3D Models of MBP, a Biologically Active Metabolite of
Bisphenol A, in Human Estrogen Receptor a and
Estrogen Receptor b
Michael E. Baker1*, Charlie Chandsawangbhuwana2
1 Department of Medicine, University of California San Diego, La Jolla, California, United States of America, 2 Department of Bioengineering, University of California San
Diego, La Jolla, California, United States of America
Abstract
Bisphenol A [BPA] is a widely dispersed environmental chemical that is of much concern because the BPA monomer is a
weak transcriptional activator of human estrogen receptor a [ERa] and ERb in cell culture. A BPA metabolite, 4-methyl-2,4bis(4-hydroxyphenyl)pent-1-ene [MBP], has transcriptional activity at nM concentrations, which is 1000-fold lower than the
concentration for estrogenic activity of BPA, suggesting that MBP may be an environmental estrogen. To investigate the
structural basis for the activity of MBP at nM concentrations and the lower activity of BPA for human ERa and ERb, we
constructed 3D models of human ERa and ERb with MBP and BPA for comparison with estradiol in these ERs. These 3D
models suggest that MBP, but not BPA, has key contacts with amino acids in human ERa and ERb that are important in
binding of estradiol by these receptors. Metabolism of BPA to MBP increases the spacing between two phenolic rings,
resulting in contacts between MBP and ERa and ERb that mimic those of estradiol with these ERs. Mutagenesis of residues
on these ERs that contact the phenolic hydroxyls will provide a test for our 3D models. Other environmental chemicals
containing two appropriately spaced phenolic rings and an aliphatic spacer instead of an estrogenic B and C ring also may
bind to ERa or ERb and interfere with normal estrogen physiology. This analysis also may be useful in designing novel
chemicals for regulating the actions of human ERa and ERb.
Citation: Baker ME, Chandsawangbhuwana C (2012) 3D Models of MBP, a Biologically Active Metabolite of Bisphenol A, in Human Estrogen Receptor a and
Estrogen Receptor b. PLoS ONE 7(10): e46078. doi:10.1371/journal.pone.0046078
Editor: Vincent Laudet, Ecole Normale Supérieure de Lyon, France
Received April 12, 2012; Accepted August 29, 2012; Published October 4, 2012
Copyright: ß 2012 Baker, Chandsawangbhuwana. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which
permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Funding: The authors have no support or funding to report.
Competing Interests: The authors have declared that no competing interests exist.
* E-mail: mbaker@ucsd.edu
BPA has some structural similarity to estradiol and diethylstilbestrol [Figure 1], and, indeed, BPA binds to human estrogen
receptor a [ERa] and ERa and is a transcriptional activator of
these ERs [17,18,19,20]. However, BPA’s binding affinity and
transcriptional activity for these ERs is over 1000-fold lower than
that of E2 [17,18,19,20], which makes it unlikely that nM
concentrations of BPA would disrupt estrogen physiology.
Nevertheless, in vivo studies indicate that BPA is active at 1 nM
to 10 nM [8,10,15,21], which raises the possibility that BPA is
metabolized to a more active endocrine disruptor. One such
candidate metabolite is 4-methyl-2,4-bis(4-hydroxyphenyl)pent-1ene [MBP] [Figure 1], which has about 1000-fold higher
estrogenic activity than BPA [22,23]. To begin to understand
the structural basis for the high estrogenic activity of MBP and its
higher affinity compared to BPA for human ERa and ERb, we
constructed 3D models of MBP and BPA in human ERa and
ERb. We find that MBP retains key contacts with human ERa
and ERb that are important in activation of these receptors by
estradiol. We also find that one phenolic ring of BPA can mimic
binding of the A ring of E2 to ERa and ERb, which would
account for the binding of BPA to these ERs. However, the second
phenolic ring on BPA lacks some key contacts that are found
between E2 and both ERs, which may explain the lower
estrogenic activity of BPA. In addition to elucidating the
Introduction
One consequence of our industrial society is the presence of
novel environmental chemicals that disrupt normal physiological
responses in humans, other vertebrates, as well as invertebrates
[1,2]. Many of these chemicals are small hydrophobic molecules
that resemble steroids, thyroid hormone, retinoids and other
lipophilic hormones and, as a result bind to their receptors in
vertebrates [3,4,5,6,7]. Some of these chemicals act like hormones,
while others act like anti-hormones. In either case, they disrupt
normal endocrine physiology.
An endocrine disruptor of much concern is bisphenol A [BPA]
because it is widely dispersed in the environment due to the
presence of BPA in polycarbonate plastics, which are used in
containers for food and water, including baby bottles, as well as the
linings of metal cans used for food and beverages [8,9,10].
Leaching of the BPA monomer from these sources into food, milk
and the environment exposes humans [11,12,13] and wildlife
[2,14] to BPA.
A consequence of the widespread use of BPA is that over 90% of
the general population is exposed to BPA [9,13,15]. BPA levels
range from 0.3 nM to 40 nM in maternal plasma and fetal human
serum [8,10,11]. Moreover, due to the lipophilic nature of BPA, it
can accumulate in fat [16].
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3D Models of MBP in Human ERa and ERb
Figure 1. Structures of MBP, BPA, E2 and DES. MBP, BPA and DES have a phenolic ring that can mimic the A ring on E2 in binding to ERa and
ERb. The spacing between the first and second phenolic hydroxyls on MBP and DES is similar to that between C3 hydroxyl and the 17b-hydroxyl on
E2. In contrast, the distance between the two phenolic hydroxyls in BPA is shorter than that in E2.
doi:10.1371/journal.pone.0046078.g001
dependent dielectric constant of 2 for 50 iterations. We docked
MBP and BPA into this PDB file of human ERb with AutoDock
4 and AutoDockVina [27] with the settings used previously for
human ERa.
The lowest energy complexes of MBP and BPA in ERa and
ERb, as calculated by AutoDock 4 and AutoDock Vina, were
refined with the Discover 3 software in Insight II. For this energy
minimization step, Discover 3 was used with the CVFF force field
and a distant dependent dielectric constant of 2 for 10,000
iterations. During this refinement step, both the amino acids on
the ERs and MBP and BPA rearrange their positions so as to
lower the Gibbs free energy of the complex.
interaction of MBP and BPA with both human ERs, this analysis
may be useful in designing novel chemicals for regulating the
actions of human ERa and ERb.
