Figure 2: Helix 12 is conformationally flexible. A. In the agonist-bound state, H12 (magenta) is packed against the receptor by hydrophobic interactions, stabilizing the AF-2 surface for coactivator binding. This state is typically referred to as the 'agonist' conformation. B. An undocked H12 conformation (often observed in apo or antagonist-bound states) where H12 occupies the coactivator-binding groove. C. An undocked H12 conformation where the helix is displaced from the AF-2 surface and a corepressor peptide (blue) is bound.