This work was supported by the grants from the Jane and Aatos Erkko Foundation and the BBSRC (BB/M021610) to Adrian Goldman, the Academy of Finland (No. 308105) to Keni Vidilaseris, (No. 310297) to Henri Xhaard, and (No. 265481) to Jari Yli-Kauhaluoma, and the University of Helsinki Research Funds to Gustav Boije af Genn&#228;s. The authors thank Bernadette Gehl for her technical help during the project.

1. Protein preparation
NOTE: The expression and purification of TmPPase has been described elsewhere13.
<ol>
	<li>Prepare 10 mL of the reactivation buffer solution containing 20 mM 2-(N-morpholino)ethanesulfonic acid (MES) pH 6.5, 3.5% (v/v) glycerol, 2 mM dithiothreitol (DTT), and 0.05% dodecyl maltoside (DDM).</li>
	<li>Prepare 10 mL of the reaction mixture containing 200 mM Tris-Cl pH 8.0, 8.0 mM MgCl2, 333 mM KCl, and 67 mM NaCl. 
	NOTE: Mg2+ is required to chelate the pyrophosphate as the substrate of mPPase, K+ is required to increase the enzyme activity as TmPPase is a potassium dependent mPPase, and Na+ is needed for the enzyme activity during sodium ion translocation by TmPPase.</li>
	<li>Prepare 30 mg/mL liposomes for enzyme reactivation.
	<ol>
		<li>Add 10 mL of 20 mM Tris-HCl pH 8.0 with 1 mM DTT to 0.3 g of L-&#945;-phosphatidylcholine from soybean to 10 mL of 20 mM Tris-HCl pH 8.0 with 1 mM DTT.</li>
		<li>Put the liposome on ice, and sonicate with 1 second pulse interval for 1 minute, pause for 1 minute, and repeat until the solution becomes transparent yellow.</li>
		<li>Aliquot the liposomes, freeze in liquid nitrogen and store at -80 &#176;C until used.</li>
	</ol>
	</li>
	<li>Reactivate the enzyme.
	<ol>
		<li>Mix 40 &#181;L of the liposomes solution with 22.5 &#181;L of 20% DDM.</li>
		<li>Heat the mixture at 55 &#176;C for 15 min and allow it to cool to room temperature.</li>
		<li>Add 36.5 &#181;L of the reactivation buffer solution, mix, and add 1 &#181;L of concentrated protein (13 mg/mL) to make a total concentration of 0.13 mg/mL. 
		NOTE: Protein is usually frozen in 10 &#181;L aliquots after purification and thawed on ice before use.</li>
	</ol>
	</li>
	<li>Take 20 &#181;L of the reactivated enzyme and add to 1,480 &#181;L of the reaction mixture, then mix gently. 
	NOTE: The addition of the reactivated enzyme to the reaction mixture should be performed just before it is used.</li>
</ol>
2. Compound preparation
<ol>
	<li>Dissolve the compounds in dimethyl sulfoxide (DMSO) to make stock solutions of 25&#8722;100 mM in 50&#8722;200 &#181;L, based on the availability of the compounds. 
	NOTE: All compounds used here (Figure 2A) have been published previously9. If the compound solubility is low, the stock concentration can be adjusted accordingly.</li>
	<li>Prepare three different concentrations of each compound in water. 
	NOTE: The final concentrations in the reaction mixture will be 1, 5, and 50 micromolar or 1, 5, and 20 micromolar for soluble and sparingly soluble compounds, respectively.
	<ol>
		<li>Dilute the stock solution with water to 1 mL in microtubes to give 2 &#181;M, 10 &#181;M and 100 &#181;M for soluble compounds, or alternatively 2 &#181;M, 10 &#181;M and 40 &#181;M for sparingly soluble compounds.</li>
		<li>Vortex the compound solution instantly after dilution of the stock solution for proper mixing.</li>
	</ol>
	</li>
	<li>Check for compound aggregation using a nephelometer. 
	NOTE: This was studied as triplicates in three concentrations (1 &#181;M, 5 &#181;M and 20 &#181;M) and normalized to the blank in a 96 well plate.
	<ol>
		<li>Dispense 75 &#181;L of the reaction mixture into each well using a multichannel pipette.</li>
		<li>Add 75 &#181;L of each compound (for the blank, use 75 &#181;L of water instead) and mix by pipetting up and down 5&#215;.</li>
		<li>Measure each well at 300 V using a microplate nephelometer.</li>
	</ol>
	</li>
</ol>
3. Reagents for the assay preparation
<ol>
	<li>Prepare the arsenite-citrate solution.
	<ol>
		<li>Weigh 5 g of sodium arsenite and 5 g of trisodium citrate dihydrate. 
		CAUTION: Sodium arsenite is toxic, thus use proper protective equipment and handle with special care. As precaution, do not handle before all necessary safety precautions have been read and understood. Handle only in a fume hood in order not to inhale dust/vapors of the compound or its solution(s). If inhaled, move to fresh air and obtain medical attention. Wear appropriate chemical safety goggles, protective gloves and clothing to avoid ingestion and eye/skin contact. If swallowed, call immediately a poison center or doctor/physician. If it gets on the skin or in the eye(s), wash with plenty of water and obtain medical attention.</li>
		<li>Dissolve into 100 mL of water.</li>
		<li>Add 5 mL of glacial acetic acid, mix, and add water to 250 mL.</li>
		<li>Store at room temperature protected from light. 
		NOTE: The solution is stable for more than a year.</li>
	</ol>
	</li>
	<li>Prepare solution A and solution B.
	<ol>
		<li>For solution A, add 10 mL of ice cold 0.5 M HCl to 0.3 g of ascorbic acid. Dissolve the ascorbic acid by vortexing.</li>
		<li>For solution B, add 1 mL of ice cold water to 70 mg of ammonium heptamolybdate tetrahydrate and vortex to dissolve. 
		NOTE: Store both solutions on ice until use. For the consistency of the assay result, both solutions can be stored on ice for a maximum of one&#160;week.</li>
	</ol>
	</li>
	<li>Prepare the phosphate (Pi) standard with the concentration of 0 &#181;M, 62.5 &#181;M, 250 &#181;M and 500 &#181;M for calibration.
	<ol>
		<li>Add 0 &#181;L, 25 &#181;L, 50 &#181;L, and 100 &#181;L of 5 mM Na2HPO4 dihydrate to four microtubes containing 370 &#181;L of the reaction mixture.</li>
		<li>Top up to 1 mL with water.</li>
	</ol>
	</li>
</ol>
4. Activity assay for one 96 well plate
NOTE: See Figure 1 for the schematic workflow of the assay.
<ol>
	<li>Add 1 mL of solution B to 10 mL of solution A, mix by vortexing and store the solution on ice. 
	NOTE: This solution should be transparent and yellow. Keep solution A + B on ice for at least 30 min prior to use. However, use the solution within 3 h as it will go bad after long-term storage.</li>
	<li>Add 40 &#181;L of 0 &#181;M, 62.5 &#181;M, 250 &#181;M and 500 &#181;M Pi standard to the tube strips in triplicate using a multichannel pipette. 
	NOTE: The reaction mixture with no Pi added will be used as a blank.</li>
	<li>Add 25 &#181;L of compound solution to the tube strips using a multichannel pipette. 
	NOTE: Each compound has three different concentrations in triplicate which is enough for initial estimation of the half maximal inhibitory concentration (IC50). For a more accurate IC50 determination, eight different compound concentrations can be used. For the uninhibited enzyme the compound solution is replaced with equal amount of water. As positive controls 2.5 &#181;M, 25 &#181;M, and 250 &#181;M of imidodiphosphate (IDP) sodium salt were used.</li>
	<li>Add 15 &#181;L of mPPase solution mixture to the tube strips (except to the tubes containing Pi standard) using a multichannel pipette.</li>
	<li>Seal the tube strips with an adhesive sealing sheet. Cut the sealing sheet to separate each tube strip.</li>
	<li>Pre-incubate the samples for 5 min at 71 &#176;C. Place the samples on the heating block with 20 s interval between each strip in order to minimize the time consumption during the subsequent steps.</li>
	<li>For each strip, open the adhesive sealing. Add 10 &#181;L of 2 mM sodium pyrophosphate dibasic using a multichannel pipette and mix by pipetting up and down for 5&#215;. Seal the tube strip again using the same sealing. 
	NOTE: This step might initially be difficult to accomplish in 20 s; however, it will become easier after some assays.</li>
	<li>Incubate at 71 &#176;C for 5 min.</li>
	<li>Place the samples on the cooling apparatus with 20 s interval between each strip. Let them cool for 10 min but centrifuge each strip briefly after 5 min of cooling, to decant water drops under the sealing sheet, then put it back to the cooling apparatus and remove the sealing. 
	NOTE: The cooling apparatus can simply be made by placing a 96 well PCR plate on a polystyrene Petri dish (size 150 mm &#215; 15 mm) filled with water and frozen for at least 1 h. The apparatus should be taken out from the freezer about 5 min prior to the beginning of the assay. Do not take out the cooling apparatus right before sample cooling as it will freeze the reaction mixture and hinder color development.</li>
	<li>After 10 min of cooling, add 60 &#181;L of solution A + B, mix by pipetting up and down for 5&#215; and keep the tube strips on the cooling apparatus for 10 min.</li>
	<li>Add 90 &#181;L of the arsenite-citrate solution and keep at room temperature for at least 30 min to produce a stable blue color. 
	CAUTION: Due to its toxicity all solutions containing sodium arsenite should be handled with extra care at all time. Thus, the addition of arsenite-citrate solution should be done in a fume hood.</li>
	<li>Dispense 180 &#181;L of each reaction mixture into a clear 96 well polystyrene microplate.</li>
	<li>Measure the absorbance of each well at 860 nm using a microplate spectrophotometer.</li>
</ol>
5. Result analysis
<ol>
	<li>Average the triplicates of each sample and the Pi standards. Then subtract with the blank to eliminate the background signal.</li>
	<li>Make a calibration curve by plotting the absorbance (A860) values against the amount of Pi standard (nmol) and perform a linear regression to obtain the trendline function using the following formula: 
	<img alt="Equation 1" src="/files/ftp_upload/60619/60619equ01a.jpg" /></li>
	<li>Calculate the phosphate amount (nmol) released from the enzymatic reaction based on the linear regression formula above.</li>
	<li>Calculate the specific activity using the following formula: 
	<img alt="Equation 2" src="/files/ftp_upload/60619/60619equ02a.jpg" /> 
	where nPi is the amount of phosphate released from the reaction (nmol), t is the reaction time (min), and mTmPPase is the amount of the pure TmPPase used in the assay (mg).</li>
	<li>Calculate the percent activity for each inhibitor concentration using the following formula: 
	<img alt="Equation 3" src="/files/ftp_upload/60619/60619equ03a.jpg" /> 
	where SAi is the specific activity of a sample with inhibitor and SAun is the specific activity of the uninhibited sample.</li>
	<li>Calculate the logIC50 (estimate) and IC50 (estimate) with a nonlinear regression fit from the four-parameter dose-response curve using the following formula: 
	<img alt="Equation 4" src="/files/ftp_upload/60619/60619equ04a.jpg" /> 
	where X is log of concentration ( &#181;M), Y is activity (%), Top and Bottom are plateaus in the same unit as Y (100% and 0%, respectively), logIC50 has the same log units as X, and HillSlope = slope factor or hill slope, which is unitless. 
	NOTE: Software (Table of Materials) is used for the fitting. Use the concentration of 0.01 &#181;M (instead of 0.00 &#181;M) for the sample without inhibitor as the logarithm of zero is not defined.</li>
</ol>

