Differential estrogen receptor binding of estrogenic substances: a speciescomparison

The study investigated the ability of 34 natural and synthetic chemicals to compete with [H-3]17 beta -estradiol (E2) for binding to bacterially expre ssed glutathione-S-transferase (GST)-estrogen receptors (ER) fusion protein s from five different species. Fusion proteins consisted of the ER D, E and F domains of human alpha (GST-hER alpha def), mouse alpha (GST-mER alpha d ef), chicken (GST-cERdef), green anole (GST-aERdef) and rainbow trout ERs ( GST-rtERdef). All five fusion proteins displayed high affinity for E2 with dissociation constants (K-d) ranging from 0.3 to 0.9 nM. Although, the fusi on proteins exhibited similar binding preferences and binding affinities fo r many of the chemicals, several differences were observed. For example, al pha -zearalenol bound with greater affinity to GST-rtERdef than E2, which w as in contrast to other GST-ERdef fusion proteins examined. Coumestrol, gen istein and naringenin bound with higher affinity to the GST-aERdef, than to the other GST-ERdef fusion proteins. Many of the industrial chemicals exam ined preferentially bound to GST-rtERdef. Bisphenol A, 4-t-octylphenol and o,p' DDT bound with approximately a ten-fold greater affinity to GST-rtERde f than to other GST-ERdefs. Methoxychlor, p,p'-DDT, o,p'-DDE, p,p'-DDE, alp ha -endosulfan and dieldrin weakly bound to the ERs from the human, mouse, chicken and green anole. In contrast, these compounds completely displaced [H-3]E2 from GST-rtERdef. These results demonstrate that ERs from different species exhibit differential ligand preferences and relative binding affin ities for estrogenic compounds and that these differences may be due to the variability in the amino acid sequence within their respective ER ligand b inding domains. (C) 2000 Elsevier Science Ltd. All rights reserved.