Data Supplement

• Supplemental Figures -

  Supplemental Figure S1. Structures of the endogenous neurosteroid 3α-hydroxy-5β-pregnan-20-one (3α5βP, top) and the synthetic neuroactive steroid 3α-hydroxy-5α-androstane-17β-carbonitrile (ACN, bottom).

  Supplemental Figure S2. The figure shows a side view of the transmembrane domains (TMD) of one α (khaki) and one β (light blue) subunit, viewed from the lipid membrane.

  Supplemental Figure S3. The figure shows the external end of the TMDs of all 5 subunits (α khaki, β light blue and γ cyan) viewed from the extracellular fluid.

  Supplemental Figure S4. The figure shows the internal end of the TMDs of all 5 subunits (α khaki, β light blue and γ cyan) viewed from the cytoplasm.