Fig. 7: Mechanistic insights into Arabidopsis complex III2.
a, Overview of complex III cofactors involved in respiratory electron transport. Each monomer binds haems c1, bH, bL (red), a Rieske FeS cluster (orange) and a Q (magenta) at the reduction/oxidation site (Qi and Qo). In both monomers of complex III2, the Rieske head domain (dark red) is found in the b state. Complex III monomers proximal or distal to the ubiquinone binding site of complex I (C1-Q) are shown in different shades of pink divided by a black dotted line. Distances between the cofactors are shown for the distal complex III monomer. Distances from Qi and Qo to the quinol binding site in complex I (C1-Q) are shown for the proximal monomer. b, Detailed view of the proximal Qo site. Hydrogen network for release of the two protons during ubiquinol oxidation at the Qo site are shown by black dotted lines. One proton is transferred along a chain of water molecules (light red) via Cyt b Y280 and H259; the other can be transferred directly to H237 of the Rieske head domain. The three participating sidechains are indicated by black ellipses. Cyt b E278 (grey) may be involved in proton translocation, faces away from the bound native Q and is not part of a proton pathway (grey dotted lines). Red arrows indicate routes for proton release to the bulk solvent of the cristae lumen. For further details, see Extended Data Figs. 8 and 9.
