Name: water in oil emulsions: a new system for assembling water-soluble chlorophyll-binding proteins with hydrophobic pigments
Uploaded: 2016-03-21T14:00:00
Description: Watch this Scientific Journal Video about Water in Oil Emulsions: A New System for Assembling Water-soluble Chlorophyll-binding Proteins with Hydrophobic Pigments at JoVE.com

DN acknowledges support from EU FP7 projects PEPDIODE (GA 256672) and REGPOT-2012-2013-1(GA 316157), and a personal research grant (No. 268/10) from the Israel Science Foundation. We thank Prof. Shmuel Rubinstein, School of Engineering and Applied Sciences, Harvard University, Cambridge MA, USA for taking the confocal microscopy images.

1. Preparing Chl a Stock Solutions
<ol>
	<li>CRITICAL STEP: Perform all the steps of chlorophyll preparation in a chemical hood, under green light (520 nm) or in the dark in order to minimize photodamage. Always add Nitrogen or Argon before freezing the pigments for storage. Ensure that all solvents are analytical grade.</li>
	<li>Weigh about 5 mg of lyophilized Spirulina platensis cells or other cyanobacterium cells containing only Chl a in thylakoid membranes and crush it using a mortar and pestle.<...

<ol>
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Cell Biol. 89, 990-997 (2010).</li><li>Renger, G., 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=Water+soluble+chlorophyll+binding+protein+of+higher+plants:+a+most+suitable+model+system+for+basic+analyses+of+pigment-pigment+and+pigment-protein+interactions+in+chlorophyll+protein+complexes.">Water soluble chlorophyll binding protein of higher plants: a most suitable model system for basic analyses of pigment-pigment and pigment-protein interactions in chlorophyll protein complexes.</a> J. Plant Physiol. 168, 1462-1472 (2011).</li><li>Satoh, H., Uchida, A., Nakayama, K., Okada, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Water-soluble+chlorophyll+protein+in+Brassicaceae+plants+is+a+stress-induced+chlorophyll-binding+protein.">Water-soluble chlorophyll protein in Brassicaceae plants is a stress-induced chlorophyll-binding protein.</a> Plant Cell Physiol. 42, 906-911 (2001).</li><li>Bektas, I., Fellenberg, C., Paulsen, H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Water-soluble+chlorophyll+protein+(WSCP)+of+Arabidopsis+is+expressed+in+the+gynoecium+and+developing+silique.">Water-soluble chlorophyll protein (WSCP) of Arabidopsis is expressed in the gynoecium and developing silique.</a> Planta. 236, 251-259 (2012).</li><li>Damaraju, S., Schlede, S., Eckhardt, U., Lokstein, H., Grimm, B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Functions+of+the+water+soluble+chlorophyll-binding+protein+in+plants.">Functions of the water soluble chlorophyll-binding protein in plants.</a> J. Plant Physiol. 168, 1444-1451 (2011).</li><li>Horigome, D., 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=Structural+mechanism+and+photoprotective+function+of+water-soluble+chlorophyll-binding+protein.">Structural mechanism and photoprotective function of water-soluble chlorophyll-binding protein.</a> J. Biol. Chem. 282, 6525-6531 (2007).</li><li>Reinbothe, C., Satoh, H., Alcaraz, J. -. 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Chem. 273, 30568-30575 (1998).</li><li>Schmidt, K., Fufezan, C., Krieger-Liszkay, A., Satoh, H., Paulsen, H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Recombinant+water-soluble+chlorophyll+protein+from+Brassica+oleracea+var.+Botrys+binds+various+chlorophyll+derivatives.">Recombinant water-soluble chlorophyll protein from Brassica oleracea var. Botrys binds various chlorophyll derivatives.</a> Biochemistry. 42, 7427-7433 (2003).</li><li>Takahashi, 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=Molecular+cloning,+characterization+and+analysis+of+the+intracellular+localization+of+a+water-soluble+Chl-binding+protein+from+Brussels+sprouts+(Brassica+oleracea+var.+gemmifera).">Molecular cloning, characterization and analysis of the intracellular localization of a water-soluble Chl-binding protein from Brussels sprouts (Brassica oleracea var. gemmifera).</a> Plant Cell Physiol. 53, 879-891 (2012).</li><li>Takahashi, S., Ono, M., Uchida, A., Nakayama, K., Satoh, H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Molecular+cloning+and+functional+expression+of+a+water-soluble+chlorophyll-binding+protein+from+Japanese+wild+radish.">Molecular cloning and functional expression of a water-soluble chlorophyll-binding protein from Japanese wild radish.</a> J. Plant Physiol. 170, 406-412 (2013).</li><li>Boex-Fontvieille, E., Rustgi, S., von Wettstein, D., Reinbothe, S., Reinbothe, C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Water-soluble+chlorophyll+protein+is+involved+in+herbivore+resistance+activation+during+greening+of+Arabidopsis+thaliana.">Water-soluble chlorophyll protein is involved in herbivore resistance activation during greening of Arabidopsis thaliana.</a> Proc. Natl. Acad. Sci. U. S. A. 112, 7303-7308 (2015).</li><li>Hughes, J. L., 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=Magneto-optic+spectroscopy+of+a+protein+tetramer+binding+two+exciton-coupled+chlorophylls.">Magneto-optic spectroscopy of a protein tetramer binding two exciton-coupled chlorophylls.</a> J. Am. Chem. Soc. 128, 3649-3658 (2006).</li><li>Bednarczyk, D., Takahashi, S., Satoh, H., Noy, D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Assembly+of+water-soluble+chlorophyll-binding+proteins+with+native+hydrophobic+chlorophylls+in+water-in-oil+emulsions.">Assembly of water-soluble chlorophyll-binding proteins with native hydrophobic chlorophylls in water-in-oil emulsions.</a> BBA - Bioenergetics. 1847, 307-313 (2015).</li><li>Fiedor, L., Rosenbach-Belkin, V., Scherz, 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+stereospecific+interaction+between+chlorophylls+and+chlorophyllase.+Possible+implication+for+chlorophyll+biosynthesis+and+degradation.">The stereospecific interaction between chlorophylls and chlorophyllase. Possible implication for chlorophyll biosynthesis and degradation.</a> J. Biol. Chem. 267, 22043-22047 (1992).</li><li>Kamimura, Y., Mori, T., Yamasaki, T., Katoh, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Isolation,+properties+and+a+possible+function+of+a+water-soluble+chlorophyll+a/b-protein+from+brussels+sprouts.">Isolation, properties and a possible function of a water-soluble chlorophyll a/b-protein from brussels sprouts.</a> Plant Cell Physiol. 38, 133-138 (1997).</li><li>Murata, T., Itoh, R., Yakushiji, E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Crystallization+of+water-soluble+chlorophyll-proteins+from+Lepidium+virginicum.">Crystallization of water-soluble chlorophyll-proteins from Lepidium virginicum.</a> Biochim. Biophys. Acta. 593, 167-170 (1980).</li></ol>

