The respiratory supercomplex from C. glutamicum.

Corynebacterium glutamicum is a preferentially aerobic gram-positive bacterium belonging to the phylum Actinobacteria, which also includes the pathogen Mycobacterium tuberculosis. In these bacteria, respiratory complexes III and IV form a CIIICIV supercomplex that catalyzes oxidation of menaquinol and reduction of dioxygen to water. 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 dimer flanked by a CIV on two sides. A menaquinone is bound in each of the Q and Q sites in each CIII and an additional menaquinone is positioned ∼14 Å from heme b. A di-heme cyt. cc subunit electronically connects each CIII with an adjacent CIV, with the Rieske iron-sulfur protein positioned with the iron near heme b. Multiple subunits interact to form a convoluted sub-structure at the cytoplasmic side of the supercomplex, which defines a path for proton transfer into CIV.