Name: studying protein import into chloroplasts using protoplasts
Uploaded: 2018-12-10T13:00:00
Description: Watch this Scientific Journal Video about Studying Protein Import into Chloroplasts Using Protoplasts at JoVE.com

This work was carried out with the supports of Cooperative Research Program for Agriculture Science and Technology Development (Project No. PJ010953012018), Rural Development Administration, and the National Research Foundation (Korea) grant funded by the Ministry of Science and ICT (No. 2016R1E1A1A02922014), Republic of Korea.

1. Growth of Arabidopsis Plants
<ol>
	<li>Prepare 1 L Gamborg B5 (B5) medium by adding 3.2 g of B5 medium including vitamins, 20 g of sucrose, 0.5 g of 2-(N-morpholino) ethane sulfonic acid (MES) to approximately 800 mL of deionized water, and adjust the pH to 5.7 with potassium hydroxide (KOH). Add more deionized water bring the total volume to 1 L. Add 8 g of phytoagar and autoclave for 15 min at 121 &#176;C.</li>
	<li>Allow the medium to cool down to 55 &#176;C and pour 20 &#8211; 25 mL of the B5 medium into a Petri...

<ol>
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M., Chiu, C. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Protein+Transport+into+Chloroplasts.">Protein Transport into Chloroplasts.</a> Annual Review of Plant Biology. 61, 157-180 (2010).</li><li>Keegstra, K., Cline, K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Protein+import+and+routing+systems+of+chloroplasts.">Protein import and routing systems of chloroplasts.</a> Plant Cell. 11 (4), 557-570 (1999).</li><li>Gasser, S. M., Daum, G., Schatz, G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Import+of+proteins+into+mitochondria.+Energy-dependent+uptake+of+precursors+by+isolated+mitochondria.">Import of proteins into mitochondria. Energy-dependent uptake of precursors by isolated mitochondria.</a> Journal of Biological Chemistry. 257 (21), 13034-13041 (1982).</li><li>Smeekens, S., Bauerle, C., Hageman, J., Keegstra, K., Weisbeek, P. <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+the+transit+peptide+in+the+routing+of+precursors+toward+different+chloroplast+compartments.">The role of the transit peptide in the routing of precursors toward different chloroplast compartments.</a> Cell. 46 (3), 365-375 (1986).</li><li>Lee, D. W., 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=Arabidopsis+nuclear-encoded+plastid+transit+peptides+contain+multiple+sequence+subgroups+with+distinctive+chloroplast-targeting+sequence+motifs.">Arabidopsis nuclear-encoded plastid transit peptides contain multiple sequence subgroups with distinctive chloroplast-targeting sequence motifs.</a> Plant Cell. 20 (6), 1603-1622 (2008).</li><li>Lee, 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=Mitochondrial+targeting+of+the+Arabidopsis+F1-ATPase+gamma-subunit+via+multiple+compensatory+and+synergistic+presequence+motifs.">Mitochondrial targeting of the Arabidopsis F1-ATPase gamma-subunit via multiple compensatory and synergistic presequence motifs.</a> Plant Cell. 24 (12), 5037-5057 (2012).</li><li>Jin, J. 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=A+new+dynamin-like+protein,+ADL6,+is+involved+in+trafficking+from+the+trans-Golgi+network+to+the+central+vacuole+in+Arabidopsis.">A new dynamin-like protein, ADL6, is involved in trafficking from the trans-Golgi network to the central vacuole in Arabidopsis.</a> Plant Cell. 13 (7), 1511-1526 (2001).</li><li>Lee, K. H., Kim, D. H., Lee, S. W., Kim, Z. H., Hwang, I. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=In+vivo+import+experiments+in+protoplasts+reveal+the+importance+of+the+overall+context+but+not+specific+amino+acid+residues+of+the+transit+peptide+during+import+into+chloroplasts.">In vivo import experiments in protoplasts reveal the importance of the overall context but not specific amino acid residues of the transit peptide during import into chloroplasts.</a> Molecules and Cells. 14 (3), 388-397 (2002).</li><li>Lee, D. W., Lee, S., Oh, Y. J., Hwang, I. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Multiple+sequence+motifs+in+the+rubisco+small+subunit+transit+peptide+independently+contribute+to+Toc159-dependent+import+of+proteins+into+chloroplasts.">Multiple sequence motifs in the rubisco small subunit transit peptide independently contribute to Toc159-dependent import of proteins into chloroplasts.</a> Plant Physiology. 151 (1), 129-141 (2009).</li><li>Lee, D. W., Woo, S., Geem, K. R., Hwang, I. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Sequence+motifs+in+transit+peptides+act+as+independent+functional+units+and+can+be+transferred+to+new+sequence+contexts.">Sequence motifs in transit peptides act as independent functional units and can be transferred to new sequence contexts.</a> Plant Physiology. 169 (1), 471-484 (2015).</li><li>Lee, 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=Both+the+hydrophobicity+and+a+positively+charged+region+flanking+the+C-terminal+region+of+the+transmembrane+domain+of+signal-anchored+proteins+play+critical+roles+in+determining+their+targeting+specificity+to+the+endoplasmic+reticulum+or+endosymbiotic+organelles+in+Arabidopsis+cells.">Both the hydrophobicity and a positively charged region flanking the C-terminal region of the transmembrane domain of signal-anchored proteins play critical roles in determining their targeting specificity to the endoplasmic reticulum or endosymbiotic organelles in Arabidopsis cells.</a> Plant Cell. 23 (4), 1588-1607 (2011).</li><li>Cleary, S. 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=Isolated+plant+mitochondria+import+chloroplast+precursor+proteins+in+vitro+with+the+same+efficiency+as+chloroplasts.">Isolated plant mitochondria import chloroplast precursor proteins in vitro with the same efficiency as chloroplasts.</a> Journal of Biological Chemistry. 277 (7), 5562-5569 (2002).</li></ol>