Our goal was to develop a new general system for assembly of water-soluble chlorophyll-binding proteins with hydrophobic pigments. Here it is shown that the new reconstitution system based on W/O emulsion is a general approach proven to work for assembly of WSCP apoproteins from Brussels sprouts, cauliflower, Japanese horseradish and Virginia pepperweed recombinantly expressed in E. coli. Here results are presented from reconstitution of 1 mg of WSCP with 10-fold molar excess of Chl a. However it is als...

Hydrophobic pigments such as chlorophylls (Chls), bacteriochlorophylls (BChls) and carotenoids are the primary cofactors in photosynthetic reaction centers and light harvesting proteins that carry out electron transport, and light energy capture and transfer. The reaction centers and most of the Chl-binding light harvesting complexes are transmembrane proteins. The Fenna-Matthews-Olson (FMO) protein of non-oxygenic photosynthetic green-sulfur bacteria 1,2, and the peridinin-Chl protein (PCP) of dinoflagellates 3 are exceptional examples of water soluble light harvesting proteins. The water-soluble chlorophyll binding proteins (WSCPs) of Brassicaceae, Polygonaceae, Chenopodiaceae and Amaranthaceae plants 4,5 are another unique example, yet in contrast to FMO and PCP, these are neither involved in light harvesting nor in any of the primary photosynthetic reaction, and their precise physiological functions are yet unclear 5-8. Their high Chl-binding affinity have led to a suggested function as transient carriers of Chls and Chl derivatives 9,10. Alternatively, it was hypothesized that WSCP plays a role in scavenging Chls in damaged cells and protects against Chl-induced photooxidative damage 7,11-13. More recently, it was suggested that WSCP functions as a protease inhibitor and plays a role during herbivore resistance as well regulates cell death during flower development 14. WSCPs are divided into two main classes according to their photophysical properties. The first class (class I, e.g. from Chenopodium album) may undergo photoconversion upon illumination. Class II WSCPs from Brassica plants, that do not undergo photoconversion 5,10, are further subdivided into class IIa (e.g., from Brassica oleracea, Raphanus sativus) and IIb (e.g., from Lepidium virginicum). The structure of class IIb WSCP from Lepidium virginicum was solved by X-ray crystallography at 2.0 &#197; resolution 8. It reveals a symmetric homotetramer in which the protein subunits form a hydrophobic core. Each subunit binds a single Chl which results in a tight arrangement of four closely packed Chls within the core.This simple all Chl arrangement makes WSCPs a potentially useful model system for studying binding and assembly of Chl-protein complexes, and the effects of neighboring Chls and protein environments on the spectral and electronic properties of individual Chls. Furthermore, it may provide templates for constructing artificial Chl-binding proteins that may be used for light-harvesting modules in artificial photosynthetic devices.
Rigorous studies of native WSCPs are not feasible because the complexes purified from plants always contain a heterogeneous mixture of tetramers with different combinations of Chl a and Chl b 9. Thus, a method for assembling recombinantly expressed WSCPs with Chls in vitro is required. This is challenged by the negligible water-solubility of Chls which makes it impossible to assemble the complex in&#160;vitro by simply mixing the water-soluble apoproteins with pigments in aqueous solutions. In&#160;vitro assembly by mixing the apoproteins with thylakoid membranes 15 was demonstrated, but this method is limited to the native Chls present in the thylakoids. Schmidt et al. reported on assembling several Chl and BChl derivatives with WSCP from cauliflower (CaWSCP) by recombinantly expressing a histidine-tagged protein in E. coli immobilizing it onto a Ni-affinity column and introducing Chl derivatives solubilized in detergents 11. Successfully reconstitution of recombinant WSCPs from A. thaliana 6, and Brussels sprouts (BoWSCP), Japanese wild radish (RshWSCP) and Virginia pepperweed (LvWSCP) by a similar method were also reported.
Here, we present a novel, general, straightforward method for assembling Chls with WSCP that does not require tagging or immobilizing the proteins. It relies on preparing emulsions from their aqueous solutions of the water-soluble apoproteins in mineral oil. The proteins are thus encapsulated in water-in-oil (W/O) microdroplets with very high surface to volume ratio 16. The hydrophobic cofactors are then dissolved in the oil and are readily introduced into the droplets from the oil phase. We report on using the method for assembling of several variants of WSCP apoproteins recombinantly expressed in E. coli with Chl a. We demonstrate the assembly from crude lysate of WSCP-overexpressing bacteria which may be used as a screening system for developing novel Chl binding proteins.

