Name: a facile protocol to generate site-specifically acetylated proteins in escherichia coli
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Description: Watch this Scientific Journal Video about A Facile Protocol to Generate Site-Specifically Acetylated Proteins in Escherichia Coli at JoVE.com

This work was supported by the NIH (AI119813), the start-up from the University of Arkansas, and the award from Arkansas Biosciences Institute.

1. Site-Directed Mutagenesis of the Target Gene
Note: MDH is expressed under T7 promoter in the pCDF-1 vector with the CloDF13 origin and a copy number of 20 to 4034.
<ol>
	<li>Introduce the amber stop codon at the position 140 in the gene by primers (forward primer: GGTGTTTATGACTAGAACAAACTGTTCGGCG and reverse primer: GGCTTTTTTCAGCACTTCAGCAGCAATTGC), following the instruction of the site-directed mutagenesis kit.</li>
	<li>Amplify th...

<ol>
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K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Lysine+acetylation:+the+tale+of+a+modification+from+transcription+regulation+to+metabolism.">Lysine acetylation: the tale of a modification from transcription regulation to metabolism.</a> Chembiochem. 11 (11), 1501-1504 (2010).</li><li>Cohen, T., Yao, T. P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=AcK-knowledge+reversible+acetylation.">AcK-knowledge reversible acetylation.</a> Science's STKE : signal transduction knowledge environment. (245), pe42 (2004).</li><li>Drazic, A., Myklebust, L. M., Ree, R., Arnesen, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+world+of+protein+acetylation.">The world of protein acetylation.</a> Biochim Biophys Acta. 1864 (10), 1372-1401 (2016).</li><li>Escalante-Semerena, J. 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A., Sengupta, N., Zhang, X., Seto, E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Acetylation+and+deacetylation+of+non-histone+proteins.">Acetylation and deacetylation of non-histone proteins.</a> Gene. 363, 15-23 (2005).</li><li>Close, P., 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+emerging+role+of+lysine+acetylation+of+non-nuclear+proteins.">The emerging role of lysine acetylation of non-nuclear proteins.</a> Cell Mol Life Sci. 67 (8), 1255-1264 (2010).</li><li>Iyer, A., Fairlie, D. P., Brown, L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Lysine+acetylation+in+obesity,+diabetes+and+metabolic+disease.">Lysine acetylation in obesity, diabetes and metabolic disease.</a> Immunol Cell Biol. 90 (1), 39-46 (2012).</li><li>You, L., Nie, J., Sun, W. J., Zheng, Z. Q., Yang, X. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Lysine+acetylation:+enzymes,+bromodomains+and+links+to+different+diseases.">Lysine acetylation: enzymes, bromodomains and links to different diseases.</a> Essays Biochem. 52, 1-12 (2012).</li><li>Bonnaud, E. M., Suberbielle, E., Malnou, C. E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Histone+acetylation+in+neuronal+(dys)function.">Histone acetylation in neuronal (dys)function.</a> Biomol Concepts. 7 (2), 103-116 (2016).</li><li>Fukushima, A., Lopaschuk, G. D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Acetylation+control+of+cardiac+fatty+acid+beta-oxidation+and+energy+metabolism+in+obesity,+diabetes,+and+heart+failure.">Acetylation control of cardiac fatty acid beta-oxidation and energy metabolism in obesity, diabetes, and heart failure.</a> Biochim Biophys Acta. 1862 (12), 2211-2220 (2016).</li><li>Kaypee, S., 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=Aberrant+lysine+acetylation+in+tumorigenesis:+Implications+in+the+development+of+therapeutics.">Aberrant lysine acetylation in tumorigenesis: Implications in the development of therapeutics.</a> Pharmacol Ther. 162, 98-119 (2016).</li><li>Tapias, A., Wang, Z. Q. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Lysine+Acetylation+and+Deacetylation+in+Brain+Development+and+Neuropathies.">Lysine Acetylation and Deacetylation in Brain Development and Neuropathies.</a> Genomics Proteomics Bioinformatics. 15 (1), 19-36 (2017).</li><li>Hu, L. I., Lima, B. P., Wolfe, A. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Bacterial+protein+acetylation:+the+dawning+of+a+new+age.">Bacterial protein acetylation: the dawning of a new age.</a> Molecular microbiology. 77 (1), 15-21 (2010).</li><li>Jones, J. D., O'Connor, C. D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Protein+acetylation+in+prokaryotes.">Protein acetylation in prokaryotes.</a> Proteomics. 11 (15), 3012-3022 (2011).</li><li>Bernal, V., 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=Regulation+of+bacterial+physiology+by+lysine+acetylation+of+proteins.">Regulation of bacterial physiology by lysine acetylation of proteins.</a> New biotechnol. 31 (6), 586-595 (2014).</li><li>Hentchel, K. L., Escalante-Semerena, J. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Acylation+of+Biomolecules+in+Prokaryotes:+a+Widespread+Strategy+for+the+Control+of+Biological+Function+and+Metabolic+Stress.">Acylation of Biomolecules in Prokaryotes: a Widespread Strategy for the Control of Biological Function and Metabolic Stress.</a> Microbiology and molecular biology reviews : MMBR. 79 (3), 321-346 (2015).</li><li>Ouidir, T., Kentache, T., Hardouin, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Protein+lysine+acetylation+in+bacteria:+Current+state+of+the+art.">Protein lysine acetylation in bacteria: Current state of the art.</a> Proteomics. 16 (2), 301-309 (2016).</li><li>Wolfe, A. 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C., Schultz, P. G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Adding+new+chemistries+to+the+genetic+code.">Adding new chemistries to the genetic code.</a> Annu Rev Biochem. 79, 413-444 (2010).</li><li>Mukai, T., Lajoie, M. J., Englert, M., Soll, D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Rewriting+the+Genetic+Code.">Rewriting the Genetic Code.</a> Annu Rev Microbiol. , (2017).</li><li>O'Donoghue, P., Ling, J., Wang, Y. S., Soll, D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Upgrading+protein+synthesis+for+synthetic+biology.">Upgrading protein synthesis for synthetic biology.</a> Nat Chem Biol. 9 (10), 594-598 (2013).</li><li>Chin, J. 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The genetic incorporation of noncanonical amino acids (ncAAs) is based on the suppression of an assigned codon, mostly the amber stop codon UAG36,37,38,39, by the ncAA-charged tRNA containing the corresponding anticodon. As is known, the UAG codon is recognized by the release factor-1 (RF1) in bacteria, and it can also be suppressed by near cognate tRNAs from hosts charged by canonical amino ac...