Methods
Human ERa [24] was downloaded from the Protein Data Bank
[PDB] as a template for docking of MBP and BPA. ChemDraw
3D was used to create PDB files for MBP and BPA, which were
docked to human ERa [PDB:1G50] with AutoDock 4 [25,26] and
AutoDock Vina [27]. The grid was centered over the estrogen
binding site in human ERa. AutoDock 4 was run using the
Lamarckian Genetic Algorithm for 250 trials of 5 million energy
evaluations. AutoDock Vina was run with a setting of 20 for
exhaustiveness and poses for the 100 lowest energies were
collected.
The crystal structure of ERb complexed with E2
[PDB:3OLS] [28] was selected for docking MBP and BPA. As
was found in other ERb structures in the PDB, 3OLS lacks
coordinates for five amino acids corresponding to residues 416–
420. To model the missing amino acids, we used the Homology
option in Insight II and the 1G50 structure for human ERa as a
template. A PDB file of the complete ERb with E2 was refined
with Discover 3 with the CVFF force field and a distant
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Docking Energy Analysis
We used X-Score [29,30] and DSX [DrugScore eXtended]
[31] to estimate the relative binding energy of MBP and BPA in
the various configurations in ERa and ERb. X-Score uses an
empirical scoring function to estimate the affinity of a ligand for
a protein. DSX uses a knowledge-based scoring function based
on the DrugScore formalism [32] to estimate the affinity of a
ligand for a protein. In comparing the score of two ligands for a
protein, the ligand with the larger negative score has the higher
affinity.
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3D Models of MBP in Human ERa and ERb
Figure 2. Analysis of two 3D models of MBP in human ERa. A. 3D model of MBP in orientation 1 in human ERa. The first phenolic ring on MBP
contacts Glu-353, Arg-394 and Phe-404 on ERa and the second phenolic ring contacts Gly-521, His-524 and Leu-525. Favorable van der Waals contacts
have a distance of 4.25 Å or less between MBP and amino acids on ERa. B. 3D model of MBP in orientation 2 in human ERa. The first phenolic ring on
MBP contacts Glu-353, Arg-394 and Phe-404 on ERa, and the second phenolic ring contacts Gly-521, His-524 and Leu-525. However, in contrast to
Orientation 1, the backbone oxygen on Leu-387 does not contact the phenolic hydroxyl on MBP. Phe-404 and Met-421 do not have van der Waals
contacts with the linker between the two phenolic rings on MBP.
doi:10.1371/journal.pone.0046078.g002
[Figure 1]. BPA also had two poses for one of the rings in ERa and
ERb. We analyzed both poses for MBP and BPA in human ERa
and ERb. In our analysis of the 3D models of MBP and BPA in
both ERs, we use the term ‘‘first phenolic ring’’ to describe the ring
that has contacts with ERa and ERb that are similar to the A ring
of E2.
Results
Docking of MBP and BPA to Human ERa and ERb
Docking of MBP into human ERa and ERb using AutoDock 4
[25,26] and AutoDock Vina [27] gave two symmetric poses, which
is not surprising because MBP has a phenolic ring at each end
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3D Models of MBP in Human ERa and ERb
Table 1. Distances between MBP and ERa.
Figure 2A
ERa
MBP
Distance
Orientation 1
Oe2, Glu-353
O4’
3.1 Å
Ng2, Arg-394
O4’
3.1 Å
O, Leu-387
O4’
2.8 Å
Cb, Leu-391
O4’
3.7 Å
Ce2, Phe-404
C2’
3.9 Å
Ce2, Phe-404
C1
3.8 Å
Nd1, His-524
O4’’
3.0 Å
O, Gly-521
O4’’
2.8 Å
Cb, Leu-525
C4’’
4.0 Å
Sd, Met-343
C3’’
3.7 Å
Sd, Met-421
O4’’
4.1 Å
Ce, Met-421
C3’’
3.8 Å
Cd2, Leu384
C6
3.9 Å
Cd1, Leu384
C6
3.7 Å
Cd2, Thr-347
C5
3.6 Å
Cb, Ala-350
C6
3.8 Å
Figure 2B
ERa
MBP
Distance
Orientation 2
Oe2, Glu-353
O4’’
2.6 Å
Ng2, Arg-394
O4’’
3.2 Å
O, Leu-387
O4’’
6.6 Å
Cb, Leu-391
O4’’
3.7 Å
Cd2, Phe-404
C3’’
3.9 Å
Ce2, Phe-404
C6
4.5 Å
Nd1, His-524
O4’
3.0 Å
O, Gly-521
O4’
2.8 Å
Cb, Leu-525
C3’
3.9 Å
Sd, Met-343
C5’
4.0 Å
Sd, Met-421
C5’
3.9 Å
Ce, Met-421
C5’
3.9 Å
Ce, Met-421
C6
5.2 Å
Cd1, Leu384
C2’
3.7 Å
Cd2, Leu384
C3’
3.9 Å
Cd2, Thr-347
C1
3.6 Å
Cb, Ala-350
C5
3.8 Å
doi:10.1371/journal.pone.0046078.t001
ring. The distances between MBP and ERa are shown in
Figure 2A and Table 1. For comparison, in Figure 3A and
Table 2 we show the distances between E2 and human ERa
[33,35,36,37,38].
The first phenolic ring on MBP has contacts that are similar to
that of the A ring on E2 with human ERa [33,34,39]. The
phenolic hydroxyl on MBP is 3.1 Å from Oe2 on Glu-353, 3.1 Å
from Ng2 on Arg-394 and 2.8 Å from the backbone oxygen of
Leu-387. MBP is 3.9 Å from Ce2 on Phe-404 [Figure 2A,
Table 1]. These contacts are similar to that for E2 with human
ERa, except that Cd2 on Leu-387 does not contact the phenolic
hydroxyl on MBP, in contrast to the contact between Leu-387 and
E2 in human ERa [Figure 3A, Table 2].
Analysis of the crystal structures of ERa complexed with E2
[33,34] and other estrogens [35] revealed that Glu-353 and
Arg394 have important stabilizing contacts with the C3 hydroxyl
on the A ring and His-524 with the 17b-hydroxyl on the D ring.
Glu-305, Arg-346 and His-475 on ERb have similar stabilizing
contacts with estrogens. As reported below, the presence or
absence of these contacts in the 3D models of ERa and ERb with
BPA and MBP is important analyzing the interaction between
these chemicals and the ERs.
