a, Inhibition of serotonin uptake by ibogaine or noribogaine for ts2. The mean IC 50 of ibogaine and noribogaine inhibition of serotonin transport was determined from the curve with the error of the fit (s.e.m.) (black circles, ibogaine IC 50 : 7 ± 2 µM; noribogaine IC 50 : 1.1 ± 0.7 µM), N177L (blue circles, 1 ± 1 µM; 40 ± 10 µM), N177V (green triangles, 0.17 ± 0.04 µM; 24 ± 5 µM), N177A (red squares, 0.6 ± 0.3 µM; 300 ± 200 µM), N177T (cyan diamonds, 1.0 ± 0.2 µM; 8 ± 2 µM), and N177Q (magenta inverted triangles, 1.1 ± 0.7 µM; 1.0 ± 0.5 µM). Data are mean ± s.e.m. (n = 6 and n = 3 biological replicates for ibogaine and noribogaine, respectively). The experiment was performed three times independently with the same results. b, Comparison of EL4 and TM1b in the X-ray structure of the ts3–paroxetine complex (PDB code: 5I6X, purple)28 and the cryo-EM structure of the ts2 active–ibogaine complex in outward-open conformation (grey). Residues Tyr110 (ts2-active) and Ala110 (ts3) are shown in sticks. c, Comparison of the TM helices of the outward-open (grey), occluded (orange), and inward-open (blue) conformations viewed from the extracellular side of the membrane. The positions of TM2, TM4, TM5 and TM12 for each conformation are shown (middle). Right, the helical displacement measured from marker positions in each TM to a position in TM3 (Tyr186); from the outward-open to the occluded conformation (filled circles) and from the occluded to the inward-open conformation (open circles). The TM marker positions are described further in the Methods section ‘Measurements’. Error bars represent the s.d. d, Comparison of the TM helices viewed from the intracellular side of the membrane. The positions of TM5, TM9, TM11 and TM12 for each conformation are shown (middle). Right, the helical displacement measured from marker positions in each TM to a position in TM3 (Gly160); from the outward-open to the occluded conformation (filled circles) and from the occluded to the inward-open conformation (open circles). Error bars represent the s.d. e, Angular changes of TMs associated with transition from the outward-open to the occluded conformation (filled circles) and from the occluded to the inward-open conformation (open circles). Error bars represent the s.d. f, The intracellular region of TM5 ‘unwinds’ in the inward-open conformation. Gly278 and Pro288 in the GX 9 P motif are shown in sticks. g, Alignment of TM5 of SERT, dopamine transporter (DAT) and noradrenaline transporter (NET) with LeuT and MhsT. The position of the GX 9 P motif is indicated. h, Comparison of EL3, EL4 and EL6 in the outward-open (grey), the occluded (orange) and the inward-open (blue) conformations.