Post-translational modifications (PTMs) of proteins occur after the translation process, and arise from covalent addition of functional groups to amino acid residues, playing important roles in almost all the biological processes, including gene transcription, stress response, cellular differentiation, and metabolism1,2,3. To date, about 400 distinctive PTMs have been identified4. The intricacy of the genome and the proteome is amplified to a great extent by protein PTMs, as they regulate protein activity and localization, and affect the interaction with other molecules such as proteins, nucleic acids, lipids, and cofactors5.
Protein acetylation has been at the forefront of PTMs studies in the last two decades6,7,8,9,10,11,12. Lysine acetylation was first discovered in histones more than 50 years ago13,14, has been well scrutinized, and is known to exist in more than 80 transcription factors, regulators, and various proteins15,16,17. Studies on protein acetylation have not only provided us with a deeper understanding of its regulatory mechanisms, but also guided treatments for a number of diseases caused by dysfunctional acetylation18,19,20,21,22,23. It was believed that lysine acetylation only happens in eukaryotes, but recent studies have shown that protein acetylation also plays key roles in bacterial physiology, including chemotaxis, acid resistance, activation, and stabilization of pathogenicity islands and other virulence related proteins24,25,26,27,28,29.
A commonly used method to biochemically characterize lysine acetylation is using site-directed mutagenesis. Glutamine is used as a mimic of acetyllysine because of its similar size and polarity. Arginine is utilized as a non-acetylated lysine mimic, since it preserves its positive charge under physiological conditions but cannot be acetylated. However, both mimics are not real isosteres and do not always yield the expected results30. The most rigorous approach is to generate homogeneously acetylated proteins at specific lysine residues, which is difficult or impossible for most classical methods due to the low stoichiometry of lysine acetylation in nature7,11. This challenge has been unraveled by the genetic code expansion strategy, which employs an engineered pyrrolysyl-tRNA synthetase variant from Methanosarcinaceae species to charge tRNAPyl with acetyllysine, utilizes the host translational machinery to suppress the UAG stop codon in the mRNA, and directs the incorporation of acetyllysine in the designed position of the target protein31. Recently, we have optimized this system with an improved EF-Tu-binding tRNA32 and an upgraded acetyllysyl-tRNA synthetase33. Furthermore, we have applied this enhanced incorporation system in acetylation studies of malate dehydrogenase34 and tyrosyl-tRNA synthetase35. Herein, we demonstrate the protocol for generating purely acetylated proteins from the molecular cloning to biochemical identification by using malate dehydrogenase (MDH), which we have extensively studied as a demonstrative example.