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	<tbody>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Mineral oil</td>
			<td style="width:83px;">Sigma</td>
			<td style="width:119px;">M5904</td>
			<td style="width:196px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Span80</td>
			<td style="width:83px;">Sigma</td>
			<td style="width:119px;">85548</td>
			<td style="width:196px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Tween80</td>
			<td style="width:83px;">Sigma</td>
			<td style="width:119px;">P8074</td>
			<td style="width:196px;"></td>
		</tr>
		<tr height="63">
			<td height="63" style="height:63px;width:216px;">Bio-Scale Mini Profinity eXact Cartridges</td>
			<td style="width:83px;">Bio Rad</td>
			<td style="width:119px;">10011164</td>
			<td style="width:196px;">Affinity chromatography for WSCP purification with native sequence.</td>
		</tr>
		<tr height="84">
			<td height="84" style="height:84px;width:216px;">His Trap HF column</td>
			<td style="width:83px;">GE Healthcare Life Science</td>
			<td style="width:119px;">17-5248-02</td>
			<td style="width:196px;">Affinity chromatography for WSCP purification with His-tag</td>
		</tr>
		<tr height="84">
			<td height="84" style="height:84px;width:216px;">DEAE Sepharose Fast Flow</td>
			<td style="width:83px;">GE Healthcare Life Science</td>
			<td style="width:119px;">17-0709-01</td>
			<td style="width:196px;">Chromatography medium for chlorophyll purification</td>
		</tr>
	</tbody>
</table>

water in oil emulsions: a new system for assembling water-soluble chlorophyll-binding proteins with hydrophobic pigments

Chlorophylls (Chls) and bacteriochlorophylls (BChls) are the primary cofactors that carry out photosynthetic light harvesting and electron transport. Their functionality critically depends on their specific organization within large and elaborate multisubunit transmembrane protein complexes. In order to understand at the molecular level how these complexes facilitate solar energy conversion, it is essential to understand protein-pigment, and pigment-pigment interactions, and their effect on excited dynamics. One way of gaining such understanding is by constructing and studying complexes of Chls with simple water-soluble recombinant proteins. However, incorporating the lipophilic Chls and BChls into water-soluble proteins is difficult. Moreover, there is no general method, which could be used for assembly of water-soluble proteins with hydrophobic pigments. Here, we demonstrate a simple and high throughput system based on water-in-oil emulsions, which enables assembly of water-soluble proteins with hydrophobic Chls. The new method was validated by assembling recombinant versions of the water-soluble chlorophyll binding protein of Brassicaceae plants (WSCP) with Chl a. We demonstrate the successful assembly of Chl a using crude lysates of WSCP expressing E. coli cell, which may be used for developing a genetic screen system for novel water-soluble Chl-binding proteins, and for studies of Chl-protein interactions and assembly processes.

Recombinant WSCP apoproteins were assembled with Chl a in W/O emulsions according to the protocol described in the previous section. The protocol was implemented using aqueous phases containing either pure WSCPs, or lysates E.coli cells overexpressing WSCP (Figure 1). The protocol is simple, fast and does not require any special equipment except a tissue homogenizer.
The absorbance and CD spect...