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	<li>Terstappen, G. C., Reggiani, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=In+silico+research+in+drug+discovery.">In silico research in drug discovery.</a> Trends in Pharmacological Sciences. 22 (1), 23-26 (2001).</li><li>Rask-Andersen, M., Almen, M. S., Schioth, H. B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Trends+in+the+exploitation+of+novel+drug+targets.">Trends in the exploitation of novel drug targets.</a> Nature Reviews Drug Discovery. 10 (8), 579-590 (2011).</li><li>Shah, N. R., Vidilaseris, K., Xhaard, H., Goldman, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Integral+membrane+pyrophosphatases:+a+novel+drug+target+for+human+pathogens.">Integral membrane pyrophosphatases: a novel drug target for human pathogens.</a> AIMS Biophysics. 3 (1), 171-194 (2016).</li><li>Baykov, A. A., Malinen, A. M., Luoto, H. H., Lahti, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Pyrophosphate-Fueled+Na++and+H++Transport+in+Prokaryotes.">Pyrophosphate-Fueled Na+ and H+ Transport in Prokaryotes.</a> Microbiology and Molecular Biology Reviews. 77 (2), 267-276 (2013).</li><li>Serrano, A., Perez-Castineira, J. R., Baltscheffsky, M., Baltscheffsky, H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=H+-PPases:+yesterday,+today+and+tomorrow.">H+-PPases: yesterday, today and tomorrow.</a> IUBMB Life. 59 (2), 76-83 (2007).</li><li>Liu, 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=A+vacuolar-H+-pyrophosphatase+(TgVP1)+is+required+for+microneme+secretion,+host+cell+invasion,+and+extracellular+survival+of+Toxoplasma+gondii.">A vacuolar-H+-pyrophosphatase (TgVP1) is required for microneme secretion, host cell invasion, and extracellular survival of Toxoplasma gondii.</a> Molecular Microbiology. 93 (4), 698-712 (2014).</li><li>Lemercier, 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=A+pyrophosphatase+regulating+polyphosphate+metabolism+in+acidocalcisomes+is+essential+for+Trypanosoma+brucei+virulence+in+mice.">A pyrophosphatase regulating polyphosphate metabolism in acidocalcisomes is essential for Trypanosoma brucei virulence in mice.</a> Journal of Biological Chemistry. 279 (5), 3420-3425 (2004).</li><li>Belogurov, G. A., 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=Membrane-bound+pyrophosphatase+of+Thermotoga+maritima+requires+sodium+for+activity.">Membrane-bound pyrophosphatase of Thermotoga maritima requires sodium for activity.</a> Biochemistry. 44 (6), 2088-2096 (2005).</li><li>Vidilaseris, K., 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=Asymmetry+in+catalysis+by+Thermotoga+maritima+membrane-bound+pyrophosphatase+demonstrated+by+a+nonphosphorus+allosteric+inhibitor.">Asymmetry in catalysis by Thermotoga maritima membrane-bound pyrophosphatase demonstrated by a nonphosphorus allosteric inhibitor.</a> Science Advances. 5 (5), (2019).</li><li>Lin, S. M., 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=Crystal+structure+of+a+membrane-embedded+H+-translocating+pyrophosphatase.">Crystal structure of a membrane-embedded H+-translocating pyrophosphatase.</a> Nature. 484 (7394), 399-403 (2012).</li><li>Fiske, C. H., Subbarow, Y. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+colorimetric+determination+of+phosphorus.">The colorimetric determination of phosphorus.</a> Journal of Biological Chemistry. 66 (2), 375-400 (1925).</li><li>Nagul, E. A., McKelvie, I. D., Worsfold, P., Kolev, S. D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+molybdenum+blue+reaction+for+the+determination+of+orthophosphate+revisited:+Opening+the+black+box.">The molybdenum blue reaction for the determination of orthophosphate revisited: Opening the black box.</a> Analytica Chimica Acta. 890, 60-82 (2015).</li><li>Kellosalo, J., Kajander, T., Palmgren, M. G., Lopez-Marques, R. L., Goldman, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Heterologous+expression+and+purification+of+membrane-bound+pyrophosphatases.">Heterologous expression and purification of membrane-bound pyrophosphatases.</a> Protein Expression and Purification. 79 (1), 25-34 (2011).</li><li>Vidilaseris, K., Kellosalo, J., Goldman, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+high-throughput+method+for+orthophosphate+determination+of+thermostable+membrane-bound+pyrophosphatase+activity.">A high-throughput method for orthophosphate determination of thermostable membrane-bound pyrophosphatase activity.</a> Analytical Methods. 10 (6), 646-651 (2018).</li><li>He, Z. Q., Honeycutt, C. W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+modified+molybdenum+blue+method+for+orthophosphate+determination+suitable+for+investigating+enzymatic+hydrolysis+of+organic+phosphates.">A modified molybdenum blue method for orthophosphate determination suitable for investigating enzymatic hydrolysis of organic phosphates.</a> Communications in Soil Science and Plant Analysis. 36 (9-10), 1373-1383 (2005).</li><li>Martin, B., Pallen, C. J., Wang, J. H., Graves, D. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Use+of+fluorinated+tyrosine+phosphates+to+probe+the+substrate+specificity+of+the+low+molecular+weight+phosphatase+activity+of+calcineurin.">Use of fluorinated tyrosine phosphates to probe the substrate specificity of the low molecular weight phosphatase activity of calcineurin.</a> Journal of Biological Chemistry. 260 (28), 14932-14937 (1985).</li><li>Strauss, J., Wilkinson, C., Vidilaseris, K., Harborne, S. P. D., Goldman, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+simple+strategy+to+determine+the+dependence+of+membrane-bound+pyrophosphatases+on+K++as+a+cofactor.">A simple strategy to determine the dependence of membrane-bound pyrophosphatases on K+ as a cofactor.</a> Methods in Enzymology. 607, 131-156 (2018).</li></ol>

