title: A-ring nitro- and amino-substituted estradiol analogs produce a negative cooperative or noncooperative [3H]estradiol-estrogen receptor binding mechanism.
abstract: We have investigated the relation between ligand structure and binding mechanism between the calf uterine estrogen receptor. A series of structurally altered estradiol analogs was used in which either an amino- or a nitro group had been added to the 2 or 4 position on the phenolic A-ring. The binding affinity of both amino analogs and the 4-nitro analog for the estrogen receptor was reduced relative to that of estradiol, as measured by competitive binding assay; the values were between 0.008% and 8% of estradiol's affinity. The slope of the displacement curve for the 4-nitro analog was also significantly different from that of estradiol (p < 0.05), indicating that the binding mechanism of these two ligands was different. The affinity of the 2-nitroestradiol ligand for the receptor was too low to be measured. The binding mechanism was then further investigated by measuring the Hill coefficient of [3H]estradiol binding in the presence of the analog. The presence of a nitro group on C4 eliminated the positive cooperativity of the [3H]estradiol-estrogen receptor interaction; the Hill coefficient of [3H]estradiol binding in the presence of the analog was 0.99 compared with 1.7 for [3H]estradiol alone. Most interestingly, the presence of an amino group on either C2 or C4 brought about a switch from a positive to a negative cooperative binding interaction; the Hill coefficients of [3H]estradiol binding in the presence of the analogs were between 0.6 and 0.7. These results provide additional support for an induced-fit mechanism of ligand-estrogen receptor interactions.
authors.affiliation: Department of Physiology, Wayne State University School of Medicine, Detroit, Michigan 48201.
authors.forename: J A
authors.initials: JA
authors.lastname: Schwartz
authors.forename: D F
authors.initials: DF
authors.lastname: Skafar
mesh_terms: D000818:Animals; D001667:Binding, Competitive; D002417:Cattle; D004958:Estradiol / Q000031:analogs & derivatives* / Q000138:chemical synthesis; D005260:Female; D008954:Models, Biological; D011487:Protein Conformation; D011869:Radioligand Assay; D011940:Receptor Aggregation; D011959:Receptors, Estradiol / Q000378:metabolism*; D011960:Receptors, Estrogen / Q000378:metabolism*; D015398:Signal Transduction; D014599:Uterus / Q000378:metabolism
chemical_list: D011959:Receptors, Estradiol; D011960:Receptors, Estrogen; D004958:Estradiol