Analysis of MBP in Orientation 1 in Human ERa
In Figure 2A, we show the 3D model of MBP in human ERa
in Orientation 1, in which C1 on MBP is closest to first phenolic
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3D Models of MBP in Human ERa and ERb
Figure 3. Interaction of E2 with amino acids in human ERa and ERb. A. Interaction of E2 with human ERa [24,33,34,36,37,38,39]. The phenolic
hydroxyl of E2 contacts Glu-353, Arg-394 and Leu-387. The 17b-hydroxyl contacts His524 and Leu-525. The D ring contacts Met343, Met421, Gly-521
and Ile-424. Favorable van der Waals contacts have a distance of 4.25 Å or less between E2 and amino acids on ERa. B. Interaction of E2 with human
ERb [28]. The phenolic hydroxyl of E2 contacts Glu-305, Arg-346 and Leu-339. The 17b-hydroxyl contacts Gly-472, His473 and Leu-476. The D ring
contacts Met-336 and Ile-373. Favorable van der Waals contacts have a distance of 4.25 Å or less between E2 and amino acids on ERb.
doi:10.1371/journal.pone.0046078.g003
The second phenolic hydroxyl in MBP is 3 Å, 2.8 Å and 4 Å
from Nd1 on His-524, the backbone oxygen on Gly-521 and Cb
on Leu-525, respectively, on ERa [Figure 2A]. This phenolic
hydroxyl also contacts Met-343 and Met-421 on ERa. These
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five residues stabilize the D ring on E2 in human ERa
[Figure 3A].
There are, however, differences in some interactions between
ERa and MBP compared to that with E2. While Gly-521 and
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3D Models of MBP in Human ERa and ERb
Table 2. Distances between E2 and ERa and ERb.
Figure 3A
ERa
E2
Distance
Crystal Structure
Oe2, Glu-353
O3
2.8 Å
PDB: 1G50
Ng2, Arg-394
O3
2.9 Å
O, Leu-387
O3
3.0 Å
3.0 Å
Cd2, Leu-387
O3
Ce2, Phe-404
C10
3.6 Å
Nd1, His-524
O17
2.8 Å
O, Gly-521
O17
O, Gly-521
C16
3.4 Å
3.5 Å
Cd1 Leu-525
O17
Cd1 Leu-525
C18
3.9 Å
Sd, Met-343
O17
3.8 Å
Ce, Met-421
O16
3.6 Å
Sd, Met-421
O17
Cd2, Leu384
C18
5.2 Å
Cd1, Leu384
C18
4.6 Å
Cb, Ala-350
C1
4.2 Å
Cb, Leu-391
C4
3.8 Å
Cd2, Leu-391
C4’
3.9 Å
Figure 3B
ERb
E2
Distance
Crystal Structure
Oe2, Glu-305
O3
2.6 Å
PDB: 3OLS
Ng2, Arg-346
O3
3.0 Å
O, Leu-339
O3
3.4 Å
Cb, Leu-339
C2
4.0 Å
Cd1, Leu-343
C4
4.0 Å
3.9 Å
Cd2, Leu-343
C4
Ce2, Phe-356
C5
3.7 Å
Cb, Ala-302
C1
3.9 Å
O, Gly-472
O17
3.9 Å
Nd1, His-475
O17
3.0 Å
Cb, Leu-476
O17
3.4 Å
Cd2 Leu-476
C18
3.9 Å
Ce, Met-295
O17
3.5 Å
Sd, Met-336
C18
3.7 Å
Ce2, Met-336
C18
3.4 Å
Cd1, Ile-373
C16
3.8 Å
Ce, Met-421
O17
3.5 Å
doi:10.1371/journal.pone.0046078.t002
der Waals contacts with C1 on MBP, which has no equivalent
in E2 in ERa.
Met-421 contact the second phenolic hydroxyl on MBP
[Figure 2A], Gly-521 and Met-421 contact C16 on E2 in
ERa [Figure 3A]. While Leu-384 has two van der Waals
contacts with MBP, Leu-384 does not contact E2 in ERa.
While Thr-347 has a van der Waals contact with MBP, Thr347 does not contact E2 in ERa. While Cb on Leu-391 is
3.7 Å from the first phenolic hydroxyl on MBP, this contact is
absent between ERa and E2. While Ala-350 contacts the linker
between the two phenolic rings on MBP, Ala-350 contacts C1
on the A ring in E2 in ERa. Phe-404 and Met-421 have van
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Analysis of MBP in Orientation 2 in Human ERa
As shown in Figure 2B and Table 1, analysis of ERa with MBP
in Orientation 2 reveals that MBP has contacts with Glu-353, Arg394, Phe-404, Met-343, Leu-384, Met-421, Gly-521, His-524 and
Leu-525 that are similar to those found in Orientation 1 of MBP in
ERa. Due to the reversed orientation of MBP in ERa, C1 on MBP
has a van der Waals contact with Thr-347, and the other part of
the linker contacts Ala-350.
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3D Models of MBP in Human ERa and ERb
Figure 4. Analysis of two 3D models of MBP in human ERb. A. 3D model of MBP in orientation 1 in human ERb. The first phenolic ring on MBP
contacts Glu-305, Arg-346, Leu-339, Leu-343 and Phe-356. The second phenolic ring contacts Gly-472, His-475 and Leu-476, which are important in
the interaction of the D ring of E2 with ERb. B. 3D model of MBP in orientation 2 in human ERb. The first phenolic ring on MBP contacts the backbone
oxygen on Leu-339, Cb on Ala-302 and Leu-343. These contacts are absent between MBP in Orientation 2 in ERa [Figure 2B].
doi:10.1371/journal.pone.0046078.g004
human ERa [Figure 2A, Table 2] and between E2 and ERb
[Figure 3B]. Like the A ring in E2, the first phenolic ring on MBP
has stabilizing contacts with Glu-305, Arg-346, Phe-356, Leu-339
and Leu-343 in ERb. The second phenolic ring contacts His-475,
Gly-472, Leu-476, Ile-373 and Ile-376 [Figure 4A, Table 3].
Analysis of MBP in Orientation 1 in Human ERb
Figure 4A shows MBP in Orientation 1 in human ERb. For
comparison, in Figure 3B, we show E2 in human ERb [28]. Many
of the contacts between MBP and human ERb shown in Figure 4A
and Table 3 are similar to that between MBP in Orientation 1 and
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3D Models of MBP in Human ERa and ERb
Table 3. Distances between MBP and ERb.
