Name: a "dual-addition" calcium fluorescence assay for the high-throughput screening of recombinant g protein-coupled receptors
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This work was supported by the USDA-NIFA-AFRI Animal Health and Well-Being Award (Award number 2022-67015-36336, PVP [Project Director]) and from competitive funds from the Texas A&#38;M AgriLife Research Insect Vector Diseases Grant Program (FY&#39;22-23) to P.V.P. The A.W.E.S.O.M.E. faculty group of the College of Agriculture and Life Sciences, TAMU, is acknowledged for help editing the manuscript. Supplemental Table S2 contains data from an in-house, random, small-molecule library obtained from Dr. James Sacchettini&#39;s laboratory at Texas A&#38;M University and Texas A&#38;M AgriLife Research.

1. Cell maintenance
NOTE: A CHO-K1 cell line that stably expresses the kinin receptor from R. microplus, named BMLK3, was developed by Holmes et al.16. The details of the development of the cell line are presented elsewhere14. All the following steps are performed under sterile conditions in a class II biosafety cabinet.
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	<li>Grow the recombinant cell line in selective media (F-12K medium containing 10%...

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A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Tracing+the+evolutionary+origins+of+insect+renal+function.">Tracing the evolutionary origins of insect renal function.</a> Nature Communications. 6, 6800 (2015).</li><li>Pietrantonio, P. V., Jagge, C., Taneja-Bageshwar, S., Nachman, R. J., Barhoumi, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+mosquito+Aedes+aegypti+(L.)+leucokinin+receptor+is+a+multiligand+receptor+for+the+three+Aedes+kinins.">The mosquito Aedes aegypti (L.) leucokinin receptor is a multiligand receptor for the three Aedes kinins.</a> Insect Molecular Biology. 14 (1), 55-67 (2005).</li><li>Radford, J. C., Davies, S. A., Dow, J. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Systematic+G-protein-coupled+receptor+analysis+in+Drosophila+melanogaster+identifies+a+leucokinin+receptor+with+novel+roles.">Systematic G-protein-coupled receptor analysis in Drosophila melanogaster identifies a leucokinin receptor with novel roles.</a> Journal of Biological Chemistry. 277 (41), 38810-38817 (2002).</li><li>Brock, C. 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V. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Mosquito+Aedes+aegypti+(L.)+leucokinin+receptor+is+critical+for+in+vivo+fluid+excretion+post+blood+feeding.">Mosquito Aedes aegypti (L.) leucokinin receptor is critical for in vivo fluid excretion post blood feeding.</a> FEBS letters. 585 (22), 3507-3512 (2011).</li><li>Kwon, H., 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=Leucokinin+mimetic+elicits+aversive+behavior+in+mosquito+Aedes+aegypti+(L.)+and+inhibits+the+sugar+taste+neuron.">Leucokinin mimetic elicits aversive behavior in mosquito Aedes aegypti (L.) and inhibits the sugar taste neuron.</a> Proceedings of the National Academy of Sciences of the United States of America. 113 (25), 6880-6885 (2016).</li><li>Xiong, C., Baker, D., Pietrantonio, P. 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The goal of HTS is to identify hit molecules through screening massive numbers of small molecules. Therefore, the results from this example only represent a small part of a conventional HTS experiment. Furthermore, the hit molecules identified need to be validated in downstream assays such as a dose-dependent assay on the same recombinant cell line and on a CHO-K1 cell line carrying only the empty vector, which can be performed simultaneously to save small molecules. Cytotoxicity assays will help demonstrate that a lack ...

