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Figure 3
Rieske domain (red) in the b position. (a) shows the cryo-EM density of the ISP. The hinge (black arrowhead) extended when atovaquone was bound (Darrouzet et al., 2000BB16; Birth et al., 2014BB5). When the high-potential chain was reduced by ascorbate, density at the hinge and the surface (black square) of the Rieske domain was weak, indicating local heterogeneity despite strong density for the [2Fe–2S] cluster (yellow) and the surrounding tip region. When the high-potential chain was oxidized with ferricyanide, the hinge rigidified and turned into an α-helix. Details of the docking crater, which is formed by cyt b (light green), are depicted in (b) with density for the Qo site. Atovaquone induced tight docking of the Rieske domain, as shown by strong density for the Rieske domain in (a) and close interaction of the tip of the Rieske domain with the docking crater and atovaquone in (b). When CIII2 was reduced with ascorbate, the Rieske domain was within hydrogen-bonding distance of cyt b and potential Qo-site occupants. Density in the Qo site, in a similar position to atovaquone, increased when decylubiquinone was added together with ascorbate. The Rieske domain was beyond hydrogen-bonding distance to cyt b in the b positions that were observed with an oxidized high-potential chain (+FCN) and also the other tested conditions (Supplementary Fig. S4). For better visualization, a positive B factor of +10 Å2 was applied to limit the map resolution. Exemplary maps coloured by local resolution are shown in Supplementary Fig. S5.

ISSN: 2052-2525