Abstract
The crystal structure of a triple cysteine to serine mutant ERalpha ligand-binding domain (LBD), complexed with estradiol, shows that despite the presence of a tightly bound agonist ligand, the protein exhibits an antagonist-like conformation, similar to that observed in raloxifen and 4-hydroxytamoxifen-bound structures. This mutated receptor binds estradiol with wild type affinity and displays transcriptional activity upon estradiol stimulation, but with limited potency (about 50%). This partial activity is efficiently repressed in antagonist competition assays. The comparison with available LBD structures reveals key features governing the positioning of helix H12 and highlights the importance of cysteine residues in promoting an active conformation. Furthermore the present study reveals a hydrogen bond network connecting ligand binding to protein trans conformation. These observations support a dynamic view of H12 positioning, where the control of the equilibrium between two stable locations determines the partial agonist character of a given ligand.
Highlights
Steroid hormones regulate the transcription of target genes in the cell by binding to transcription regulators that belong to the superfamily of nuclear receptors
The present study reveals a hydrogen bond network connecting ligand binding to protein trans conformation
We present the comparison of the wild type hER␣ ligand-binding domain (LBD) crystal structure [16] with that of a mutant protein complexed with estradiol, where three cysteine residues were mutated in serine
Summary
Steroid hormones regulate the transcription of target genes in the cell by binding to transcription regulators that belong to the superfamily of nuclear receptors. In most antagonist-bound complexes [11, 12], H12 has been observed positioned in a structurally conserved cleft where the LXXLL motif of the coactivator molecule binds. In the structure of the Cys 3 Ser triple mutant hER␣ LBD, we observed an antagonist conformation despite the presence of a tightly bound estradiol in the ligand-binding cavity. This antagonist conformation, together with the transcriptional activity of the single, double, and triple cysteine to serine mutant receptors, supports the view of the agonist-antagonist equilibrium of H12 and gives some insight into the molecular mechanism for the conformational switch that drives the receptor in an agonist or antagonist conformation
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
