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Structural and functional profiling of environmental ligands for estrogen receptors.

Delfosse V, Grimaldi M, Cavaillès V, Balaguer P, Bourguet W - Environ. Health Perspect. (2014)

Bottom Line: However, most of these compounds are chemically unrelated to natural hormones, so their binding modes and associated hormonal activities are hardly predictable.We observed xenoestrogens binding to both ERs-with affinities ranging from subnanomolar to micromolar values-and acting in a subtype-dependent fashion as full agonists or partial agonists/antagonists by using different combinations of the activation functions 1 and 2 of ERα and ERβ.The precise characterization of the interactions between major environmental pollutants and two of their primary biological targets provides rational guidelines for the design of safer chemicals, and will increase the accuracy and usefulness of structure-based computational methods, allowing for activity prediction of chemicals in risk assessment.

View Article: PubMed Central - PubMed

Affiliation: Inserm (Institut national de la santé et de la recherche médicale) U1054, Montpellier, France.

ABSTRACT

Background: Individuals are exposed daily to environmental pollutants that may act as endocrine-disrupting chemicals (EDCs), causing a range of developmental, reproductive, metabolic, or neoplastic diseases. With their mostly hydrophobic pocket that serves as a docking site for endogenous and exogenous ligands, nuclear receptors (NRs) can be primary targets of small molecule environmental contaminants. However, most of these compounds are chemically unrelated to natural hormones, so their binding modes and associated hormonal activities are hardly predictable.

Objectives: We conducted a correlative analysis of structural and functional data to gain insight into the mechanisms by which 12 members of representative families of pollutants bind to and activate the estrogen receptors ERα and ERβ.

Methods: We used a battery of biochemical, structural, biophysical, and cell-based approaches to characterize the interaction between ERs and their environmental ligands.

Results: Our study revealed that the chemically diverse compounds bound to ERs via varied sets of protein-ligand interactions, reflecting their differential activities, binding affinities, and specificities. We observed xenoestrogens binding to both ERs-with affinities ranging from subnanomolar to micromolar values-and acting in a subtype-dependent fashion as full agonists or partial agonists/antagonists by using different combinations of the activation functions 1 and 2 of ERα and ERβ.

Conclusions: The precise characterization of the interactions between major environmental pollutants and two of their primary biological targets provides rational guidelines for the design of safer chemicals, and will increase the accuracy and usefulness of structure-based computational methods, allowing for activity prediction of chemicals in risk assessment.

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Related in: MedlinePlus

Xenoestrogens use diverse binding modes. (A) The entire structure of the ERα LBD in complex with E2 and SRC-1 coactivator peptide (yellow); the structure shows the AF‑2 surface formed by helices H3, H5, and H12 (green), and the lower part of the LBD (blue) encloses the ligand-binding pocket (LBP). (B–E) Interaction networks of BP-2 (B; pink), α-ZA (C; orange), ferutinine (D; green), and butylparaben (E; purple) with residues of the LBP compared with that of E2 (gray). In (E), red dashed lines represent the interactions lost in the butylparaben complex structure. (F) HPTE and DDE adopt the orientation previously observed for BPC allowing HPTE to interact with residue T347. This position results in the disruption of the hydrophobic network involving helices H3 and H11 and the loop preceding H12, thereby destabilizing the AF‑2 surface. Color code: red, oxygen; blue, nitrogen; cyan, carbon; yellow, sulfur; green, chlorine; dashed lines, hydrogen bonds and hydrophobic interactions.
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f4: Xenoestrogens use diverse binding modes. (A) The entire structure of the ERα LBD in complex with E2 and SRC-1 coactivator peptide (yellow); the structure shows the AF‑2 surface formed by helices H3, H5, and H12 (green), and the lower part of the LBD (blue) encloses the ligand-binding pocket (LBP). (B–E) Interaction networks of BP-2 (B; pink), α-ZA (C; orange), ferutinine (D; green), and butylparaben (E; purple) with residues of the LBP compared with that of E2 (gray). In (E), red dashed lines represent the interactions lost in the butylparaben complex structure. (F) HPTE and DDE adopt the orientation previously observed for BPC allowing HPTE to interact with residue T347. This position results in the disruption of the hydrophobic network involving helices H3 and H11 and the loop preceding H12, thereby destabilizing the AF‑2 surface. Color code: red, oxygen; blue, nitrogen; cyan, carbon; yellow, sulfur; green, chlorine; dashed lines, hydrogen bonds and hydrophobic interactions.

