 |
PDBsum entry 2q1h
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
 |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
Transcription
|
PDB id
|
|
|
|
2q1h
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
References listed in PDB file
|
|
|
Key reference
|
|
|
Title
|
|
Crystal structure of an ancient protein: evolution by conformational epistasis.
|
|
|
Authors
|
|
E.A.Ortlund,
J.T.Bridgham,
M.R.Redinbo,
J.W.Thornton.
|
|
|
Ref.
|
|
Science, 2007,
317,
1544-1548.
[DOI no: ]
|
|
|
PubMed id
|
|
|
|
|
|
Abstract
|
|
|
The structural mechanisms by which proteins have evolved new functions are known
only indirectly. We report x-ray crystal structures of a resurrected ancestral
protein-the approximately 450 million-year-old precursor of vertebrate
glucocorticoid (GR) and mineralocorticoid (MR) receptors. Using structural,
phylogenetic, and functional analysis, we identify the specific set of
historical mutations that recapitulate the evolution of GR's hormone specificity
from an MR-like ancestor. These substitutions repositioned crucial residues to
create new receptor-ligand and intraprotein contacts. Strong epistatic
interactions occur because one substitution changes the conformational position
of another site. "Permissive" mutations-substitutions of no immediate
consequence, which stabilize specific elements of the protein and allow it to
tolerate subsequent function-switching changes-played a major role in
determining GR's evolutionary trajectory.
|
|
|
|
|
|
|
|
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).
|
|
Figure 4.
Fig. 4. Structural identification of an ancient permissive
substitution. (A) Comparison of the structures of AncCR (blue)
and AncGR2 (yellow). Y27R generates a novel cation-  interaction in
AncGR2 (dotted cyan line), replacing the weaker ancestral
hydrogen bond (dotted red) and imparting additional stability to
helix 3. (B) Y27R is permissive for the substitutions that
confer GR function. Reporter gene activation by AncGR1 + XYZ
(upper right) is abolished when Y27R is reversed (lower right).
(Left) Y27R has negligible effect in the AncCR background (or in
AncGR1, fig. S9). Green, orange, and purple lines show
aldosterone, DOC, and cortisol responses, respectively. Green
arrows, likely pathway through functional intermediates.
|
|
|
|
|
|
The above figures are
reprinted
by permission from the AAAs:
Science
(2007,
317,
1544-1548)
copyright 2007.
|
|
|
|
|
|
|
