bims-tricox 2024-06-16 papers

Issue of 2024–06–16
three papers selected by
Yash Verma, University of Zurich

Front Cell Dev Biol. 2024 ;12 1410245

Molecular pathways in mitochondrial disorders due to a defective mitochondrial protein synthesis.

Álvaro Antolínez-Fernández, Paula Esteban-Ramos, Miguel Ángel Fernández-Moreno, Paula Clemente.

Mitochondria play a central role in cellular metabolism producing the necessary ATP through oxidative phosphorylation. As a remnant of their prokaryotic past, mitochondria contain their own genome, which encodes 13 subunits of the oxidative phosphorylation system, as well as the tRNAs and rRNAs necessary for their translation in the organelle. Mitochondrial protein synthesis depends on the import of a vast array of nuclear-encoded proteins including the mitochondrial ribosome protein components, translation factors, aminoacyl-tRNA synthetases or assembly factors among others. Cryo-EM studies have improved our understanding of the composition of the mitochondrial ribosome and the factors required for mitochondrial protein synthesis and the advances in next-generation sequencing techniques have allowed for the identification of a growing number of genes involved in mitochondrial pathologies with a defective translation. These disorders are often multisystemic, affecting those tissues with a higher energy demand, and often present with neurodegenerative phenotypes. In this article, we review the known proteins required for mitochondrial translation, the disorders that derive from a defective mitochondrial protein synthesis and the animal models that have been established for their study.

Keywords: OxPhos; mitochondria; mitochondrial disorders; mitoribosome; translation

DOI: https://doi.org/10.3389/fcell.2024.1410245

Trends Cell Biol. 2024 Jun 08. pii: S0962-8924(24)00097-7. [Epub ahead of print]

Unique architectural features of mammalian mitochondrial protein synthesis.

Oliver Rackham, Martin Saurer, Nenad Ban, Aleksandra Filipovska.

Mitochondria rely on coordinated expression of their own mitochondrial DNA (mtDNA) with that of the nuclear genome for their biogenesis. The bacterial ancestry of mitochondria has given rise to unique and idiosyncratic features of the mtDNA and its expression machinery that can be specific to different organisms. In animals, the mitochondrial protein synthesis machinery has acquired many new components and mechanisms over evolution. These include several new ribosomal proteins, new stop codons and ways to recognise them, and new mechanisms to deliver nascent proteins into the mitochondrial inner membrane. Here we describe the mitochondrial protein synthesis machinery in mammals and its unique mechanisms of action elucidated to date and highlight the technologies poised to reveal the next generation of discoveries in mitochondrial translation.

Keywords: RNA; mitochondria; mitochondrial disease; ribosomes; translation

DOI: https://doi.org/10.1016/j.tcb.2024.05.001

FEBS J. 2024 Jun 10.

Privileged proteins with a second residence: dual targeting and conditional re-routing of mitochondrial proteins.

Ophry Pines, Margalit Horwitz, Johannes M Herrmann.

Almost all mitochondrial proteins are encoded by nuclear genes and synthesized in the cytosol as precursor proteins. Signals in the amino acid sequence of these precursors ensure their targeting and translocation into mitochondria. However, in many cases, only a certain fraction of a specific protein is transported into mitochondria, while the rest either remains in the cytosol or undergoes reverse translocation to the cytosol, and can populate other cellular compartments. This phenomenon is called dual localization which can be instigated by different mechanisms. These include alternative start or stop codons, differential transcripts, and ambiguous or competing targeting sequences. In many cases, dual localization might serve as an economic strategy to reduce the number of required genes; for example, when the same groups of enzymes are required both in mitochondria and chloroplasts or both in mitochondria and the nucleus/cytoplasm. Such cases frequently employ ambiguous targeting sequences to distribute proteins between both organelles. However, alternative localizations can also be used for signaling, for example when non-imported precursors serve as mitophagy signals or when they represent transcription factors in the nucleus to induce the mitochondrial unfolded stress response. This review provides an overview regarding the mechanisms and the physiological consequences of dual targeting.

Keywords: dual targeting; mitochondria; protein import; start codon; targeting signals

DOI: https://doi.org/10.1111/febs.17191