bims-cytox1 2023-01-29 papers

Issue of 2023‒01‒29
four papers selected by
Gavin McStay
Liverpool John Moores University

EMBO J. 2023 Jan 27. e112309

MitoStores: chaperone-controlled protein granules store mitochondrial precursors in the cytosol.

Lena Krämer, Niko Dalheimer, Markus Räschle, Zuzana Storchová, Jan Pielage, Felix Boos, Johannes M Herrmann.

Hundreds of nucleus-encoded mitochondrial precursor proteins are synthesized in the cytosol and imported into mitochondria in a post-translational manner. However, the early processes associated with mitochondrial protein targeting remain poorly understood. Here, we show that in Saccharomyces cerevisiae, the cytosol has the capacity to transiently store mitochondrial matrix-destined precursors in dedicated deposits that we termed MitoStores. Competitive inhibition of mitochondrial protein import via clogging of import sites greatly enhances the formation of MitoStores, but they also form during physiological cell growth on nonfermentable carbon sources. MitoStores are enriched for a specific subset of nucleus-encoded mitochondrial proteins, in particular those containing N-terminal mitochondrial targeting sequences. Our results suggest that MitoStore formation suppresses the toxic potential of aberrantly accumulating mitochondrial precursor proteins and is controlled by the heat shock proteins Hsp42 and Hsp104. Thus, the cytosolic protein quality control system plays an active role during the early stages of mitochondrial protein targeting through the coordinated and localized sequestration of mitochondrial precursor proteins.

Keywords: chaperones; mitochondria; proteasome; protein aggregates; protein translocation

DOI: https://doi.org/10.15252/embj.2022112309

Nature. 2023 Jan 25.

Mitochondrial complexome reveals quality-control pathways of protein import.

Mitochondria have crucial roles in cellular energetics, metabolism, signalling and quality control1-4. They contain around 1,000 different proteins that often assemble into complexes and supercomplexes such as respiratory complexes and preprotein translocases1,3-7. The composition of the mitochondrial proteome has been characterized1,3,5,6; however, the organization of mitochondrial proteins into stable and dynamic assemblies is poorly understood for major parts of the proteome1,4,7. Here we report quantitative mapping of mitochondrial protein assemblies using high-resolution complexome profiling of more than 90% of the yeast mitochondrial proteome, termed MitCOM. An analysis of the MitCOM dataset resolves >5,200 protein peaks with an average of six peaks per protein and demonstrates a notable complexity of mitochondrial protein assemblies with distinct appearance for respiration, metabolism, biogenesis, dynamics, regulation and redox processes. We detect interactors of the mitochondrial receptor for cytosolic ribosomes, of prohibitin scaffolds and of respiratory complexes. The identification of quality-control factors operating at the mitochondrial protein entry gate reveals pathways for preprotein ubiquitylation, deubiquitylation and degradation. Interactions between the peptidyl-tRNA hydrolase Pth2 and the entry gate led to the elucidation of a constitutive pathway for the removal of preproteins. The MitCOM dataset-which is accessible through an interactive profile viewer-is a comprehensive resource for the identification, organization and interaction of mitochondrial machineries and pathways.

DOI: https://doi.org/10.1038/s41586-022-05641-w

Nature. 2023 Jan 25.

A census of complexes formed by mitochondrial proteins.

Keywords: Biochemistry; Cell biology; Metabolism; Proteomics

DOI: https://doi.org/10.1038/d41586-023-00095-0

Adv Sci (Weinh). 2023 Jan 22. e2206144

Reprogramming of Mitochondrial Respiratory Chain Complex by Targeting SIRT3-COX4I2 Axis Attenuates Osteoarthritis Progression.

Yijian Zhang, Yang Liu, Mingzhuang Hou, Xiaowei Xia, Junlin Liu, Yong Xu, Qin Shi, Zhongmin Zhang, Liang Wang, Yifan Shen, Huilin Yang, Fan He, Xuesong Zhu.

Mitochondrial homeostasis is of great importance for cartilage integrity and associated with the progression of osteoarthritis (OA); however, the underlying mechanisms are unknown. This study aims to investigate the role of mitochondrial deacetylation reaction and investigate the mechanistic relationship OA development. Silent mating type information regulation 2 homolog 3 (SIRT3) expression has a negative correlation with the severity of OA in both human arthritic cartilage and mice inflammatory chondrocytes. Global SIRT3 deletion accelerates pathological phenotype in post-traumatic OA mice, as evidenced by cartilage extracellular matrix collapse, osteophyte formation, and synovial macrophage M1 polarization. Mechanistically, SIRT3 prevents OA progression by targeting and deacetylating cytochrome c oxidase subunit 4 isoform 2 (COX4I2) to maintain mitochondrial homeostasis at the post-translational level. The activation of SIRT3 by honokiol restores cartilage metabolic equilibrium and protects mice from the development of post-traumatic OA. Collectively, the loss of mitochondrial SIRT3 is essential for the development of OA, whereas SIRT3-mediated proteins deacetylation of COX4I2 rescues OA-impaired mitochondrial respiratory chain functions to improve the OA phenotype. Herein, the induction of SIRT3 provides a novel therapeutic candidate for OA treatment.

Keywords: COX4I2; SIRT3; deacetylation; mitochondria; osteoarthritis

DOI: https://doi.org/10.1002/advs.202206144