Figure 4.

Modular exchange of the EcR LBD for the ER^T2 LBD reprograms the VgEcR scaffold to respond to ER ligands. (a) Schematic of the LBD replacement strategy for obtaining VgER^T2/RXR (created with BioRender.com). (b) The engineered VgER^T2/RXR pair activates luciferase reporter expression in response to the ER ligands 17β-estradiol (E2), 17α-ethynylestradiol (EE2), and 4-hydroxytamoxifen (4OHT) in co-transfected HEK293 cells (n ≥ 5). (c) A simultaneously present RXR agonist (BEX) can boost 4OHT-activated and E2-activated responses for VgER^T2/RXR, while having little effect on its own (n = 9). The data points at 10 μM were excluded from the curve fits due to the slight drop-off in reporter levels under these conditions. Curve fits represent a three-parameter dose–response curve (Methods). Error bars represent standard deviation.