<table border="0" cellpadding="0" cellspacing="0" width="615">
	<tbody>
		<tr height="20">
			<td height="20" style="height:20px;width:216px;">Bradford protein assay</td>
			<td style="width:113px;">Bio-Rad</td>
			<td style="width:119px;">5000006</td>
			<td style="width:167px;">Protein concentration</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;width:216px;">4x Laemmli Sample Buffer</td>
			<td style="width:113px;">Bio-Rad</td>
			<td style="width:119px;">1610747</td>
			<td style="width:167px;">SDS sample buffer</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;width:216px;">Coomassie G-250 Stain</td>
			<td style="width:113px;">Bio-Rad</td>
			<td style="width:119px;">1610786</td>
			<td style="width:167px;">SDS-PAGE gel staining</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;width:216px;">4-20% SDS-PAGE ready gel</td>
			<td style="width:113px;">Bio-Rad</td>
			<td style="width:119px;">4561093</td>
			<td style="width:167px;">Protein determination</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;width:216px;">Ac-K-100 (HRP Conjugate)</td>
			<td style="width:113px;">Cell Signaling</td>
			<td style="width:119px;">6952</td>
			<td style="width:167px;">Antibody</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;width:216px;">IPTG</td>
			<td style="width:113px;">CHEM-IMPEX</td>
			<td style="width:119px;">194</td>
			<td style="width:167px;">Expression inducer</td>
		</tr>
		<tr height="23">
			<td height="23" style="height:23px;width:216px;">N&#949;-Acetyl-L-lysine</td>
			<td style="width:113px;">CHEM-IMPEX</td>
			<td style="width:119px;">5364</td>
			<td style="width:167px;">Noncanonical amino acid</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;width:216px;">PD-10 desalting column</td>
			<td style="width:113px;">GE Healthcare</td>
			<td style="width:119px;">17085101</td>
			<td style="width:167px;">Desalting</td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;width:216px;">Q5 Site-Directed Mutagenesis Kit</td>
			<td style="width:113px;">NEB</td>
			<td style="width:119px;">E0554</td>
			<td style="width:167px;">Introducing the stop codon</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;width:216px;">BL21 (DE3) cells</td>
			<td style="width:113px;">NEB</td>
			<td style="width:119px;">C2527</td>
			<td style="width:167px;">Expressing strain</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;width:216px;">QIAprep Spin Miniprep Kit</td>
			<td style="width:113px;">QIAGEN</td>
			<td style="width:119px;">27106</td>
			<td style="width:167px;">Extracting plasmids</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;width:216px;">Ni-NTA resin</td>
			<td style="width:113px;">QIAGEN</td>
			<td style="width:119px;">30210</td>
			<td style="width:167px;">Affinity purification resin</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;width:216px;">nicotinamide</td>
			<td style="width:113px;">Sigma-Aldrich</td>
			<td style="width:119px;">N3376</td>
			<td style="width:167px;">Deacetylase inhibitor</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;width:216px;">&#946;-Mercaptoethanol</td>
			<td style="width:113px;">Sigma-Aldrich</td>
			<td style="width:119px;">M6250</td>
			<td style="width:167px;">Reducing agent</td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;width:216px;">BugBuster Protein Extraction Reagent</td>
			<td style="width:113px;">Sigma-Aldrich</td>
			<td style="width:119px;">70584</td>
			<td style="width:167px;">Breaking cells</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;width:216px;">Benzonase nuclease</td>
			<td style="width:113px;">Sigma-Aldrich</td>
			<td style="width:119px;">E1014</td>
			<td style="width:167px;">DNase</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;width:216px;">ECL Western Blotting Substrate</td>
			<td style="width:113px;">ThermoFisher</td>
			<td style="width:119px;">32106</td>
			<td style="width:167px;">Chemiluminescence</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;width:216px;">Premixed LB Broth</td>
			<td style="width:113px;">VWR</td>
			<td style="width:119px;">97064</td>
			<td style="width:167px;">Cell growth medium</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;width:216px;">Bovine serum albumin</td>
			<td style="width:113px;">VWR</td>
			<td style="width:119px;">97061-416</td>
			<td style="width:167px;">western blots blocking</td>
		</tr>
	</tbody>
</table>

