Fig. 3.

The O_o and I_f conformations differ by local twisting of TM5. a In the O_o state, TM5 (green) in the N-terminal domain is partially distorted, resulting in Cα displacements compared to the I_f state of up to 2.9 Å (Met146^TM5). The side chain of Met146^TM5 rests against the phenolic side chain of Tyr127^TM4, whose hydroxyl moiety is ca. 2.5 Å from the side chain carboxylate group of Glu26^TM1. b TM5 adopts an almost ideal α-helical conformation in the I_f state through displacement of the Tyr127^TM4 side chain by that of Met146^TM5. TM5 straightens, rotating around its axis such that its hydrophobic side chains can engage/disengage the C-terminal domain. c Electron density for TM5 in the O_o conformation, superimposed with coordinates of the final (green) and initial (orange) models. See also Supplementary Fig. 3 and Supplementary Movie