Figure 4A
ERb
MBP
Distance
Orientation 1
Oe2, Glu-305
O4’
2.6 Å
Ng2, Arg-346
O4’
3.1 Å
O, Leu-339
O4’
3.4 Å
Cb, Leu-343
O4’
3.9 Å
Cd2, Phe-356
C2’
4.0 Å
Ce2, Phe-356
C1
4.0 Å
Nd1, His-475
O4’’
3.0 Å
O, Gly-472
O4’’
3.6 Å
Cb, Leu-476
C3’’
4.1 Å
Ce, Met-295
O4’’
5.7 Å
3.9 Å
Cb, Ala-302
C6
Sd, Met-336
C6
3.5 Å
Cd1, Ile-373
O4’’
3.6 Å
Cd1, Ile-376
O4’’
3.2 Å
Figure 4B
ERb
MBP
Distance
Orientation 2
Oe2, Glu-305
O4’’
2.6 Å
Ng2, Arg-346
O4’’
3.3 Å
O, Leu-339
C4’’
3.6 Å
Cb, Leu-343
C5’’
4.1 Å
Cd2, Leu-343
C6’’
4.1 Å
Cd2, Phe-356
C5’’
3.9 Å
Ce2, Phe-356
C1
4.6 Å
Nd1, His-475
O4’
3.2 Å
O, Gly-472
C5’
3.6 Å
Cb, Leu-476
O4’
3.3 Å
Ce, Met-295
O4’
3.3 Å
Cb, Ala-302
C5
4.0 Å
Cb, Ala-302
C2’’
4.0 Å
Sd, Met-336
C6
3.5 Å
Ce, Met-336
C5’
4.0 Å
Cd1, Ile-373
C1
3.9 Å
Cc, Ile-376
C1
3.7 Å
Cd1, Ile-376
O4’
6.0 Å
doi:10.1371/journal.pone.0046078.t003
Figure 4B shows MBP in Orientation 2 in human ERb. Many
of the contacts between MBP in Orientation 2 and human ERb
[Table 3] are similar to that between MBP in Orientation 1 and
human ERb [Figure 4A, Table 3]] and between E2 and ERb
[Table 2]. The backbone oxygen on Leu-339, Cb on Ala-302 and
the side chains on Leu-343 contact the first phenolic ring on MBP.
These contacts are absent between MBP in Orientation 2 in ERa
[Figure 2B, Table 1].
on Phe-404 and Cb on Ala-350 [Figure 5A, Table 4]. However,
the backbone oxygen on Leu-387 is 6.4 Å from the phenolic
hydroxyl and Leu-391 does not have a van der Waals contact with
the phenolic ring.
The second phenolic ring does not contact either Gly-521, His524 or Leu-525 [Table 4]. Instead, phenolic ring moves so that it
contacts Ce2 and Cg on Phe-404, Ce on Met-421 and Cd2 on Ile424. Also, Ala-350 and Leu-384 and Thr-347 contact the linker on
BPA.
Analysis of BPA in Orientation 1 in Human ERa
Analysis of BPA in Orientation 2 in Human ERa
Figure 5A shows BPA in Orientation 1 in human ERa. The
phenolic ring on BPA, corresponding to the A ring of E2, has
stabilizing contacts with Oe2 on Glu-353, Ng2 on Arg-394, Cd2
In Figure 5B, we show BPA in Orientation 2 in human ERa.
The first phenolic ring on BPA contacts Oe2 on Glu-353, Ng2 on
Arg-394, Cd2 on Phe-404 and Cb on Ala-350 [Figure 5B,
Analysis of MBP in Orientation 2 in Human ERb
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3D Models of MBP in Human ERa and ERb
Figure 5. Analysis of two 3D models of BPA in human ERa. A. 3D model of BPA in orientation 1 in human ERa. The first phenolic ring on BPA
contacts Glu-353, Arg-394 and Phe-404 on ERa, but does not contact either Leu-387 or Leu-391. Moreover, the second phenolic ring does not contact
either Gly-521, His-524 or Leu-525. Instead, the second phenolic ring contacts Phe-404, Met-421 and Ile-424. B. 3D model of BPA in orientation 2 in
human ERa. The first phenolic ring on BPA contacts Glu-353 and Arg-394 on ERa, but does not contact Leu-387 or Phe-404. The second phenolic ring
does not contact either Gly-521 or His-524. Instead, the second phenolic ring has novel contacts with Thr-347 and Leu-384.
doi:10.1371/journal.pone.0046078.g005
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Table 4. Distances between BPA and ERa.
Figure 5A
ERa
BPA
Distance
Orientation 1
Oe2, Glu-353
O4’
2.6 Å
Ng2, Arg-394
O4’
3.3 Å
O, Leu-387
O4’
6.4 Å
Cd2, Phe-404
C3’
3.9 Å
Ce2, Phe-404
C6’’
3.6 Å
Cg, Phe-404
C5’’
3.6 Å
Nd1, His-524
O4’’
6.8 Å
Cd1, Leu-384
C1
3.5 Å
Cb, Ala-350
C1
4.1 Å
Cb, Ala-350
C1’
4.0 Å
Ce, Met-421
O4’’
3.3 Å
Cd2, Ile-424
O4’’
3.5 Å
Cd2, Thr-347
C3
4.3 Å
Figure 5B
ERa
BPA
Distance
Orientation 2
Oe2, Glu-353
O4’
2.6 Å
Ng2, Arg-394
O4’
3.2 Å
O, Leu-387
O4’
6.2 Å
Cd2 Leu-391
C6’
3.9 Å
Cd2 Leu-391
C3
4.0 Å
Ce2, Phe-404
C3
4.1 Å
Nd1, His-524
O4’’
7.8 Å
O, Gly-521
O4’’
7.4 Å
Cb, Leu-525
O4’’
3.3 Å
Cd1, Leu-525
O4’’
3.5 Å
Sd, Met-343
C5’’
5.7 Å
Sd, Met-421
C5’’
7.7 Å
Ce, Met-421
C5’’
7.6 Å
Ce, Met-421
C6’’
7.1 Å
Cd1, Leu384
C3’’
4.0 Å
Cd2, Thr-347
O4’’
3.4 Å
Cb, Ala-350
C2’’
3.8 Å
Cb, Ala-350
C2’
3.7 Å
doi:10.1371/journal.pone.0046078.t004
The second phenolic ring contacts Gly-472, His-475, Leu-476,
Ile-373 and Met-336, but the second phenolic ring does not
contact Met-295.
Table 4]. Leu-391 has a van der Waals contact with the phenolic
ring. However, the backbone oxygen on Leu-387 does not contact
BPA.
The second phenolic ring on BPA does not contact either Gly521, His-524, Met-421 or Ile-424 [Table 4]. Instead, the phenolic
hydroxyl contacts Leu-525 and Thr-347. Leu-384 and Ala-350
also contact the second phenolic ring.
Analysis of BPA in Orientation 2 in Human ERb
In Figure 6B, we show the minimized structure of BPA in
Orientation 2 in human ERb. The first phenolic ring on BPA
contacts Oe2 on Glu-305, Ng2 on Arg-346, Ce2 on Phe-404, Cb
on Ala-350, Cd2 on Leu-343 and the backbone oxygen on Leu339 [Figure 6B, Table 5].