Mentions: The structures display the canonical active conformation, with helix H12 capping the ligand-binding pocket (LBP) and the SRC-1 peptide bound to the “AF-2 surface” formed by helices H3, H5, and H12 (Figure 4A). Most compounds could be precisely placed in their respective electron density, revealing different binding modes (Figure 2). Some ligands, such as BP-2, α-ZA, BPA, and TCBPA, adopted a binding mode reminiscent of that used by E2, with two phenol groups hydrogen-bonded to three polar residues located at the two ends of the LBP, namely H524 (H11) on one side and E353 (H3) and R394 (H6) on the other side. However, we also noticed significant differences in the geometry of the interactions between H524, E353, R394, and the hydroxyl moieties of E2 and the ligands with possible functional and/or binding implications. Indeed, none of the compounds recapitulated the exact hydrogen bond network seen in the E2-containing complex. The remaining contacts involved essentially van der Waals interactions, the number of which varies from one compound to another and accounts in part for the various binding affinities of the ligands. Several compounds did not interact with H524 because they lack a second hydroxyl group (ferutinine, 4-OP, butylparaben, and DDE) or because they adopt a position that draws this hydroxyl moiety toward T347 in H3 (BPC, HPTE, and DDE). Finally, two compounds, BBP and chlordecone, were not engaged in any direct interaction with either of these polar residues, the latter being indirectly hydrogen bonded to E353 via water molecules. As shown in Figure 2, the position of DDE could not be precisely determined because of the absence of electron density for some regions of the ligand. This poorly defined electron density reflects a higher dynamic for DDE. Finally, the docking of two BBP molecules with distinct positions was necessary to fully account for the observed electron density, indicating that this molecule can adopt two alternate orientations in the LBP.


Structural and functional profiling of environmental ligands for estrogen receptors.

Delfosse V, Grimaldi M, Cavaillès V, Balaguer P, Bourguet W - Environ. Health Perspect. (2014)

Xenoestrogens use diverse binding modes. (A) The entire structure of the ERα LBD in complex with E2 and SRC-1 coactivator peptide (yellow); the structure shows the AF‑2 surface formed by helices H3, H5, and H12 (green), and the lower part of the LBD (blue) encloses the ligand-binding pocket (LBP). (B–E) Interaction networks of BP-2 (B; pink), α-ZA (C; orange), ferutinine (D; green), and butylparaben (E; purple) with residues of the LBP compared with that of E2 (gray). In (E), red dashed lines represent the interactions lost in the butylparaben complex structure. (F) HPTE and DDE adopt the orientation previously observed for BPC allowing HPTE to interact with residue T347. This position results in the disruption of the hydrophobic network involving helices H3 and H11 and the loop preceding H12, thereby destabilizing the AF‑2 surface. Color code: red, oxygen; blue, nitrogen; cyan, carbon; yellow, sulfur; green, chlorine; dashed lines, hydrogen bonds and hydrophobic interactions.
© Copyright Policy - public-domain
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4256047&req=5

