| Previous studies demonstrated a novel helix 3-helix 5 interaction in a mutant mineralocorticoid receptor (MR) that markedly alters receptor activity and specificity. Sequence homology reveals that the potential for such interactions are conserved in nuclear receptors, including glucocorticoid (GR) and progesterone receptors (PR). To better understand the functional significance of this interaction, a series of mutants of human GR and PR at helix 3 and/or helix 5 were created based MR mutation. Luciferase assays for COS-7 cells transfected with the wild-type or mutant GR or PR plasmids revealed that alteration of residues involved in helix 3-helix 5 interaction produces a gain-of-function in both GR and PR. The Scatchard binding showed GR L604 was higher binding affinity than that of wild-type of GR. These data mark helix 3-helix 5 interaction as a key "molecular switch" regulating the activity of steroid hormone receptors, and suggest this site as a potential target for pharmacologic intervention. |