We provided a detailed protocol for the use of protoplasts of Arabidopsis to study protein import into chloroplasts. This method is powerful for investigating the protein import process. This simple, versatile technique is useful for examining the targeting of the intended cargo proteins to chloroplasts. Using this method, protoplasts are prepared from leaf tissues of Arabidopsis11,12 which can be obtained from plants at many different growth st...

The chloroplast is one of the most important organelles in plants. One of the main functions of chloroplasts is to carry out photosynthesis1. Chloroplasts also carry out many other biochemical reactions for the production of fatty acids, amino acids, nucleotides, and numerous secondary metabolites1,2. For all of these reactions, chloroplasts require a large number of different types of proteins. However, the chloroplast genome contains only approximately 100 genes3,4. Therefore, chloroplasts must import the majority of their proteins from the cytosol. In fact, most chloroplast proteins were shown to be imported from the cytosol after translation4,5,6. Plant cells require specific mechanisms to import proteins from the cytosol to chloroplasts. However, although these protein import mechanisms have been investigated for the past several decades, we still do not fully understand them at the molecular level. Here, we provide a detailed method for preparing protoplasts and exogenously expressing genes in protoplasts. This method could be valuable for elucidating the molecular mechanisms underlying protein import into chloroplasts in detail.
Protein import can be studied using many different approaches. One of these methods involves the use of an in vitro protein import system7,8. Using this approach, in vitro-translated protein precursors are incubated with purified chloroplasts in vitro, and protein import is analyzed by SDS-PAGE followed by western blot analysis. The advantage of this approach is that each step of protein import into chloroplasts can be studied in detail. Thus, this method has been widely used to define the components of the protein import molecular machinery and to dissect sequence information for transit peptides. More recently, another approach involving the use of protoplasts from leaf tissues was developed and it has become widely used to study protein import into chloroplasts9,10. The advantage of this approach is that protoplasts provide a cellular environment that is closer to that of intact cells than the in vitro system. Thus, the protoplast system allows us to address many additional aspects of this process, such as the associated cytosolic events and how the specificity of targeting signals is determined. Here, we present a detailed protocol for the use of protoplasts to study protein import into chloroplasts.

