A portable site: a binding element for 17β-estradiol can be placed on any subunit of a nicotinic α4β2 receptor

Endogenous steroids can modulate the activity of transmitter-gated channels by directly interacting with the receptor. 17β-Estradiol potentiates activation of neuronal nicotinic α4β2 receptors by interacting with a 4 aa sequence at the extreme C terminus of the α4 subunit, but it is not known whether potentiation requires that the sequence be placed on a specific subunit (e.g., an α4 subunit that is involved in forming an acetylcholine-binding site). By using concatemers of subunits and chimeric subunits, we have found that the C-terminal domain can be moved from the α4 to the β2 subunit and still result in potentiation. In addition, the sequence can be placed on a subunit that contributes to an acetylcholine-binding site or on the structural subunit. The data indicate that this estradiol-binding element is a discrete sequence and suggest that the effect of 17β-estradiol is mediated by actions on single subunits and that the overall consequences for gating occur because of the summation of independent energetic contributions to overall gating of this receptor.