G protein-coupled receptors (GPCRs), which are present from yeast to humans, represent the largest superfamily of receptors in many organisms1. They play critical roles in regulating nearly all biological processes in animals. There are 50-200 GPCRs in the genome of arthropods, meaning they represent the largest membrane receptor superfamily2. They are classified into six major classes, A-F, based on their sequence similarity and functions3. GPCRs transduce various extracellular signals, such as those of hormones, neuropeptides, biogenic amines, glutamate, proton, lipoglycoproteins, and photons4. GPCRs couple to heterotrimer G proteins (G&#945;, G&#946;, and G&#947;) to transmit downstream signals. GPCRs coupled to G&#945;s or G&#945;i/o proteins increase or decrease, respectively, the intracellular 3&#39;, 5&#39;-cyclic adenosine monophosphate (cAMP) levels by activating or inhibiting adenylyl cyclase. GPCRs coupled to G&#945;q/11 induce calcium release from the endoplasmic reticulum calcium stores by activating the phospholipase C (PLC)-inositol-1,4,5-triphosphate (IP3) pathway. GPCRs coupled to G&#945;12/13 activate RhoGTPase nucleotide exchange factors5,6. GPCRs are the target of more than 50% of human drugs and an acaricide, amitraz4. As GPCRs transduce such diverse signals, they are promising targets for developing novel pesticides that disrupt invertebrate-specific physiological functions.
The goal of HTS is to identify hit molecules that can modulate receptor functions. HTS involves assay development, miniaturization, and automation7. Arthropod neuropeptide GPCRs are involved in most physiological functions, such as development, molting and ecdysis, excretion, energy mobilization, and reproduction4. Most of the neuropeptide GPCRs of arthropods and metazoans signal through the calcium signaling cascade2,6,8,9,10, such as in the myoinhibitory peptide and SIFamide receptors of the blacklegged tick Ixodes scapularis; their ligands are antagonistic in hindgut motility assays, with SIF eliciting contraction and MIP inhibiting it11,12. An NPY-like receptor of the yellow fever mosquito, Aedes aegypti, regulates female host seeking13. Compared to other alternative calcium mobilization assays such as the aequorin calcium bioluminescence assay14, the calcium fluorescence assay is easy to perform, does not require the transfection of other recombinant calcium detecting proteins, and is cost-effective. The calcium fluorescence assay produces a prolonged signal compared to the fast kinetic signal obtained in the aequorin calcium bioluminescence assay14,15.
In the example here, the kinin receptor from the cattle fever tick, Rhipicephalus microplus, was recombinantly expressed in the CHO-K1 cell line and used for the calcium fluorescence assay. There is only one kinin receptor gene found in R. microplus; the receptor signals through a Gq protein-dependent signaling pathway and triggers the efflux of Ca2+ from calcium stores into the intracellular space16. This process can be detected and quantified by a fluorophore, which elicits a fluorescence signal when binding calcium ions (Figure 1).
The kinin receptor is an invertebrate-specific GPCR, which belongs to the Class A Rhodopsin-like receptors. Kinin is an ancient signaling neuropeptide that is present in Mollusca, Crustacea, Insecta, and Acari4,17,18. Coleopterans (beetles) lack the kinin signaling system; in the mosquito Aedes aegypti, there is only one kinin receptor that binds three aedeskinins, while Drosophila melanogaster has one kinin receptor with drosokinin as a unique ligand19,20,21. There are no homologous kinins or kinin receptors in vertebrates. Although the exact function of kinin is unknown in ticks, the kinin receptor RNAi-silenced females of R. microplus show significantly reduced reproductive fitness22. Kinins are pleotropic peptides in insects. In Drosophila melanogaster, they are involved in both the central and peripheral nervous regulatory systems23, pre-ecdysis24, feeding25, metabolism26, and sleep activity patterns26,27, as well as larval locomotion28. Kinins regulate hindgut contraction, diuresis, and feeding in the mosquito A. aegypti29,30,31. The kinin peptides have a conserved C-terminal pentapeptide Phe-X1-X2-Trp-Gly-NH2, which is the minimum required sequence for biological activity32. The arthropod specificity, the small size of the endogenous ligand, which makes them amenable to small-molecule interference, and the pleiotropic functions in insects make the kinin receptor a promising target for pest control4.
The &#34;dual-addition&#34; assay (Figure 2) allows the identification of agonists or antagonists in the same HTS assay15. It is adapted from a &#34;dual-addition&#34; assay that is commonly used in the pharmaceutical industry for drug discovery33. In brief, the first addition of drugs into the cell plate allows the identification of potential agonists in the chemical library when a higher fluorescence signal is detected compared to the application of the solvent control. After 5 min of incubation with these small molecules, a known agonist (kinin peptide) is applied to all the wells. Those wells that randomly received an antagonist from the drug plate display a lower fluorescence signal upon agonist addition compared to the control wells that received the solvent in the first addition. This assay then allows the identification of potential agonists and antagonists with the same cells. In a standard HTS project, these hit molecules would be further validated through dose-response assays and by additional biological activity assays, which are not shown here.
<img alt="Figure 1" class="xfigimg" src="/files/ftp_upload/64505/64505fig01.jpg" /> 
Figure 1: Illustration of the calcium fluorescence assay mechanism. The Gq protein triggers the intracellular calcium signaling pathway. The kinin receptor (G protein-coupled receptor) was recombinantly expressed in CHO-K1 cells. When the agonist ligand binds to the receptor, the Gq protein associated with the kinin receptor activates PLC, which catalyzes the conversion of a PIP2 molecule into IP3 and DAG. IP3 then binds to the IP3R on the surface of the endoplasmic reticulum, leading to the release of Ca2+ into the cytoplasm, where Ca2+ ions bind to the fluorophores and elicit a fluorescence signal. The fluorescence signal can be obtained by excitation at 490 nm and detected at 514 nm. Abbreviations: GPCR = G protein-coupled receptor; PLC = phospholipase C; PIP2 = phosphatidylinositol 4,5-bisphosphate; IP3 = inositol trisphosphate; DAG = diacylglycerol; IP3R = IP3 receptor. Created with BioRender.com.&#160;<a href="https://www.jove.com/files/ftp_upload/64505/64505fig01large.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/64505/64505fig02.jpg" /> 
