Figure 5. Individual roles of the two β+/α− interfaces in channel modulation by compounds 31, 132 and 4-O-methylhonokiol.

(a) Scheme showing the four concatenated wild-type and mutant receptors. 1 and 2 refer to the two different β+/α− subunit interfaces, interface 1 and interface 2. The location of the β₂N265I mutations is indicated in red color. Concatenated receptors were prepared containing no mutation (α₁-β₂-α₁/γ₂-β₂, non M), a mutation at interface 1 (α₁-β₂-α₁/γ₂-β₂M, interface 1 M), a mutation at interface 2 (α₁-β₂M-α₁/γ₂-β₂, interface 2 M), or mutations in both sites (α₁-β₂M-α₁/γ₂-β₂M, double M). Interface 2 harbors a binding site for GABA with higher apparent affinity for channel gating than the one positioned at the interface 1⁵⁴. (b) Potentiation by compound 31 (3 μM), compound 132 (3 μM), and 4-O-methylhonokiol (1 μM), using an EC_0.5–1.5 concentration of GABA for each concatenated receptor subtype. Bars indicate mean ± SD, n = 3.