<table>
	<tbody>
		<tr>
			<td>GAMBORG B5 MEDIUM INCLUDING VITAMINS</td>
			<td>Duchefa Biochemie</td>
			<td>G0210.0050</td>
			<td></td>
		</tr>
		<tr>
			<td>SUCROSE</td>
			<td>Duchefa Biochemie</td>
			<td>S0809.5000</td>
			<td></td>
		</tr>
		<tr>
			<td>MES MONOHYDRATE</td>
			<td>Duchefa Biochemie</td>
			<td>M1503.0250</td>
			<td></td>
		</tr>
		<tr>
			<td>Agar, powder</td>
			<td>JUNSEI</td>
			<td>24440S1201</td>
			<td></td>
		</tr>
		<tr>
			<td>Micropore Surgical tape</td>
			<td>3M</td>
			<td>1530-0</td>
			<td></td>
		</tr>
		<tr>
			<td>Surgical blade stainless No.10</td>
			<td>FEATHER</td>
			<td>Unavailable</td>
			<td></td>
		</tr>
		<tr>
			<td>Conical Tube, 50ml</td>
			<td>SPL LIFE SCIENCES</td>
			<td>50050</td>
			<td></td>
		</tr>
		<tr>
			<td>Macerozyme R-10</td>
			<td>YAKULT PHARMACEUTICAL IND.</td>
			<td>Unavailable</td>
			<td></td>
		</tr>
		<tr>
			<td>Cellulase ONOZUKA R-10</td>
			<td>YAKULT PHARMACEUTICAL IND.</td>
			<td>Unavailable</td>
			<td></td>
		</tr>
		<tr>
			<td>ALBUMIN, BOVINE (BSA)</td>
			<td>VWR</td>
			<td>0332-100G</td>
			<td></td>
		</tr>
		<tr>
			<td>D-Mannitol</td>
			<td>SIGMA</td>
			<td>M1902-1KG</td>
			<td></td>
		</tr>
		<tr>
			<td>CALCIUM CHLORIDE, DIHYDRATE</td>
			<td>MP BIOMEDICALS</td>
			<td>0219463505-5KG</td>
			<td></td>
		</tr>
		<tr>
			<td>Twister</td>
			<td>VISION SCIENTIFIC</td>
			<td>VS-96TW</td>
			<td></td>
		</tr>
		<tr>
			<td>Screen cup for CD-1</td>
			<td>SIGMA</td>
			<td>S1145</td>
			<td></td>
		</tr>
		<tr>
			<td>Screens for CD-1</td>
			<td>SIGMA</td>
			<td>S3895</td>
			<td></td>
		</tr>
		<tr>
			<td>Petri Dish</td>
			<td>SPL LIFE SCIENCES</td>
			<td>10090</td>
			<td></td>
		</tr>
		<tr>
			<td>Pasteur pipette</td>
			<td>HILGENBERG</td>
			<td>3150102</td>
			<td></td>
		</tr>
		<tr>
			<td>LABORATORY CENTRIFUGE / BENCH-TOP</td>
			<td>VISION SCIENTIFIC</td>
			<td>VS-5500N</td>
			<td></td>
		</tr>
		<tr>
			<td>Sodium chloride</td>
			<td>JUNSEI</td>
			<td>19015S0350</td>
			<td></td>
		</tr>
		<tr>
			<td>Potassium chloride</td>
			<td>SIGMA</td>
			<td>P3911-1KG</td>
			<td></td>
		</tr>
		<tr>
			<td>D-GLUCOSE, ANHYDROUS</td>
			<td>BIO BASIC</td>
			<td>GB0219</td>
			<td></td>
		</tr>
		<tr>
			<td>Potassium Hydroxide</td>
			<td>DUKSAN</td>
			<td>40</td>
			<td></td>
		</tr>
		<tr>
			<td>Calcium nitrate tetrahydrate</td>
			<td>SIGMA</td>
			<td>C2786-500G</td>
			<td></td>
		</tr>
		<tr>
			<td>Poly(ethylene glycol)</td>
			<td>SIGMA</td>
			<td>P2139-2KG</td>
			<td></td>
		</tr>
		<tr>
			<td>Magnesium chloride hexahydrate</td>
			<td>SIGMA</td>
			<td>M2393-500G</td>
			<td></td>
		</tr>
		<tr>
			<td>Tube 13ml, 100x16mm, PP</td>
			<td>SARSTEDT</td>
			<td>55.515</td>
			<td></td>
		</tr>
		<tr>
			<td>Microscope slides</td>
			<td>MARIENFELD</td>
			<td>1000412</td>
			<td></td>
		</tr>
		<tr>
			<td>Microscope Cover Glasses</td>
			<td>MARIENFELD</td>
			<td>101030</td>
			<td></td>
		</tr>
		<tr>
			<td>Counting Chamber</td>
			<td>MARIENFELD</td>
			<td>650030</td>
			<td></td>
		</tr>
		<tr>
			<td>Axioplan 2 Imaging Microscope</td>
			<td>Carl Zeiss</td>
			<td>Unavailable</td>
			<td></td>
		</tr>
		<tr>
			<td>Micro tube 1.5ml</td>
			<td>SARSTEDT</td>
			<td>72.690.001</td>
			<td></td>
		</tr>
		<tr>
			<td>2-Mercaptoethanol</td>
			<td>SIGMA</td>
			<td>M3148-250ML</td>
			<td></td>
		</tr>
		<tr>
			<td>Sodium Dodecyl Sulfate (SDS), Proteomics Grade</td>
			<td>VWR</td>
			<td>M107-500G</td>
			<td></td>
		</tr>
		<tr>
			<td>TRIS, Ultra Pure Grade</td>
			<td>VWR</td>
			<td>0497-5KG</td>
			<td></td>
		</tr>
		<tr>
			<td>DTT (DL-Dithiothreitol), Biotechnology Grade</td>
			<td>VWR</td>
			<td>0281-25G</td>
			<td></td>
		</tr>
		<tr>
			<td>Bromophenol blue sodium salt ACS</td>
			<td>VWR</td>
			<td>0312-50G</td>
			<td></td>
		</tr>
		<tr>
			<td>Glycerol</td>
			<td>JUNSEI</td>
			<td>27210S0350</td>
			<td></td>
		</tr>
		<tr>
			<td>Living Colors A.v. Monoclonal Antibody (JL-8)</td>
			<td>TAKARA</td>
			<td>632381</td>
			<td></td>
		</tr>
	</tbody>
</table>

