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Assay Method Information

Assay Name:  FRET Activity Assay
Description:  The human FXRalpha LBD was expressed in E. coli strain BL21(DE3) as an N-terminally GST tagged fusion protein. The DNA encoding the FXR ligand binding domain was cloned into vector pDEST15 (Invitrogen). Expression was under control of an IPTG inducible T7 promoter. The amino acid boundaries of the ligand binding domain were amino acids 187-472 of Database entry NM_005123 (RefSeq). Expression and purification of the FXR-LBD: An overnight preculture of a transformed E. coli strain was diluted 1:20 in LB-Ampicillin medium and grown at 30 C. to an optical density of OD600=0.4-0.6. Gene expression was then induced by addition of 0.5 mM IPTG. Cells were incubated an additional 6 h at 30 C., 180 rpm. Cells were collected by centrifugation (7000g, 7 min, rt). Per liter of original cell culture, cells were resuspended in 10 mL lysis buffer (50 mM Glucose, 50 mM Tris pH 7.9, 1 mM EDTA and 4 mg/mL lysozyme) and left on ice for 30 min. Cells were then subjected to sonication and cell debris removed via centrifugation (22000g, 30 min, 4 C.). Per 10 mL of supernatant 0.5 mL prewashed Glutathione 4B sepharose slurry (Qiagen) was added and the suspension kept slowly rotating for 1 h at 4 C. Glutathione 4B sepharose beads were pelleted by centrifugation (2000 g, 15 sec, 4 C.) and washed twice in wash buffer (25 mM Tris, 50 mM KCl, 4 mM MgCl2 and IM NaCl). The pellet was resuspended in 3 mL elution buffer per liter of original culture (elution buffer: 20 mM Tris, 60 mM KCl, 5 mM MgCl2 and 80 mM glutathione added immediately prior to use as powder). The suspension was left rotating for 15 min at 4 C., the beads pelleted and eluted again with half the volume of elution buffer than the first time. The eluates were pooled and dialysed overnight in 20 mM Hepes buffer (pH 7.5) containing 60 mM KCl, 5 mM MgCl2 as well as 1 mM dithiothreitol and 10% (v/v) glycerol. The protein was analysed by SDS-Page.
Affinity data for this assay
 

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Last update November 1, 2007
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