a facile protocol to generate site-specifically acetylated proteins in escherichia coli

Post-translational modifications that occur at specific positions of proteins have been shown to play important roles in a variety of cellular processes. Among them, reversible lysine acetylation is one of the most widely distributed in all domains of life. Although numerous mass spectrometry-based acetylome studies have been performed, further characterization of these putative acetylation targets has been limited. One possible reason is that it is difficult to generate purely acetylated proteins at desired positions by most classic biochemical approaches. To overcome this challenge, the genetic code expansion technique has been applied to use the pair of an engineered pyrrolysyl-tRNA synthetase variant, and its cognate tRNA from Methanosarcinaceae species, to direct the cotranslational incorporation of acetyllysine at the specific site in the protein of interest. After first application in the study of histone acetylation, this approach has facilitated acetylation studies on a variety of proteins. In this work, we demonstrated a facile protocol to produce site-specifically acetylated proteins by using the model bacterium Escherichia coli as the host. Malate dehydrogenase was used as a demonstration example in this work.

The yield of acetylated MDH protein was 15 mg per 1 L culture, while that of wild-type MDH was 31 mg per 1 L culture. Purified proteins were analyzed by SDS-PAGE as shown in Figure 1. The wild-type MDH was used as a positive control34. The protein purified from cells harboring the acetyllysine (AcK) incorporation system and the mutant mdh gene, but without AcK in growth media, was used as a negative control. Lysine acetylation...

Watch this Scientific Journal Video about A Facile Protocol to Generate Site-Specifically Acetylated Proteins in Escherichia Coli at JoVE.com

A Facile Protocol to Generate Site-Specifically Acetylated Proteins in Escherichia Coli

Genetic code expansion serves as a powerful tool to study a wide range of biological processes, including protein acetylation. Here we demonstrate a facile protocol to exploit this technique for generating homogeneously acetylated proteins at specific sites in Escherichia coli cells.

A Facile Protocol to Generate Site-Specifically Acetylated Proteins in Escherichia Coli

Post-translational modifications that occur at specific positions of proteins have been shown to play important roles in a variety of cellular processes. ...

