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Nature. 2018 May;557(7703):123-126. doi: 10.1038/s41586-018-0061-y. Epub 2018 Apr 25.

Structure of the alternative complex III in a supercomplex with cytochrome oxidase.

Author information

1
Department of Biochemistry, University of Illinois, Urbana, IL, USA.
2
NIH Center for Macromolecular Modeling and Bioinformatics, Beckman Institute for Advanced Science and Technology, University of Illinois, Urbana, IL, USA.
3
Molecular Medicine Program, The Hospital for Sick Children Research Institute, Toronto, Ontario, Canada.
4
Department of Microbiology and Molecular Genetics, University of California, Davis, Davis, CA, USA.
5
Center for Biophysics and Quantitative Biology, University of Illinois, Urbana, IL, USA.
6
Department of Biochemistry, University of Mississippi Medical Center, Jackson, MS, USA.
7
Department of Biochemistry, University of Illinois, Urbana, IL, USA. emad@life.illinois.edu.
8
NIH Center for Macromolecular Modeling and Bioinformatics, Beckman Institute for Advanced Science and Technology, University of Illinois, Urbana, IL, USA. emad@life.illinois.edu.
9
Center for Biophysics and Quantitative Biology, University of Illinois, Urbana, IL, USA. emad@life.illinois.edu.
10
Molecular Medicine Program, The Hospital for Sick Children Research Institute, Toronto, Ontario, Canada. john.rubinstein@utoronto.ca.
11
Department of Medical Biophysics, The University of Toronto, Toronto, Ontario, Canada. john.rubinstein@utoronto.ca.
12
Department of Biochemistry, The University of Toronto, Toronto, Ontario, Canada. john.rubinstein@utoronto.ca.
13
Department of Biochemistry, University of Illinois, Urbana, IL, USA. r-gennis@illinois.edu.

Abstract

Alternative complex III (ACIII) is a key component of the respiratory and/or photosynthetic electron transport chains of many bacteria1-3. Like complex III (also known as the bc1 complex), ACIII catalyses the oxidation of membrane-bound quinol and the reduction of cytochrome c or an equivalent electron carrier. However, the two complexes have no structural similarity4-7. Although ACIII has eluded structural characterization, several of its subunits are known to be homologous to members of the complex iron-sulfur molybdoenzyme (CISM) superfamily 8 , including the proton pump polysulfide reductase9,10. We isolated the ACIII from Flavobacterium johnsoniae with native lipids using styrene maleic acid copolymer11-14, both as an independent enzyme and as a functional 1:1 supercomplex with an aa3-type cytochrome c oxidase (cyt aa3). We determined the structure of ACIII to 3.4 Å resolution by cryo-electron microscopy and constructed an atomic model for its six subunits. The structure, which contains a [3Fe-4S] cluster, a [4Fe-4S] cluster and six haem c units, shows that ACIII uses known elements from other electron transport complexes arranged in a previously unknown manner. Modelling of the cyt aa3 component of the supercomplex revealed that it is structurally modified to facilitate association with ACIII, illustrating the importance of the supercomplex in this electron transport chain. The structure also resolves two of the subunits of ACIII that are anchored to the lipid bilayer with N-terminal triacylated cysteine residues, an important post-translational modification found in numerous prokaryotic membrane proteins that has not previously been observed structurally in a lipid bilayer.

PMID:
29695868
PMCID:
PMC6004266
DOI:
10.1038/s41586-018-0061-y
[Indexed for MEDLINE]
Free PMC Article

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