To investigate tetracycline-inducible expression system for producing clinically usable, highquality
liver X receptor ligand-binding domain recombinant protein.
In this study, we have expressed and purified the recombinant liver X receptor β-ligand
binding domain proteins in E. coli
using a tetracycline inducible system. To allow for biological activities,
we subcloned into pPROTet.E HN vector, expressed in E. coli
cells under optimized conditions, purified
and characterized the recombinant liver X receptor β-ligand-binding domain proteins using fluorescence
The use of pPROTet.E HN vector simplified downstream purification processes, including
cleavage and elution thereby increasing the solubility and yield of the protein of interest. There was a
2.3-fold increase in the efficiency of recombinant LXR β-ligand binding domain (LBD) production by
optimizing the expression temperature to 15 °C when compared to those induced at 37°C during the
induction procedures. A typical dose-response curve obtained using increasing concentrations of the
purified recombinant LXR β-LBD (197-461) and measuring fluorescence intensity (FI) as an index of
fluorescent peptide binding to LBD showed 50 % effective dose (ED50
) value of 533 nM. The
recombinant LXR β-LBDs were substantially soluble and should be useful for future biological,
biophysical and structural analyses of nuclear receptor complexes. This may represent a new approach
to high expression of other nuclear receptors and may be useful as well for other classes of
heterodimeric protein partners.
These findings indicate that recombinant LXR β-LBD protein is a promising target for the
development of molecular ligands with improved therapeutic windows.