f4: Xenoestrogens use diverse binding modes. (A) The entire structure of the ERα LBD in complex with E2 and SRC-1 coactivator peptide (yellow); the structure shows the AF‑2 surface formed by helices H3, H5, and H12 (green), and the lower part of the LBD (blue) encloses the ligand-binding pocket (LBP). (B–E) Interaction networks of BP-2 (B; pink), α-ZA (C; orange), ferutinine (D; green), and butylparaben (E; purple) with residues of the LBP compared with that of E2 (gray). In (E), red dashed lines represent the interactions lost in the butylparaben complex structure. (F) HPTE and DDE adopt the orientation previously observed for BPC allowing HPTE to interact with residue T347. This position results in the disruption of the hydrophobic network involving helices H3 and H11 and the loop preceding H12, thereby destabilizing the AF‑2 surface. Color code: red, oxygen; blue, nitrogen; cyan, carbon; yellow, sulfur; green, chlorine; dashed lines, hydrogen bonds and hydrophobic interactions.
Mentions: The structures display the canonical active conformation, with helix H12 capping the ligand-binding pocket (LBP) and the SRC-1 peptide bound to the “AF-2 surface” formed by helices H3, H5, and H12 (Figure 4A). Most compounds could be precisely placed in their respective electron density, revealing different binding modes (Figure 2). Some ligands, such as BP-2, α-ZA, BPA, and TCBPA, adopted a binding mode reminiscent of that used by E2, with two phenol groups hydrogen-bonded to three polar residues located at the two ends of the LBP, namely H524 (H11) on one side and E353 (H3) and R394 (H6) on the other side. However, we also noticed significant differences in the geometry of the interactions between H524, E353, R394, and the hydroxyl moieties of E2 and the ligands with possible functional and/or binding implications. Indeed, none of the compounds recapitulated the exact hydrogen bond network seen in the E2-containing complex. The remaining contacts involved essentially van der Waals interactions, the number of which varies from one compound to another and accounts in part for the various binding affinities of the ligands. Several compounds did not interact with H524 because they lack a second hydroxyl group (ferutinine, 4-OP, butylparaben, and DDE) or because they adopt a position that draws this hydroxyl moiety toward T347 in H3 (BPC, HPTE, and DDE). Finally, two compounds, BBP and chlordecone, were not engaged in any direct interaction with either of these polar residues, the latter being indirectly hydrogen bonded to E353 via water molecules. As shown in Figure 2, the position of DDE could not be precisely determined because of the absence of electron density for some regions of the ligand. This poorly defined electron density reflects a higher dynamic for DDE. Finally, the docking of two BBP molecules with distinct positions was necessary to fully account for the observed electron density, indicating that this molecule can adopt two alternate orientations in the LBP.

Bottom Line: However, most of these compounds are chemically unrelated to natural hormones, so their binding modes and associated hormonal activities are hardly predictable.We observed xenoestrogens binding to both ERs-with affinities ranging from subnanomolar to micromolar values-and acting in a subtype-dependent fashion as full agonists or partial agonists/antagonists by using different combinations of the activation functions 1 and 2 of ERα and ERβ.The precise characterization of the interactions between major environmental pollutants and two of their primary biological targets provides rational guidelines for the design of safer chemicals, and will increase the accuracy and usefulness of structure-based computational methods, allowing for activity prediction of chemicals in risk assessment.

View Article: PubMed Central - PubMed

Affiliation: Inserm (Institut national de la santé et de la recherche médicale) U1054, Montpellier, France.

ABSTRACT

Background: Individuals are exposed daily to environmental pollutants that may act as endocrine-disrupting chemicals (EDCs), causing a range of developmental, reproductive, metabolic, or neoplastic diseases. With their mostly hydrophobic pocket that serves as a docking site for endogenous and exogenous ligands, nuclear receptors (NRs) can be primary targets of small molecule environmental contaminants. However, most of these compounds are chemically unrelated to natural hormones, so their binding modes and associated hormonal activities are hardly predictable.

Objectives: We conducted a correlative analysis of structural and functional data to gain insight into the mechanisms by which 12 members of representative families of pollutants bind to and activate the estrogen receptors ERα and ERβ.

Methods: We used a battery of biochemical, structural, biophysical, and cell-based approaches to characterize the interaction between ERs and their environmental ligands.

Results: Our study revealed that the chemically diverse compounds bound to ERs via varied sets of protein-ligand interactions, reflecting their differential activities, binding affinities, and specificities. We observed xenoestrogens binding to both ERs-with affinities ranging from subnanomolar to micromolar values-and acting in a subtype-dependent fashion as full agonists or partial agonists/antagonists by using different combinations of the activation functions 1 and 2 of ERα and ERβ.

Conclusions: The precise characterization of the interactions between major environmental pollutants and two of their primary biological targets provides rational guidelines for the design of safer chemicals, and will increase the accuracy and usefulness of structure-based computational methods, allowing for activity prediction of chemicals in risk assessment.

Show MeSH
Related in: MedlinePlus