studying protein import into chloroplasts using protoplasts

The chloroplast is an essential organelle that is responsible for various cellular processes in plants, such as photosynthesis and the production of many secondary metabolites and lipids. Chloroplasts require a large number of proteins for these various physiological processes. Over 95% of chloroplast proteins are nucleus-encoded and imported into chloroplasts from the cytosol after translation on cytosolic ribosomes. Thus, the proper import or targeting of these nucleus-encoded chloroplast proteins to chloroplasts is essential for the proper functioning of chloroplasts as well as the plant cell. Nucleus-encoded chloroplast proteins contain signal sequences for specific targeting to chloroplasts. Molecular machinery localized to the chloroplast or cytosol recognize these signals and carry out the import process. To investigate the mechanisms of protein import or targeting to chloroplasts in vivo, we developed a rapid, efficient protoplast-based method to analyze protein import into chloroplasts of Arabidopsis. In this method, we use protoplasts isolated from leaf tissues of Arabidopsis. Here, we provide a detailed protocol for using protoplasts to investigate the mechanism by which proteins are imported into chloroplasts.

The import of proteins into chloroplasts can be examined using two approaches: fluorescence microscopy and immunoblot analysis after SDS-PAGE-mediated separation. Here, we used RbcS-nt:GFP, a fusion construct encoding the 79 N-terminal amino acid residues of RbcS containing the transit peptide fused to GFP. When proteins are imported into chloroplasts, green fluorescence signals from the target protein RbcS-nt:GFP should merge with the red fluorescent signals from chlorophyll auto-fluores...

Watch this Scientific Journal Video about Studying Protein Import into Chloroplasts Using Protoplasts at JoVE.com

Studying Protein Import into Chloroplasts Using Protoplasts

Here we describe a protocol to express proteins into protoplasts by using PEG-mediated transformation method. The method provides easy expression of proteins of interest, and efficient investigation of protein localization and the import process for various experimental conditions in vivo.

The chloroplast is an essential organelle that is responsible for various cellular processes in plants, such as photosynthesis and the production of many ...

This mystery can help answer a few questions in the field of cell biology such as protein input into chloroplasts. The main advantage of this technology is that protein input into chloroplasts can be studied under en vivo conditions. Demonstrating the procedure will be Junho Lee and Hyangju Kang, two post outs from my laboratory.To begin, harvest intact leaf tissues from two-week-old plants from one to two B5 plates. Use a surgical knife to harvest the leaves and place them into a 50 milliliter conical tube containing 25 milliliters of enzyme solution. Place the tube horizontally on a rotary shaker and incubate with gentle agitation at 22 degrees Celsius in the dark for eight to 12 hours until only petioles and stems remain in the solution.After completing incubation, filter the enzyme solution containing released protoplasts through a 140 micrometer pore size mesh into a fresh Petri dish. Then carefully layer the solution on top of 15 milliliters of 21%sucrose solution in a 50 milliliter conical tube. Centrifuge the tube in a swinging bucket rotor at 98 gs for 10 minutes with the lowest acceleration and deceleration settings.After that, use patura pipette to carefully removed the protoplasts from the uppermost layer containing enzyme solution and from the interface between the enzymes solution and sucrose solution. Transfer this solution to a 50 milliliter conical tube containing 30 milliliters of W5 solution and invert the tube to mix. Centrifuge the tube at 51 gs for six minutes.Use a pipette to discard this supernatant carefully without disturbing the protoplasts in the pellet. Add 25 milliliters of W5 solution and gently re-suspend the protoplasts. For stabilization, incubate in a four Celsius refrigerator for a minimum of one hour.After four degree Celsius incubation, pellet the protoplasts completely by centrifuging them at 46 gs for two minutes. Carefully remove the supernatent completely and add MANG solution to the protoplast pellet to achieve five times ten to the six per milliliter. Use a pipette to add 10 micrograms of the plasma DNA and 300 microliters of protoplast solution to a fresh 13 milliliter round bottomed tube.Mix by gently rotating the tubes by hand and then immediately add 300 microliters of freshly prepared 40%PEG solution. Mix completely by tilting the tube almost horizontally and rotating it gentle several times by hand. Incubate at room temperature for 30 minutes.Then add one milliliter of W5 solution and mix completely by gently rotating the tube by hand as previously. Incubate the sample for 10 minutes at room temperature. Repeat two more times with adding first 1.5 milliliter and then two milliliters of W5 and after the final addition and mixing, incubate for 30 minutes.Centrifuge the tube at 46 gs for four minutes and then discard the supernatant. Add two milliliters of W5 solution to the pellet and mix gently, but completely, in the same manner as previously. Incubate at 22 degrees Celsius in a dark chamber for 18 hours.To analyze the protein import using florescence microscopy, use a pipette with a trimmed tip to place 10 microliters of the protoplast solution on a glass slide. Use a cover slip to carefully cover the solution to avoid damaging the protoplasts. Place the slide on the stage of a fluorescence microscope with an excitation admission filter that is set for observing green fluorescent protein and chlorophyll autofluorescence.Use a cooled charge couple device camera to capture images and process them using an imagine editing software to produce pseudo-color images. For total protein extraction and immunoblotting, remove one milliliter from the protoplast solution and mix the remaining one milliliter. Transfer this protoplast solution into a centrifuge tube and centrifuge at 46 gs for four minutes.Remove the supernatant after completing centrifugation and add 80 microliters of denaturation buffer. Vortex vigoriously for five seconds. Add five XDS sample buffer, mix well and boil for 10 minutes to denature.Proceed with standard STS page and immunoblotting with anti-GFP antibody. RbcS and TGFT, a fusion construct encoding the 79 end terminal amino acid residues of RBCS containing the transit peptide fused to GFP, was used to study the import of proteins into chloroplasts by florescence microscopy and immunoblotting. When examined by florescence microscopy, green fluorescent signals from the target protein merged with the red fluorescent signals from chlorophyll autoflorescence indicating protein import into chloroplasts.After isolating total protein, two protein bands are observed in the immunoblot, showing that a protein was properly imported into chloroplasts. The upper band corresponds to the full length precursor and the lower band to the processed form after import into chloroplasts. The amount of the processed form of the protein increased in a time-dependent manner, suggesting that the protein is imported into chloroplasts.At this development, this technique paved the way for researchers in the field of cell biology to explore protein tiring or membrane thread picking in Arabidopsis.