Figure 2: The workflow for the high-throughput screening of small molecules on a G protein-coupled receptor expressed in CHO-K1 cells. (A)&#160;Recombinant CHO-K1 cells stably expressing the kinin receptor were added to the 384-well plate (10,000 cells/well) using a liquid handling system (25 &#181;L/well) and incubated in a humidified CO2 incubator for 12-16 h. (B)&#160;The assay buffer containing the fluorescent dye (25 &#181;L/well) was added into the cell plate using a liquid handling system. The plate was incubated for 30 min at 37 &#176;C for 30 min and equilibrated at RT for another 30 min. (C) The background fluorescence signal of the cells in each well was measured with a plate reader. (D)&#160;Drug solutions from a 384-well library plate and blank solvent (all at 0.5 &#181;L/well) were added into the cellular assay plate using a liquid handling system. (E) Cellular calcium fluorescence responses were measured with the plate reader immediately after the addition of the drug solutions; compound(s) eliciting higher than average fluorescence signals were picked out as agonist hit(s). Antagonist hits that block the GPCR (icon below) were revealed after the addition of the peptide agonist during step G. (F)&#160;In the same assay plate, after 5 min of incubation of the cells with screening compounds, an endogenous agonist peptide Rhimi-K-1 (QFSPWGamide) of the tick kinin receptor was added to each well (1 &#181;M). (G) Cellular fluorescence responses after the agonist peptide addition were measured by the plate reader immediately. Compound(s) inhibiting the fluorescence signal were selected as antagonist hit(s). Abbreviations: GPCR = G protein-coupled receptor; RT = room temperature; RFU = relative fluorescence units. Created with BioRender.com.&#160;<a href="https://www.jove.com/files/ftp_upload/64505/64505fig02large.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>0.25% trypsin-EDTA</td>
			<td>Gibco Invitrogen</td>
			<td>15050-065</td>
			<td>with phenol red</td>
		</tr>
		<tr>
			<td>0.4% trypan blue</td>
			<td>MilliporeSigma</td>
			<td>T8154</td>
			<td>liquid, sterile</td>
		</tr>
		<tr>
			<td>1.5 mL microcentrifuge tubes</td>
			<td>Thermo Fisher</td>
			<td>AM12400</td>
			<td>RNase-free Microfuge Tubes</td>
		</tr>
		<tr>
			<td>5 mL serological pipette</td>
			<td>Corning</td>
			<td>29443-045</td>
			<td>Corning Costar Stripette individually wrapped&#160;</td>
		</tr>
		<tr>
			<td>10 mL serological pipette</td>
			<td>Corning</td>
			<td>29443-047</td>
			<td>Corning Costar Stripette individually wrapped&#160;</td>
		</tr>
		<tr>
			<td>15 mL conical tubes</td>
			<td>Falcon</td>
			<td>352196</td>
			<td>sterile</td>
		</tr>
		<tr>
			<td>20 &#181;L filter tips</td>
			<td>USA Scientifc Inc.</td>
			<td>P1121</td>
			<td>sterile, barrier</td>
		</tr>
		<tr>
			<td>25 mL serological pipette</td>
			<td>Corning</td>
			<td>29443-049</td>
			<td>Corning Costar Stripette individually wrapped&#160;</td>
		</tr>
		<tr>
			<td>50 mL conical tubes</td>
			<td>Corning</td>
			<td>430828</td>
			<td>graduated, sterile</td>
		</tr>
		<tr>
			<td>150 mL auto-friendly reservior</td>
			<td>Integra Bioscience</td>
			<td>6317</td>
			<td>sterile, individually wrapped for cell seeding in day 1</td>
		</tr>
		<tr>
			<td>150 mL auto-friendly reservior</td>
			<td>Integra Bioscience</td>
			<td>6318</td>
			<td>sterile, stacked, for loading dye in day 2</td>
		</tr>
		<tr>
			<td>384/ 12.5 &#181;L low retention tips</td>
			<td>Integra Bioscience</td>
			<td>6405</td>
			<td>long, sterile filter</td>
		</tr>
		<tr>
			<td>384/ 12.5 &#181;L tips</td>
			<td>Integra Bioscience</td>
			<td>6404</td>
			<td>long, sterile filter</td>
		</tr>
		<tr>
			<td>384-well plate</td>
			<td>Greiner</td>
			<td>781091</td>
			<td>CELLSTAR, clear polystyrene, &#181;Clear, Black/Flat</td>
		</tr>
		<tr>
			<td>Aluminum plate seals</td>
			<td>Axygen Scientific</td>
			<td>PCR-AS-200</td>
			<td>polyester-based</td>
		</tr>
		<tr>
			<td>Aluminum foil wrap</td>
			<td>Walmart</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Biosafty cabinet II</td>
			<td>NuAire</td>
			<td>NU-540-300</td>
			<td></td>
		</tr>
		<tr>
			<td>Cell counter</td>
			<td>Nexcelom</td>
			<td>AutoT4</td>
			<td></td>
		</tr>
		<tr>
			<td>cell counting slides</td>
			<td>Nexcelom</td>
			<td>SD-100</td>
			<td>20 &#181;L chamber</td>
		</tr>
		<tr>
			<td>CO2 humidified incubator</td>
			<td>Thermo Fisher</td>
			<td>Forma Series II</td>
			<td></td>
		</tr>
		<tr>
			<td>Desk Lamp</td>
			<td>SunvaleeyTEK</td>
			<td>RS1000B</td>
			<td></td>
		</tr>
		<tr>
			<td>Dimethyl sulfoxide</td>
			<td>MilliporeSigma</td>
			<td>276855</td>
			<td>anhydous, &#62;99.9%</td>
		</tr>
		<tr>
			<td>Drug plate</td>
			<td>Corning</td>
			<td>3680</td>
			<td></td>
		</tr>
		<tr>
			<td>Dulbecco&#39;s phosphate-buffered saline</td>
			<td>Corning</td>
			<td>21-031-CV</td>
			<td>DPBS, 1x without calcium amd magnesium</td>
		</tr>
		<tr>
			<td>Ethanol</td>
			<td>Koptec</td>
			<td>2000</td>
			<td></td>
		</tr>
		<tr>
			<td>F-12K Nutrient Mixture&#160;</td>
			<td>Corning</td>
			<td>45000-354</td>
			<td>(Kaighn&#39;s Mod.) with L-glutamine</td>
		</tr>
		<tr>
			<td>Fetal bovine serum</td>
			<td>Equitech-Bio</td>
			<td>SFBU30</td>
			<td></td>
		</tr>
		<tr>
			<td>Fluorescent calcium assay kit</td>
			<td>ENZO Lifescience</td>
			<td>ENZ-51017</td>
			<td>10x96 tests</td>
		</tr>
		<tr>
			<td>G418 sulfate</td>
			<td>Gibco Invitrogen</td>
			<td>10131-027</td>
			<td>Geneticin selective antibiotic 50 mg/mL</td>
		</tr>
		<tr>
			<td>Hank&#39;s buffer</td>
			<td>MilliporeSigma</td>
			<td>55037C</td>
			<td>HBSS modified, with calcium, with magnesium, without phenol read</td>
		</tr>
		<tr>
			<td>HEPES buffer</td>
			<td>Gibco Invitrogen</td>
			<td>15630-080</td>
			<td>1 Molar</td>
		</tr>
		<tr>
			<td>HTS data storage plateform</td>
			<td>CDD vault&#160;</td>
			<td></td>
			<td>https://www.collaborativedrug.com/</td>
		</tr>
		<tr>
			<td>Liquid handling system</td>
			<td>Integra Bioscience</td>
			<td>Viaflo</td>
			<td>384/12.5 &#181;L</td>
		</tr>
		<tr>
			<td>Plate centrifuge</td>
			<td>Thermo Fisher</td>
			<td>Sorvall ST8</td>
			<td></td>
		</tr>
		<tr>
			<td>Plate reader</td>
			<td>BMG technology</td>
			<td>Clariostar</td>
			<td></td>
		</tr>
		<tr>
			<td>Poly-D-lysine</td>
			<td>MilliporeSigma</td>
			<td>P6407</td>
			<td></td>
		</tr>
		<tr>
			<td>Rhimi-K-1 agonist peptide</td>
			<td>Genscript</td>
			<td>custom order</td>
			<td>QFSPWGamide</td>
		</tr>
		<tr>
			<td>T-75 flask</td>
			<td>Falcon</td>
			<td>353136</td>
			<td></td>
		</tr>
	</tbody>
</table>

