7 alpha-17 alpha-Dimethyl-19-nortestosterone (mibolerone) induces conformational changes in progesterone receptors distinct from those induced by ORG 2058.

Using synthetic peptides with sequences derived from specific regions of human estrogen (ER) and progesterone (PR) receptors, we have developed site-directed monoclonal and polyclonal antibodies to specific domains of these receptors. These antibodies interact specifically with the native (nondenatured) receptors and detect changes in the conformation of these proteins. Monoclonal antibody PR-AT 4.14 bound more tightly to PR-ORG 2058 complexes than to PR-7 alpha,17 alpha-dimethyl-19-nor-testosterone (7 alpha,17 alpha, DMNT; mibolerone) complexes, suggesting possible ligand-induced conformational changes in PR. In the absence of the antibody, PR-[3H]ORG 2058 complexes sedimented as 4S-5S entity on sucrose density gradients (SDG) containing 0.4 M KCl. In the presence of the antibody, PR-[3H]ORG 2058 complexes sedimented as 7-8S complexes. In contrast, at the same concentrations of antibody, PR-[3H]7 alpha,17 alpha, DMNT complexes sedimented at 4S-5S region in the absence of the antibody and as two populations in the presence of the antibody, suggesting that the antibody did not recognize all of the PR-7 alpha,17 alpha, DMNT complexes. To exclude the possibility that the inability of the antibody to recognize receptor-[3H]7 alpha,17 alpha, DMNT complexes was due to its binding to androgen receptors, unlabeled 5 alpha-dihydrotestosterone (5 alpha-DHT) (50 nM) was added to the incubation to inhibit 7 alpha,17 alpha, DMNT binding to androgen receptors. While PR-[3H]ORG 2058 complexes were immunoprecipitated in the presence of the antibody, PR-[3H]7 alpha,17 alpha, DMNT complexes were only partially immunoprecipitated, further confirming the results obtained with SDG.(ABSTRACT TRUNCATED AT 250 WORDS)