Cryo-EM structures of engineered active bc1-cbb3 type CIII2CIV super-complexes and electronic communication between the complexes

Nat Commun. 2021 Feb 10;12(1):929. doi: 10.1038/s41467-021-21051-4.


Respiratory electron transport complexes are organized as individual entities or combined as large supercomplexes (SC). Gram-negative bacteria deploy a mitochondrial-like cytochrome (cyt) bc1 (Complex III, CIII2), and may have specific cbb3-type cyt c oxidases (Complex IV, CIV) instead of the canonical aa3-type CIV. Electron transfer between these complexes is mediated by soluble (c2) and membrane-anchored (cy) cyts. Here, we report the structure of an engineered bc1-cbb3 type SC (CIII2CIV, 5.2 Å resolution) and three conformers of native CIII2 (3.3 Å resolution). The SC is active in vivo and in vitro, contains all catalytic subunits and cofactors, and two extra transmembrane helices attributed to cyt cy and the assembly factor CcoH. The cyt cy is integral to SC, its cyt domain is mobile and it conveys electrons to CIV differently than cyt c2. The successful production of a native-like functional SC and determination of its structure illustrate the characteristics of membrane-confined and membrane-external respiratory electron transport pathways in Gram-negative bacteria.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Bacterial Proteins / chemistry*
  • Bacterial Proteins / genetics
  • Bacterial Proteins / metabolism*
  • Catalytic Domain
  • Coenzymes / chemistry
  • Coenzymes / metabolism
  • Cryoelectron Microscopy
  • Electron Transport
  • Electron Transport Complex III / chemistry*
  • Electron Transport Complex III / genetics
  • Electron Transport Complex III / metabolism*
  • Electron Transport Complex IV / chemistry*
  • Electron Transport Complex IV / genetics
  • Electron Transport Complex IV / metabolism*
  • Genetic Engineering
  • Rhodobacter capsulatus / chemistry
  • Rhodobacter capsulatus / enzymology*
  • Rhodobacter capsulatus / genetics
  • Rhodobacter capsulatus / metabolism


  • Bacterial Proteins
  • Coenzymes
  • cbb3 oxidase
  • Electron Transport Complex IV
  • Electron Transport Complex III