Figure 4.

Binding properties and transcriptional features of BPAF and BPC showed the importance of ERβ W335 for their receptor binding and activation. A, detailed competitive binding curves of BPA, BPAF, BPC, and 4OHT using [³H]4OHT illustrated a diphasic binding curve, in which chemicals compete with [³H]4OHT in two binding sites on WT ERβ. B, ERβ(W335A) competitive binding assays showed typical sigmoidal binding curves. C, the reporter gene assay indicated that BPAF and BPC induced weak transcriptional activity in WT ERβ, whereas E2 and BPA showed strong transcriptional activity. D, ERβ(W335A) lost E2 or BPA-induced transcriptional activity, indicating that Trp335 substitution disrupted active conformation. E, in ERβ agonist form, amino acid residues surrounding Trp335 within 4.5 Å are represented as green and purple stick models. (PDB ID: 3OLL). [³H]4OHT, tritium-labeled 4OHT; BPAF, 2,2-Bis(4-hydroxyphenyl)hexafluoropropane; BPC, bisphenol C; E2, 17-β estradiol; ERs, estrogen receptors.