studying-protein-import-into-chloroplasts-using-protoplasts

Research

JoVE Journal

Biochemistry

Using Scaffold Liposomes to Reconstitute Lipid-proximal Protein-protein Interactions In Vitro

Studies of integral membrane proteins in vitro are frequently complicated by the presence of a hydrophobic transmembrane domain. Further complicating these studies, reincorporation of detergent-solubilized membrane proteins into liposomes is a stochastic process where protein topology is impossible to enforce. This paper offers an alternative method to these challenging techniques that utilizes a liposome-based scaffold. Protein solubility is enhanced by deletion of the transmembrane domain, and these amino acids are replaced with a tethering moiety, such as a His-tag. This tether interacts with an anchoring group (Ni2+ coordinated by nitrilotriacetic acid (NTA(Ni2+)) for His-tagged proteins), which enforces a uniform protein topology at the surface of the liposome. An example is presented wherein the interaction between Dynamin-related protein 1 (Drp1) with an integral membrane protein, Mitochondrial Fission Factor (Mff), was investigated using this scaffold liposome method. In this work, we have demonstrated the ability of Mff to efficiently recruit soluble Drp1 to the surface of liposomes, which stimulated its GTPase activity. Moreover, Drp1 was able to tubulate the Mff-decorated lipid template in the presence of specific lipids. This example demonstrates the effectiveness of scaffold liposomes using structural and functional assays and highlights the role of Mff in regulating Drp1 activity.

Using Scaffold Liposomes to Reconstitute Lipid-proximal Protein-protein Interactions In Vitro

This paper describes a method for assessing the interactions and assemblies of integral membrane proteins in vitro with various partner factors in a lipid-proximal environment.

Studies of integral membrane proteins in vitro are frequently complicated by the presence of a hydrophobic transmembrane domain. Further complicating ...

Time-resolved ElectroSpray Ionization Hydrogen-deuterium Exchange Mass Spectrometry for Studying Protein Structure and Dynamics

Intrinsically disordered proteins (IDPs) have long been a challenge to structural biologists due to their lack of stable secondary structure elements. Hydrogen-Deuterium Exchange (HDX) measured at rapid time scales is uniquely suited to detect structures and hydrogen bonding networks that are briefly populated, allowing for the characterization of transient conformers in native ensembles. Coupling of HDX to mass spectrometry offers several key advantages, including high sensitivity, low sample consumption and no restriction on protein size. This technique has advanced greatly in the last several decades, including the ability to monitor HDX labeling times on the millisecond time scale. In addition, by incorporating the HDX workflow onto a microfluidic platform housing an acidic protease microreactor, we are able to localize dynamic properties at the peptide level. In this study, Time-Resolved ElectroSpray Ionization Mass Spectrometry (TRESI-MS) coupled to HDX was used to provide a detailed picture of residual structure in the tau protein, as well as the conformational shifts induced upon hyperphosphorylation.