The second phenolic ring does not contact either Gly-472, His475, Leu-476 or Met-295 [Table 5]. Instead, the phenolic
hydroxyl contacts Phe-377 and Ile-373. Interestingly, Phe-356
contacts the second phenolic ring and Met-336 contacts the linker
on BPA.
Analysis of BPA in Orientation 1 in Human ERb
In Figure 6A, we show BPA in Orientation 1 in human ERb.
The first phenolic ring on BPA contacts Oe2 on Glu-305, Ng2 on
Arg-346, Ce2 on Phe-404, Cb on Leu339 and the backbone
nitrogen on Ala-302 [Figure 6A, Table 5]. The backbone oxygen
on Leu-339 does not contact the phenolic hydroxyl. Cb on Ala302 and Cd2 on Leu-343 do not contact the phenolic ring.
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3D Models of MBP in Human ERa and ERb
Figure 6. Analysis of two 3D models of BPA in human ERb. A. 3D model of BPA in orientation 1 in human ERb. The first phenolic ring on BPA
contacts Glu-305, Arg-346, and Phe-356, but does not contact either the backbone oxygen on Leu-339 or Cd2 on Leu-343. The second phenolic ring
contacts Gly-472, His-475 and Leu-476. B. 3D model of BPA in orientation 2 in human ERb. The first phenolic ring on BPA contacts Glu-305, Arg-346,
Phe-356, the backbone oxygen on Leu-339 and Cd2 on Leu-343. The second phenolic ring does not contact either Gly-472, His-475 or Leu-476.
doi:10.1371/journal.pone.0046078.g006
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3D Models of MBP in Human ERa and ERb
Table 5. Distances between BPA and ERb.
Figure 6A
ERb
BPA
Distance
Orientation 1
Oe2, Glu-305
O4’
2.6 Å
Ng2, Arg-346
O4’
4.3 Å
O, Leu-339
O4’
5.7 Å
Cb, Leu-339
O4’
4.0 Å
Cd2, Leu-343
C4’
5.3 Å
Cd2, Phe-356
C3’
4.0 Å
Ce2, Phe-356
C2’
3.8 Å
Ce2, Phe-356
C3
3.8 Å
Nd1, His-475
O4’’
3.2 Å
O, Gly-472
O4’’
2.8 Å
Cb, Leu-476
O4’’
3.5 Å
Ce, Met-295
O4’’
4.3 Å
Cb, Ala-302
C6’
5.5 Å
N, Ala-302
O4’
3.4 Å
Sd, Met-336
C2’’
3.5 Å
Ce, Met-336
C3’’
3.6 Å
Cd1, Ile-373
C5’’
3.7 Å
Cd1, Ile-376
C6’’
3.6 Å
Figure 6B
ERb
BPA
Distance
Orientation 2
Oe2, Glu-305
O4’
2.6 Å
Ng2, Arg-346
O4’
3.2 Å
O, Leu-339
C4’
4.0 Å
Cd2, Leu-343
C5’
3.9 Å
Ce2, Phe-356
C6’
4.2 Å
Ce2, Phe-356
C6’’
3.6 Å
Cf2, Phe-356
C5’’
3.7 Å
Nd1, His-475
O4’’
7.1 Å
O, Gly-472
O4’’
8.4 Å
Cb, Leu-476
O4’’
10.2 Å
Ce, Met-295
O4’’
8.5 Å
4.1 Å
Cb, Ala-302
C2’
Sd, Met-336
C3
3.2 Å
Ce, Met-336
C3
3.7 Å
Cd1, Ile-373
C1
3.9 Å
Cc1, Ile-376
O4’’
3.5 Å
O, Ile-376
O4’’
3.8 Å
Ce1, Phe-377
O4’’
3.6 Å
N, Phe-377
O4’’
3.4 Å
doi:10.1371/journal.pone.0046078.t005
Docking Energy Analysis
Discussion
We used X-Score [31] and DSX [31] to estimate the affinity of
MBP and BPA in their different orientations in ERa and ERb.
Tables 6 and 7 summarize these analyses for the X-Score and
DSX. For both algorithms, MBP has an affinity for ERa and ERb
that is closer to that of E2 than is BPA for these receptors. This is
consistent with previous assays of the activity of MBP and BPA
[22,23].
PLOS ONE | www.plosone.org
The leaching of BPA monomers from polycarbonate containers
and from liners of metal containers for food and beverages has
contributed to the widespread exposure of humans to BPA
[2,11,12,13,15]. The relatively low affinity of BPA, compared to
E2, for human ERa and ERb [17,19,20] would, at first glance,
make it unlikely that BPA would be a problem as an estrogenic
endocrine disruptor at nM concentrations [9,10,11]. However, it is
12
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3D Models of MBP in Human ERa and ERb
synthetic bisphenols [39,40] indicate the length of the carbon
linker between bisphenols and side chain substitutents on the
cyclohexane ring on cyclofenils are important in establishing
contacts that lead to high affinity binding to the ER. This is
consistent with the analysis of our 3D models of BPA and MBP
in ERa and ERb as discussed below.
Table 6. Docking analysis of MBP and BPA in ERa and ERb.
Receptor
Ligand
Score
Figure
ERa
E2
7.4
Figure 3A
ERa
MBP Orientation 1
7.2
Figure 2A
ERa
MBP Orientation 2
7.2
Figure 2B
ERa
BPA Orientation 1
6.5
Figure 4A
ERa
BPA Orientation 2
6.5
Figure 4B
ERb
E2
7.5
Figure 3A
ERb
MBP Orientation 1
7.1
Figure 5A
ERb
MBP Orientation 2
7.2
Figure 5B
ERb
BPA Orientation 1
6.7
Figure 6A
ERb
BPA Orientation 2
6.7
Figure 6B
MBP Retains Important Contacts found between E2 and
ERa and ERb
Our 3D models of MBP and BPA in human ERa and ERb
[Figures 2, 4–6] identify contacts that can explain MBP’s high
affinity and BPA’s low affinity for both estrogen receptors. A
key structural difference between BPA and MBP is the longer
spacing between the two phenolic rings in MBP [Figure 1]. As a
result, both phenolic rings on MBP form stabilizing contacts
with ERa and ERb that are similar to that between the A and
D
rings of
E2 and
human ERa
and
ERb
[28,33,34,35,38,39,41]. These 3D models predict that the
second phenolic hydroxyl on MBP has a hydrogen bond with
His-524 on ERa and His-475 on ERb. Our 3D models can be
tested by investigating transcriptional activation by MBP of
ERa and ERb in which His-524 and His-475, respectively,
have been mutated.
