Fig. 5: P. denitrificans CI is in a homogeneous closed state.

a The conformations of the loops that form the ubiquinone-binding site and the location of the bound ubiquinone-10 in the lower section of the channel. b Cryo-EM densities for key structural elements that define the closed state. c The ubiquinone-binding site (determined by CASTp analysis) is closed and sealed from the cytoplasm (shown from the same orientation as panel a). d The corner between the hydrophilic and hydrophobic domains showing the N-terminus of NDUFS2 and the bound Ca²⁺ ion. e Coordination of the corner bound Ca²⁺ ion and the packing of surrounding subunits; locations of three additional bound Ca²⁺ are also indicated.