The authors have nothing to disclose.

Here we report a detailed protocol for simple screening of inhibitors for membrane-bound pyrophosphatase from T. maritima in a 96 well plate format based on Vidilaseris et al.14. This protocol is inexpensive and based on 12-phosphomolybdic acid, which is formed from orthophosphate and molybdate under acidic conditions and reduced to phosphomolybdenum species with a distinct blue color12. This method is preferred over other protocols, such as the more sensitive malachite green assay16, because this method does not show interference in the presence of high phospholipid concentration which is required for TmPPase reactivation14.
The workflow of the screening protocol is depicted in Figure 1 and this process can be fully accomplished in 1 h. This protocol is optimized for TmPPase with the optimal working temperature at 71 &#176;C and a 5 min reaction time. As water will evaporate at this temperature from the reaction mixture, an adhesive sealing sheet (sliced to fit and cover the strips) is applied to prevent evaporation14 and the evaporated water is simply recollected with centrifugation. The 5 min incubation time is chosen as it is still in the linear range of the enzymatically released phosphate and sufficient for reliable screening14. In this protocol, the timing and pipetting skills are important factors to obtain a good and reliable result. Addition of reagents during the assay with 20 s interval between strips is an optimized timing option for ease of performing the subsequent steps.
For different mPPases, the optimum temperature and incubation time should be determined separately prior to use in the inhibition assay. The enzyme reactivation protocol above is optimized for TmPPase and other mPPases might need a different reactivation protocol. For example, DDM should not be added for reactivation of mPPase from Pyrobaculum aerophilum as it will decrease its enzymatic activity17. As the enzyme will become less active if prepared well in advance, the addition of reactivated enzyme should be added to the reaction mixture shortly before the assay is initiated. After addition of the arsenite-citrate solution the reaction product is stable for at least 5 h14. Therefore, the next batch of the assay can be performed immediately, and the absorbance measurement can be done later to all batches at once.

