Assay Report Card

ID: ALA3889136

Type: Binding

Description: TR-FRET Assay: TR-FRET assay for retinol-induced RBP4-TTR interaction Binding of a desired RBP4 antagonist displaces retinol and induces hindrance for RBP4-TTR interaction resulting in the decreased FRET signal (FIG. 7). Bacterially expressed MBP-RBP4 and untagged TTR were used in this assay. For the use in the TR-FRET assay the maltose binding protein (MBP)-tagged human RBP4 fragment (amino acids 19-201) was expressed in the Gold(DE3)pLysS E. coli strain (Stratagene) using the pMAL-c4x vector. Following cell lysis, recombinant RBP4 was purified from the soluble fraction using the ACTA FPLC system (GE Healthcare) equipped with the 5-ml the MBP Trap HP column. Human untagged TTR was purchased from Calbiochem. Untagged TTR was labeled directly with Eu3+ Cryptate-NHS using the HTRF Cryptate Labeling kit from CisBio following the manufacturer's recommendations. HTRF assay was performed in white low volume 384 well plates (Greiner-Bio) in a final assay volume of 16 ul per well. The reaction buffer contained 10 mM Tris-HCl pH 7.5, 1 mM DTT, 0.05% NP-40, 0.05% Prionex, 6% glycerol, and 400 mM KF. Each reaction contained 60 nM MBP-RBP4 and 2 nM TTR-Eu along with 26.7 nM of anti-MBP antibody conjugated with d2 (Cisbio). Titration of test compounds in this assay was conducted in the presence of 1 uM retinol. All reactions were assembled in the dark under dim red light and incubated overnight at +4° C. wrapped in aluminum foil. TR-FRET signal was measured in the SpectraMax M5e Multimode Plate Reader (Molecular Device). Fluorescence was excited at 337 nm and two readings per well were taken: Reading 1 for time-gated energy transfer from Eu(K) to d2 (337 nm excitation, 668 nm emission, counting delay 75 microseconds, counting window 100 microseconds) and Reading 2 for Eu(K) time-gated fluorescence (337 nm excitation, 620 nm emission, counting delay 400 microseconds, counting window 400 microseconds).

Organism: Homo sapiens