Watch this Scientific Journal Video about Water in Oil Emulsions: A New System for Assembling Water-soluble Chlorophyll-binding Proteins with Hydrophobic Pigments at JoVE.com

Water in Oil Emulsions: A New System for Assembling Water-soluble Chlorophyll-binding Proteins with Hydrophobic Pigments

This manuscript describes a simple and high-throughput method for assembling water-soluble proteins with hydrophobic pigments that is based on water-in-oil emulsions. We demonstrate the effectiveness of the method in the assembly of native chlorophylls with four variants of recombinant water-soluble-chlorophyll binding proteins (WSCPs) of Brassica plants expressed in E. coli.

Chlorophylls (Chls) and bacteriochlorophylls (BChls) are the primary cofactors that carry out photosynthetic light harvesting and electron transport. ...

The overall goal of this technique is to enable incorporation of water-insoluble chlorophylls into the binding sites of water-soluble proteins. This method enables assembly of chlorophylls with recombinant proteins, which allows rigorous studies of chlorophyll-protein interactions and opens up new possibilities for constructing novel chlorophyll-protein complexes. The main advantage of this technique is that it does not require tagging or immobilizing the proteins.Thus, it is well-suited for screening assays. Demonstrating the procedure will be Dominica Bednarczyk, a post-doc in my research group. While preparing the following stock solutions perform all chlorophyll preparation steps under a chemical hood under green light or in the dark to minimize photo damage.Always add nitrogen or argon before freezing the pigments for storage and ensure that all solvents are analytical grade. To begin, weigh about five grams of lyophilized Spirulina platensis cells or other cyanobacterium cells containing only chlorophyll a or chlorophyll-a in thylakoid membranes and use a mortar and pestle to crush it. The critical step during the chlorophyll extraction is to make sure that cyanobacteria cells are thoroughly lyophilized and to ensure the complete removal of water from the DEAE-Sepharose by several washes with acetone.Load the crushed cells onto a glass column and with about 50-100 milliliters of 100%acetone wash the tissue to remove the carotenoids. After washing, discard the eluted orange-green fraction. The actual color may vary from orange-green to green depending on the cyanobacteria culture and growth conditions.Exchange the acetone with 100%methanol and collect the green fraction containing chlorophyll a. When the color of the eluted fraction turns from dark green to pale green stop the elution. Next, using a rotary evaporator with a water bath that does not exceed 30 degrees Celsius evaporate the methanol until the extract is completely dry then use a small volume of diethyl ether to completely dissolve the pigments from the dried extracts and filter the solution through cotton wool, using additional small volume of ether to wash pigments off the cotton wool.Evaporate the diethyl ether until the pigments are completely dry. If stopping at this point, keep the dry pigments under nitrogen or argon at 20 degrees Celsius in the dark until further processing. To proceed with chlorophyll a preparation partially dissolve the dry pigments in the smallest volume possible of 100%acetone, then add 4 milliliters of acetone to the suspension and swirl the flask to completely dissolve the pigments.Using a Pasteur pipette gently load the sample onto a DEAE-Sepharose column equilibriated in 100%acetone, and with 100%acetone, elute the carotenoids. Then use a 3:1 volume-to-volume acetone-methanol mixture to elute the chlorophyll a. You may use a flashlight to briefly illuminate the column during elution in order to observe the actual pigment colors.With thin-layer chromatography, verify chlorophyll a purity using a 68:25:5:2 volume-to-volume ratio of dichloromethane and hexane, isopropanol and methanol to elute the sample. Then, using a rotary evaporator, evaporate the solvent until the chlorophyll a is completely dry. To prepare a chlorophyll a stock solution re-dissolve the dry chlorophyll a in 2-4 milliliters of 100%methanol.To prepare the organic phase of the emulsion, in a 50 milliliter tube weigh 0.2 grams of Tween 80, 1.8 grams of Span 80, and 38 grams of mineral oil. Mix the components well and place the solution on ice to cool. To prepare an aqueous phase containing purified water-soluble chlorophyll-binding protein, or WSCP, grow E.coli BL21 bacteria containing the WSCP gene in 1 liter of LB medium at 37 degrees Celsius to an OD600 of 0.3 to 0.6.Add 1 millimolar IPTG to induce protein expression and grow the bacteria at 30 degrees Celsius for 12-16 hours, then harvest the bacteria by centrifugation at 5000 G and 4 degrees Celsius for 10 minutes. With a buffer suitable for the affinity chromatography dissolve the pellet, transfer the bacterial suspension to smaller tubes and sonicate on ice. After spinning down the lysate, purify the recombinant tagged WSCP proteins using the appropriate commercially-available affinity chromatography system for protein purification following the manufacturer's instructions.Prepare the aqueous phase of the emulsion by exchanging the buffer to 50 millimolar phosphate buffer pH 7.8 and adjusting the purified WSCP concentration to 0.5 to 1 milligram per milliliter. To prepare an aqueous phase containing crude bacterial lysate with WSCP, grow E.coli BL21 cells containing a plasmid expressing WSCP in 250 milliliters of LB at 37 degrees Celsius to log phase. Add 1 millimolar IPTG to induce protein expression and grow the bacteria at 30 degrees Celsius overnight.The following day, after harvesting the bacterial cells use 1-2 milliliters of 50 millimolar sodium phosphate buffer pH 7.8 to dissolve the pellet. Then, after sonicating, centrifuge the lysate at 12, 000 G and 4 degrees Celsius for 30 minutes. Prepare the aqueous phase of the emulsion by mixing 0.125 milliliters of supernatant with 0.875 milliliters of 50 millimolar sodium phosphate buffer pH 7.8.To assemble WSCP with chlorophyll a in emulsion, transfer 5 milliliters of a thoroughly-mixed oil-surfactant mixture into a glass vial and cool on ice. Add 1 milliliter of ice-cold aqueous phase just prepared and use a tissue homogenizer at 9, 500 RPM on ice for two minutes to mix both phases. From this point forward, performing all steps under green light to minimize photodamage, add 20 microliters of 25 millimolar chlorophyll a stock solution to the emulsion.Disperse by flicking and inverting the glass vial ensuring that the chlorophyll a is evenly distributed in the emulsion, then incubate on ice in the dark for 1-2 hours. The critical step during emulsion preparation is to cool down both the water phase and organic phase before mixing. Next, in order to break down the emulsion and separate the water droplets from the organic phase, transfer the emulsion to 1.5-milliliter plastic tubes and centrifuge at 14, 000 G at room temperature for five minutes.Dispose of the upper oil phase and add 1 milliliter of mineral oil to the lower phase, then mix well by vortexing or by flipping the tube. After spinning the sample, remove the upper oil phase and repeat the addition of mineral oil and centrifugation until a clear meniscus separating the aqueous and mineral oil phases without an intermediate emulsion is achieved. Now, to the aqueous phase add 1 milliliter of water-saturated diethyl ether.Then, after vortexing the sample, spin it down at 14, 000 G for 5 minutes at room temperature. After the third centrifugation, in the hood, remove the diethyl ether and leave the tubes open for 5-20 minutes. Finally, load the aqueous phase containing the WSCP-chlorophyll a complex onto a desalting column and elute with a buffer appropriate for future experiments.Store the sample at 4 degrees Celsius away from light for up to one month. Using the protocol described in this video, recombinant WSCP apoproteins were assembled with chlorophyll a in water and oil emulsions. Shown here are the absorbances and CD spectra of chlorophyll a complexes with four recombinant WSCP variants.The results are similar in band-shaped end position to previously reported spectra of the respective native complexes. This figure shows the positive assembly of WSCP with chlorophyll a in lysates from WSCP-expressing cells as seen by the green color of the aqueous phase. This result demonstrates the potential of water and oil emulsions as a fast screening system for positive assembly of WSCPs with chlorophylls.As demonstrated here, droplets of WSCP-containing lysates feature distinct chlorophyll a fluorescence in confocal microscope images. This implies that successful assembly of WSCP-chlorophyll complexes can be detected directly in the water droplets and it may provide a basis for water-and-oil-emulsion-based screening systems. Once mastered, this technique can be done for five hours if it's performed properly.While attempting this procedure, it is important to remember that working with chlorophylls should be done quickly, without exposing chlorophyll to light and oxygen. After its development, this technique enabled us to prepare a wide range of water-soluble chlorophyll-binding proteins that are used to explore the effect of protein environment on the electrolytic and spectral properties of chlorophylls. After watching this video, you should have a good understanding of how to extract and purify chlorophylls from cyanobacteria and assemble them in water-soluble proteins by using water and oil emulsions.Don't forget that working with organic solvents, such as ether, methanol or acetone, can be harmful and precautions, such as working in a chemical hood, should always be taken while performing this procedure.

