Homogeneous GTP binding assay employing QRET technology.
Functional cell signaling assays have become important tools for measuring ligand-induced receptor activation in cell-based biomolecular screening. Guanosine-5'-triphosphate (GTP) is a generic signaling marker responsible for the first intracellular signaling event of the G-protein-coupled receptors (GPCRs). [(35)S]GTPgammaS binding assay is the classical well-established method for measuring agonist-induced G-protein activation requiring a separation of free and bound fractions prior to measurement. Here a novel, separation-free, time-resolved fluorescence GTP binding assay has been developed based on a non-fluorescence resonance energy transfer (FRET) single-label approach and quenching of a nonbound europium-labeled, nonhydrolyzable GTP analog (Eu-GTP). The quenching resonance energy transfer (QRET) method relies on the use of Eu-GTP, providing a time-resolved fluorescent detection as an alternative to the radiolabel [(35)S]GTPgammaS assay. Upon activation of recombinant human alpha(2A)-adrenoceptors (alpha(2A)-AR) expressed in Chinese hamster ovary cells, guanosine-5'-diphosphate is released from the alpha-subunit of Gi-proteins, enabling the subsequent binding of Eu-GTP. Activation of alpha(2A)-AR with 5 different alpha(2)-AR agonists was measured quantitatively using the developed QRET GTP assay and compared to [(35)S]GTPgammaS and heterogeneous Eu-GTP filtration assays. Equal potencies and efficacy rank orders were observed in all 3 assays but with a lower signal-to-background ratio and increased assay variation in the QRET assay compared to the Eu-GTP filtration and the nonhomogeneous [(35)S]GTPgammaS binding assays.
Rozwandowicz-Jansen
Anita
A
Laboratory of Biophysics, Institute of Biomedicine, University of Turku, Finland. aniroz@utu.fi
Laurila
Jonne
J
Martikkala
Eija
E
Frang
Heini
H
Hemmilä
Ilkka
I
Scheinin
Mika
M
Hänninen
Pekka
P
Härmä
Harri
H
D000818:Animals; D001681:Biological Assay / Q000379:methods*; D016466:CHO Cells; D006224:Cricetinae; D003412:Cricetulus; D004735:Energy Transfer; D005453:Fluorescence; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000378:metabolism; D006160:Guanosine Triphosphate / Q000378:metabolism*; D006801:Humans; D008565:Membrane Proteins / Q000378:metabolism; D013997:Time Factors
D008565:Membrane Proteins; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D006160:Guanosine Triphosphate