a "dual-addition" calcium fluorescence assay for the high-throughput screening of recombinant g protein-coupled receptors

G protein-coupled receptors (GPCRs) represent the largest superfamily of receptors and are the targets of numerous human drugs. High-throughput screening (HTS) of random small molecule libraries against GPCRs is used by the pharmaceutical industry for target-specific drug discovery. In this study, an HTS was employed to identify novel small-molecule ligands of invertebrate-specific neuropeptide GPCRs as probes for physiological studies of vectors of deadly human and veterinary pathogens.
The invertebrate-specific kinin receptor was chosen as a target because it regulates many important physiological processes in invertebrates, including diuresis, feeding, and digestion. Furthermore, the pharmacology of many invertebrate GPCRs is poorly characterized or not characterized at all; therefore, the differential pharmacology of these groups of receptors with respect to the related GPCRs in other metazoans, especially humans, adds knowledge to the structure-activity relationships of GPCRs as a superfamily. An HTS assay was developed for cells in 384-well plates for the discovery of ligands of the kinin receptor from the cattle fever tick, or southern cattle tick, Rhipicephalus microplus. The tick kinin receptor was stably expressed in CHO-K1 cells.
The kinin receptor, when activated by endogenous kinin neuropeptides or other small molecule agonists, triggers Ca2+ release from calcium stores into the cytoplasm. This calcium fluorescence assay combined with a &#34;dual-addition&#34; approach can detect functional agonist and antagonist &#34;hit&#34; molecules in the same assay plate. Each assay was conducted using drug plates carrying an array of 320 random small molecules. A reliable Z&#39; factor of 0.7 was obtained, and three agonist and two antagonist hit molecules were identified when the HTS was at a 2 &#181;M final concentration. The calcium fluorescence assay reported here can be adapted to screen other GPCRs that activate the Ca2+ signaling cascade.

