| Purification and Quality Control | The His-tag recombinant protein is purified by affinity chromatography in combination with FPLC columns. The purified FXR-LBD is greater than 95% homogeneous based on SDS-PAGE analysis. | | Unit Definition (Activity) | 1 unit equals 1 nanogram of purified protein. 20 units are sufficient for a gel-mobility shift assay and 100 units are sufficient for a protein-protein interaction assay. | | Applications | FXR has been applied in DNA and protein-protein interactions assays. | | Formulation and Storage | The protein is in 20mM Tris-HCl pH7.9,100mM NaCl, 0.2mM EDTA, 1mM DTT and 20% glycerol. Stored at -70°C before use. Avoid repeated freeze thaw cycles. | | Synonym | Human farnesol receptor HRR-1 and retinoid receptor. | | Protein Sequence | QTVNEDSEGR DLRQVTSTTK SCREKTELTP DQQTLLHFIM DSYNKQRMPQ EITNKILKEE
FSAEENFLIL TEMATNHVQV LVEFTKKLPG FQTLDHEDQI ALLKGSAVEA MFLRSAEIFN
KKLPSGHSDL LEERIRNSGI SDEYITPMFS FYKSIGELKM TQEEYALLTA IVILSPDRQY
IKDREAVEKL QEPLLDVLQK LCKIHQPENP QHFACLLGRL TELRTFNHHH AEMLMSWRVN
DHKFTPLLCE IWDVQ | | Background | Farnesoid-X-activated receptor (FXR) was originally identified and cloned in rat as an orphan nuclear hormone receptor based on hybridization with a degenerate oligonucleotide designed from the highly conserved nuclear hormone receptor DNA binding domain (1). FXR functions as a heterodimer with RXR and binds to sequence elements in the promoters of target genes. The FXR/RXR heterodimer binds with highest affinity to inverted repeats separated by 1 bp (IR-1) and with low affinity to direct repeats separated by 4 and 5 bp (DR-4 and DR-5) (1, 2). As is the case for other nuclear hormone receptors, FXR regulates target gene activity in response to ligand. While initial studies suggested that farnesol and retinoid metabolites were likely ligands for FXR, current data support the notion that FXR is a bile acid sensor that plays an integral role in bile acid synthesis and transport (1, 3-6). In the small intestine, FXR regulates bile acid uptake through the upregulation of the ileal bile acid binding protein gene via binding to an upstream response element (7). The FXR/RXR heterodimer can be activated by the bile salt chenodeoxycholic acid (CDCA) and FXR is required for the bile salt-dependent transcriptional control of the human ABCB11 gene (the bile salt export pump) (8). In addition, FXR has been shown to inhibit the cholesterol 7-hydrolase gene (CYP7A1) transcription (9). | | References | 1. Forman et al., (1995) Cell 81, 687-693
2. Seol et al., (1995) Mol. Endocrinol. 9, 72-85
3. Zavacki et al., (1997) Proc. Natl. Acad. Sci. 94, 7909-7914
4. Makishima et al., (1999) Science 284, 1362-1365
5. Parks et al., (1999) Science 284, 1365-1368
6. Wang et al., (1999) Mol. Cell 3, 543-553
7. Grober et al., (1999) J. Biol. Chem. 274, 29749-29754
8. Plass et al., (2002) Hepatology 35, 589-596
9. Chiang et al., (2001) Gene 262, 257-265 |
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