title: Identification of sulfhydryl-modified cysteine residues in the ligand binding pocket of retinoic acid receptor beta.
abstract: The diverse biological functions of retinoic acid (RA) are mediated through retinoic acid receptors (RARs) and retinoid X receptors. RARs contain a high affinity binding site for RA which is sensitive to treatment with sulfhydryl modification reagents. In an attempt to identify which Cys residues are important for this loss of binding, we created three site-specific RARbeta mutants: C228A, C258A, and C267A. The affinity for RA of all three mutant receptors was in the range of that of the wild type protein, suggesting that none of these Cys residues are critical for RA binding. Rather, these modified Cys residue(s) function to sterically hinder RA binding; however, the modified Cys residues critical for the inhibition of binding differ depending on the reagent employed. Only modification of Cys228 is necessary to inhibit RA binding when RARbeta is modified by reagents which transfer large bulky groups while both Cys228 and Cys267 must be modified when a small functional group is transferred. These data suggest that both Cys228 and Cys267 but not Cys258 lie in the ligand binding pocket of RARbeta. However, Cys228 lies closer to the opening of the RARbeta ligand binding pocket whereas Cys267 lies more deeply buried.
authors.affiliation: Department of Biochemistry, Temple University School of Medicine, Philadelphia, Pennsylvania 19140, USA.
authors.forename: C L
authors.initials: CL
authors.lastname: Wolfgang
authors.forename: Z
authors.initials: Z
authors.lastname: Zhang
authors.forename: J L
authors.initials: JL
authors.lastname: Gabriel
authors.forename: R A
authors.initials: RA
authors.lastname: Pieringer
authors.forename: K J
authors.initials: KJ
authors.lastname: Soprano
authors.forename: D R
authors.initials: DR
authors.lastname: Soprano
mesh_terms: D001665:Binding Sites; D015153:Blotting, Western; D003545:Cysteine / Q000737:chemistry*; D004228:Dithionitrobenzoic Acid / Q000494:pharmacology; D005033:Ethylmaleimide / Q000494:pharmacology; D006902:Hydroxymercuribenzoates / Q000494:pharmacology; D016297:Mutagenesis, Site-Directed; D010957:Plasmids; D016133:Polymerase Chain Reaction; D011480:Protease Inhibitors / Q000494:pharmacology; D018168:Receptors, Retinoic Acid / Q000378:metabolism*; D000072482:Retinoic Acid Receptor alpha; D013329:Structure-Activity Relationship; D013439:Sulfhydryl Reagents / Q000378:metabolism*; D014212:Tretinoin / Q000378:metabolism; D000097768:Retinoic Acid Receptor gamma
chemical_list: D003545:Cysteine; D004228:Dithionitrobenzoic Acid; D005033:Ethylmaleimide; D006902:Hydroxymercuribenzoates; D011480:Protease Inhibitors; D018168:Receptors, Retinoic Acid; D000072482:Retinoic Acid Receptor alpha; D013439:Sulfhydryl Reagents; D014212:Tretinoin; D000097768:Retinoic Acid Receptor gamma; C082925:retinoic acid receptor beta; C030601:4-hydroxymercuribenzoate