Conformational flexibility plays a critical role in protein function. Herein, we describe the use of time-resolved electrospray ionization mass spectrometry coupled to hydrogen-deuterium exchange for probing the rapid structural changes that drive function in ordered and disordered proteins.

Intrinsically disordered proteins (IDPs) have long been a challenge to structural biologists due to their lack of stable secondary structure elements. ...

mRNA Interactome Capture from Plant Protoplasts

RNA-binding proteins (RBPs) determine the fates of RNAs. They participate in all RNA biogenesis pathways and especially contribute to post-transcriptional gene regulation (PTGR) of messenger RNAs (mRNAs). In the past few years, a number of mRNA-bound proteomes from yeast and mammalian cell lines have been successfully isolated through the use of a novel method called &#34;mRNA interactome capture,&#34; which allows for the identification of mRNA-binding proteins (mRBPs) directly from a physiological environment. The method is composed of in vivo ultraviolet (UV) crosslinking, pull-down and purification of messenger ribonucleoprotein complexes (mRNPs) by oligo(dT) beads, and the subsequent identification of the crosslinked proteins by mass spectrometry (MS). Very recently, by applying the same method, several plant mRNA-bound proteomes have been reported simultaneously from different Arabidopsis tissue sources: etiolated seedlings, leaf tissue, leaf mesophyll protoplasts, and cultured root cells. Here, we present the optimized mRNA interactome capture method for Arabidopsis thaliana leaf mesophyll protoplasts, a cell type that serves as a versatile tool for experiments that include various cellular assays. The conditions for optimal protein yield include the amount of starting tissue and the duration of UV irradiation. In the mRNA-bound proteome obtained from a medium-scale experiment (107 cells), RBPs noted to have RNA-binding capacity were found to be overrepresented, and many novel RBPs were identified. The experiment can be scaled up (109 cells), and the optimized method can be applied to other plant cell types and species to broadly isolate, catalog, and compare mRNA-bound proteomes in plants.

Here, we present an interactome capture protocol applied to Arabidopsis thaliana leaf mesophyll protoplasts. This method critically relies on in vivo UV crosslinking and allows for the isolation and identification of plant mRNA-binding proteins from a physiological environment.

RNA-binding proteins (RBPs) determine the fates of RNAs. They participate in all RNA biogenesis pathways and especially contribute to post-transcriptional ...

Anaerobic Protein Purification and Kinetic Analysis via Oxygen Electrode for Studying DesB Dioxygenase Activity and Inhibition

Oxygen-sensitive proteins, including those enzymes which utilize oxygen as a substrate, can have reduced stability when purified using traditional aerobic purification methods. This manuscript illustrates the technical details involved in the anaerobic purification process, including the preparation of buffers and reagents, the methods for column chromatography in a glove box, and the desalting of the protein prior to kinetics. Also described are the methods for preparing and using an oxygen electrode to perform kinetic characterization of an oxygen-utilizing enzyme. These methods are illustrated using the dioxygenase enzyme DesB, a gallate dioxygenase from the bacterium Sphingobium sp. strain SYK-6.

Here we present a protocol for anaerobic protein purification, anaerobic protein concentration, and subsequent kinetic characterization using an oxygen electrode system. The method is illustrated using the enzyme DesB, a dioxygenase enzyme which is more stable and active when purified and stored in an anaerobic environment.

Oxygen-sensitive proteins, including those enzymes which utilize oxygen as a substrate, can have reduced stability when purified using traditional aerobic ...

High Sensitivity Measurement of Transcription Factor-DNA Binding Affinities by Competitive Titration Using Fluorescence Microscopy

Accurate quantification of transcription factor (TF)-DNA interactions is essential for understanding the regulation of gene expression. Since existing approaches suffer from significant limitations, we have developed a new method for determining TF-DNA binding affinities with high sensitivity on a large scale. The assay relies on the established fluorescence anisotropy (FA) principle but introduces important technical improvements. First, we measure a full FA competitive titration curve in a single well by incorporating TF and a fluorescently labeled reference DNA in a porous agarose gel matrix. Unlabeled DNA oligomer is loaded on the top as a competitor and, through diffusion, forms a spatio-temporal gradient. The resulting FA gradient is then read out using a customized epifluorescence microscope setup. This improved setup greatly increases the sensitivity of FA signal detection, allowing both weak and strong binding to be reliably quantified, even for molecules of similar molecular weights. In this fashion, we can measure one titration curve per well of a multi-well plate, and through a fitting procedure, we can extract both the absolute dissociation constant (KD) and active protein concentration. By testing all single-point mutation variants of a given consensus binding sequence, we can survey the entire binding specificity landscape of a TF, typically on a single plate. The resulting position weight matrices (PWMs) outperform those derived from other methods in predicting in vivo TF occupancy. Here, we present a detailed guide for implementing HiP-FA on a conventional automated fluorescent microscope and the data analysis pipeline.