Approximately 25% of the total cellular proteins are membrane proteins and about 60% of them are drug targets1,2. One of the potential drug targets3, membrane-bound pyrophosphatases (mPPases), are dimeric enzymes that pump proton and/or sodium ion across the membrane by hydrolysis of pyrophosphate into two orthophosphates4. mPPases can be found in various organisms5 such as bacteria, archaea, plants, and protist parasites, with the exception of humans and animals4. In protist parasites, for example Plasmodium falciparum, Toxoplasma gondii and Trypanosoma brucei, mPPases are essential for the parasite virulence6 and knockout of this expression in the parasites lead to failure in maintaining intracellular pH upon exposure to the external basic pH7. Due to their importance and lack of homologous protein present in vertebrates, mPPases can be considered as potential drug targets for protistal diseases3.
The in vitro screening of mPPase inhibitors in this work is based on a TmPPase model system. TmPPase is a sodium ion pumping and potassium ion dependent mPPase from T. maritima and has its optimum activity at 71 &#176;C8. Benefits of this enzyme are for example its ease in production and purification, good thermal stability and high specific activity. TmPPase shows both high similarity in addition to the complete conservation of the position as well as identity of all catalytic residues to the protist mPPases3,9 and to the solved structure of Vigna radiata10 mPPase. The available structures of TmPPase in different conformations are also useful for structure-based drug design experiment (as virtual screening and de novo design).
Here we report a detailed protocol for screening of TmPPase inhibitors in a 96 well plate format (Figure 1). The protocol is based on the colorimetric method of the molybdenum blue reaction, which was first developed by Fiske and Subbarow11. This method involves the formation of 12-phosphomolybdic acid from orthophosphate and molybdate under acidic conditions, which is then reduced to give characteristic blue-colored phosphomolybdenum species12.

<table>
	<tbody>
		<tr>
			<td>Adhesive sealing sheet</td>
			<td>Thermo Scientific</td>
			<td>AB0558</td>
			<td></td>
		</tr>
		<tr>
			<td>Ammonium heptamolybdate tetrahydrate</td>
			<td>Merck</td>
			<td>F1412481 636</td>
			<td></td>
		</tr>
		<tr>
			<td>Ascorbic acid</td>
			<td>Sigma-Aldrich</td>
			<td>95212-250G</td>
			<td></td>
		</tr>
		<tr>
			<td>BioLite 96Well Multidish</td>
			<td>Thermo Scientific</td>
			<td>130188</td>
			<td></td>
		</tr>
		<tr>
			<td>Dimethyl sulfoxide (DMSO)</td>
			<td>Merck</td>
			<td>1167431000</td>
			<td></td>
		</tr>
		<tr>
			<td>8-well PCR Tube Strips 0.2 ml without caps (120)</td>
			<td>Nippon genetics</td>
			<td>FG-028</td>
			<td></td>
		</tr>
		<tr>
			<td>Dodecyl maltoside (DDM)</td>
			<td>Melford</td>
			<td>B2010-100G</td>
			<td></td>
		</tr>
		<tr>
			<td>Ethanol</td>
			<td>Merck</td>
			<td>1009901001</td>
			<td></td>
		</tr>
		<tr>
			<td>Glacial acetic acid</td>
			<td>Merck</td>
			<td>1000631011</td>
			<td></td>
		</tr>
		<tr>
			<td>Hydrochloric acid</td>
			<td>Sigma-Aldrich</td>
			<td>258148-500ML</td>
			<td></td>
		</tr>
		<tr>
			<td>Imidodiphosphate sodium salt</td>
			<td>Sigma-Aldrich</td>
			<td>I0631-1G</td>
			<td></td>
		</tr>
		<tr>
			<td>L-&#945;-Phosphatidyl choline from soybean lecithin</td>
			<td>Sigma</td>
			<td>429415-100GM</td>
			<td></td>
		</tr>
		<tr>
			<td>Magnesium chloride</td>
			<td>Sigma-Aldrich</td>
			<td>8147330500</td>
			<td></td>
		</tr>
		<tr>
			<td>Multiplate 96-Well PCR Plates</td>
			<td>Bio-Rad</td>
			<td>MLL9651</td>
			<td></td>
		</tr>
		<tr>
			<td>MultiSkan Go</td>
			<td>Thermo Scientific</td>
			<td>10680879</td>
			<td></td>
		</tr>
		<tr>
			<td>Nepheloskan Ascent (Type 750)</td>
			<td>Labsystems</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Polystyrene Petri dish (size 150 mm x 15 mm)</td>
			<td>Sigma-Aldrich</td>
			<td>P5981-100EA</td>
			<td></td>
		</tr>
		<tr>
			<td>Potassium chloride</td>
			<td>Merck</td>
			<td>104936</td>
			<td></td>
		</tr>
		<tr>
			<td>Prism 6 software</td>
			<td>GraphPad</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>QBT2 Heating block</td>
			<td>Grant Instruments</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Sodium meta-arsenite</td>
			<td>Fisher Chemical</td>
			<td>12897692</td>
			<td></td>
		</tr>
		<tr>
			<td>Sodium phosphate dibasic (Pi)</td>
			<td>Sigma</td>
			<td>S0876-1KG</td>
			<td></td>
		</tr>
		<tr>
			<td>Sodium pyrophosphate dibasic</td>
			<td>Fluka</td>
			<td>71501-100G</td>
			<td></td>
		</tr>
		<tr>
			<td>Trisodium citrate dihydrate</td>
			<td>Fluka</td>
			<td>71404-1KG</td>
			<td></td>
		</tr>
	</tbody>
</table>

screening for thermotoga maritima membrane-bound pyrophosphatase inhibitors

Membrane-bound pyrophosphatases (mPPases) are dimeric enzymes that occur in bacteria, archaea, plants, and protist parasites. These proteins cleave pyrophosphate into two orthophosphate molecules, which is coupled with proton and/or sodium ion pumping across the membrane. Since no homologous proteins occur in animals and humans, mPPases are good candidates in the design of potential drug targets. Here we present a detailed protocol to screen for mPPase inhibitors utilizing the molybdenum blue reaction in a 96 well plate system. We use mPPase from the thermophilic bacterium Thermotoga maritima (TmPPase) as a model enzyme. This protocol is simple and inexpensive, producing a consistent and robust result. It takes only about one hour to complete the activity assay protocol from the start of the assay until the absorbance measurement. Since the blue color produced in this assay is stable for a long period of time, subsequent assay(s) can be performed immediately after the previous batch, and the absorbance can be measured later for all batches at once. The drawback of this protocol is that it is done manually and thus can be exhausting as well as require good skills of pipetting and time keeping. Furthermore, the arsenite-citrate solution used in this assay contains sodium arsenite, which is toxic and should be handled with necessary precautions.