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High-pressure Sapphire Cell for Phase Equilibria Measurements of CO2/Organic/Water Systems

The high pressure sapphire cell apparatus was constructed to visually determine the composition of multiphase systems without physical sampling. Specifically, the sapphire cell enables visual data collection from multiple loadings to solve a set of material balances to precisely determine phase composition. Ternary phase diagrams can then be established to determine the proportion of each component in each phase at a given condition. In principle, any ternary system can be studied although ternary systems (gas-liquid-liquid) are the specific examples discussed herein. For instance, the ternary THF-Water-CO2 system was studied at 25 and 40&#160;&#176;C and is described herein. Of key importance, this technique does not require sampling. Circumventing the possible disturbance of the system equilibrium upon sampling, inherent measurement errors, and technical difficulties of physically sampling under pressure is a significant benefit of this technique. Perhaps as important, the sapphire cell also enables the direct visual observation of the phase behavior. In fact, as the CO2 pressure is increased, the homogeneous THF-Water solution phase splits at about 2 MPa. With this technique, it was possible to easily and clearly observe the cloud point and determine the composition of the newly formed phases as a function of pressure.
The data acquired with the sapphire cell technique can be used for many applications. In our case, we measured swelling and composition for tunable solvents, like gas-expanded liquids, gas-expanded ionic liquids and Organic Aqueous Tunable Systems (OATS)1-4. For the latest system, OATS, the high-pressure sapphire cell enabled the study of (1) phase behavior as a function of pressure and temperature, (2) composition of each phase (gas-liquid-liquid) as a function of pressure and temperature and (3) catalyst partitioning in the two liquid phases as a function of pressure and composition. Finally, the sapphire cell is an especially effective tool to gather accurate and reproducible measurements in a timely fashion.

