bims-cytox1 2022-09-04 papers

Issue of 2022‒09‒04
three papers selected by
Gavin McStay
Liverpool John Moores University

Mol Cell. 2022 Aug 23. pii: S1097-2765(22)00764-X. [Epub ahead of print]

The human mitochondrial genome contains a second light strand promoter.

Benedict G Tan, Christian D Mutti, Yonghong Shi, Xie Xie, Xuefeng Zhu, Pedro Silva-Pinheiro, Katja E Menger, Héctor Díaz-Maldonado, Wei Wei, Thomas J Nicholls, Patrick F Chinnery, Michal Minczuk, Maria Falkenberg, Claes M Gustafsson.

The human mitochondrial genome must be replicated and expressed in a timely manner to maintain energy metabolism and supply cells with adequate levels of adenosine triphosphate. Central to this process is the idea that replication primers and gene products both arise via transcription from a single light strand promoter (LSP) such that primer formation can influence gene expression, with no consensus as to how this is regulated. Here, we report the discovery of a second light strand promoter (LSP2) in humans, with features characteristic of a bona fide mitochondrial promoter. We propose that the position of LSP2 on the mitochondrial genome allows replication and gene expression to be orchestrated from two distinct sites, which expands our long-held understanding of mitochondrial gene expression in humans.

Keywords: DdCBE; LSP2; POLRMT; light strand promoter; mitochondria; mitochondrial DNA; mitochondrial gene expression; mitochondrial promoter; mtDNA; transcription

DOI: https://doi.org/10.1016/j.molcel.2022.08.011

Nat Commun. 2022 Sep 02. 13(1): 5164

Protein import motor complex reacts to mitochondrial misfolding by reducing protein import and activating mitophagy.

Jonas Benjamin Michaelis, Melinda Elaine Brunstein, Süleyman Bozkurt, Ludovico Alves, Martin Wegner, Manuel Kaulich, Christian Pohl, Christian Münch.

Mitophagy is essential to maintain mitochondrial function and prevent diseases. It activates upon mitochondria depolarization, which causes PINK1 stabilization on the mitochondrial outer membrane. Strikingly, a number of conditions, including mitochondrial protein misfolding, can induce mitophagy without a loss in membrane potential. The underlying molecular details remain unclear. Here, we report that a loss of mitochondrial protein import, mediated by the pre-sequence translocase-associated motor complex PAM, is sufficient to induce mitophagy in polarized mitochondria. A genome-wide CRISPR/Cas9 screen for mitophagy inducers identifies components of the PAM complex. Protein import defects are able to induce mitophagy without a need for depolarization. Upon mitochondrial protein misfolding, PAM dissociates from the import machinery resulting in decreased protein import and mitophagy induction. Our findings extend the current mitophagy model to explain mitophagy induction upon conditions that do not affect membrane polarization, such as mitochondrial protein misfolding.

DOI: https://doi.org/10.1038/s41467-022-32564-x

Hum Mutat. 2022 Aug 28.

Biallelic pathogenic variants in COX11 are associated with an infantile-onset mitochondrial encephalopathy.

Rocio Rius, Neal K Bennett, Kaustuv Bhattacharya, Lisa G Riley, Zafer Yüksel, Luke E Formosa, Alison G Compton, Russell C Dale, Mark J Cowley, Velimir Gayevskiy, Saeed Al Tala, Abdulrahman A Almehery, Michael T Ryan, David R Thorburn, Ken Nakamura, John Christodoulou.

Primary mitochondrial diseases are a group of genetically and clinically heterogeneous disorders resulting from oxidative phosphorylation (OXPHOS) defects. COX11 encodes a copper chaperone that participates in the assembly of complex IV (CIV) and has not been previously linked to human disease. In a previous study, we identified that COX11 knockdown decreased cellular ATP derived from respiration, and that ATP levels could be restored with CoQ10 supplementation. This finding is surprising since COX11 has no known role in CoQ10 biosynthesis. Here, we report a novel gene-disease association by identifying biallelic pathogenic variants in COX11 associated with infantile-onset mitochondrial encephalopathies in two unrelated families using trio genome and exome sequencing. Functional studies showed that mutant COX11 fibroblasts had decreased ATP levels which could be rescued by CoQ10 . These results not only suggest that COX11 variants cause defects in energy production but reveal a potential metabolic therapeutic strategy for patients with COX11 variants. This article is protected by copyright. All rights reserved.

Keywords: COX11; Coenzyme Q; OXPHOS; mitochondrial disorders

DOI: https://doi.org/10.1002/humu.24453