An in-house drug plate (SAC2-34-6170) composed of 320 random small molecules was used for demonstrating this HTS assay as an example. The HTS had excellent assay quality with a Z&#39; factor of 0.7 (Table 1). This&#160;Z&#39; factor reflects the assay quality independent of the tested compounds34. A Z&#8242;-factor of 0.5 or greater indicates a good assay signal dynamic range between the RFUs of the positive controls and the negative controls. Assays with a Z...

Watch this Scientific Journal Video about A "Dual-Addition" Calcium Fluorescence Assay for the High-Throughput Screening of Recombinant G Protein-Coupled Receptors at JoVE.com

A &quot;Dual-Addition&quot; Calcium Fluorescence Assay for the High-Throughput Screening of Recombinant G Protein-Coupled Receptors

In this work, a high-throughput, intracellular calcium fluorescence assay for 384-well plates to screen small molecule libraries on recombinant G protein-coupled receptors (GPCRs) is described. The target, the kinin receptor from the cattle fever tick, Rhipicephalus microplus, is expressed in CHO-K1 cells. This assay identifies agonists and antagonists using the same cells in one "dual-addition" assay.

A "Dual-Addition" Calcium Fluorescence Assay for the High-Throughput Screening of Recombinant G Protein-Coupled Receptors

G protein-coupled receptors (GPCRs) represent the largest superfamily of receptors and are the targets of numerous human drugs. High-throughput screening ...

The High-Throughput screening calcium fluorescence dual addition assay allows identification of novel small molecule ligands of a G protein-coupled receptor that signals through the intracellular calcium cascade. The main advantage of the dual addition assay is the detection of agonist and antagonist HTS in a single assay with the same cells provided the fluorescence signal last two minutes. This method can be applied to any GPCR that signals through the calcium cascade, which includes most of the arthropod neuron peptide family, a GPCRs.For assay reproducibility, it is important to optimize the cell density, injection speed, and concentration of the known agonist for the second edition. Demonstrating the procedure will be Bianca Henriques-Santos, Post-doctoral research associate in my laboratory. Begin the calcium fluorescence assay by removing the spent medium from T-75 flask containing 70 to 90%confluent BMLK three cells.Wash the cells with 10 milliliters of Dulbecco's phosphate-buffered saline or DPBS. After removing the DPBS, detach the cells using two milliliters of 0.25%trypsin ethylenediaminetetraacetic acid or EDTA and incubate for three to five minutes at 37 degrees Celsius. Add eight milliliters of selective medium and transfer the cell suspension into a 15 milliliter conical tube.Before centrifuging the cell suspension at 1000 x g for three minutes. Discard the supernatant and resuspend the cell pellet in 10 milliliters of F-12K medium containing 1%fetal bovine serum or FBS and 400 micrograms per milliliter G418 sulfate. To determine the cell density of the suspension for further dilution, mix 20 microliters of cell suspension into 20 microliters of 0.4%trypan blue, and then load 20 microliters mixture into a cell counting chamber to be read by a cell counter for cell density.Dilute the cell suspension using the same F-12K medium and make up the final volume to 15 milliliters at a density of four times 10 to the fifth cells per milliliter. To seed the cells in the Poly-D lysine or PDL coded 384 well plate. Add 25 microliters of the diluted cell suspension into 384 wells of the plate using a liquid handling system.Incubate the plate overnight at 37 degrees Celsius and 5%carbon dioxide in the humidified incubator. On the next day, quickly invert the 90%confluent 384 well plate. To remove the spent medium and gently blotted on sterile paper towels two to three times to remove all the liquid from the plate.Carry out the next steps in the soft dim light inside the biosafety cabinet. Next, add 25 microliters of the loading dye into each well using a liquid handling system by dispensing 12.5 microliters into each well with an aspiration and dispensing speed of 3.8 microliters per second. Repeat this pipetting step to reach a final volume of 25 microliters in each well.Once done, cover the plate with aluminum foil to protect it from ambient light and incubate at 37 degrees Celsius in the carbon dioxide humidified incubator for 30 minutes. After equilibrating the covered plate for another 30 minutes, the cells are ready for high throughput screening or HTS. Next, centrifuge the drug plate at 1200 x g in a plate centrifuge for one minute.Transfer the 10x agonist peptide solution of Rhimi-K-1 into a 150 milliliter auto-friendly reservoir. In the plate reader, click manage protocols. Then in the endpoint fluorescent intensity protocol, select Flow Forte pre-read, click start measurement to measure the background signal for the entire HTS assay.Insert the cell plate into the plate reader. In the instrument panel, click on a random well on the plate then click on new focus height. Click on focus adjustment.Click on gain adjustment. Assign it as 5%to 10%of the maximum measurable fluorescence value. Click start adjustment.Click start measurement to read the whole plate for the background fluorescence signal in relative fluorescence units or RFU. While the plate is reading, click current state to see the real time reading value. For the dual-addition assay, pipette 10 microliters of the drug solution up and down three times using the liquid handling system and aspirate 1.5 microliters from each well of the drug plate at an aspiration speed of 1.0 microliters per second.Dispense 0.5 microliters of the compounds into the cell assay to reach a final concentration of two micromolar in 0.2%dimethyl sulfoxide or DMSO. After adding the screening compounds, place the assay plate immediately into the plate reader. Click the preset reading program and read the plate in the forward and reverse reading directions.Dispose of one microliter of drug solution remaining in the tips by immersing the tips into a 150 milliliter waste reservoir containing approximately 50 milliliters of DPBS. Incubate the screening compounds with the cells for a total of five minutes, including the time inside the plate reader in the biosafety cabinet with the lights off. Next, add three microliters of the agonist peptide Rhimi-K-1 from the reservoir into the assay plate using the liquid handling system using 384 12.5 microliters tips.Place the plate into the plate reader immediately. Click the preset reading program and read the plate in the forward and reverse reading directions. Once done manually calculate the Z'factor for the quality control of each plate assay.Manually select the hit molecules from the heat maps on the online HTS data platform and calculate the normalized percent activation or NPA and inhibitory activity, or I0 for the agonist hits and antagonist hits. An in-house drug plate SAC2-34-6170 composed of 320 random small molecules was used for demonstrating this HTS assay. The HTS had excellent assay quality with a Z'factor of 0.7 reflecting that the assay quality independent of the tested compounds.It is essential to read the plate immediately after adding the agonist because the fluorescence signal is short-lived. After this procedure, the identified hit molecule should be validated through dose response assays and tested in cells that do not express the target GPCR to exclude off-target hits.