High-pressure Sapphire Cell for Phase Equilibria Measurements of CO2/Organic/Water Systems

The high pressure sapphire cell apparatus is a unique tool to study, without sampling, phase behavior under a wide range of pressures. Using a cathetometer, very precise volume measurements can be recorded to measure liquid expansion and phase composition. Thus, this synthetic method enables the study of (1) phase equilibria of multi-component mixtures and (2) the partition behavior of catalyst or model compounds as a function of pressure.

The high pressure sapphire cell apparatus was constructed to visually determine the composition of multiphase systems without physical sampling. ...

In Situ Characterization of Hydrated Proteins in Water by SALVI and ToF-SIMS

This work demonstrates in situ characterization of protein biomolecules in the aqueous solution using the System for Analysis at the Liquid Vacuum Interface (SALVI) and time-of-flight secondary ion mass spectrometry (ToF-SIMS). The fibronectin protein film was immobilized on the silicon nitride (SiN) membrane that forms the SALVI detection area. During ToF-SIMS analysis, three modes of analysis were conducted including high spatial resolution mass spectrometry, two-dimensional (2D) imaging, and depth profiling. Mass spectra were acquired in both positive and negative modes. Deionized water was also analyzed as a reference sample. Our results show that the fibronectin film in water has more distinct and stronger water cluster peaks compared to water alone. Characteristic peaks of amino acid fragments are also observable in the hydrated protein ToF-SIMS spectra. These results illustrate that protein molecule adsorption on a surface can be studied dynamically using SALVI and ToF-SIMS in the liquid environment for the first time.

In Situ Characterization of Hydrated Proteins in Water by SALVI and ToF-SIMS

This work presents a protocol for liquid handling and sample introduction to a microchannel for in situ time-of-flight secondary ion mass spectrometry analysis of protein biomolecules in an aqueous solution.

This work demonstrates in situ characterization of protein biomolecules in the aqueous solution using the System for Analysis at the Liquid Vacuum ...

Synthesis of Protein Bioconjugates via Cysteine-maleimide Chemistry

The chemical linking or bioconjugation of proteins to fluorescent dyes, drugs, polymers and other proteins has a broad range of applications, such as the development of antibody drug conjugates (ADCs) and nanomedicine, fluorescent microscopy and systems chemistry. For many of these applications, specificity of the bioconjugation method used is of prime concern. The Michael addition of maleimides with cysteine(s) on the target proteins is highly selective and proceeds rapidly under mild conditions, making it one of the most popular methods for protein bioconjugation.
We demonstrate here the modification of the only surface-accessible cysteine residue on yeast cytochrome c with a ruthenium(II) bisterpyridine maleimide. The protein bioconjugation is verified by gel electrophoresis and purified by aqueous-based fast protein liquid chromatography in 27% yield of isolated protein material. Structural characterization with MALDI-TOF MS and UV-Vis is then used to verify that the bioconjugation is successful. The protocol shown here is easily applicable to other cysteine - maleimide coupling of proteins to other proteins, dyes, drugs or polymers.

Synthesis of Protein Bioconjugates via Cysteine-maleimide Chemistry

This protocol details the important steps required for the bioconjugation of a cysteine containing protein to a maleimide, including reagent purification, reaction conditions, bioconjugate purification and bioconjugate characterization.

The chemical linking or bioconjugation of proteins to fluorescent dyes, drugs, polymers and other proteins has a broad range of applications, such as the ...

Synthesis of a Water-soluble Metal&#8211;Organic Complex Array

We demonstrate a method for the synthesis of a water-soluble multimetallic peptidic array containing a predetermined sequence of metal centers such as Ru(II), Pt(II), and Rh(III). The compound, named as a water-soluble metal-organic complex array (WSMOCA), is obtained through 1) the conventional solution-chemistry-based preparation of the corresponding metal complex monomers having a 9-fluorenylmethyloxycarbonyl (Fmoc)-protected amino acid moiety and 2) their sequential coupling together with other water-soluble organic building units on the surface-functionalized polymeric resin by following the procedures originally developed for the solid-phase synthesis of polypeptides, with proper modifications. Traces of reactions determined by mass spectrometric analysis at the representative coupling steps in stage 2 confirm the selective construction of a predetermined sequence of metal centers along with the peptide backbone. The WSMOCA cleaved from the resin at the end of stage 2 has a certain level of solubility in aqueous media dependent on the pH value and/or salt content, which is useful for the purification of the compound.

A potential general method for the synthesis of water-soluble multimetallic peptidic arrays containing a predetermined sequence of metal centers is presented.

