bims-resufa 2020-09-06 papers

Issue of 2020–09–06
two papers selected by
Vera Strogolova, Marquette University

J Cell Sci. 2020 Sep 02. pii: jcs.248492. [Epub ahead of print]

Increased supra-organization is a dynamic multistep remodelling of respiratory complexes against proteostasis stress.

Shivali Rawat, Suparna Ghosh, Debodyuti Mondal, Valpadashi Anusha, Swasti Raychaudhuri.

Proteasome-mediated degradation of misfolded proteins prevents aggregation inside and outside mitochondria. But how do cells safeguard mitochondrial proteome and function despite increased aggregation during proteasome-inactivation? Here, using a novel two-dimensional complexome profiling strategy, we report increased supra-organizations of respiratory complexes (RCs) in proteasome-inhibited cells simultaneous to pelletable aggregation of RC-subunits inside mitochondria. Complex-II (CII) and CV-subunits are increasingly incorporated into oligomers. CI, CIII and CIV-subunits are engaged into supercomplex formation. We unravel unique quinary-states of supercomplexes at early-stress that exhibit plasticity and inequivalence of constituent RCs. Core stoichiometry of CI and CIII is preserved whereas CIV-composition varies. These partially disintegrated supercomplexes remain functionally competent via conformational optimization. Subsequently, increased stepwise integration of RC-subunits into holocomplex and supercomplexes re-establish steady-state stoichiometry. Overall, the mechanism of increased supra-organization of RCs mimics the cooperative unfolding and folding pathways for protein-folding, restricted to RCs only and not observed for any other mitochondrial protein complexes.

Keywords: Increased supercomplex; Multistep proteome remodelling; Proteostasis; Quinary supercomplex; Respiratory complex biogenesis; Two-dimensional complexome profiling

DOI: https://doi.org/10.1242/jcs.248492

Mol Cell. 2020 Aug 04. pii: S1097-2765(20)30515-3. [Epub ahead of print]

Molecular Connectivity of Mitochondrial Gene Expression and OXPHOS Biogenesis.

Abeer Prakash Singh, Roger Salvatori, Wasim Aftab, Andreas Aufschnaiter, Andreas Carlström, Ignasi Forne, Axel Imhof, Martin Ott.

Mitochondria contain their own gene expression systems, including membrane-bound ribosomes dedicated to synthesizing a few hydrophobic subunits of the oxidative phosphorylation (OXPHOS) complexes. We used a proximity-dependent biotinylation technique, BioID, coupled with mass spectrometry to delineate in baker's yeast a comprehensive network of factors involved in biogenesis of mitochondrial encoded proteins. This mitochondrial gene expression network (MiGENet) encompasses proteins involved in transcription, RNA processing, translation, or protein biogenesis. Our analyses indicate the spatial organization of these processes, thereby revealing basic mechanistic principles and the proteins populating strategically important sites. For example, newly synthesized proteins are directly handed over to ribosomal tunnel exit-bound factors that mediate membrane insertion, co-factor acquisition, or their mounting into OXPHOS complexes in a special early assembly hub. Collectively, the data reveal the connectivity of mitochondrial gene expression, reflecting a unique tailoring of the mitochondrial gene expression system.

Keywords: assembly; co-factor acquisition; gene expression; mitochondria; network; proximity interactions; respiratory chain; ribosome; translation; tunnel exit

DOI: https://doi.org/10.1016/j.molcel.2020.07.024