a-dual-addition-calcium-fluorescence-assay-for-high-throughput

Research

JoVE Journal

Biochemistry

High-throughput Screening of Carbohydrate-degrading Enzymes Using Novel Insoluble Chromogenic Substrate Assay Kits

Carbohydrates active enzymes (CAZymes) have multiple roles in vivo and are widely used for industrial processing in the biofuel, textile, detergent, paper and food industries. A deeper understanding of CAZymes is important from both fundamental biology and industrial standpoints. Vast numbers of CAZymes exist in nature (especially in microorganisms) and hundreds of thousands have been cataloged and described in the carbohydrate active enzyme database (CAZy). However, the rate of discovery of putative enzymes has outstripped our ability to biochemically characterize their activities. One reason for this is that advances in genome and transcriptome sequencing, together with associated bioinformatics tools allow for rapid identification of candidate CAZymes, but technology for determining an enzyme's biochemical characteristics has advanced more slowly. To address this technology gap, a novel high-throughput assay kit based on insoluble chromogenic substrates is described here. Two distinct substrate types were produced: Chromogenic Polymer Hydrogel (CPH) substrates (made from purified polysaccharides and proteins) and Insoluble Chromogenic Biomass (ICB) substrates (made from complex biomass materials). Both CPH and ICB substrates are provided in a 96-well high-throughput assay system. The CPH substrates can be made in four different colors, enabling them to be mixed together and thus increasing assay throughput. The protocol describes a 96-well plate assay and illustrates how this assay can be used for screening the activities of enzymes, enzyme cocktails, and broths.

A high-throughput assay for enzyme screening is described. This multiplexed ready-to-use assay kit comprises of pre-chosen Chromogenic Polymer Hydrogel (CPH) substrates and complex Insoluble Chromogenic Biomass (ICB) substrates. Target enzymes are polysaccharide degrading endo-enzymes and proteases.

Carbohydrates active enzymes (CAZymes) have multiple roles in vivo and are widely used for industrial processing in the biofuel, textile, detergent, paper ...

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 ...

Measuring G-protein-coupled Receptor Signaling via Radio-labeled GTP Binding

G-Protein-Coupled Receptors (GPCRs) are a large family of transmembrane receptors that play critical roles in normal cellular physiology and constitute a major pharmacological target for multiple indications, including analgesia, blood pressure regulation, and the treatment of psychiatric disease. Upon ligand binding, GPCRs catalyze the activation of intracellular G-proteins by stimulating the incorporation of guanosine triphosphate (GTP). Activated G-proteins then stimulate signaling pathways that elicit cellular responses. GPCR signaling can be monitored by measuring the incorporation of a radiolabeled and non-hydrolyzable form of GTP, [35S]guanosine-5&#39;-O-(3-thio)triphosphate ([35S]GTP&#947;S), into G-proteins. Unlike other methods that assess more downstream signaling processes, [35S]GTP&#947;S binding measures a proximal event in GPCR signaling and, importantly, can distinguish agonists, antagonists, and inverse agonists. The present protocol outlines a sensitive and specific method for studying GPCR signaling using crude membrane preparations of an archetypal GPCR, the &#181;-opioid receptor (MOR1). Although alternative approaches to fractionate cells and tissues exist, many are cost-prohibitive, tedious, and/or require non-standard laboratory equipment. The present method provides a simple procedure that enriches functional crude membranes. After isolating MOR1, various pharmacological properties of its agonist, [D-Ala, N-MePhe, Gly-ol]-enkephalin (DAMGO), and antagonist, naloxone, were determined.

