Fig. 4: Structure of Tt-CII.
From: Structures of Tetrahymena thermophila respiratory megacomplexes on the tubular mitochondrial cristae
a Cryo-EM map (left) and atomic model (right) of Tt-CII colored by individual subunits. b Structural silhouette of Tt-CII, with subunits conserved as in Opisthokonta (left) or ciliate-specific (right) shown in solid surfaces. c Prosthetic groups of Tt-CII. The FeS clusters are shown as atomic spheres and colored by atoms. The FAD, Qp site ubiquinone, an interfacial heme c between Tt-CII and Tt-CIV2, and a cardiolipin molecule in place of the heme b in type A–C SDHs are shown as atomic sticks. Distances between the electron-transporting FAD and FeS clusters are labeled. d Structural superposition of T. thermophila (colored by subunits) and Sus scrofa (colored by different shades of gray, PDB: 1ZOY)24 CIIs’ TM subunits SDHC and SDHD. TMH 1–6 of the classic six-helix bundle of mammalian CII membrane domain are labeled by Roman numbers. The Qp site ubiquinone is shown as an atomic stick with its map density, the cardiolipin in place of the heme b in type A–C SDHs is shown as an atomic stick. e Structural conservation of Tt-CII subunit SDHTT1 (pink) and Tt-CI subunit NDUA9 (gray). NDP group of NDUA9 and the interfacial heme c SDHTT1 with its coordinating residues are shown as atomic sticks.
