bims-mitpro 2025-08-03 papers

Issue of 2025–08–03
five papers selected by
Andreas Kohler, Umeå University

Commun Biol. 2025 Jul 29. 8(1): 1122

Tom40 functions as a channel for protein retrotranslocation in the mitochondria-associated degradation (MAD) pathway.

Pin-Chao Liao, Tzu-Ying Lin, Catherine A Tsang, Chen-Jing Huang, Katherine Filpo, Istvan Boldogh, Liza A Pon.

The mitochondria-associated degradation pathway (MAD) mediates removal and elimination of damaged, unfolded mitochondrial proteins by the ubiquitin-proteasome system (UPS). Previous studies revealed that MAD is critical for mitochondrial protein quality control and that MAD function extends beyond mitochondrial outer membrane (MOM) to proteins within the organelle. Here, we reconstitute retrotranslocation of MAD substrates from the mitochondrial matrix across mitochondrial inner and outer membranes in cell-free systems. This retrotranslocation is ATP-dependent but membrane potential-independent. We also identify a role for the TOM complex, the protein import channel in the MOM, in this process. Inhibition of protein translocation across the Tom40p channel reduces the retrotranslocation of MAD substrates. Our studies support the model that the TOM complex is a bidirectional protein channel in the MOM: it mediates retrotranslocation of damaged mitochondrial proteins across the MOM in the MAD pathway for mitochondrial protein quality control in addition to its function in import of proteins into the organelle.

DOI: https://doi.org/10.1038/s42003-025-08549-z

Adv Sci (Weinh). 2025 Jul 29. e03408

SENP6 Maintains Mitochondrial Homeostasis by Regulating Mitochondrial Protein Import Through deSUMOylation of TOM40.

Liubing Hu, Jianshuang Li, Haolin Guo, Lei Su, Peina Dong, Juan Huang, Yanyan Liu, Xinjie Liu, Zhenhuan Luo, Wei Xiong, Zhenyu Ju, Qinghua Zhou, Hao Wang, Wenjun Wang.

SUMOylation, a reversible post-translational modification, regulates various mitochondrial processes, including biogenesis, dynamics, mitophagy, and the mitochondrial unfolded protein response. Although SUMOylation is shown to be triggered by mitochondrial protein import failure in yeast, its impact on mammalian mitochondrial protein import remains unclear. Here, it is demonstrated that SENP6 knockdown-induced SUMOylation causes loss of mitochondrial proteostasis, which impairs mitochondrial morphology and function. Mechanistically, SENP6 knockdown dampens TOM complex assembly by SUMOylating TOM40, thereby hindering the mitochondrial protein import process, including TOM40 precursor, and ultimately disrupts mitochondrial homeostasis. Additionally, it is observed that CCCP treatment resulted in a decrease of SENP6 within mitochondria fraction, accompanied by increased TOM40 SUMOylation in the brains of 3×Tg-Alzheimer's disease (AD) mice or Aβ1-42 peptide-stimulated cells. Collectively, the results suggest that Aβ1-42 accumulation may enhance TOM40 SUMOylation by suppressing SENP6, thereby impairing mitochondrial homeostasis through protein import failure and potentially contributing to the pathological process of AD. This study elucidates the role of TOM40 SUMOylation/deSUMOylation in regulating the mitochondrial import process during mitochondrial stress.

Keywords: Mitochondrial protein import; SENP6; SUMOylation; TOM complex; TOM40

DOI: https://doi.org/10.1002/advs.202503408

J Cell Sci. 2025 Jul 30. pii: jcs.263680. [Epub ahead of print]

Mitochondrial protein aggregates recruit key chaperones and are sequestered in a fission/fusion-dependent process.

Laura Ruland, Marc Sylvester, Lydia Maus, Hannes Beckert, Wolfgang Voos.

The potential proteotoxicity of mitochondrial aggregates in yeast cells is reduced by a sequestration of affected polypeptides into a mitochondrial protein quality control compartment (IMiQ). Based on the expression of an aggregation-prone protein in the mitochondrial matrix, we determined the effect of organelle dynamics on aggregate sequestration. Fusion deficient cells were unable to accumulate the aggregates in the IMiQ, resulting in a stress-sensitive phenotype. In contrast, fission deficient cells could not separate the aggregate from the mitochondrial network. In these mitochondria, the aggregates were neutralized by the formation of a shell formed by mitochondrial chaperones. We also performed quantitative mass spectrometry to analyse the mitochondrial proteome and the extent of co-aggregation of mitochondrial proteins. While only minor changes of the total proteome were detected in response to aggregate accumulation, we found a recruitment of proteins of the respiratory chain complexes and of the protein quality control system (PQC). In particular members of the Hsp70 chaperone family were prominently associated with the aggregate. We conclude that this chaperone-dependent neutralization prevents a major co-aggregation of endogenous mitochondrial proteins.

Keywords: Cell biology; Chaperone; Hsp70; Mitochondria; Protein aggregation; Proteostasis; Yeast

DOI: https://doi.org/10.1242/jcs.263680

Nat Commun. 2025 Jul 25. 16(1): 6854

Oligomer-based functions of mitochondrial porin.

Porin, or the voltage-dependent anion channel (VDAC), is a primary β-barrel channel in the mitochondrial outer membrane. It transports small metabolites and ions through its β-barrel pore and plays key roles in apoptosis and inflammatory response. Here we report the cryo-electron microscopy structure of yeast porin (Por1) in its hexameric form at 3.2 Å resolution. This structure allows us to introduce various mutations at the protomer interfaces, uncovering three critical functions of Por1 assembly beyond transport. Por1 binds unassembled Tom22, a subunit of the mitochondrial protein import gate (the TOM complex), to facilitate protein import into the intermembrane space, maintains proper mitochondrial lipid composition in the outer membrane through lipid scramblase activity, and contributes to the retention and regulated loss of mitochondrial DNA, in cooperation with nucleases identified through screening enabled by the obtained Por1 mutant.

DOI: https://doi.org/10.1038/s41467-025-62021-4

Mitochondrion. 2025 Jul 28. pii: S1567-7249(25)00072-8. [Epub ahead of print] 102075

Role of Prohibitins as Guardians of mitochondrial homeostasis.

Sabrina Champsi, David A Hood.

Mitochondria are complex organelles critical to the maintenance of cellular homeostasis. Central to this regulation are Prohibitins (PHBs), a novel set of proteins involved in several mitochondrial quality control pathways, including protein folding, biogenesis, and mitophagy. PHBs mediate various cellular responses including cell survival and myogenesis, suggesting that their roles are intricate and multifaceted. While evidence suggests that PHBs facilitate mitochondrial homeostasis, their exact mechanism of action remains unclear. Elucidating the precise mechanisms driving PHB-mediated adaptations will ultimately enable the development of therapeutic strategies aimed towards the treatment of age-related diseases, characterized by mitochondrial perturbations.

Keywords: Aging; Apoptosis; Mitochondria; Mitophagy; Prohibitin

DOI: https://doi.org/10.1016/j.mito.2025.102075