Guanosine triphosphate (GTP) binding is one of the earliest events in G-Protein-Coupled Receptor (GPCR) activation. This protocol describes how to pharmacologically characterize specific GPCR-ligand interactions by monitoring the binding of the radio-labeled GTP analog, [35S]guanosine-5&#39;-O-(3-thio)triphosphate ([35S]GTP&#947;S), in response to a ligand of interest.

G-Protein-Coupled Receptors (GPCRs) are a large family of transmembrane receptors that play critical roles in normal cellular physiology and constitute a ...

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 ...

A High-Throughput Luciferase Assay to Evaluate Proteolysis of the Single-Turnover Protease PCSK9

Proprotein convertase subtilisin/kexin type 9 (PCSK9) is a single-turnover protease which regulates serum low-density lipoprotein (LDL) levels and, consequently, cardiovascular disease. Although PCSK9 proteolysis is required for its full hypercholesterolemic effect, the evaluation of its proteolytic function is challenging: PCSK9 is only known to cleave itself, undergoes only a single turnover, and after proteolysis, retains its substrate in its active site as an auto-inhibitor. The methods presented here describe an assay which overcomes these challenges. The assay focuses on intermolecular proteolysis in a cell-based context and links successful cleavage to the secreted luciferase activity, which can be easily read out in the conditioned medium. Via sequential steps of mutagenesis, transient transfection, and a luciferase readout, the assay can probe PCSK9 proteolysis under conditions of either genetic or molecular perturbation in a high-throughput manner. This system is well suited for both the biochemical evaluation of clinically discovered missense single-nucleotide polymorphisms (SNPs), as well as for the screening of small-molecule inhibitors of PCSK9 proteolysis.

This protocol presents a method to evaluate the proteolytic activity of an intrinsically low-activity, single turnover protease in a cellular context. Specifically, this method is applied to evaluate the proteolytic activity of PCSK9, a key driver of lipid metabolism whose proteolytic activity is required for its ultimate hypercholesterolemic function.

Proprotein convertase subtilisin/kexin type 9 (PCSK9) is a single-turnover protease which regulates serum low-density lipoprotein (LDL) levels and, ...

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 ...

High-Throughput Total Internal Reflection Fluorescence and Direct Stochastic Optical Reconstruction Microscopy Using a Photonic Chip

Total internal reflection fluorescence (TIRF) is commonly used in single molecule localization based super-resolution microscopy as it gives enhanced contrast due to optical sectioning. The conventional approach is to use high numerical aperture microscope TIRF objectives for both excitation and collection, severely limiting the field of view and throughput. We present a novel approach to generating TIRF excitation for imaging with optical waveguides, called chip-based nanoscopy. The aim of this protocol is to demonstrate how chip-based imaging is performed in an already built setup. The main advantage of chip-based nanoscopy is that the excitation and collection pathways are decoupled. Imaging can then be done with a low magnification lens, resulting in large field of view TIRF images, at the price of a small reduction in resolution. Liver sinusoidal endothelial cells (LSECs) were imaged using direct stochastic optical reconstruction microscopy (dSTORM), showing a resolution comparable to traditional super-resolution microscopes. In addition, we demonstrate the high-throughput capabilities by imaging a 500 &#181;m x 500 &#181;m region with a low magnification lens, providing a resolution of 76 nm. Through its compact character, chip-based imaging can be retrofitted into most common microscopes and can be combined with other on-chip optical techniques, such as on-chip sensing, spectroscopy, optical trapping, etc. The technique is thus ideally suited for high throughput 2D super-resolution imaging, but also offers great opportunities for multi-modal analysis.

Chip-based super-resolution optical microscopy is a novel approach to fluorescence microscopy and offers advantages in cost effectiveness and throughput. Here, the protocols for chip preparation and imaging are shown for TIRF microscopy and localization-based super-resolution microscopy.

Total internal reflection fluorescence (TIRF) is commonly used in single molecule localization based super-resolution microscopy as it gives enhanced ...

Strategic Screening and Characterization of the Visual GPCR-mini-G Protein Signaling Complex for Successful Crystallization

The key to determining crystal structures of membrane protein complexes is the quality of the sample prior to crystallization. In particular, the choice of detergent is critical, because it affects both the stability and monodispersity of the complex. We recently determined the crystal structure of an active state of bovine rhodopsin coupled to an engineered G protein, mini-Go, at 3.1 &#197; resolution. Here, we detail the procedure for optimizing the preparation of the rhodopsin&#8211;mini-Go complex. Dark-state rhodopsin was prepared in classical and neopentyl glycol (NPG) detergents, followed by complex formation with mini-Go under light exposure. The stability of the rhodopsin was assessed by ultraviolet-visible (UV-VIS) spectroscopy, which monitors the reconstitution into rhodopsin of the light-sensitive ligand, 9-cis retinal. Automated size-exclusion chromatography (SEC) was used to characterize the monodispersity of rhodopsin and the rhodopsin&#8211;mini-Go complex. SDS-polyacrylamide electrophoresis (SDS-PAGE) confirmed the formation of the complex by identifying a 1:1 molar ratio between rhodopsin and mini-Go after staining the gel with Coomassie blue. After cross-validating all this analytical data, we eliminated unsuitable detergents and continued with the best candidate detergent for large-scale preparation and crystallization. An additional problem arose from the heterogeneity of N-glycosylation. Heterologously-expressed rhodopsin was observed on SDS-PAGE to have two different N-glycosylated populations, which would probably have hindered crystallogenesis. Therefore, different deglycosylation enzymes were tested, and endoglycosidase F1 (EndoF1) produced rhodopsin with a single species of N-glycosylation. With this strategic pipeline for characterizing protein quality, preparation of the rhodopsin&#8211;mini-Go complex was optimized to deliver the crystal structure. This was only the third crystal structure of a GPCR&#8211;G protein signaling complex. This approach can also be generalized for other membrane proteins and their complexes to facilitate sample preparation and structure determination.