We demonstrate a method for the synthesis of a water-soluble multimetallic peptidic array containing a predetermined sequence of metal centers such as ...

Probing the Structure and Dynamics of Interfacial Water with Scanning Tunneling Microscopy and Spectroscopy

Water/solid interfaces are ubiquitous and play a key role in many environmental, biophysical, and technological processes. Resolving the internal structure and probing the hydrogen-bond (H-bond) dynamics of the water molecules adsorbed on solid surfaces are fundamental issues of water science, which remains a great challenge owing to the light mass and small size of hydrogen. Scanning tunneling microscopy (STM) is a promising tool for attacking these problems, thanks to its capabilities of sub-&#197;ngstr&#246;m spatial resolution, single-bond vibrational sensitivity, and atomic/molecular manipulation. The designed experimental system consists of a Cl-terminated tip and a sample fabricated by dosing water molecules in situ onto the Au(111)-supported NaCl(001) surfaces. The insulating NaCl films electronically decouple the water from the metal substrates, so the intrinsic frontier orbitals of water molecules are preserved. The Cl-tip facilitates the manipulation of the single water molecules, as well as gating the orbitals of water to the proximity of Fermi level (EF) via tip-water coupling. This paper outlines the detailed methods of submolecular resolution imaging, molecular/atomic manipulation, and single-bond vibrational spectroscopy of interfacial water. These studies open up a new route for investigating the H-bonded systems at the atomic scale.

Here, we present a protocol to investigate the structure and dynamics of interfacial water at the atomic scale, in terms of submolecular resolution imaging, molecular manipulation, and single-bond vibrational spectroscopy.

Water/solid interfaces are ubiquitous and play a key role in many environmental, biophysical, and technological processes. Resolving the internal ...

Heterogeneous Removal of Water-Soluble Ruthenium Olefin Metathesis Catalyst from Aqueous Media Via Host-Guest Interaction

A highly efficient transition metal catalyst removal method is developed. The water-soluble catalyst contains a newly-designed NHC ligand for the catalyst removal via host-guest interactions. The new NHC ligand possesses an adamantyl (guest) tethered linear ethylene glycol units for hydrophobic inclusion into the cavity of a &#946;-cyclodextrin (&#946;-CD) host compound. The new NHC ligand was applied to a Ru-based olefin metathesis catalyst. The Ru catalyst demonstrated excellent activity in representative ring-closing metathesis (RCM) and ring-opening metathesis polymerization (ROMP) reactions in aqueous media as well as organic solvent, CH2Cl2. After the reaction was complete, the lingering Ru residue was removed from the aqueous solution with the efficiency of more than 99% (53 ppm of Ru residue) by simple filtration utilizing a host-guest interaction between insoluble silica-grafted &#946;-CD (host) and the adamantyl moiety (guest) on the catalyst. The new Ru catalyst also demonstrated high removal efficiency via extraction when the reaction is run in organic solvent by partitioning the crude reaction mixture between layers of diethyl ether and water. In this way, the catalyst stays in aqueous layer only. In organic layer, the residual Ru amount was only 0.14 ppm in the RCM reactions of diallyl compounds.

A removable water-soluble N-heterocyclic carbene (NHC) ligand in aqueous media via host-guest interaction has been developed. We demonstrated representative olefin metathesis reactions in water as well as in dichloromethane. Via either host-guest interaction or extraction, the residual ruthenium (Ru) catalyst was as low as 0.14 ppm after the reaction.

A highly efficient transition metal catalyst removal method is developed. The water-soluble catalyst contains a newly-designed NHC ligand for the catalyst ...

A New Straightforward Method for Lipophilicity (logP) Measurement using 19F NMR Spectroscopy

Fluorination has become an effective tool to optimize physicochemical properties of bioactive compounds. One of the applications of fluorine introduction is to modulate the lipophilicity of the compound. In our group, we are interested in the study of the impact of fluorination on lipophilicity of aliphatic fluorohydrins and fluorinated carbohydrates. These are not UV-active, resulting in a challenging lipophilicity determination. Here, we present a straightforward method for the measurement of lipophilicity of fluorinated compounds by 19F NMR spectroscopy. This method requires no UV-activity. Accurate solute mass, solvent and aliquot volume are also not required to be measured. Using this method, we measured the lipophilicities of a large number of fluorinated alkanols and carbohydrates.

A New Straightforward Method for Lipophilicity logP Measurement using 19F NMR Spectroscopy

A novel and straightforward variation of the shake-flask method was developed for accurate lipophilicity measurement of fluorinated compounds by 19F NMR spectroscopy.

Fluorination has become an effective tool to optimize physicochemical properties of bioactive compounds. One of the applications of fluorine introduction ...

