Met909 Plays a Key Role in the Activation of the Progesterone Receptor and Also in the High Potency of 13-Ethyl Progestins

Abstract

Many progestins have been developed for use in contraception, menopausal hormone therapy, and treatment of gynecological diseases. They are derived from either progesterone or testosterone, and they act by binding to the progesterone receptor (PR), a hormone-inducible transcription factor belonging to the nuclear receptor superfamily. Unlike mineralocorticoid, glucocorticoid, and androgen receptors, the steroid-receptor contacts that trigger the switch of the ligand-binding domain from an inactive to an active conformation have not yet been identified for the PR. With this aim, we solved the crystal structure of the ligand-binding domain of the human PR complexed with levonorgestrel, a potent testosterone-derived progestin characterized by a 13-ethyl substituent. Via mutagenesis analysis and functional studies, we identified Met909 of the helix 12 as the key residue for PR activation by both testosterone-and progesterone-derived progestins with a 13-methyl or a 13-ethyl substituent. We also showed that Asn719 contributes to PR activation by testosterone-derived progestins only, and that Met759 and Met909 are responsible for the high potency of 19-norprogestins and of 13-ethyl progestins, respectively. Our findings provide a structural guideline for the rational synthesis of potent PR agonist and antagonist ligands that could have therapeutic uses in women's health.

Nuclear Receptors and Their Selective Pharmacologic Modulators

“…Interestingly, this structure showed that the PR homodimer structure is smaller and less stable than previously published RXR and ER dimer structures. Other structures have been solved with PR LBD bound to synthetic ligands, including metribolone, mometasone furoate, norethindrone, tanaproget, mifepristone, levonorgestrel, and several pyrrolidine ligands (Matias et al, 2000;Madauss et al, 2004;Zhang et al, 2005;Petit-Topin et al, 2009;Raaijmakers et al, 2009;Thompson et al, 2009;Kallander et al, 2010). Two other structures were published showing PR bound to asoprisnil and corepressor proteins, specifically NCoR and SMRT (Madauss et al, 2007).…”

Structural Basis for Agonism and Antagonism for a Set of Chemically Related Progesterone Receptor Modulators

“…X-ray crystallography studies of PR bound to the 11␤-substituted steroids, asoprisnil (20) and RU486 (21), along with the full PR agonist levonorgestrel (22) clearly indicate a crucial function for Met 909 in the agonism/antagonism balance. This has also been shown to be true for nonsteroidal SPRMs (11,12).…”

Evolutionary analysis of the segment from helix 3 through helix 5 in vertebrate progesterone receptors

“…Fig. 6 shows the overlap at these four sites and some other residues in the steroid binding domain of the "ancestor-like" 3D model and the crystal structure of wildtype human PR complexed with progesterone [15,[32][33][34]. There is excellent overlap of all amino acids.…”

“…A 59 residue segment from the human PR corresponding to helix 3 through helix 5 [15,16,27,[32][33][34] was used as a probe by BLAST to search GenBank and Ensembl for the corresponding segment in [29,46], but not in humans [49,50]. 15␣-Hydroxy-progesterone may be the active progestin in lampreys [15,47,48].…”