bims-mitran 2022-12-11 papers

Issue of 2022–12–11
five papers selected by
Andreas Kohler, University of Graz

Nature. 2022 Dec 08.

Principles of mitoribosomal small subunit assembly in eukaryotes.

Nathan J Harper, Chloe Burnside, Sebastian Klinge.

Mitochondrial ribosomes (mitoribosomes) synthesize proteins encoded within the mitochondrial genome that are assembled into oxidative phosphorylation complexes. Thus, mitoribosome biogenesis is essential for ATP production and cellular metabolism1. Here we used cryo-electron microscopy to determine 9 structures of native yeast and human mitoribosomal small subunit assembly intermediates at resolutions from 2.4 to 3.8 Å, illuminating the mechanistic basis for how GTPases are employed to control early steps of decoding center formation, how initial rRNA folding and processing events are mediated, and how mitoribosomal proteins play active roles during assembly. Furthermore, this series of intermediates from two species with divergent mitoribosomal architecture uncovers both conserved principles and species-specific adaptations that govern the maturation of mitoribosomal small subunits in eukaryotes. By revealing the dynamic interplay between assembly factors, mitoribosomal proteins, and rRNA required to generate functional subunits, our structural analysis provides a vignette for how molecular complexity and diversity can evolve in large ribonucleoprotein assemblies.

DOI: https://doi.org/10.1038/s41586-022-05621-0

Elife. 2022 Dec 08. pii: e77460. [Epub ahead of print]11

Structure of the mitoribosomal small subunit with streptomycin reveals Fe-S clusters and physiological molecules.

Yuzuru Itoh, Vivek Singh, Anas Khawaja, Andreas Naschberger, Minh Duc Nguyen, Joanna Rorbach, Alexey Amunts.

The mitoribosome regulates cellular energy production, and its dysfunction is associated with aging. Inhibition of the mitoribosome can be caused by off-target binding of antimicrobial drugs and was shown to be coupled with a bilateral decreased visual acuity. Previously, we reported mitochondria-specific protein aspects of the mitoribosome, and in this article we present a 2.4-Å resolution structure of the small subunit in a complex with the anti-tuberculosis drug streptomycin that reveals roles of non-protein components. We found iron-sulfur clusters that are coordinated by different mitoribosomal proteins, nicotinamide adenine dinucleotide (NAD) associated with rRNA insertion, and posttranslational modifications. This is the first evidence of inter-protein coordination of iron-sulfur, and the finding of iron-sulfur clusters and NAD as fundamental building blocks of the mitoribosome directly links to mitochondrial disease and aging. We also report details of streptomycin interactions, suggesting that the mitoribosome-bound streptomycin is likely to be in hydrated gem-diol form and can be subjected to other modifications by the cellular milieu. The presented approach of adding antibiotics to cultured cells can be used to define their native structures in a bound form under more physiological conditions, and since streptomycin is a widely used drug for treatment, the newly resolved features can serve as determinants for targeting.

Keywords: Fe–S cluster; aging; antibiotics; human; mitochondria; mitoribosome; molecular biophysics; structural biology; translation

DOI: https://doi.org/10.7554/eLife.77460

Nat Biomed Eng. 2022 Dec 05.

A library of base editors for the precise ablation of all protein-coding genes in the mouse mitochondrial genome.

Pedro Silva-Pinheiro, Christian D Mutti, Lindsey Van Haute, Christopher A Powell, Pavel A Nash, Keira Turner, Michal Minczuk.

The development of curative treatments for mitochondrial diseases, which are often caused by mutations in mitochondrial DNA (mtDNA) that impair energy metabolism and other aspects of cellular homoeostasis, is hindered by an incomplete understanding of the underlying biology and a scarcity of cellular and animal models. Here we report the design and application of a library of double-stranded-DNA deaminase-derived cytosine base editors optimized for the precise ablation of every mtDNA protein-coding gene in the mouse mitochondrial genome. We used the library, which we named MitoKO, to produce near-homoplasmic knockout cells in vitro and to generate a mouse knockout with high heteroplasmy levels and no off-target edits. MitoKO should facilitate systematic and comprehensive investigations of mtDNA-related pathways and their impact on organismal homoeostasis, and aid the generation of clinically meaningful in vivo models of mtDNA dysfunction.

DOI: https://doi.org/10.1038/s41551-022-00968-1

Elife. 2022 Dec 08. pii: e84702. [Epub ahead of print]11

Teaching old drugs new tricks.

Alexandre Faille, Alan J Warren.

Understanding the mechanism by which streptomycin binds to the small subunit of the mitoribosome may help researchers design less toxic derivatives of this antibiotic.

Keywords: Fe-S cluster; antibiotics; bacteria; human; mitochondria; mitoribosome; molecular biophysics; ototoxicity; structural biology

DOI: https://doi.org/10.7554/eLife.84702

Cell Rep. 2022 Dec 06. pii: S2211-1247(22)01657-6. [Epub ahead of print]41(10): 111774

Mitochondrial cristae architecture protects against mtDNA release and inflammation.

Baiyu He, Huatong Yu, Shanshan Liu, Huayun Wan, Song Fu, Siqi Liu, Jun Yang, Zihan Zhang, Huanwei Huang, Qi Li, Fengchao Wang, Zhaodi Jiang, Qinghua Liu, Hui Jiang.

Mitochondrial damage causes mitochondrial DNA (mtDNA) release to activate the type I interferon (IFN-I) response via the cGAS-STING pathway. mtDNA-induced inflammation promotes autoimmune- and aging-related degenerative disorders. However, the global picture of inflammation-inducing mitochondrial damages remains obscure. Here, we have performed a mitochondria-targeted CRISPR knockout screen for regulators of the IFN-I response. Strikingly, our screen reveals dozens of hits enriched with key regulators of cristae architecture, including phospholipid cardiolipin and protein complexes such as OPA1, mitochondrial contact site and cristae organization (MICOS), sorting and assembly machinery (SAM), mitochondrial intermembrane space bridging (MIB), prohibitin (PHB), and the F1Fo-ATP synthase. Disrupting these cristae organizers consistently induces mtDNA release and the STING-dependent IFN-I response. Furthermore, knocking out MTX2, a subunit of the SAM complex whose null mutations cause progeria in humans, induces a robust STING-dependent IFN-I response in mouse liver. Taken together, beyond revealing the central role of cristae architecture to prevent mtDNA release and inflammation, our results mechanistically link mitochondrial cristae disorganization and inflammation, two emerging hallmarks of aging and aging-related degenerative diseases.

Keywords: CP: Cell biology; CP: Molecular biology; MICOS; Metaxin2; OPA1; SAM; cGAS-STING; cristae architecture; inflammation; mtDNA release; type I interferon response

DOI: https://doi.org/10.1016/j.celrep.2022.111774