Figure 1. The conformational space of TmrAB.

a, Two distinct IF conformations from TmrAB_turnover. In IF^wide, the intracellular gate has opened by 4.4 Å, allowing access for bulky substrates. Wide and narrow IF conformations were also found in the control datasets and in absence of nucleotides and/or substrate. Densities for nucleotides were observed in all IF conformations in TmrAB_turnover and TmrA^EQB_ATP-ADP datasets, but not in TmrAB_apo and TmrAB_C4F, as no nucleotides were added in the latter cases. b, In the ATP-bound state, the NBDs are tightly dimerized and the exporter exhibits either an OF^open or OF^occluded conformation. The same two OF conformations are observed in both TmrA^EQB_ATP and TmrA^EQB_ATP-ADP datasets (E523Q mutation in TmrA); therefore, only maps from TmrA^EQB_ATP-ADP are shown here due to the higher resolution. c, OF^open and OF^occluded conformations also dominate in the vanadate-trapped state. d, The asymmetric states from TmrAB_turnover resemble an OF^occluded conformation with a slightly separated NBD interface. In contrast to the OF^occluded conformations of TmrA^EQB_ATP-ADP and TmrAB_ATP-Vi, the intracellular gate is opened by 1.5 Å and 3.0 Å in UR^asym and UR^asym*, respectively, while the extracellular gate is tightly sealed. The top and bottom rows show experimental maps and deposited models, respectively. OF densities and models in b and c are rotated by 90° with respect to panel a and d to illustrate the opening of the extracellular gate. TmrA is blue, TmrB yellow, and the nanobody light grey. All structures and morphs between conformers are highlighted in the Supplementary Video 1 and 2.