ALBERT

Description: Background: Resveratrol, a naturally occurring stilbene, has been categorized as phytoestrogen due to its capability to compete with natural estrogens for binding to estrogen receptor alpha (ERalpha) and thus modulating the biological responses exerted by the receptor. Biological effects of resveratrol (RES) on estrogen receptor alpha (ERalpha) remain highly controversial, since both estrogenic and anti-estrogenic properties were observed. Results: Here, we provide insight into the structural basis of the agonist/antagonist effects of RES on ERalpha ligand binding domain (LBD). Using atomistic simulation, we found that RES bound ERalpha monomer in antagonist conformation, where Helix 12 moves away from the ligand pocket and orients into the co-activator binding groove of LBD, is more stable than RES bound ERalpha in agonist conformation, where Helix 12 lays over the ligand binding pocket. Upon dimerization, the agonistic conformation of RES-ERalpha dimer becomes more stable compared to the corresponding monomer but still remains less stable compared to the corresponding dimer in antagonist conformation. Interestingly, while the binding pocket and the binding contacts of RES to ERalpha are similar to those of pure agonist diethylstilbestrol (DES), the binding energy is much less and the hydrogen bonding contacts also differ providing clues for the partial agonistic character of RES on ERalpha. Conclusions: Our Molecular Dynamics simulation of RES-ERalpha structures with agonist and antagonist orientations of Helix 12 suggests RES action is more similar to Selective Estrogen Receptor Modulator (SERM) opening up the importance of cellular environment and active roles of co-regulator proteins in a given system. Our study reveals that potential co-activators must compete with the Helix 12 and displace it away from the activator binding groove to enhance the agonistic activity.