Fig. 1: Cyt bcc-aa3 supercomplex.
From: Structural basis for safe and efficient energy conversion in a respiratory supercomplex
a Schematic presentation of energy conversion in the obligate respiratory supercomplex. The cyt bcc complex operates a Q cycle with menaquinol oxidation at the Qo site coupled to proton release to the electropositive membrane side (H+P), and menaquinone reduction at the Qi site with proton uptake from the electronegative membrane side (H+N), linked through bifurcated electron transfer. The oxidase operates as a redox-driven proton pump. Electron transfer routes are mapped on catalytic subunits with redox-active cofactors: QcrB (haem bL, haem bH), QcrA (2Fe-2S cluster, FeS), di-haem QcrC (haem ck, haem cj), CtaC (CuA), CtaD (haem a, haem a3, CuB). The net reaction for reducing one dioxygen molecule is shown. Δp denotes the 200 mV proton motive force of C. glutamicum56. Redox midpoint potentials were taken from the previous study21. b Cryo-EM structure of cyt bcc-aa3 supercomplex. The atomic model of the homodimer is viewed parallel to the membrane shown in transparent surface and superimposed in cartoon representation. Subunits are colour-coded with matching underlined labels. QcrA crosses the dimer and in homology to the mitochondrial cyt bc1 complex, the subunit is assigned to that protomer, in which the transmembrane anchor of the catalytic domain is associated. QcrA´ thus denotes the subunit of the other protomer. Cofactors and selected ligands are shown in the ball-and-stick presentation. P and N denote the periplasmic/electropositive and cytosolic/electronegative side of the membrane, respectively. c 3D reconstruction of supercomplex with dimensions and detergent micelle. P and N denote the electro-positive and -negative sides of the membrane, respectively. The contour level of the experimental map was set to 3.5 root mean square deviation (rmsd).