X-Score Analysis of MBP and BPA in ERa and ERb [29,30].
doi:10.1371/journal.pone.0046078.t006
clear that nM concentrations of BPA have estrogenic activity
[8,21]. The discovery that MBP, a metabolite of BPA, has a nM
affinity for human ERa and ERb, suggests that metabolism of
BPA to MBP could explain some of effects of BPA on estrogen
physiology [22,23].
There is a structural basis for considering BPA and MBP as
potential ligands for ERa and ERb because BPA and MBP have
some structural similarities to known synthetic estrogens
[Figure 7]. BPA is a bisphenol linked by one carbon atom
[Figure 1] as are cyclofenil-type estrogens [Figure 7], some of
which have high affinity for ERa and ERb [40]. MBP is a
bisphenol linked by three carbon atoms [Figure 1] as is
benzestrol [Figure 7], which has a high affinity for ERa and
ERb [39]. Hexestrol, which is linked by two carbon atoms, also
has a high affinity for ERa and ERb [18,39]. Thus, it is
reasonable to be concerned about potential endocrine disruption
by synthetic bisphenols. However, as discussed below, our 3D
model of BPA in ERs indicates that BPA does not have the
contacts with an ER as is found between fluorine-substituted
cyclofenil derivatives [40]. Studies with a wide variety of
BPA Lacks some Contacts found between E2 and ERa
and ERb
Like the A ring on E2, one phenolic ring on BPA has
stabilizing contacts with Glu-353, Arg-394 and Phe-404 in ERa
[Figure 5]. Interestingly, Phe-404 also contacts the second
phenolic ring. However, the second phenolic ring on BPA does
not contact either Gly-521 or His-524 on ERa, which is
significant because contacts between E2 and Gly-521 and His524 in ERa are important in binding of E2 [28,33,35,39,41].
Also, Leu-387 does not contact the first phenolic ring of BPA in
either Orientation 1 or Orientation 2. The loss of these contacts
between BPA and ERa may explain the lower affinity of BPA for
ERa.
In the 3D model of BPA in Orientation 1 in ERb [Figure 6A],
one phenolic ring on BPA has stabilizing contacts with Glu305, Arg-346 and Phe-356 in ERb. Moreover, the second
phenolic ring on BPA contacts Gly-472, His-475 and Leu-476
on ERb. Thus, some of the key interactions between the ERb
and the A and D rings on E2 [Figure 3B] are conserved for
BPA in Orientation 1 in ERb. However, neither Leu-339 nor
Leu-343 contacts the first phenolic ring on BPA. The loss of
these contacts would be expected to lower affinity of BPA for
ERb.
Although BPA in Orientation 2 in ERb [Figure 6B] has contacts
with Glu-305, Arg-346, Phe-356, Leu-339 and Leu-343, BPA does
not contact either Gly-472, His-475 or Leu-476 on ERb. Instead,
the second phenolic ring has novel contacts with Ile-373, Ile-376,
Phe-377 and Phe-356.
Table 7. Docking analysis of MBP and BPA in ERa and ERb.
Receptor
Ligand
Score
Figure
ERa
E2
2116
Figure 3A
ERa
MBP Orientation 1
2103
Figure 2A
ERa
MBP Orientation 2
2110
Figure 2B
ERa
BPA Orientation 1
284
Figure 4A
ERa
BPA Orientation 2
291
Figure 4B
ERb
E2
2123
Figure 3B
ERb
MBP Orientation 1
2112
Figure 5A
ERb
MBP Orientation 2
2116
Figure 5B
ERb
BPA Orientation 1
290
Figure 6A
ERb
BPA Orientation 2
289
Figure 6B
Cellular Context Influences Estrogenic Activity of MBP
and BPA
The presence of two phenolic rings in MBP and BPA and the
flexibility in the estrogen binding site in ERa and ERb
[7,33,35,42,43,44,45,46] are important factors in the binding
of MBP and BPA to these ERs. The equilibrium dissociation
constant of BPA for ERa and ERb is about 195 nM and 35 nM
respectively [18]. Using a different binding assay, IC50s [23]
for binding of BPA and MBP to ERa and ERb were reported.
BPA and MBP have IC50s of 1.8 mM and 52 nM, respectively
DSX Analysis of MBP and BPA in ERa and ERb [31,32].
doi:10.1371/journal.pone.0046078.t007
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3D Models of MBP in Human ERa and ERb
Also important for transcriptional activation of ERs and
other nuclear receptors by steroids and endocrine disruptors
is the binding of co-regulators to the ligand-receptor complex
[47,48,49,50,51,52,53]. Thus, even a low affinity ligand such
as 27-hydroxy-cholesterol can have transcriptional activity
for the ER in the presence of the appropriate co-activator
[44].
The interaction of complexes of ERa and ERb with
different co-regulators may explain the report by Yoshihara
et al. [23] that transcriptional activation of ERa and ERb by
MBP and BPA depended on the cellular context. That is, the
estrogenic activity of MBP and BPA is altered in the presence
or absence of co-regulators [20,48,50,51,54,55]. In the yeast
estrogen screening (YES) assay, the EC50 potencies for
transcriptional activation of ERa by MBP and BPA were
0.7 mM and 160 mM, respectively. In experiments, which
included the Transcriptional Intermediary Factor 2 [TIF2]
co-activator in the assay, the EC50s for transcriptional
activation of rat ERa with TIF2 by MBP and BPA were
8.3 nM and 14 mM, respectively, and the EC50s for rat ERb
with TIF2, by MBP and BPA were 8.3 nM and 13 m M,
respectively. Thus, transcriptional activation of ERs by MBP
and BPA in an assay containing TIF2, which mimicked
conditions in some mammalian cells, increased by about 10fold compared to the assay in yeast cells.
Further evidence for the importance of cellular context on
transcriptional potency of MBP and BPA comes from
experiments using an ERE-luciferase reporter assay in 3T3
cells. Yoshihara et al. [23] found that the EC50s for MBP
and BPA for ERa were 0.68 nM and 1 m M, respectively. For
ERb in 3T3 cells, the EC50s for MBP and BPA were
0.46 nM and 89 nM, respectively. Together these experiments by Yoshihara et al. suggest that MBP is a potential
disruptor of physiological responses that are mediated by
ERa and ERb.
Although MBP and benzestrol have a three carbon linker
between their two phenols, their linkers are different. Despite
this difference, nM concentrations of MBP activate transcription
of the ER in mammalian cells. This raises the possibility that
other environmental chemicals with two phenolic rings connected with novel aliphatic linkers may have a physiologically
relevant activity towards ERa and ERb in cells with coactivators that can activate the chemical-ER complex. We also
note that the 3D models of MBP in ERa and ERb may be useful
in the development of new chemicals for use as selective ER
agonists or antagonists.
