Fig. 2: Molecular mechanism of AdTx1’s antagonist activity.

a Structure comparison of the AdTx1-bound α_1AAR structure (orange) with the tamsulosin-bound inactive state α_1AAR structure (gray, PDB code: 7YMJ) and the oxymetazoline-bound active state α_1AAR structure (green, PDB code: 7YM8). Finger loop 1 and finger loop 2 of AdTx1 prevent the inward movement of TM6 and TM7, which are required for the α_1AAR activation (orange rectangle). AdTx1 binding causes a more outward conformation of TM7 (orange arrow) and stabilizes the PIF motif at the inactive conformation (cyan rectangle). b Mutating finger loop 1 (K7A, S8A, and I9A) has the largest effect on AdTx1 function in a ³H prazosin competition binding assay, mutating finger loop 2 (Y30A, V32A, and K34A) also reduced AdTx1 function, while mutating finger loop 3 (Y52A and S54A) does not have much effect on AdTx1 function. Data are given as means ± SEM of 6 independent samples. c Compared to tamsulosin-bound inactive α_1AAR, conformational changes of F308^7.35, F312^7.39 are observed upon AdTx1 binding. d K34 at the finger loop 2 of AdTx1 directly interacts with D106^3.32 and distorts the conformation of D106^3.32, thus altering the shape of the orthosteric pocket of α_1AAR. V32 at the finger loop 2 of AdTx1 extrudes the F308^7.35, leading to the outward movement of TMs 6 and 7 of α_1AAR. Compared to the oxymetazoline-bound active α_1AAR, conformational changes of F288^6.51, F308^7.35, F312^7.39, and W285^6.48 are observed upon AdTx1 binding. e K34A mutation impairs the function of AdTx1 in a ³H prazosin competition binding assay. Data are given as means ± SEM of 6 independent samples.