Analysis of the conformational heterogeneity of the Rieske iron–sulfur protein in complex III<sub>2</sub>by cryo-EM
Jan-Philip Wieferig, Werner Kühlbrandt
Abstract
Movement of the Rieske domain of the iron–sulfur protein is essential for intramolecular electron transfer within complex III 2 (CIII 2 ) of the respiratory chain as it bridges a gap in the cofactor chain towards the electron acceptor cytochrome c . We present cryo-EM structures of CIII 2 from Yarrowia lipolytica at resolutions up to 2.0 Å under different conditions, with different redox states of the cofactors of the high-potential chain. All possible permutations of three primary positions were observed, indicating that the two halves of the dimeric complex act independently. Addition of the substrate analogue decylubiquinone to CIII 2 with a reduced high-potential chain increased the occupancy of the Q o site. The extent of Rieske domain interactions through hydrogen bonds to the cytochrome b and cytochrome c 1 subunits varied depending on the redox state and substrate. In the absence of quinols, the reduced Rieske domain interacted more closely with cytochrome b and cytochrome c 1 than in the oxidized state. Upon addition of the inhibitor antimycin A, the heterogeneity of the cd 1 -helix and ef -loop increased, which may be indicative of a long-range effect on the Rieske domain.