bims-cytox1 2022-05-08 papers

Issue of 2022–05–08
four papers selected by
Gavin McStay, Staffordshire University

RSC Adv. 2021 Sep 27. 11(51): 32476-32493

Protein import in mitochondria biogenesis: guided by targeting signals and sustained by dedicated chaperones.

Anna-Roza Dimogkioka, Jamie Lees, Erik Lacko, Kostas Tokatlidis.

Mitochondria have a central role in cellular metabolism; they are responsible for the biosynthesis of amino acids, lipids, iron-sulphur clusters and regulate apoptosis. About 99% of mitochondrial proteins are encoded by nuclear genes, so the biogenesis of mitochondria heavily depends on protein import pathways into the organelle. An intricate system of well-studied import machinery facilitates the import of mitochondrial proteins. In addition, folding of the newly synthesized proteins takes place in a busy environment. A system of folding helper proteins, molecular chaperones and co-chaperones, are present to maintain proper conformation and thus avoid protein aggregation and premature damage. The components of the import machinery are well characterised, but the targeting signals and how they are recognised and decoded remains in some cases unclear. Here we provide some detail on the types of targeting signals involved in the protein import process. Furthermore, we discuss the very elaborate chaperone systems of the intermembrane space that are needed to overcome the particular challenges for the folding process in this compartment. The mechanisms that sustain productive folding in the face of aggregation and damage in mitochondria are critical components of the stress response and play an important role in cell homeostasis.

DOI: https://doi.org/10.1039/d1ra04497d

Obesity (Silver Spring). 2022 May 02.

Mitochondrial genome variations, mitochondrial-nuclear compatibility, and their association with metabolic diseases.

Agnieszka H Ludwig-Słomczyńska, Markus Rehm.

Two genomes regulate the energy metabolism of eukaryotic cells: the nuclear genome, which codes for most cellular proteins, and the mitochondrial genome, which, together with the nuclear genome, coregulates cellular bioenergetics. Therefore, mitochondrial genome variations can affect, directly or indirectly, all energy-dependent cellular processes and shape the metabolic state of the organism. This review provides a current and up-to-date overview on how codependent these two genomes are, how they appear to have coevolved, and how variations within the mitochondrial genome might be associated with the manifestation of metabolic diseases. This review summarizes and structures results obtained from epidemiological studies that identified links between mitochondrial haplogroups and individual risks for developing obesity and diabetes. This is complemented by findings on the compatibility of mitochondrial and nuclear genomes and cellular bioenergetic fitness, which have been acquired from well-controlled studies in conplastic animal models. These elucidate, more mechanistically, how single-nucleotide variants can influence cellular metabolism and physiology. Overall, it seems that certain mitochondrial genome variations negatively affect mitochondrial-nuclear compatibility and are statistically linked with the onset of metabolic diseases, whereas, for others, greater uncertainty exists, and additional research into this exciting field is required.

DOI: https://doi.org/10.1002/oby.23424

Hum Genome Var. 2022 May 04. 9(1): 12

Novel NARS2 variant causing leigh syndrome with normal lactate levels.

Ryosuke Tanaka, Ryo Takeguchi, Mami Kuroda, Nao Suzuki, Yoshio Makita, Kumiko Yanagi, Tadashi Kaname, Satoru Takahashi.

Leigh syndrome is the most genetically heterogenous phenotype of mitochondrial disease. We describe a patient with Leigh syndrome whose diagnosis had not been confirmed because of normal metabolic screening results at the initial presentation. Whole-exome sequencing identified pathogenic variants in NARS2, the gene encoding a mitochondrial asparaginyl-tRNA synthetase. One of the biallelic variants was novel. This highlights the essential role of genetic testing for a definite diagnosis of Leigh syndrome.

DOI: https://doi.org/10.1038/s41439-022-00191-z

J Mol Biol. 2022 Apr 29. pii: S0022-2836(22)00198-X. [Epub ahead of print] 167618

Stress Responses Elicited by Misfolded Proteins Targeted to Mitochondria.

Kannan Boosi Narayana Rao, Pratima Pandey, Rajasri Sarkar, Asmita Ghosh, Shemin Mansuri, Mudassar Ali, Priyanka Majumder, K Ranjith Kumar, Arjun Ray, Swasti Raychaudhuri, Koyeli Mapa.

The double-membrane-bound architecture of mitochondria, essential for ATP production, sub-divides the organelle into inter-membrane space (IMS) and matrix. IMS and matrix possess contrasting oxido-reductive environments and discrete protein quality control (PQC) machineries resulting inherent differences in their protein folding environments. To understand the nature of stress response elicited by equivalent proteotoxic stress to these sub-mitochondrial compartments, we took misfolding and aggregation-prone stressor proteins and fused it to well described signal sequences to specifically target and impart stress to yeast mitochondrial IMS or matrix. We show, mitochondrial proteotoxicity leads to growth arrest of yeast cells of varying degrees depending on nature of stressor proteins and the intra-mitochondrial location of stress. Next, by employing transcriptomics and proteomics, we report a comprehensive stress response elicited by stressor proteins specifically targeted to mitochondrial matrix or IMS. A general response to proteotoxic stress by mitochondria-targeted misfolded proteins is mitochondrial fragmentation, and an adaptive abrogation of mitochondrial respiration with concomitant upregulation of glycolysis. Beyond shared stress responses, specific signatures due to stress within mitochondrial sub-compartments are also revealed. We report that stress-imparted by bipartite signal sequence-fused stressor proteins to IMS, leads to specific upregulation of IMS-chaperones and TOM complex components. In contrast, matrix-targeted stressors lead to specific upregulation of matrix-chaperones and cytosolic PQC components. Finally, by systematic genetic interaction using deletion strains of differentially upregulated genes, we found prominent modulatory role of TOM complex components during IMS-stress response. In contrast, VMS1 markedly modulates the stress response originated from matrix.

Keywords: Mitochondrial Unfolded Protein Response; Molecular Chaperone; Protein misfolding; Proteostasis; Proteotoxic stress; Ribosome Quality Control; Stress Response; TOM complex; Vms1

DOI: https://doi.org/10.1016/j.jmb.2022.167618