Here we present a novel method for determining binding affinities at equilibrium and in solution with high sensitivity on a large scale. This improves the quantitative analysis of transcription factor-DNA binding. The method is based on automated fluorescence anisotropy measurements in a controlled delivery system.

Accurate quantification of transcription factor (TF)-DNA interactions is essential for understanding the regulation of gene expression. Since existing ...

Studying RNA Interactors of Protein Kinase RNA-Activated during the Mammalian Cell Cycle

Protein kinase RNA-activated (PKR) is a member of the innate immune response proteins and recognizes the double-stranded secondary structure of viral RNAs. When bound to viral double-stranded RNAs (dsRNAs), PKR undergoes dimerization and subsequent autophosphorylation. Phosphorylated PKR (pPKR) becomes active and induces phosphorylation of the alpha subunit of eukaryotic initiation factor 2 (eIF2&#945;) to suppress global translation. Increasing evidence suggests that PKR can be activated under physiological conditions such as during the cell cycle or under various stress conditions without infection. However, our understanding of the RNA activators of PKR is limited due to the lack of a standardized experimental method to capture and analyze PKR-interacting dsRNAs. Here, we present an experimental protocol to specifically enrich and analyze PKR bound RNAs during the cell cycle using HeLa cells. We utilize the efficient crosslinking activity of formaldehyde to fix PKR-RNA complexes and isolate them via immunoprecipitation. PKR co-immunoprecipitated RNAs can then be further processed to generate a high-throughput sequencing library. One major class of PKR-interacting cellular dsRNAs is mitochondrial RNAs (mtRNAs), which can exist as intermolecular dsRNAs through complementary interaction between the heavy-strand and the light-strand RNAs. To study the strandedness of these duplex mtRNAs, we also present a protocol for strand-specific qRT-PCR. Our protocol is optimized for the analysis of PKR-bound RNAs, but it can be easily modified to study cellular dsRNAs or RNA-interactors of other dsRNA binding proteins.

We present experimental approaches for studying RNA-interactors of double-stranded RNA binding protein kinase RNA-activated (PKR) during the mammalian cell cycle using HeLa cells. This method utilizes formaldehyde to crosslink RNA-PKR complexes and immunoprecipitation to enrich PKR-bound RNAs. These RNAs can be further analyzed through high-throughput sequencing or qRT-PCR.

Protein kinase RNA-activated (PKR) is a member of the innate immune response proteins and recognizes the double-stranded secondary structure of viral ...

Application of Biolayer Interferometry (BLI) for Studying Protein-Protein Interactions in Transcription

A transcription factor&#160;(TF) is a protein that regulates gene expression by interacting with the RNA polymerase, another TF, and/or template DNA. GrgA is a novel transcription activator found specifically in the obligate intracellular bacterial pathogen Chlamydia. Protein pulldown assays using affinity beads have revealed that GrgA binds two &#963; factors, namely &#963;66 and &#963;28, which recognize different sets of promoters for genes whose products are differentially required at developmental stages. We have used BLI to confirm and further characterize the interactions. BLI demonstrates several advantages over pulldown: 1) It reveals real-time association and dissociation between binding partners, 2) It generates quantitative kinetic parameters, and 3) It can detect bindings that pulldown assays often fail to detect. These characteristics have enabled us to deduce the physiological roles of GrgA in gene expression regulation in Chlamydia, and possible detailed interaction mechanisms. We envision that this relatively affordable technology can be extremely useful for studying transcription and other biological processes.

Application of Biolayer Interferometry BLI for Studying Protein-Protein Interactions in Transcription

Interactions of transcription factors (TFs) with the RNA polymerase are usually studied using pulldown assays. We apply a Biolayer Interferometry (BLI) technology to characterize the interaction of GrgA with the chlamydial RNA polymerase. Compared to pulldown assays, BLI detects real-time association and dissociation, offers higher sensitivity, and is highly quantitative.

A transcription factor&#160;(TF) is a protein that regulates gene expression by interacting with the RNA polymerase, another TF, and/or template DNA. GrgA ...

