bims-resufa 2021-05-23 papers

Issue of 2021–05–23
three papers selected by
Vera Strogolova, Strong Microbials, Inc

J Cell Sci. 2020 Jan 01. 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

J Cell Sci. 2020 Jan 01. pii: jcs.240374. [Epub ahead of print]

Cardiolipin is required for membrane docking of mitochondrial ribosomes and protein synthesis.

Richard G Lee, Junjie Gao, Stefan J Siira, Anne-Marie Shearwood, Judith A Ermer, Vinzenz Hofferek, James C Mathews, Minghao Zheng, Gavin E Reid, Oliver Rackham, Aleksandra Filipovska.

The mitochondrial inner membrane contains a unique phospholipid known as cardiolipin (CL), which stabilises the protein complexes embedded in the membrane and supports its overall structure. Recent evidence indicates that the mitochondrial ribosome may associate with the inner membrane to facilitate co-translational insertion of the hydrophobic oxidative phosphorylation (OXPHOS) proteins into the inner membrane. We generated three mutant knockout cell lines for the cardiolipin biosynthesis gene Crls1 to investigate the effects of cardiolipin loss on mitochondrial protein synthesis. Reduced CL levels caused altered mitochondrial morphology and transcriptome-wide changes that were accompanied by reduced uncoordinated mitochondrial translation rates and impaired respiratory supercomplex formation. Aberrant protein synthesis was caused by impaired formation and distribution of mitochondrial ribosomes. Reduction or loss of cardiolipin resulted in divergent mitochondrial and endoplasmic reticulum stress responses. We show that cardiolipin is required to stabilise the interaction of the mitochondrial ribosome with the membrane via its association with OXA1 during active translation. This interaction facilitates insertion of newly synthesised mitochondrial proteins into the inner membrane and stabilises the respiratory supercomplexes.

Keywords: Mitochondrial membranes; Mitochondrial ribosomes; Protein synthesis

DOI: https://doi.org/10.1242/jcs.240374

J Exp Biol. 2020 Jan 01. pii: jeb.223776. [Epub ahead of print]

Stable mitochondrial CICIII2 supercomplex interactions in reptiles compared to homeothermic vertebrates.

Amanda Bundgaard, Andrew M James, Michael E Harbour, Michael P Murphy, Angela Fago.

The association of complex I (CI), complex III (CIII) and complex IV (CIV) of the mitochondrial electron transport chain into stable high-molecular weight supercomplexes (SCs) has been observed in several prokaryotes and eukaryotes, but among vertebrates it has only been examined in mammals. The biological role of these SCs is unclear but suggestions so far include enhanced electron transfer between complexes, decreased production of the reactive oxygen species (ROS) O2·- and H2O2, or enhanced structural stability. Here, we provide the first overview on the stability, composition and activity of mitochondrial SCs in representative species of several vertebrate classes to determine patterns of SC variation across endotherms and ectotherms. We found that the stability of the CICIII2 SC and the inclusion of CIV within SC varied considerably. Specifically, when solubilized by the detergent DDM, mitochondrial CICIII2 SCs were unstable in endotherms (birds and mammals) and highly stable in reptiles. Using mass-spectrometric complexomics, we confirmed that the CICIII2 is the major SC in the turtle, and that 90% of CI is found in this highly stable SC. Interestingly, the presence of stable SCs did not prevent mitochondrial H2O2 production and was not associated with elevated respiration rates of mitochondria isolated from the examined species. Together, these data show that SC stability varies among vertebrates and is greatest in poikilothermic reptiles and weakest in endotherms. This pattern suggests an adaptive role of SCs to varying body temperature, but not necessarily a direct effect on electron transfer or in the prevention of ROS production.

Keywords: Bioenergetics; Complexomics; Mass spectrometry; Mitochondria; Oxidative phosphorylation; Reactive oxygen species

DOI: https://doi.org/10.1242/jeb.223776