bims-mitran 2023-09-17 papers

Issue of 2023–09–17
three papers selected by
Andreas Kohler, University of Graz

IUBMB Life. 2023 Sep 15.

Early steps in the biogenesis of mitochondrially encoded oxidative phosphorylation subunits.

Sung-Jun Jung, Sagar Sridhara, Martin Ott.

The complexes mediating oxidative phosphorylation (OXPHOS) in the inner mitochondrial membrane consist of proteins encoded in the nuclear or the mitochondrial DNA. The mitochondrially encoded membrane proteins (mito-MPs) represent the catalytic core of these complexes and follow complicated pathways for biogenesis. Owing to their overall hydrophobicity, mito-MPs are co-translationally inserted into the inner membrane by the Oxa1 insertase. After insertion, OXPHOS biogenesis factors mediate the assembly of mito-MPs into complexes and participate in the regulation of mitochondrial translation, while protein quality control factors recognize and degrade faulty or excess proteins. This review summarizes the current understanding of these early steps occurring during the assembly of mito-MPs by concentrating on results obtained in the model organism baker's yeast.

Keywords: eukaryotic gene expression; mitochondria; protein folding; protein synthesis

DOI: https://doi.org/10.1002/iub.2784

Cell Rep. 2023 Sep 12. pii: S2211-1247(23)01123-3. [Epub ahead of print]42(9): 113112

A ribosome-bound tRNA half stimulates mitochondrial translation during stress recovery in Trypanosoma brucei.

Rebecca Brogli, Marina Cristodero, André Schneider, Norbert Polacek.

The protozoan parasite Trypanosoma brucei and its disease-causing relatives are among the few organisms that barely regulate the transcription of protein-coding genes. Yet, alterations in its gene expression are essential to survive in different host environments. Recently, tRNA-derived RNAs have been implicated as regulators of many cellular processes within and beyond translation. Previously, we identified the tRNAThr-3'-half (AGU) as a ribosome-associated non-coding RNA able to enhance global translation. Here we report that the tRNAThr-3'-half is generated upon starvation inside the mitochondria. The tRNAThr-3'-half associates with mitochondrial ribosomes and stimulates translation during stress recovery, positively affecting mitochondrial activity and, consequently, cellular energy production capacity. Our results describe an organelle ribosome-associated ncRNA involved in translation regulation to boost the central hub of energy metabolism as an immediate stress recovery response.

Keywords: CP: Microbiology; CP: Molecular biology; mitochondria; mitoribosome; protein synthesis; stress response; tRNA fragment; tRNA half; translation regulation

DOI: https://doi.org/10.1016/j.celrep.2023.113112

Biochimie. 2023 Sep 08. pii: S0300-9084(23)00215-8. [Epub ahead of print]

Targeting of CRISPR-Cas12a crRNAs into human mitochondria.

Natalia Nikitchina, Egor Ulashchik, Vadim Shmanai, Anne-Marie Heckel, Ivan Tarassov, Ilya Mazunin, Nina Entelis.

Mitochondrial gene editing holds great promise as a therapeutic approach for mitochondrial diseases caused by mutations in the mitochondrial DNA (mtDNA). Current strategies focus on reducing mutant mtDNA heteroplasmy levels through targeted cleavage or base editing. However, the delivery of editing components into mitochondria remains a challenge. Here we investigate the import of CRISPR-Cas12a system guide RNAs (crRNAs) into human mitochondria and study the structural requirements for this process by northern blot analysis of RNA isolated from nucleases-treated mitoplasts. To investigate whether the fusion of crRNA with known RNA import determinants (MLS) improve its mitochondrial targeting, we added MLS hairpin structures at 3'-end of crRNA and demonstrated that this did not impact crRNA ability to program specific cleavage of DNA in lysate of human cells expressing AsCas12a nuclease. Surprisingly, mitochondrial localization of the fused crRNA molecules was not improved compared to non-modified version, indicating that structured scaffold domain of crRNA can probably function as MLS, assuring crRNA mitochondrial import. Then, we designed a series of crRNAs targeting different regions of mtDNA and demonstrated their ability to program specific cleavage of mtDNA fragments in cell lysate and their partial localization in mitochondrial matrix in human cells transfected with these RNA molecules. We hypothesize that mitochondrial import of crRNAs may depend on their secondary structure/sequence. We presume that imported crRNA allow reconstituting the active crRNA/Cas12a system in human mitochondria, which can contribute to the development of effective strategies for mitochondrial gene editing and potential future treatment of mitochondrial diseases.

Keywords: Cas12a; Human mitochondria; MitoCRISPR; RNA import; Targeting; crRNA

DOI: https://doi.org/10.1016/j.biochi.2023.09.006