Synthesis and Bioconjugation of Thiol-Reactive Reagents for the Creation of Site-Selectively Modified Immunoconjugates

Maleimide-bearing bifunctional probes have been employed for decades for the site-selective modification of thiols in biomolecules, especially antibodies. Yet maleimide-based conjugates display limited stability in vivo because the succinimidyl thioether linkage can undergo a retro-Michael reaction. This, of course, can lead to the release of the radioactive payload or its exchange with thiol-bearing biomolecules in circulation. Both of these processes can produce elevated activity concentrations in healthy organs as well as decreased activity concentrations in target tissues, resulting in reduced imaging contrast and lower therapeutic ratios. In 2018, we reported the creation of a modular, stable, and easily accessible phenyloxadiazolyl methyl sulfone reagent &#8212; dubbed &#8216;PODS&#8217; &#8212; as a platform for thiol-based bioconjugations. We have clearly demonstrated that PODS-based site-selective bioconjugations reproducibly and robustly create homogenous, well-defined, highly immunoreactive, and highly stable radioimmunoconjugates. Furthermore, preclinical experiments in murine models of colorectal cancer have shown that these site-selectively labeled radioimmunoconjugates exhibit far superior in vivo performance compared to radiolabeled antibodies synthesized via maleimide-based conjugations. In this protocol, we will describe the four-step synthesis of PODS, the creation of a bifunctional PODS-bearing variant of the ubiquitous chelator DOTA (PODS-DOTA), and the conjugation of PODS-DOTA to the HER2-targeting antibody trastuzumab.

In this protocol, we will describe the synthesis of PODS, a phenyoxadiazolyl methyl sulfone-based reagent for the site-selective attachment of cargos to the thiols of biomolecules, particularly antibodies. In addition, we will describe the synthesis and characterization of a PODS-bearing bifunctional chelator and its conjugation to a model antibody.

Maleimide-bearing bifunctional probes have been employed for decades for the site-selective modification of thiols in biomolecules, especially antibodies. ...

An Intestine/Liver Microphysiological System for Drug Pharmacokinetic and Toxicological Assessment

The recently introduced microphysiological systems (MPS) cultivating human organoids are expected to perform better than animals in the preclinical tests phase of drug developing process because they are genetically human and recapitulate the interplay among tissues. In this study, the human intestinal barrier (emulated by a co-culture of Caco-2 and HT-29 cells) and the liver equivalent (emulated by spheroids made of differentiated HepaRG cells and human hepatic stellate cells) were integrated into a two-organ chip (2-OC) microfluidic device to assess some acetaminophen (APAP) pharmacokinetic (PK) and toxicological properties. The MPS had three assemblies: Intestine only 2-OC, Liver only 2-OC, and Intestine/Liver 2-OC with the same media perfusing both organoids. For PK assessments, we dosed the APAP in the media at preset timepoints after administering it either over the intestinal barrier (emulating the oral route) or in the media (emulating the intravenous route), at 12 &#181;M and 2 &#181;M respectively. The media samples were analyzed by reversed-phase high-pressure liquid chromatography (HPLC). Organoids were analyzed for gene expression, for TEER values, for protein expression and activity, and then collected, fixed, and submitted to a set of morphological evaluations. The MTT technique performed well in assessing the organoid viability, but the high content analyses (HCA) were able to detect very early toxic events in response to APAP treatment. We verified that the media flow does not significantly affect the APAP absorption whereas it significantly improves the liver equivalent functionality. The APAP human intestinal absorption and hepatic metabolism could be emulated in the MPS. The association between MPS data and in silico modeling has great potential to improve the predictability of the in vitro methods and provide better accuracy than animal models in pharmacokinetic and toxicological studies.

We exposed a microphysiological system (MPS) with intestine and liver organoids to acetaminophen (APAP). This article describes the methods for organoid production and APAP pharmacokinetic and toxicological property assessments in the MPS. It also describes the tissue functionality analyses necessary to validate the results.

The recently introduced microphysiological systems (MPS) cultivating human organoids are expected to perform better than animals in the preclinical tests ...

Resolving Water, Proteins, and Lipids from In Vivo Confocal Raman Spectra of Stratum Corneum through a Chemometric Approach

Development of this in vivo confocal Raman spectroscopic method enables the direct measurement of water, proteins, and lipids with depth resolution in human subjects. This information is very important for skin-related diseases and characterizing skin care product performance. This protocol illustrates a method for confocal Raman spectra collection and the subsequent analysis of the spectral dataset leveraging chemometrics. The goal of this method is to establish a standard protocol for data collection and provide general guidance for data analysis. Preprocessing (e.g., removal of outlier spectra) is a critical step when processing large datasets from clinical studies. As an example, we provide guidance based on prior knowledge of a dataset to identify the types of outliers and develop specific strategies to remove them. A principal component analysis is performed, and the loading spectra are compared with spectra from reference materials to select the number of components used in the final multivariate curve resolution (MCR) analysis. This approach is successful for extracting meaningful information from a large spectral dataset.

Here, we present a protocol for collection of confocal Raman spectra from human subjects in clinical studies combined with chemometric approaches for spectral outlier removal and the subsequent extraction of key features.

Development of this in vivo confocal Raman spectroscopic method enables the direct measurement of water, proteins, and lipids with depth resolution in ...