Figure 7. Structures of bisphenols that are potent synthetic
estrogens. Bisphenols, linked with one, two or three carbons, can have
high affinity for ERs. 3-(3-fluoropropyl)cyclofenil, hexestrol and benzestrol have a higher affinity for ERa that does E2 [18,39,40].
doi:10.1371/journal.pone.0046078.g007
Author Contributions
Conceived and designed the experiments: MEB. Performed the experiments: CC. Analyzed the data: CC MEB. Wrote the paper: MEB.
for ERa and IC50s of 0.74 mM and 0.12 mM, respectively, for
ERb.
References
5. le Maire A, Bourguet W, Balaguer P (2010) A structural view of nuclear
hormone receptor: endocrine disruptor interactions. Cell Mol Life Sci 67: 1219–
1237.
6. Sladek FM (2011) What are nuclear receptor ligands? Mol Cell Endocrinol 334:
3–13.
7. Baker ME (2011) Insights from the structure of estrogen receptor into the
evolution of estrogens: Implications for endocrine disruption. Biochem
Pharmacol 82: 1–8.
8. Welshons WV, Nagel SC, vom Saal FS (2006) Large effects from small
exposures. III. Endocrine mechanisms mediating effects of bisphenol A at levels
of human exposure. Endocrinology 147: S56–69.
1. Colborn T, vom Saal FS, Soto AM (1993) Developmental effects of endocrinedisrupting chemicals in wildlife and humans. Environ Health Perspect 101: 378–
384.
2. Diamanti-Kandarakis E, Bourguignon JP, Giudice LC, Hauser R, Prins GS, et
al. (2009) Endocrine-disrupting chemicals: an Endocrine Society scientific
statement. Endocr Rev 30: 293–342.
3. Baker ME (2005) Xenobiotics and the evolution of multicellular animals:
emergence and diversification of ligand-activated transcription factors. Integrative and Comparative Biology 45: 172–178.
4. Markov GV, Tavares R, Dauphin-Villemant C, Demeneix BA, Baker ME, et al.
(2009) Independent elaboration of steroid hormone signaling pathways in
metazoans. Proc Natl Acad Sci U S A 106: 11913–11918.
PLOS ONE | www.plosone.org
14
October 2012 | Volume 7 | Issue 10 | e46078
3D Models of MBP in Human ERa and ERb
9. Melzer D, Rice NE, Lewis C, Henley WE, Galloway TS (2010) Association of
urinary bisphenol a concentration with heart disease: evidence from NHANES
2003/06. PLoS One 5: e8673.
10. Vandenberg LN, Chahoud I, Heindel JJ, Padmanabhan V, Paumgartten FJ, et
al. (2010) Urinary, circulating, and tissue biomonitoring studies indicate
widespread exposure to bisphenol A. Environ Health Perspect 118: 1055–1070.
11. Schonfelder G, Wittfoht W, Hopp H, Talsness CE, Paul M, et al. (2002) Parent
bisphenol A accumulation in the human maternal-fetal-placental unit. Environ
Health Perspect 110: A703–707.
12. Vandenberg LN, Hauser R, Marcus M, Olea N, Welshons WV (2007) Human
exposure to bisphenol A (BPA). Reprod Toxicol 24: 139–177.
13. Calafat AM, Ye X, Wong LY, Reidy JA, Needham LL (2008) Exposure of the
U.S. population to bisphenol A and 4-tertiary-octylphenol: 2003–2004. Environ
Health Perspect 116: 39–44.
14. Oehlmann J, Schulte-Oehlmann U, Kloas W, Jagnytsch O, Lutz I, et al. (2009)
A critical analysis of the biological impacts of plasticizers on wildlife. Philos
Trans R Soc Lond B Biol Sci 364: 2047–2062.
15. Vandenberg LN, Maffini MV, Sonnenschein C, Rubin BS, Soto AM (2009)
Bisphenol-A and the great divide: a review of controversies in the field of
endocrine disruption. Endocr Rev 30: 75–95.
16. Fernandez MF, Arrebola JP, Taoufiki J, Navalon A, Ballesteros O, et al. (2007)
Bisphenol-A and chlorinated derivatives in adipose tissue of women. Reprod
Toxicol 24: 259–264.
17. Krishnan AV, Stathis P, Permuth SF, Tokes L, Feldman D (1993) Bisphenol-A:
an estrogenic substance is released from polycarbonate flasks during autoclaving.
Endocrinology 132: 2279–2286.
18. Kuiper GG, Carlsson B, Grandien K, Enmark E, Haggblad J, et al. (1997)
Comparison of the ligand binding specificity and transcript tissue distribution of
estrogen receptors alpha and beta. Endocrinology 138: 863–870.
19. Kuiper GG, Lemmen JG, Carlsson B, Corton JC, Safe SH, et al. (1998)
Interaction of estrogenic chemicals and phytoestrogens with estrogen receptor
beta. Endocrinology 139: 4252–4263.
20. Gould JC, Leonard LS, Maness SC, Wagner BL, Conner K, et al. (1998)
Bisphenol A interacts with the estrogen receptor alpha in a distinct manner from
estradiol. Mol Cell Endocrinol 142: 203–214.
21. Richter CA, Taylor JA, Ruhlen RL, Welshons WV, Vom Saal FS (2007)
Estradiol and Bisphenol A stimulate androgen receptor and estrogen receptor
gene expression in fetal mouse prostate mesenchyme cells. Environ Health
Perspect 115: 902–908.
22. Okuda K, Takiguchi M, Yoshihara S (2010) In vivo estrogenic potential of 4methyl-2,4-bis(4-hydroxyphenyl)pent-1-ene, an active metabolite of bisphenol A,
in uterus of ovariectomized rat. Toxicol Lett 197: 7–11.
23. Yoshihara S, Mizutare T, Makishima M, Suzuki N, Fujimoto N, et al. (2004)
Potent estrogenic metabolites of bisphenol A and bisphenol B formed by rat liver
S9 fraction: their structures and estrogenic potency. Toxicol Sci 78: 50–59.
24. Eiler S, Gangloff M, Duclaud S, Moras D, Ruff M (2001) Overexpression,
purification, and crystal structure of native ER alpha LBD. Protein Expr Purif
22: 165–173.
25. Huey R, Morris GM, Olson AJ, Goodsell DS (2007) A semiempirical free energy
force field with charge-based desolvation. J Comput Chem 28: 1145–1152.
26. Morris GM, Huey R, Lindstrom W, Sanner MF, Belew RK, et al. (2009)
AutoDock4 and AutoDockTools4: Automated docking with selective receptor
flexibility. J Comput Chem.