In this protocol, eight compounds (1&#8722;8) were tested (Figure 2A) together with IDP, a common inhibitor of pyrophosphatases, as a positive control. Each compound was tested at three different concentrations (1 &#181;M, 5 &#181;M and 20 &#181;M) in triplicate. The workflow of the screening is depicted in Figure 1, starting from sample and reagent preparation until the absorbance measurement at 860 nm.
At the end of this protocol, after the addition of solution A + B and arsenite-citrate, the solutions develop a stable blue color with the maximum absorption at 709 nm and 860 nm14 due to the complex formation of phosphate ions with molybdate that can be observed and shows the occurrence of the enzymatic reaction. For this experiment, we use the absorbance at 860 nm for the measurement of Pi amount released as it has better detection limit and sensitivity compared to the absorbance at 709 nm15. The blue color is fully developed in 30 min of incubation at room temperature and stable for at least 5 h14. The assay has the sensitivity down to Pi concentration of 10 &#181;M and the absorbance is linear over a concentration range of 10&#8722;800 &#181;M14. In the representative result here, wells E1&#8722;E3 (Figure 2C) contain the reaction mixture without inhibitor and the blue solution can be observed at the end of the assay. This can also be observed at low compound concentrations where complete inhibition has not been reached, as in wells F1&#8722;F3 for IDP and wells A4&#8722;A6 for compound 1 (ATC, a recently known uncompetitive inhibitor of TmPPase9) at the concentration of 2.5 &#181;M and 1 &#181;M, respectively. The higher concentration of IDP and compound 1, the less to no blue color can be observed (G1&#8722;G3 and H1&#8722;H3 for IDP and B4&#8722;B6 and C4&#8722;C6 for compound 1) indicating inhibition of the enzymatic activity. All three concentrations of non-inhibiting compounds (2, 3, and 8) displayed the same blue color intensity as wells E1&#8722;E3 without any inhibitor (Figure 2C).
After the absorbance measurement at 860 nm, the data can be processed and analyzed (see protocol section 5). Figure 2D shows the calibration plot of Pi standard with its linear fitting (y = 0.0576x + 0.0019; r2 = 0.999). Figure 3 shows the plot of enzymatic activity (%) against the concentration of each tested compound. For compounds with inhibition activity, a nonlinear curve fitting is also shown. IDP, used as a positive control, clearly shows a decrease in activity at higher concentration. The IC50 (estimate) calculated based on three different concentrations is 88.2 &#181;M (Table 1), which is similar to the previous measurement (80.0 &#181;M) with eight concentration points14. Compounds 1, 4, 5, 6, and 7 showed a similar trend as IDP since the concentration increased with the IC50 (estimate) of approximately 1.3 &#181;M, 7.4 &#181;M, 19.0 &#181;M, 37.4 &#181;M, and 156.1 &#181;M, respectively (Table 1). For compounds 2, 3, and 8 no reduction in activity or inhibition can be observed at the assay concentrations. An additional assay with eight concentration points can be done to generate precise IC50. Figure 4 shows the inhibition curve for compounds 1, 5, 6, 7 and 8 with an IC50 of 1.7 &#181;M, 21.4 &#181;M, 58.8 &#181;M, 239.0 &#181;M and &#62;500 &#181;M, respectively9.
<img alt="Figure 1" class="xfigimg" src="/files/ftp_upload/60619/60619fig01.jpg" /> 
Figure 1: A schematic workflow of TmPPase inhibition assay in a 96 well plate format.&#160;The red numbering shows the steps of the assay according to the protocol and the blue arrows show the interval order. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/60619/60619fig01large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 2" class="xfigimg" src="/files/ftp_upload/60619/60619fig02.jpg" /> 
Figure 2: Samples, their arrangement and color development in a 96 well plate.&#160;(A) The structures of compounds 1&#8722;8 used for the assay. The inhibition activity of these compounds has been reported in Vidilaseris et al.9. (B) Sample arrangement. (C) Color development, 30 min after the addition of arsenite-citrate solution. The concentrations of control inhibitor (IDP) and samples used, arranged from the top to the bottom, are 2.5 &#181;M, 25 &#181;M, and 250 &#181;M concentration and 1 &#181;M, 5 &#181;M, and 20 &#181;M concentration, respectively. The intensity of the blue color corresponds to the amount of Pi released due to the enzymatic reaction and the lack of color corresponds to no enzymatic reaction. (D) Calibration curve for Pi standard (nmol) against A860 with linear fitting (y = 0.0576x + 0.0019; r2 = 0.999). <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/60619/60619fig02large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 3" class="xfigimg" src="/files/ftp_upload/60619/60619fig03.jpg" /> 
Figure 3: Curve of the TmPPase percent activity for three different inhibitor concentrations.&#160;The nonlinear regression curves to calculate the IC50 (estimate) are shown for IDP as well as for compounds 1, 4, 5, 6 and 7 but not for compounds 2, 3, and 8 as they were not inhibiting TmPPase activity at the assay concentrations. The logIC50 and IC50 (estimate) of each compound is shown in Table 1. All data are shown as mean &#177; SD with&#160;three replicates. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/60619/60619fig03large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 4" class="xfigimg" src="/files/ftp_upload/60619/60619fig04.jpg" /> 
Figure 4: Inhibition curve from eight concentration points of compounds 1, 5, 6, 7 and 8.&#160;This figure is taken from Vidilaseris et al.9 with slight modification. All data are shown as mean &#177; SD with&#160;three replicates. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/60619/60619fig04large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>Sample</td>
			<td>LogIC50</td>
			<td>IC50 (estimate) (&#181;M)</td>
		</tr>
		<tr>
			<td>IDP</td>
			<td>1.95 &#177; 0.0142</td>
			<td>87.9 &#177; 2.46</td>
		</tr>
		<tr>
			<td>1</td>
			<td>0.112 &#177; 0.0274</td>
			<td>1.29 &#177; 0.0816</td>
		</tr>
		<tr>
			<td>2</td>
			<td>&#8722;</td>
			<td>no inhibition</td>
		</tr>
		<tr>
			<td>3</td>
			<td>&#8722;</td>
			<td>no inhibition</td>
		</tr>
		<tr>
			<td>4</td>
			<td>0.870 &#177; 0.0447</td>
			<td>7.39 &#177; 0.760</td>
		</tr>
		<tr>
			<td>5</td>
			<td>1.28 &#177; 0.0296</td>
			<td>19.0 &#177; 1.29</td>
		</tr>
		<tr>
			<td>6</td>
			<td>1.57 &#177; 0.0846</td>
			<td>37.4 &#177; 7.29</td>
		</tr>
		<tr>
			<td>7</td>
			<td>2.19 &#177; 0.366</td>
			<td>156 &#177; 131</td>
		</tr>
		<tr>
			<td>8</td>
			<td>&#8722;</td>
			<td>no inhibition</td>
		</tr>
	</tbody>
</table>
Table 1: LogIC50 and IC50 (estimate) of IDP and compounds 1&#8722;8 based on the data from Figure 3.

