Fine spatial assembly for construction of the phenol-binding pocket to capture bisphenol A in the human nuclear receptor estrogen-related receptor γ

Various lines of evidence have shown that bisphenol A (BPA) acts as an endocrine disruptor that affects various hormones even at merely physiological levels. We demonstrated recently that BPA binds strongly to human nuclear receptor estrogen-related receptor gamma (ERR gamma), one of 48 nuclear receptors. Based on X-ray crystal analysis of the ERR gamma ligand-binding domain (LBD)/BPA complex, we demonstrated that ERR gamma receptor residues, Glu275 and Arg316, function as the intrinsic-binding site of the phenol-hydroxyl group of BPA. If these phenol-hydroxyl <-> Glu275 and Arg316 hydrogen bonds anchor the A-benzene ring of BPA, the benzene-phenyl group of BPA would be in a pocket constructed by specific amino acid side chain structures. In the present study, by evaluating the Ala-replaced mutant receptors, we identified such a ligand-binding pocket. Leu268, Leu271, Leu309 and Tyr326, in addition to the previously reported participants Glu275 and Arg316, were found to make a receptacle pocket for the A-ring, whereas Ile279, Ile310 and Val313 were found to assist or structurally support these residues. The results revealed that each amino acid residue is an essential structural element for the strong binding of BPA to ERR gamma.