27. Trott O, Olson AJ (2010) AutoDock Vina: improving the speed and accuracy of
docking with a new scoring function, efficient optimization, and multithreading.
J Comput Chem 31: 455–461.
28. Mocklinghoff S, Rose R, Carraz M, Visser A, Ottmann C, et al. (2010) Synthesis
and crystal structure of a phosphorylated estrogen receptor ligand binding
domain. Chembiochem 11: 2251–2254.
29. Cheng T, Li X, Li Y, Liu Z, Wang R (2009) Comparative assessment of scoring
functions on a diverse test set. J Chem Inf Model 49: 1079–1093.
30. Wang R, Lai L, Wang S (2002) Further development and validation of empirical
scoring functions for structure-based binding affinity prediction. J Comput Aided
Mol Des 16: 11–26.
31. Neudert G, Klebe G (2011) DSX: a knowledge-based scoring function for the
assessment of protein-ligand complexes. J Chem Inf Model 51: 2731–2745.
32. Velec HF, Gohlke H, Klebe G (2005) DrugScore(CSD)-knowledge-based
scoring function derived from small molecule crystal data with superior
recognition rate of near-native ligand poses and better affinity prediction.
J Med Chem 48: 6296–6303.
PLOS ONE | www.plosone.org
33. Brzozowski AM, Pike AC, Dauter Z, Hubbard RE, Bonn T, et al. (1997)
Molecular basis of agonism and antagonism in the oestrogen receptor. Nature
389: 753–758.
34. Warnmark A, Treuter E, Gustafsson JA, Hubbard RE, Brzozowski AM, et al.
(2002) Interaction of transcriptional intermediary factor 2 nuclear receptor box
peptides with the coactivator binding site of estrogen receptor alpha. J Biol
Chem 277: 21862–21868.
35. Shiau AK, Barstad D, Loria PM, Cheng L, Kushner PJ, et al. (1998) The
structural basis of estrogen receptor/coactivator recognition and the antagonism
of this interaction by tamoxifen. Cell 95: 927–937.
36. Tanenbaum DM, Wang Y, Williams SP, Sigler PB (1998) Crystallographic
comparison of the estrogen and progesterone receptor’s ligand binding domains.
Proc Natl Acad Sci U S A 95: 5998–6003.
37. Baker ME, Chang DJ (2009) 3D model of amphioxus steroid receptor
complexed with estradiol. Biochem Biophys Res Commun 386: 516–520.
38. Baker ME, Chang DJ, Chandsawangbhuwana C (2009) 3D model of lamprey
estrogen receptor with estradiol and 15alpha-hydroxy-estradiol. PLoS One 4:
e6038.
39. Katzenellenbogen JA (2011) The 2010 Philip S. Portoghese Medicinal
Chemistry Lectureship: addressing the ‘‘core issue’’ in the design of estrogen
receptor ligands. J Med Chem 54: 5271–5282.
40. Seo JW, Comninos JS, Chi DY, Kim DW, Carlson KE, et al. (2006) Fluorinesubstituted cyclofenil derivatives as estrogen receptor ligands: synthesis and
structure-affinity relationship study of potential positron emission tomography
agents for imaging estrogen receptors in breast cancer. J Med Chem 49: 2496–
2511.
41. Celik L, Lund JD, Schiott B (2007) Conformational dynamics of the estrogen
receptor alpha: molecular dynamics simulations of the influence of binding site
structure on protein dynamics. Biochemistry 46: 1743–1758.
42. Manas ES, Unwalla RJ, Xu ZB, Malamas MS, Miller CP, et al. (2004)
Structure-based design of estrogen receptor-beta selective ligands. J Am Chem
Soc 126: 15106–15119.
43. Nettles KW, Bruning JB, Gil G, O’Neill EE, Nowak J, et al. (2007) Structural
plasticity in the oestrogen receptor ligand-binding domain. EMBO Rep 8: 563–
568.
44. DuSell CD, Umetani M, Shaul PW, Mangelsdorf DJ, McDonnell DP (2008) 27hydroxycholesterol is an endogenous selective estrogen receptor modulator. Mol
Endocrinol 22: 65–77.
45. Minutolo F, Macchia M, Katzenellenbogen BS, Katzenellenbogen JA (2011)
Estrogen receptor beta ligands: recent advances and biomedical applications.
Med Res Rev 31: 364–442.
46. Lappano R, Recchia AG, De Francesco EM, Angelone T, Cerra MC, et al.
(2011) The cholesterol metabolite 25-hydroxycholesterol activates estrogen
receptor alpha-mediated signaling in cancer cells and in cardiomyocytes. PLoS
One 6: e16631.
47. Heery DM, Kalkhoven E, Hoare S, Parker MG (1997) A signature motif in
transcriptional co-activators mediates binding to nuclear receptors. Nature 387:
733–736.
48. McKenna NJ, O’Malley BW (2002) Combinatorial control of gene expression by
nuclear receptors and coregulators. Cell 108: 465–474.
49. Smith CL, O’Malley BW (2004) Coregulator function: a key to understanding
tissue specificity of selective receptor modulators. Endocr Rev 25: 45–71.
50. Jeyakumar M, Carlson KE, Gunther JR, Katzenellenbogen JA (2011)
Exploration of dimensions of estrogen potency: parsing ligand binding and
coactivator binding affinities. J Biol Chem 286: 12971–12982.
51. Billon-Gales A, Krust A, Fontaine C, Abot A, Flouriot G, et al. (2011) Activation
function 2 (AF2) of estrogen receptor-alpha is required for the atheroprotective
action of estradiol but not to accelerate endothelial healing. Proc Natl Acad
Sci U S A 108: 13311–13316.
52. McInerney EM, Rose DW, Flynn SE, Westin S, Mullen TM, et al. (1998)
Determinants of coactivator LXXLL motif specificity in nuclear receptor
transcriptional activation. Genes Dev 12: 3357–3368.
53. Voegel JJ, Heine MJ, Tini M, Vivat V, Chambon P, et al. (1998) The
coactivator TIF2 contains three nuclear receptor-binding motifs and mediates
transactivation through CBP binding-dependent and -independent pathways.
EMBO J 17: 507–519.
54. Hall JM, McDonnell DP, Korach KS (2002) Allosteric regulation of estrogen
receptor structure, function, and coactivator recruitment by different estrogen
response elements. Mol Endocrinol 16: 469–486.
55. Hall JM, Korach KS (2002) Analysis of the molecular mechanisms of human
estrogen receptors alpha and beta reveals differential specificity in target
promoter regulation by xenoestrogens. J Biol Chem 277: 44455–44461.
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