Watch this Scientific Journal Video about Screening for Thermotoga maritima Membrane-Bound Pyrophosphatase Inhibitors at JoVE.com

Screening for Thermotoga maritima Membrane-Bound Pyrophosphatase Inhibitors

Here we present a screening method for membrane-bound pyrophosphatase (from Thermotoga maritima) inhibitors based on the molybdenum blue reaction in a 96 well plate format.

Screening for Thermotoga maritima Membrane-Bound Pyrophosphatase Inhibitors

Membrane-bound pyrophosphatases (mPPases) are dimeric enzymes that occur in bacteria, archaea, plants, and protist parasites. These proteins cleave ...

screening-for-thermotoga-maritima-membrane-bound-pyrophosphatase

Nanyang Technological University

Research

JoVE Journal

Biochemistry

6.5K Views.  University of Helsinki. Here we present a screening method for membrane-bound pyrophosphatase (from Thermotoga maritima) inhibitors based on the molybdenum blue reaction in a 96 well plate format.

Video: Screening for Thermotoga maritima Membrane-Bound Pyrophosphatase Inhibitors

Method for Identifying Small Molecule Inhibitors of the Protein-protein Interaction Between HCN1 and TRIP8b

Hyperpolarization-activated cyclic nucleotide-gated (HCN) channels are expressed ubiquitously throughout the brain, where they function to regulate the excitability of neurons. The subcellular distribution of these channels in pyramidal neurons of hippocampal area CA1 is regulated by tetratricopeptide repeat-containing Rab8b interacting protein (TRIP8b), an auxiliary subunit. Genetic knockout of HCN pore forming subunits or TRIP8b, both lead to an increase in antidepressant-like behavior, suggesting that limiting the function of HCN channels may be useful as a treatment for Major Depressive Disorder (MDD). Despite significant therapeutic interest, HCN channels are also expressed in the heart, where they regulate rhythmicity. To circumvent off-target issues associated with blocking cardiac HCN channels, our lab has recently proposed targeting the protein-protein interaction between HCN and TRIP8b in order to specifically disrupt HCN channel function in the brain. TRIP8b binds to HCN pore forming subunits at two distinct interaction sites, although here the focus is on the interaction between the tetratricopeptide repeat (TPR) domains of TRIP8b and the C terminal tail of HCN1. In this protocol, an expanded description of a method for purifying TRIP8b and executing a high throughput screen to identify small molecule inhibitors of the interaction between HCN and TRIP8b, is described. The method for high throughput screening utilizes a Fluorescence Polarization (FP) -based assay to monitor the binding of a large TRIP8b fragment to a fluorophore-tagged eleven amino acid peptide corresponding to the HCN1 C terminal tail. This method allows &#39;hit&#39; compounds to be identified based on the change in the polarization of emitted light. Validation assays are then performed to ensure that &#39;hit&#39; compounds are not artifactual.

The interaction between HCN channels and their auxiliary subunit has been identified as a therapeutic target in Major Depressive Disorder. Here, a fluorescence polarization-based method for identifying small molecule inhibitors of this protein-protein interaction, is presented.

Hyperpolarization-activated cyclic nucleotide-gated (HCN) channels are expressed ubiquitously throughout the brain, where they function to regulate the ...

Bacterial Inner-membrane Display for Screening a Library of Antibody Fragments

Antibodies engineered for intracellular function must not only have affinity for their target antigen, but must also be soluble and correctly folded in the cytoplasm. Commonly used methods for the display and screening of recombinant antibody libraries do not incorporate intracellular protein folding quality control, and, thus, the antigen-binding capability and cytoplasmic folding and solubility of antibodies engineered using these methods often must be engineered separately. Here, we describe a protocol to screen a recombinant library of single-chain variable fragment (scFv) antibodies for antigen-binding and proper cytoplasmic folding simultaneously. The method harnesses the intrinsic intracellular folding quality control mechanism of the Escherichia coli twin-arginine translocation (Tat) pathway to display an scFv library on the E. coli inner membrane. The Tat pathway ensures that only soluble, well-folded proteins are transported out of the cytoplasm and displayed on the inner membrane, thereby eliminating poorly folded scFvs prior to interrogation for antigen-binding. Following removal of the outer membrane, the scFvs displayed on the inner membrane are panned against a target antigen immobilized on magnetic beads to isolate scFvs that bind to the target antigen. An enzyme-linked immunosorbent assay (ELISA)-based secondary screen is used to identify the most promising scFvs for additional characterization. Antigen-binding and cytoplasmic solubility can be improved with subsequent rounds of mutagenesis and screening to engineer antibodies with high affinity and high cytoplasmic solubility for intracellular applications.

We provide a method to simultaneously screen a library of antibody fragments for binding affinity and cytoplasmic solubility by using the Escherichia coli twin-arginine translocation pathway, which has an inherent quality control mechanism for intracellular protein folding, to display the antibody fragments on the inner membrane.

Antibodies engineered for intracellular function must not only have affinity for their target antigen, but must also be soluble and correctly folded in ...

A Simple Method for High Throughput Chemical Screening in Caenorhabditis Elegans

Caenorhabditis elegans is a useful organism for testing chemical effects on physiology. Whole organism small molecule screens offer significant advantages for identifying biologically active chemical structures that can modify complex phenotypes such as lifespan. Described here is a simple protocol for producing hundreds of 96-well culture plates with fairly consistent numbers of C. elegans in each well. Next, we specified how to use these cultures to screen thousands of chemicals for effects on the lifespan of the nematode C. elegans. This protocol makes use of temperature sensitive sterile strains, agar plate conditions, and simple animal handling to facilitate the rapid and high throughput production of synchronized animal cultures for screening.

A Simple Method for High Throughput Chemical Screening in Caenorhabditis Elegans

Here we describe a simple protocol for rapidly producing hundreds of nematode growth media agar, 96-well culture plates with consistent numbers of Caenorhhabditis elegans per well. These cultures are useful for the phenotypic screening of whole organisms. We focus here on using these cultures to screen chemicals for pro-longevity effects.

Caenorhabditis elegans is a useful organism for testing chemical effects on physiology. Whole organism small molecule screens offer significant advantages ...

