bims-mitpro 2026-02-08 papers

Issue of 2026–02–08
five papers selected by
Andreas Kohler, Umeå University

bioRxiv. 2026 Jan 14. pii: 2026.01.14.699430. [Epub ahead of print]

A dynamic displacement mechanism drives protein import into mitochondria.

Iva Sucec, Undina Guillerm, Jakob Schneider, Iniyan Ganesan, Niklas Webling, Anna Kapitonova, Conny Steiert, Frank Schmelter, Antoine Feignier, Rajkumar Singh, Laura F Fielden, Julia Dung, Doron Rapaport, Beate Bersch, Karin B Busch, Francois Dehez, Nils Wiedemann, Paul Schanda.

Most mitochondrial proteins are produced in the cytosol and imported through the translocase of the outer mitochondrial membrane (TOM) to reach their final destination. Although this protein entry gate has been structurally characterized, it remains unclear how precursor proteins are handed off from the cytosolic receptor domains to the translocation pore. Here we show that the cytosolic domain of Tom22 - traditionally viewed as the central TOM receptor - acts not as a structured scaffold but as a largely disordered, flexible segment that plays an active role in precursor transfer. Atomic-level structural techniques and in vivo experiments identified a conserved short linear motif that forms a transient α-helical element within this disordered domain. By binding to the canonical precursor protein binding sites of the receptors Tom20 and Tom70, this critical α-helical segment acts as a precursor protein displacement element (PPDE). This competitive interaction facilitates the release of preproteins directly above the import pore, and thereby drives translocation across the outer mitochondrial membrane. These findings reveal that flexibility, rather than rigid structure, underlies the central transfer step of mitochondrial outer-membrane protein translocation. Our results point to a versatile mechanism for ligand displacement in chaperone, receptor, and transport systems that must balance selective binding with efficient release.

DOI: https://doi.org/10.64898/2026.01.14.699430

Plant J. 2026 Feb;125(3): e70704

PAM18-3, a J-domain protein, maintains mitochondrial integrity and plant growth and development in Arabidopsis thaliana.

Neha, Souparnika S, Chandan Sahi.

Mitochondrial protein import is indispensable for organelle biogenesis and function, and is powered by the evolutionarily conserved presequence translocase-associated motor (PAM) complex. In Arabidopsis thaliana, three paralogs: PAM18-1, PAM18-2, and PAM18-3 encode J-domain proteins homologous to yeast PAM18, which stimulates the ATPase activity of mitochondrial HSP70 (mtHSP70) during protein translocation. Here, we identify PAM18-3 as the most highly and ubiquitously expressed paralog and demonstrate its critical role in mitochondrial function and plant development. Genetic disruption of PAM18-3 caused severe vegetative and reproductive defects, including reduced root length, smaller rosette size with fewer leaves, decreased plant height, shorter siliques, reduced seed set, and increased seed abortion. These phenotypes were fully rescued in complemented lines expressing PAM18-3. Ultrastructural analyses revealed profound mitochondrial abnormalities in mutants, whereas chloroplast architecture remained unaffected. Functional assays showed reduced mitochondrial membrane potential and altered respiratory flux with a compensatory induction of the alternative oxidase (AOX) pathway. Transcript profiling revealed upregulation of AOX genes and multiple components of the mitochondrial TIM23 import apparatus and associated chaperones. Import assays demonstrated reduced mitochondrial accumulation of canonical TIM23 substrates, including IDH, ATPβ, and SHMT1, confirming a defect in matrix protein translocation. Consistently, pam18-3 mutants accumulated elevated reactive oxygen species (ROS) and exhibited strong induction of mitochondrial dysfunction stimulon (MDS) genes, including key transcription factors mediating retrograde signaling. Together, our findings establish PAM18-3 as a central component of the mitochondrial protein import machinery, supporting plant growth and development in A. thaliana.

Keywords: Arabidopsis thaliana; PAM18; TIM23 complex; mitochondria; presequence translocase‐associated motor

DOI: https://doi.org/10.1111/tpj.70704

bioRxiv. 2026 Jan 15. pii: 2026.01.14.699555. [Epub ahead of print]

LONP-1 deficiency causes dysregulated protein synthesis within mitochondria that is restored by mitoribosomal mutations.

Levi Ali, Avijit Mallick, Yunguang Du, Rui Li, Lihua Julie Zhu, Kuang Shen, Cole M Haynes.

Mitochondrial homeostasis is maintained by multiple molecular chaperones and proteases located within the organelle. The mitochondrial matrix-localized protease LONP-1 degrades oxidatively damaged or misfolded proteins. Importantly, LONP-1 also regulates mitochondrial DNA replication. Here, we show that mutations in C. elegans that impair LONP-1 function cause dysregulation of mitochondrial DNA replication, mitochondrial RNA transcription and protein synthesis within the mitochondrial matrix. LONP-1 deficient worms had reduced levels of oxidative phosphorylation proteins despite increased mtDNA-encoded protein synthesis. Via a forward genetic screen, we identified three mutations that restored mitochondrial function and the rate of development in lonp-1 mutants to levels comparable to those in wildtype worms. Interestingly, all three suppressor mutations were found in genes encoding mitochondrial ribosome proteins. A point mutation in the mitochondrial ribosome protein MRPS-38 restored oxidative phosphorylation in lonp-1 mutant worms. Combined, our results suggest that LONP-1 regulates mitochondrial protein synthesis and that the suppressor mutations within MRPS-38 or MRPS-15 enhance oxidative phosphorylation complex assembly by slowing translation.

DOI: https://doi.org/10.64898/2026.01.14.699555

Curr Biol. 2026 Feb 03. pii: S0960-9822(26)00006-0. [Epub ahead of print]

The mitochondrial intermembrane space nuclease Nuc1 (endonuclease G) prevents mitophagy-mediated mtDNA escape in yeast.

Ryan R Cupo, Eunice Domínguez-Martín, Richard Youle.

Mitochondria contain a genome (mtDNA) encoding a handful of proteins essential for cellular respiration. mtDNA can leak into the cytosol and drive fitness defects. The first genes associated with mtDNA escape were discovered in yeast and aptly named "yeast mitochondrial escape" (YME) genes. We identify the mechanism by which an intermembrane space nuclease, endonuclease G (human ENDOG; yeast Nuc1), prevents mtDNA escape to the cytosol in yeast. Nuc1 nuclease activity and mitochondrial localization are essential for preventing mtDNA escape and suggest a direct role of Nuc1 in degrading mtDNA bound for escape. We find that blocking autophagy via atg1 and atg8 mutants prevents mtDNA escape in the absence of Nuc1. We further demonstrate that blocking mitophagy via atg11 and atg32 mutants prevents mtDNA escape, whereas inducing mitophagy increases mtDNA escape in the absence of Nuc1. Finally, we demonstrate that Nuc1 degrades mtDNA bound for escape via the vacuole, as an atg15 mutant that prevents disassembly of autophagic bodies in the vacuole also prevents mtDNA escape. Overall, our results implicate vacuolar entry of mitochondria during mitophagy as an important mtDNA escape pathway in yeast, which is normally mitigated via the degradation of mtDNA by Nuc1.

Keywords: Atg1; Atg32; Drp1; NUMT; STING; autophagy; fission; lysosome; nucleoid; vacuole

DOI: https://doi.org/10.1016/j.cub.2026.01.006