Valine 571 functions as a regional organizer in programming the glucocorticoid receptor for differential binding of glucocorticoids and mineralocorticoids

The glucocorticoid receptor (GR) interacts specifically with glucocorticoid s, whereas its closest relative, the mineralocorticoid receptor (MR), inter acts with both glucocorticoids and mineralocorticoids, such as aldosterone. To investigate the mechanism underlying the glucocorticoid/mineralocortico id specificity of the GR, we used a yeast model system to screen for GR lig and-binding domain mutants, substituted with MR residues in the segment 565 -574, that can be efficiently activated by aldosterone. In all such increas ed activity mutants, valine 571 was replaced by methionine, even though mos t mutants also contained substitutions of other residues with their MR coun terparts, Further analysis in yeast and COS-7 cells has revealed that the i dentity of residue 571 determines the behavior of other MR substituted resi dues in the 565-574 segment. Generally, MR substitutions in this region are only consistent with aldosterone binding if residue 571 is also replaced w ith methionine (MR conformation). If residue 571 is valine (GR conformation ), most other MR substitution mutants drastically reduce interaction with b oth mineralocorticoid and glucocorticoid hormones. Eased on these functiona l data, we hypothesize that residue 571 functions as a regional organizer i nvolved in discriminating between glucocorticoid and mineralocorticoid horm ones, We have used a molecular model of the GR ligand-binding domain in an attempt to interpret our functional data in structural terms.