bims-mitpro 2025-08-17 papers

Issue of 2025–08–17
two papers selected by
Andreas Kohler, Umeå University

Cell. 2025 Aug 07. pii: S0092-8674(25)00811-6. [Epub ahead of print]

Principles of cotranslational mitochondrial protein import.

Zikun Zhu, Saurav Mallik, Taylor A Stevens, Riming Huang, Emmanuel D Levy, Shu-Ou Shan.

Nearly all mitochondrial proteins are translated on cytosolic ribosomes. How these proteins are subsequently delivered to mitochondria remains poorly understood. Using selective ribosome profiling, we show that nearly 20% of mitochondrial proteins can be imported cotranslationally in human cells. Cotranslational import requires an N-terminal presequence on the nascent protein and contributes to localized translation at the mitochondrial surface. This pathway does not favor membrane proteins but instead prioritizes large, multi-domain, topologically complex proteins, whose import efficiency is enhanced when targeted cotranslationally. In contrast to the early onset of cotranslational protein targeting to the endoplasmic reticulum (ER), the presequence on mitochondrial proteins is inhibited from initiating targeting early during translation until a large globular domain emerges from the ribosome. Our findings reveal a multi-layered protein sorting strategy that controls the timing and specificity of mitochondrial protein targeting.

Keywords: NAC; TOM complex; cotranslational protein import; localized translation; mitochondria; mitochondrial targeting sequence; nascent polypeptide-associated complex; protein folding; protein targeting; ribosome profiling

DOI: https://doi.org/10.1016/j.cell.2025.07.021

Nat Commun. 2025 Aug 09. 16(1): 7367

Mitochondrial damage triggers the concerted degradation of negative regulators of neuronal autophagy.

Bishal Basak, Erika L F Holzbaur.

Mutations that disrupt the clearance of damaged mitochondria via mitophagy are causative for neurological disorders including Parkinson's. Here, we identify a Mitophagic Stress Response (MitoSR) activated by mitochondrial damage in neurons and operating in parallel to canonical Pink1/Parkin-dependent mitophagy. Increasing levels of mitochondrial stress trigger a graded response that induces the concerted degradation of negative regulators of autophagy including Myotubularin-related phosphatase (MTMR)5, MTMR2 and Rubicon via the ubiquitin-proteasome pathway and selective proteolysis. MTMR5/MTMR2 inhibit autophagosome biogenesis; consistent with this, mitochondrial engulfment by autophagosomes is enhanced upon MTMR2 depletion. Rubicon inhibits lysosomal function, blocking later steps of neuronal autophagy; Rubicon depletion relieves this inhibition. Targeted depletion of both MTMR2 and Rubicon is sufficient to enhance mitophagy, promoting autophagosome biogenesis and facilitating mitophagosome-lysosome fusion. Together, these findings suggest that therapeutic activation of MitoSR to induce the selective degradation of negative regulators of autophagy may enhance mitochondrial quality control in stressed neurons.

DOI: https://doi.org/10.1038/s41467-025-62379-5