Kinase Inhibitor Screening In Self-assembled Human Protein Microarrays

The screening of kinase inhibitors is crucial for better understanding properties of a drug and for the identification of potentially new targets with clinical implications. Several methodologies have been reported to accomplish such screening. However, each has its own limitations (e.g., the screening of only ATP analogues, restriction to using purified kinase domains, significant costs associated with testing more than a few kinases at a time, and lack of flexibility in screening protein kinases with novel mutations). Here, a new protocol that overcomes some of these limitations and can be used for the unbiased screening of kinase inhibitors is presented. A strength of this method is its ability to compare the activity of kinase inhibitors across multiple proteins, either between different kinases or different variants of the same kinase. Self-assembled protein microarrays generated through the expression of protein kinases by a human-based in vitro transcription and translation system (IVTT) are employed. The proteins displayed on the microarray are active, allowing for measurement of the effects of kinase inhibitors. The following procedure describes the protocol steps in detail, from the microarray generation and screening to the data analysis.

A detailed protocol for the generation of self-assembled human protein microarrays for the screening of kinase inhibitors is presented.

The screening of kinase inhibitors is crucial for better understanding properties of a drug and for the identification of potentially new targets with ...

Kinetic Screening of Nuclease Activity using Nucleic Acid Probes

Nucleases are a class of enzymes that break down nucleic acids by catalyzing the hydrolysis of the phosphodiester bonds that link the ribose sugars. Nucleases display a variety of vital physiological roles in prokaryotic and eukaryotic organisms, ranging from maintaining genome stability to providing protection against pathogens. Altered nuclease activity has been associated with several pathological conditions including bacterial infections and cancer. To this end, nuclease activity has shown great potential to be exploited as a specific biomarker. However, a robust and reproducible screening method based on this activity remains highly desirable.
Herein, we introduce a method that enables screening for nuclease activity using nucleic acid probes as substrates, with the scope of differentiating between pathological and healthy conditions. This method offers the possibility of designing new probe libraries, with increasing specificity, in an iterative manner. Thus, multiple rounds of screening are necessary to refine the probes&#39; design with enhanced features, taking advantage of the availability of chemically modified nucleic acids. The considerable potential of the proposed technology lies in its flexibility, high reproducibility, and versatility for the screening of nuclease activity associated with disease conditions. It is expected that this technology will allow the development of promising diagnostic tools with a great potential in the clinic.

Altered nuclease activity has been associated with different human conditions, underlying its potential as a biomarker. The modular and easy to implement screening methodology presented in this paper allows the selection of specific nucleic acid probes for harnessing nuclease activity as a biomarker of disease.

Nucleases are a class of enzymes that break down nucleic acids by catalyzing the hydrolysis of the phosphodiester bonds that link the ribose sugars. ...

A Semi-High-Throughput Adaptation of the NADH-Coupled ATPase Assay for Screening Small Molecule Inhibitors

ATPase enzymes utilize the free energy stored in adenosine triphosphate to catalyze a wide variety of endergonic biochemical processes in vivo that would not occur spontaneously. These proteins are crucial for essentially all aspects of cellular life, including metabolism, cell division, responses to environmental changes and movement. The protocol presented here describes a nicotinamide adenine dinucleotide (NADH)-coupled ATPase assay that has been adapted to semi-high throughput screening of small molecule ATPase inhibitors. The assay has been applied to cardiac and skeletal muscle myosin II's, two actin-based molecular motor ATPases, as a proof of principle. The hydrolysis of ATP is coupled to the oxidation of NADH by enzymatic reactions in the assay. First, the ADP generated by the ATPase is regenerated to ATP by pyruvate kinase (PK). PK catalyzes the transition of phosphoenolpyruvate (PEP) to pyruvate in parallel. Subsequently, pyruvate is reduced to lactate by lactate dehydrogenase (LDH), which catalyzes the oxidation of NADH in parallel. Thus, the decrease in ATP concentration is directly correlated to the decrease in NADH concentration, which is followed by change to the intrinsic fluorescence of NADH. As long as PEP is available in the reaction system, the ADP concentration remains very low, avoiding inhibition of the ATPase enzyme by its own product. Moreover, the ATP concentration remains nearly constant, yielding linear time courses. The fluorescence is monitored continuously, which allows for easy estimation of the quality of data and helps to filter out potential artifacts (e.g., arising from compound precipitation or thermal changes).

A nicotinamide adenine dinucleotide (NADH)-coupled ATPase assay has been adapted to semihigh throughput screening of small molecule myosin inhibitors. This kinetic assay is run in a 384-well microplate format with total reaction volumes of only 20 &#181;L per well. The platform should be applicable to virtually any ADP producing enzyme.

ATPase enzymes utilize the free energy stored in adenosine triphosphate to catalyze a wide variety of endergonic biochemical processes in vivo that would ...

X-Ray Crystallography to Study the Oligomeric State Transition of the Thermotoga maritima M42 Aminopeptidase TmPep1050

The M42 aminopeptidases form functionally active complexes made of 12 subunits. Their assembly process appears to be regulated by their metal ion cofactors triggering a dimer-dodecamer transition. Upon metal ion binding, several structural modifications occur in the active site and at the interaction interface, shaping dimers to promote the self-assembly. To observe such modifications, stable oligomers must be isolated prior to structural study. Reported here is a method that allows the purification of stable dodecamers and dimers of TmPep1050, an M42 aminopeptidase of T. maritima, and their structure determination by X-ray crystallography. Dimers were prepared from dodecamers by removing metal ions with a chelating agent. Without their&#160;cofactor, dodecamers became less stable and were fully dissociated upon heating. The oligomeric structures were solved by the straightforward molecular replacement approach. To illustrate the methodology, the structure of a TmPep1050 variant, totally impaired in metal ion binding, is presented showing no further breakdown of dimers to monomers.

X-Ray Crystallography to Study the Oligomeric State Transition of the Thermotoga maritima M42 Aminopeptidase TmPep1050

This protocol has been developed to study the dimer-dodecamer transition of TmPep1050, an M42 aminopeptidase, at the structural level. It is a straightforward pipeline starting from protein purification to X-ray data processing. Crystallogenesis, data set indexation, and molecular replacement have been emphasized through a case of study, TmPep1050H60A H307A variant.

The M42 aminopeptidases form functionally active complexes made of 12 subunits. Their assembly process appears to be regulated by their metal ion ...