Evaluation of Protein&#8211;Protein Interactions using an On-Membrane Digestion Technique

Numerous intracellular proteins physically interact in accordance with their intracellular and extracellular circumstances. Indeed, cellular functions largely depend on intracellular protein&#8211;protein interactions. Therefore, research regarding these interactions is indispensable to facilitating the understanding of physiologic processes. Co-precipitation of associated proteins, followed by mass spectrometry (MS) analysis, enables the identification of novel protein interactions. In this study, we have provided details of the novel technique of immunoprecipitation-liquid chromatography (LC)-MS/MS analysis combined with on-membrane digestion for the analysis of protein&#8211;protein interactions. This technique is suitable for crude immunoprecipitants and can improve the throughput of proteomic analyses. Tagged recombinant proteins were precipitated using specific antibodies; next, immunoprecipitants blotted onto polyvinylidene difluoride membrane pieces were subjected to reductive alkylation. Following trypsinization, the digested protein residues were analyzed using LC-MS/MS. Using this technique, we were able to identify several candidate associated proteins. Thus, this method is convenient and useful for the characterization of novel protein&#8211;protein interactions.

Evaluation of Protein&amp;#8211;Protein Interactions using an On-Membrane Digestion Technique

Here, we present a protocol for an on-membrane digestion technique for the preparation of samples for mass spectrometry. This technique facilitates the convenient analysis of protein&#8211;protein interactions.

Numerous intracellular proteins physically interact in accordance with their intracellular and extracellular circumstances. Indeed, cellular functions ...

PeptiQuick, a One-Step Incorporation of Membrane Proteins into Biotinylated Peptidiscs for Streamlined Protein Binding Assays

Membrane proteins, including transporters, channels, and receptors, constitute nearly one-fourth of the cellular proteome and over half of current drug targets. Yet, a major barrier to their characterization and exploitation in academic or industrial settings is that most biochemical, biophysical, and drug screening strategies require these proteins to be in a water-soluble state. Our laboratory recently developed the peptidisc, a membrane mimetic offering a &#8220;one-size-fits-all&#8221; approach to the problem of membrane protein solubility. We present here a streamlined protocol that combines protein purification and peptidisc reconstitution in a single chromatographic step. This workflow, termed PeptiQuick, allows for bypassing dialysis and incubation with polystyrene beads, thereby greatly reducing exposure to detergent, protein denaturation, and sample loss. When PeptiQuick is performed with biotinylated scaffolds, the preparation can be directly attached to streptavidin-coated surfaces. There is no need to biotinylate or modify the membrane protein target. PeptiQuick is showcased here with the membrane receptor FhuA and antimicrobial ligand colicin M, using biolayer interferometry to determine the precise kinetics of their interaction. It is concluded that PeptiQuick is a convenient way to prepare and analyze membrane protein-ligand interactions within one&#160;day in a detergent-free environment.

We present a method that combines membrane protein purification and reconstitution into peptidiscs in a single chromatographic step. Biotinylated scaffolds are used for direct surface attachment and measurement of protein-ligand interactions via biolayer interferometry.

Membrane proteins, including transporters, channels, and receptors, constitute nearly one-fourth of the cellular proteome and over half of current drug ...

Creating Highly Specific Chemically Induced Protein Dimerization Systems by Stepwise Phage Selection of a Combinatorial Single-Domain Antibody Library

Protein dimerization events that occur only in the presence of a small-molecule ligand enable the development of small-molecule biosensors for the dissection and manipulation of biological pathways. Currently, only a limited number of chemically induced dimerization (CID) systems exist and engineering new ones with desired sensitivity and selectivity for specific small-molecule ligands remains a challenge in the field of protein engineering. We here describe a high throughput screening method, combinatorial binders-enabled selection of CID (COMBINES-CID), for the de novo engineering of CID systems applicable to a large variety of ligands. This method uses the two-step selection of a phage-displayed combinatorial nanobody library to obtain 1) &#34;anchor binders&#34; that first bind to a ligand of interest and then 2) &#34;dimerization binders&#34; that only bind to anchor binder-ligand complexes. To select anchor binders, a combinatorial library of over 109 complementarity-determining region (CDR)-randomized nanobodies is screened with a biotinylated ligand and hits are validated with the unlabeled ligand by bio-layer interferometry (BLI). To obtain dimerization binders, the nanobody library is screened with anchor binder-ligand complexes as targets for positive screening and the unbound anchor binders for negative screening. COMBINES-CID is broadly applicable to select CID binders with other immunoglobulin, non-immunoglobulin, or computationally designed scaffolds to create biosensors for in vitro and in vivo detection of drugs, metabolites, signaling molecules, etc.

Creating chemically induced protein dimerization systems with desired affinity and specificity for any given small molecule ligand would have many biological sensing and actuation applications. Here, we describe an efficient, generalizable method for de novo engineering of chemically induced dimerization systems via the stepwise selection of a phage-displayed combinatorial single-domain antibody library.