A single amino acid mutation of Ala-773 in the mineralocorticoid receptor confers agonist properties to 11 beta-substituted spirolactones

Sequence analysis revealed a strong homology between the ligand-binding dom ain (LBD) of the human mineralocorticoid receptor (hMR) and glucocorticoid receptor (hGR). Nevertheless, steroids with bulky C11-substituents bind to hGR, unlike hMR. In this report, a mutant hMR, in which the residue Ala-773 facing the C11 steroid position was replaced by a glycine (A773G), was ass ayed for its capacity to bind steroids, to interact with receptor coactivat ors, and to stimulate transcription. The capacity of A773G to bind aldoster one and C11-substituted spirolactones was the same as that of the wild-type receptor. The agonist properties of aldosterone, as well as the antagonist feature of compounds bearing a 11 beta-allenyl group and a C17-ketone func tion, remain unchanged. In contrast, C11-substituted steroids with a 17 gam ma-lactonic ring displayed antagonist properties with hMR and acted as pote nt agonists with A773G. An agonist-dependent hMR interaction with SRC-1 was observed for both the wild-type and the mutant receptors. The hMR activati on process is discussed in the light of the hMR-LBD homology model based on the structural data of the human progesterone receptor LBD.