor Analogues

S-Adenosyl-l-methionine (AdoMet or SAM)-dependent methyltransferases (MTase) catalyze the transfer of the activated methyl group from AdoMet to specific positions in DNA, RNA, proteins and small biomolecules. This natural methylation reaction can be expanded to a wide variety of alkylation reactions using synthetic cofactor analogues. Replacement of the reactive sulfonium center of AdoMet with an aziridine ring leads to cofactors which can be coupled with DNA by various DNA MTases. These aziridine cofactors can be equipped with reporter groups at different positions of the adenine moiety and used for Sequence-specific Methyltransferase-Induced Labeling of DNA (SMILing DNA). As a typical example we give a protocol for biotinylation of pBR322 plasmid DNA at the 5&#8217;-ATCGAT-3&#8217; sequence with the DNA MTase M.BseCI and the aziridine cofactor 6BAz in one step. Extension of the activated methyl group with unsaturated alkyl groups results in another class of AdoMet analogues which are used for methyltransferase-directed Transfer of Activated Groups (mTAG). Since the extended side chains are activated by the sulfonium center and the unsaturated bond, these cofactors are called double-activated AdoMet analogues. These analogues not only function as cofactors for DNA MTases, like the aziridine cofactors, but also for RNA, protein and small molecule MTases. They are typically used for enzymatic modification of MTase substrates with unique functional groups which are labeled with reporter groups in a second chemical step. This is exemplified in a protocol for fluorescence labeling of histone H3 protein. A small propargyl group is transferred from the cofactor analogue SeAdoYn to the protein by the histone H3 lysine 4 (H3K4) MTase Set7/9 followed by click labeling of the alkynylated histone H3 with TAMRA azide. MTase-mediated labeling with cofactor analogues is an enabling technology for many exciting applications including identification and functional study of MTase substrates as well as DNA genotyping and methylation detection.

DNA and proteins are sequence-specifically labeled with affinity or fluorescent reporter groups using DNA or protein methyltransferases and synthetic cofactor analogues. Depending on the cofactor specificity of the enzymes, aziridine or double activated cofactor analogues are employed for one- or two-step labeling.

S-Adenosyl-l-methionine (AdoMet or SAM)-dependent methyltransferases (MTase) catalyze the transfer of the activated methyl group from AdoMet to specific ...