The respiratory supercomplex from C. glutamicum

Corynebacterium glutamicum is a preferentially aerobic Gram-positive bacterium belonging to the Actinobacteria phylum, which also includes the pathogen Mycobacterium tuberculosis . In the respiratory chain of these bacteria, complexes III (CIII) and IV (CIV) form a CIII 2 CIV 2 supercomplex that catalyzes oxidation of menaquinol and reduction of dioxygen to water. Electron transfer within the CIII 2 CIV 2 supercomplex is linked to transmembrane proton translocation, which maintains an electrochemical proton gradient that drives ATP synthesis and transport processes. We isolated the C. glutamicum supercomplex and used cryo-EM to determine its structure at 2.9 Å resolution. The structure shows a central CIII 2 dimer flanked by a CIV on each side. One menaquinone is bound in each of the Q N and Q P sites in each CIII, near the cytoplasmic and periplasmic sides, respectively. In addition, we identified a menaquinone positioned ~14 Å from heme b L on the periplasmic side. A di-heme cyt. cc subunit provides an electronic connection between each CIII monomer and the adjacent CIV. In CIII 2 , the Rieske iron-sulfur (FeS) proteins are positioned with the iron near heme b L . Multiple subunits interact to form a convoluted sub-structure at the cytoplasmic side of the supercomplex, which defines a novel path that conducts protons into CIV.