In this work, we will demonstrate a facile protocol to produce homogeneously acetylated proteins at specific sites by using E.coli as the expression host. The reversible lysine acetylation of proteins is one of the most abundant post-translational modifications in nature. It plays important roles in a wide range of biological processes, including gene transcription, stress response, cellular differentiation, and metabolism.Generating purely acetylated proteins at design positions is very useful for studying protein acetylation. However, it is difficult for most classic methods. This challenge has been solved by the genetic code expansion technique.It utilizes an engineered pyrrolysyl-tRNA synthetase variate to charge tRNA-Pyl with acetyllysine, then utilizes the host translational machinery to suppress the UAG stop codon in the mRNA, and directs the incorporation of acetyllysine in the design position of the target protein. Firstly, the amber stop codon needs to be introduced into the corresponding position in the target gene by site-directed mutagenesis. Amplify the template plasmid containing the gene of the wild-type proteins, and insert the stop codon mutation from the primers by the PCR reaction.After PCR, the amplified material is added directly to the kinase-ligase-Dpn1 enzyme mix for one hour at room temperature for circularization and template removal. Add five microliters of the mix to the tube of 25 microliters thawed competent E.coli cells. Carefully flick the tube to mix, and place the mixture on ice for 30 minutes.Heat shock the mixture at 42 degrees Celsius for 30 seconds and place on ice for additional five minutes. Pipette 600 microliters of room temperature SOC media into the mixture. Incubate at 37 degrees Celsius for 60 minutes with shaking.Spread 100 microliters onto the plate with the corresponding antibiotic, and incubate overnight at 37 degrees Celsius. The plasmid from the single colony is sent for sequencing. The second step is to express and purify site-specifically acetylated protein.Pick up a single colony from the plate, which contains the mutated TAG-containing target gene and the acetyllysine incorporation system. Inoculate into 15 milliliters fresh LB media with corresponding antibiotics overnight at 37 degrees Celsius. Transfer the 15-milliliter overnight culture to 300 milliliter fresh LB media with antibiotics, and incubate at 37 degrees Celsius.Add five-millimolar acetyllysine and 20-millimolar nicotinamide as the final concentrations in growth media when absorbance reaches 5 at 600 nanometers. Grow cells for an additional one hour at 37 degrees Celsius. Then add the inducer for protein expression, and grow cells at 25 degrees Celsius overnight.Collect cells by centrifuging at 3, 000 g for 15 minutes. Discard the supernatant, and store cell pellets at negative 80 degrees. Thaw the frozen cell pellets on ice and resuspend with 15 milliliters of lysis buffer, five microliters of beta-mercaptoethanol, and one microliter of nuclease.Cells are broken by sonication. Centrifuge crude extract at 20, 000 g for 25 minutes at four degrees. Filter the supernatant with a 45-micrometer membrane filter.Load filtered sample to a column containing one milliliter of nickel NTA resin, equilibrated with 20 milliliters of lysis buffer. Wash the column with 20 milliliters of wash buffer. The target protein is eluded with two milliliters of elution buffer.The purified protein is desalted by the PD-10 column by adding 2.5 milliliter sample, and collect desalted sample with 3.5 milliliter desalting buffer. The next step is to biochemically characterize purified acetylated protein. Denature proteins with the SDS sample buffer above 100 degrees for five minutes.Centrifuge the mixture, load onto the SDS-PAGE gel, and run at 200 volts for 30 minutes. Wash the gel with distilled water and shake gently. To make the sandwich for western blotting, from cathode to anode is sponge, filter paper, transfer buffer, soaked SDS-PAGE gel, methanol-activated PVDF membrane, another filter paper, remove the bubbles in the sandwich, and another sponge.Put the stack in the transfer tank. Run at a constant current of 350 milliamps for 45 minutes. Wash the PVDF membrane with 25 milliliters TBST buffer for five minutes with gentle shaking.Block the membrane with 5%BSA and the TBST buffer for one hour at room temperature. Incubate the membrane with diluted HRP-conjugated acetyllysine antibody at room temperature for one hour or four degrees overnight with gentle shaking. Wash the membrane with 20 milliliters TBST buffer for five minutes with gentle shaking.Repeat this step four times. Apply the chemiluminescence substrate to the membrane for one minute. Capture the signal with a CCD camera base imager.The same volumes of elution fractions and protein purification were loaded on the SDS-PAGE gel. The yield of acetylated protein is about half of the wild-type protein, which is highly efficient, and the same expression strain without acetyllysine and growth media cannot produce proteins with detectable amount, indicating high purity of acetylated protein since there are no canonical amino acids incorporated at this specific position. Western blotting showed that there is no detectable acetylation in wild-type protein, indicating the low background of non-specific acetylation of this expression system, while acetylated protein had a clear band.Tandem mass spectrometry confirmed that acetylation occurs at the correct site whose corresponding position in the gene was mutated to the stop codon. To get good yields and purity of acetylated proteins, the optimized acetyllysine incorporation system should be used for both high efficiency and high purity. BL21(DE3)cells should be used for low background and nonspecific acetylation to increase the purity.The genetic incorporation system could be used in eukaryotic systems for broader applications.

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