bims-resufa 2020-03-08 papers

Issue of 2020–03–08
two papers selected by
Vera Strogolova, Marquette University

Biochim Biophys Acta Bioenerg. 2020 Feb 29. pii: S0005-2728(20)30027-X. [Epub ahead of print] 148177

Timing of dimerization of the bc1 complex during mitochondrial respiratory chain assembly.

The mitochondrial bc1 complex plays an important role in mitochondrial respiration. It transfers electrons from ubiquinol to the soluble electron shuttle cytochrome c and thereby contributes to the proton motive force across the inner mitochondrial membrane. In the yeast Saccharomyces cerevisiae, each monomer consists of three catalytic and seven accessory subunits. The bc1 complex is an obligate homo-dimer in all systems. It is currently not known when exactly during the assembly dimerization occurs. In this study, we determined that the dimer formation is an early event. Specifically, dimerization is mediated by the interaction of a stable tetramer formed by the two Cor subunits, Cor1 and Cor2, that joins assembly intermediate II, containing the fully hemylated cytochrome b and the two small accessory proteins, Qcr7 and Qcr8. Addition of cytochrome c1 and Qcr6 can either occur concomitantly or independently of dimerization. These results reveal a strict order in assembly, where dimerization occurs after stabilization of co-factor acquisition by cytochrome b. Finally, assembly is completed by addition of the remaining subunits.

Keywords: Complex III assembly; Cytochrome b; Dimerization; Mitochondrial respiration; Oxidative phosphorylation; bc(1) complex

DOI: https://doi.org/10.1016/j.bbabio.2020.148177

Biol Chem. 2020 Mar 01. pii: /j/bchm.just-accepted/hsz-2020-0112/hsz-2020-0112.xml. [Epub ahead of print]

Modular assembly of yeast mitochondrial ATP synthase and cytochrome oxidase.

Leticia Veloso Ribeiro Franco, Chen Hsien Su, Alexander Tzagoloff.

The respiratory pathway of mitochondria is composed of four electron transfer complexes and the ATP synthase. In this article we review evidence from studies of Saccharomyces cerevisiae that both ATP synthase and cytochrome oxidase (COX) are assembled from independent modules that correspond to structurally and functionally identifiable components of each complex. Biogenesis of the respiratory chain requires a coordinate and balanced expression of gene products that become partner subunits of the same complex, but are encoded in the two physically separated genomes. Current evidence indicates that synthesis of two key mitochondrial encoded subunits of ATP synthase is regulated by the F1 module. Expression of COX1 that codes for a subunit of the COX catalytic core, is also regulated by a mechanism that restricts synthesis of this subunit to the availability of a nuclear-encoded translational activator. The respiratory chain must maintain a fixed stoichiometry of the component enzyme complexes during cell growth. We propose that high molecular weight complexes composed of Cox6, a subunit of cytochrome oxidase, and of the Atp9 subunit of ATP synthase, play a key role in establishing the ratio of the two complexes during their assembly.

Keywords: ATP synthase; Atp9; Cox6; Saccharomyces cerevisiae; cytochrome oxidase; mitochondrial biogenesis

DOI: https://doi.org/10.1515/hsz-2020-0112