This report describes screening of different detergents for preparing the visual GPCR, rhodopsin, and its complex with mini-Go. Biochemical methods characterizing the quality of the complex at different stages during purification are demonstrated. This protocol can be generalized to other membrane protein complexes for their future structural studies.

The key to determining crystal structures of membrane protein complexes is the quality of the sample prior to crystallization. In particular, the choice ...

Click-Chemistry Based Fluorometric Assay for Apolipoprotein N-acyltransferase from Enzyme Characterization to High-Throughput Screening

Lipoproteins from proteobacteria are posttranslationally modified by fatty acids derived from membrane phospholipids by the action of three integral membrane enzymes, resulting in triacylated proteins. The first step in the lipoprotein modification pathway involves the transfer of a diacylglyceryl group from phosphatidylglycerol onto the prolipoprotein, resulting in diacylglyceryl prolipoprotein. In the second step, the signal peptide of prolipoprotein is cleaved, forming an apolipoprotein, which in turn is modified by a third fatty acid derived from a phospholipid. This last step is catalyzed by apolipoprotein N-acyltransferase (Lnt). The lipoprotein modification pathway is essential in most &#947;-proteobacteria, making it a potential target for the development of novel antibacterial agents. Described here is a sensitive assay for Lnt that is compatible with high-throughput screening of small inhibitory molecules. The enzyme and substrates are membrane-embedded molecules; therefore, the development of an in vitro test is not straightforward. This includes the purification of the active enzyme in the presence of detergent, the availability of alkyne-phospholipids and diacylglyceryl peptide substrates, and the reaction conditions in mixed micelles. Furthermore, in order to use the activity test in a high-throughput screening (HTS) setup, direct readout of the reaction product is preferred over coupled enzymatic reactions. In this fluorometric enzyme assay, the alkyne-triacylated peptide product is rendered fluorescent through a click-chemistry reaction and detected in a multiwell plate format. This method is applicable to other acyltransferases that use fatty acid-containing substrates, including phospholipids and acyl-CoA.

Presented here is a sensitive fluorescence assay to monitor apolipoprotein N-acyltransferase activity using diacylglyceryl peptide and alkyne-phospholipids as substrates with click-chemistry.

Lipoproteins from proteobacteria are posttranslationally modified by fatty acids derived from membrane phospholipids by the action of three integral ...

A High-Throughput Enzyme-Coupled Activity Assay to Probe Small Molecule Interaction with the dNTPase SAMHD1

Sterile alpha motif and HD domain-containing protein 1 (SAMHD1) is a pivotal regulator of intracellular deoxynucleoside triphosphate (dNTP) pools, as this enzyme can hydrolyze dNTPs into their corresponding nucleosides and inorganic triphosphates. Due to its critical role in nucleotide metabolism, its association to several pathologies, and its role in therapy resistance, intense research is currently being carried out for a better understanding of both the regulation and cellular function of this enzyme. For this reason, development of simple and inexpensive high-throughput amenable methods to probe small molecule interaction with SAMHD1, such as allosteric regulators, substrates, or inhibitors, is vital. To this purpose, the enzyme-coupled malachite green assay is a simple and robust colorimetric assay that can be deployed in a 384-microwell plate format allowing the indirect measurement of SAMHD1 activity. As SAMHD1 releases the triphosphate group from nucleotide substrates, we can couple a pyrophosphatase activity to this reaction, thereby producing inorganic phosphate, which can be quantified by the malachite green reagent through the formation of a phosphomolybdate malachite green complex. Here, we show the application of this methodology to characterize known inhibitors of SAMHD1 and to decipher the mechanisms involved in SAMHD1 catalysis of non-canonical substrates and regulation by allosteric activators, exemplified by nucleoside-based anticancer drugs. Thus, the enzyme-coupled malachite green assay is a powerful tool to study SAMHD1, and furthermore, could also be utilized in the study of several enzymes which release phosphate species.

SAMHD1 is a deoxynucleoside triphosphate triphosphohydrolase with critical roles in human health and disease. Here we present a versatile enzyme-coupled SAMHD1 activity assay, deployed in a 384-well microplate format, that allows for the evaluation of small molecules and nucleotide analogues as SAMHD1 substrates, activators, and inhibitors.

Sterile alpha motif and HD domain-containing protein 1 (SAMHD1) is a pivotal regulator of intracellular deoxynucleoside triphosphate (dNTP) pools, as this ...