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Figure 2.
Fig. 2. Mechanism for switching AncGR1's ligand preference from
aldosterone to cortisol. (A) Effect of substitutions S106P and
L111Q on the resurrected AncGR1's response to hormones. Dashed
lines indicate sensitivity to aldosterone (green), cortisol
(purple), and DOC (orange) as the EC[50] for reporter gene
activation. Green arrow shows probable pathway through a
functional intermediate; red arrow, intermediate with radically
reduced sensitivity to all hormones. (B) Structural change
conferring new ligand specificity. Backbones of helices 6 and 7
from AncGR1 (green) and AncGR2 (yellow) in complex with cortisol
are superimposed. Substitution S106P induces a kink in the
interhelical loop of AncGR2, repositioning sites 106 and 111
(arrows). In this background, L111Q forms a new hydrogen bond
with cortisol's unique C17-hydroxyl (dotted red line).
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