title: Expression of human all-trans-retinoic acid receptor beta and its ligand-binding domain in Escherichia coli.
abstract: all-trans-Retinoic acid, one of the hormonally active derivatives of vitamin A, occurs physiologically in plasma at a concentration below 10 nmol/l. The methods currently used for its quantification are based on HPLC, need about 1 ml of serum, are relatively laborious and thus not well suited for mass analysis. The affinity and specificity of retinoic acid receptors for all-trans-retinoic acid encouraged us to express both the entire human retinoic acid receptor beta (RAR-beta) and two versions of its retinoic acid-binding domain in Escherichia coli in the hope that these recombinant proteins might be used as binders in a ligand-binding assay for all-trans-retinoic acid. The recombinant receptors, the whole receptor [RAR-beta-(V7-Q448)], corresponding to domains A-F, and the ligand-binding domain [RAR-beta-(E149-Q448)], corresponding to domains D-F, were expressed in the vector pET 3d/BL21 (DE3) as inclusion bodies, solubilized with guanidinium chloride, renatured and purified by ion-exchange chromatography. RAR-beta-(P193-Q448), corresponding to domains E-F, was expressed in the vector pET 3d/BL21(DE3)pLysS, and purified by reversed-phase chromatography. Under non-denaturing conditions, the expressed whole receptor [RAR-beta-(V7-Q448)] and the D-F construct (RAR-beta-(E149-Q448)] behaved chromatographically as monomeric proteins whereas the E-F construct [RAR-beta-(P193-Q448)] had a strong tendency to aggregate. RAR-beta-(V7-Q448) and RAR-beta-(E149-Q448) had similar Kd values for all-trans-retinoic acid (1.4 and 0.6 nmol/l respectively) whereas RAR-beta-(P193-Q448) bound all-trans-retinoic acid less avidly (Kd 9.6 nmol/l). 9-cis-Retinoic acid bound to RAR-beta-(E149-Q448) and RAR-beta-(V7-Q448) as avidly as all-trans-retinoic acid. Competition experiments showed weak or no binding of 4-oxo-all-trans-retinoic acid, 4-oxo-13-cis-retinoic acid, 13-cis-retinoic acid, acitretin and retinol by RAR-beta-(E149-Q448).
authors.affiliation: Department of Clinical Chemistry, University Hospital of Lund, Sweden.
authors.forename: M
authors.initials: M
authors.lastname: Berggren Söderlund
authors.forename: G
authors.initials: G
authors.lastname: Johannesson
authors.forename: G
authors.initials: G
authors.lastname: Fex
mesh_terms: D001483:Base Sequence; D017931:DNA Primers / Q000737:chemistry; D004926:Escherichia coli; D008969:Molecular Sequence Data; D010455:Peptides / Q000737:chemistry; D018168:Receptors, Retinoic Acid / Q000737:chemistry / Q000378:metabolism*; D011994:Recombinant Proteins; D014212:Tretinoin / Q000378:metabolism*
chemical_list: D017931:DNA Primers; D010455:Peptides; D018168:Receptors, Retinoic Acid; D011994:Recombinant Proteins; C082925:retinoic acid receptor beta; D014212:Tretinoin