Abstract
Recombinant expression of the aryl hydrocarbon receptor (AhR) yields small amounts of ligand-binding-competent AhR. Therefore,
Spodoptera frugiperda (
Sf9) cells and baculovirus have been evaluated for high-level and functional expression of AhR. Rat and human AhR were expressed as soluble protein in significant amounts. Expression of ligand-binding-competent AhR was sensitive to the protein concentration of
Sf9 extract, and coexpression of the chaperone p23 failed to affect the yield of functional ligand-binding AhR. The expression system yielded high levels of functional protein, with the ligand-binding capacity (
B
max) typically 20-fold higher than that obtained with rat liver cytosol. Quantitative estimates of the ligand-binding affinity of human and rat AhR were obtained; the
K
d for recombinant rat AhR was indistinguishable from that of native rat AhR, thereby validating the expression system as a faithful model for native AhR. The human AhR bound TCDD with significantly lower affinity than the rat AhR. These findings demonstrate high-level expression of ligand-binding-competent AhR, and sufficient AhR for quantitative analysis of ligand binding.