Spectrophotometric Screening for Potential Inhibitors of Cytosolic Glutathione S-Transferases

Glutathione S-transferases (GSTs) are metabolic enzymes responsible for the elimination of endogenous or exogenous electrophilic compounds by glutathione (GSH) conjugation. In addition, GSTs are regulators of mitogen-activated protein kinases (MAPKs) involved in apoptotic pathways. Overexpression of GSTs is correlated with decreased therapeutic efficacy among patients undergoing chemotherapy with electrophilic alkylating agents. Using GST inhibitors may be a potential solution to reverse this tendency and augment treatment potency. Achieving this goal requires the discovery of such compounds, with an accurate, quick, and easy enzyme assay. A spectrophotometric protocol using 1-chloro-2,4-dinitrobenzene (CDNB) as the substrate is the most employed method in the literature. However, already described GST inhibition experiments do not provide a protocol detailing each stage of an optimal inhibition assay, such as the measurement of the Michaelis-Menten constant (Km) for CDNB or indication of the employed enzyme concentration, crucial parameters to assess the inhibition potency of a tested compound. Hence, with this protocol, we describe each step of an optimized spectrophotometric GST enzyme assay, to screen libraries of potential inhibitors. We explain the calculation of both the half-maximal inhibitory concentration (IC50) and the constant of inhibition (Ki)&#8212;two characteristics used to measure the potency of an enzyme inhibitor. The method described can be implemented using a pool of GSTs extracted from cells or pure recombinant human GSTs, namely GST alpha 1 (GSTA1), GST mu 1 (GSTM1) or GST pi 1 (GSTP1). However, this protocol cannot be applied to GST theta 1 (GSTT1), as CDNB is not a substrate for this isoform. This method was used to test the inhibition potency of curcumin using GSTs from equine liver. Curcumin is a molecule exhibiting anti-cancer properties and showed affinity towards GST isoforms after in silico docking predictions. We demonstrated that curcumin is a potent competitive GST inhibitor, with an IC50 of 31.6 &#177; 3.6 &#181;M and a Ki of 23.2 &#177; 3.2 &#181;M. Curcumin has potential to be combined with electrophilic chemotherapy medication to improve its efficacy.

Glutathione S-transferases (GSTs) are detoxification enzymes involved in the metabolism of numerous chemotherapeutic drugs. Overexpression of GSTs is correlated with cancer chemotherapy resistance. One way to counter this phenotype is to use inhibitors. This protocol describes a method using a spectrophotometric assay to screen for potential GST inhibitors.

Glutathione S-transferases (GSTs) are metabolic enzymes responsible for the elimination of endogenous or exogenous electrophilic compounds by glutathione ...

Workflow and Tools for Crystallographic Fragment Screening at the Helmholtz-Zentrum Berlin

Fragment screening is a technique that helps to identify promising starting points for ligand design. Given that crystals of the target protein are available and display reproducibly high-resolution X-ray diffraction properties, crystallography is among the most preferred methods for fragment screening because of its sensitivity. Additionally, it is the only method providing detailed 3D information of the binding mode of the fragment, which is vital for subsequent rational compound evolution. The routine use of the method depends on the availability of suitable fragment libraries, dedicated means to handle large numbers of samples, state-of-the-art synchrotron beamlines for fast diffraction measurements and largely automated solutions for the analysis of the results.
Here, the complete practical workflow and the included tools on how to conduct crystallographic fragment screening (CFS) at the Helmholtz-Zentrum Berlin (HZB) are presented. Preceding this workflow, crystal soaking conditions as well as data collection strategies are optimized for reproducible crystallographic experiments. Then, typically in a one to two-day procedure, a 96-membered CFS-focused library provided as dried ready-to-use plates is employed to soak 192 crystals, which are then flash-cooled individually. The final diffraction experiments can be performed within one day at the robot-mounting supported beamlines BL14.1 and BL14.2 at the BESSY&#160; II electron storage ring operated by the HZB in Berlin-Adlershof (Germany). Processing of the crystallographic data, refinement of the protein structures, and hit identification is fast and largely automated using specialized software pipelines on dedicated servers, requiring little user input.
Using the CFS workflow at the HZB enables routine screening experiments. It increases the chances for successful identification of fragment hits as starting points to develop more potent binders, useful for pharmacological or biochemical applications.

Crystallographic fragment screening at the Helmholtz-Zentrum Berlin is performed using a workflow with dedicated compound libraries, crystal handling tools, fast data collection facilities&#160;and largely automated data analysis. The presented protocol intends to maximize the output of such experiments to provide promising starting points for downstream structure-based ligand design.

Fragment screening is a technique that helps to identify promising starting points for ligand design. Given that crystals of the target protein are ...

NMR-Based Fragment Screening in a Minimum Sample but Maximum Automation Mode

Fragment-based screening (FBS) is a well-validated and accepted concept within the drug discovery process both in academia and industry. The greatest advantage of NMR-based fragment screening is its ability not only to detect binders over 7-8 orders of magnitude of affinity but also to monitor purity and chemical quality of the fragments and thus to produce high quality hits and minimal false positives or false negatives. A prerequisite within the FBS is to perform initial and periodic quality control of the fragment library, determining solubility and chemical integrity of the fragments in relevant buffers, and establishing multiple libraries to cover diverse scaffolds to accommodate various macromolecule target classes (proteins/RNA/DNA). Further, an extensive NMR-based screening protocol optimization with respect to sample quantities, speed of acquisition and analysis at the level of biological construct/fragment-space, in condition-space (buffer, additives, ions, pH, and temperature) and in ligand-space (ligand analogues, ligand concentration) is required. At least in academia, these screening efforts have so far been undertaken manually in a very limited fashion, leading to limited availability of screening infrastructure not only in the drug development process but also in the context of chemical probe development. In order to meet the requirements economically, advanced workflows are presented. They take advantage of the latest state-of-the-art advanced hardware, with which the liquid sample collection can be filled in a temperature-controlled fashion into the NMR-tubes in an automated manner. 1H/19F NMR ligand-based spectra are then collected at a given temperature. High-throughput sample changer (HT sample changer) can handle more than 500 samples in temperature-controlled blocks. This together with advanced software tools speeds up data acquisition and analysis. Further, application of screening routines on protein and RNA samples are described to make aware of the established protocols for a broad user base in biomacromolecular research.

Fragment-based screening by NMR is a robust method to rapidly identify small molecule binders to biomacromolecules (DNA, RNA, or proteins). Protocols describing automation-based sample preparation, NMR experiments &#38; acquisition conditions, and analysis workflows are presented. The technique allows for optimal exploitation of both 1H and 19F NMR-active nuclei for detection.

Fragment-based screening (FBS) is a well-validated and accepted concept within the drug discovery process both in academia and industry. The greatest ...