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 CIII 2 CIV 2 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 2 dimer flanked by a CIV on two sides. A menaquinone is bound in each of the Q N and Q P sites in each CIII and an additional menaquinone is positioned ∼14 Å from heme b L . 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 L . 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.