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Assay Method Information

Assay Name:  OPRK1 antagonist assay
Description:  The cell line for the OPRK1 antagonist assay stably expresses the following elements. The carboxy terminus of the OPRK1 receptor has a 7 amino acid linker, followed by the TEV protease cleavage site and a GAL4-VP16 fusion protein. The cell line also expresses a b-arrestin-2-TEV protease fusion protein and contains a reporter construct consisting of the UAS response element and the b-lactamase (bla) reporter gene. Upon activation of the receptor, g-protein receptor kinase (GRK) phosphorylates specific intracellular residues of OPKR1 and this induces recruitment of B-arrestin2-TEV protease fusion protein. The TEV protease recognizes and cleaves the TEV site, releasing the GAL4-VP16 fusion protein, which then translocates to the nucleus. The GAL4-V16 binds to the UAS element, driving expressing of the b-lactamase gene. B-lactamase expression is detected with the cell permeable, fluorescent substrate, CCF4-AM. This substrate consists of coumarin tethered to fluoroscein via a b-lactam ring. In the absence of b-lactamase, excitation of the dye with 405 nm light results in FRET from the coumarin to fluoroscein and emission of green (525 nm maximum) light. B-lactamase cleavage of the substrate separates the courmarin fluorophore from the fluorscein, and 405 nm excitation results in blue (460 nm maximum) emission. The assay is monitored by the blue/green emission ratio. The antagonist assay is performed by seeding the cells into 384 well plates and incubating them 16-24 hours at 37° C. Test antagonist compounds are added and incubated for 30 minutes at 37° C. Next an EC80 challenge of U-50488 (OKRK1 agonist) is added and the samples are incubated for 4 hours at 37° C., followed by addition of CCF4-AM substrate. The plates are then incubated 2 hours at room temperature in the dark and the blue/green ratio determined on a fluorescent plate reader. See J Biomol Screen April 2009, vol. 14 no. 4, pp 381-394.
Affinity data for this assay
 

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Last update November 1, 2007
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