bims-mitpro 2026-03-01 papers

Issue of 2026–03–01
four papers selected by
Andreas Kohler, Umeå University

Nat Struct Mol Biol. 2026 Feb 27.

Stress adaptation of mitochondrial protein import by OMA1-mediated degradation of DNAJC15.

Lara Kroczek, Hendrik Nolte, Yvonne Lasarzewski, Ishita Agrawal, Thibaut Molinié, Daniel Curbelo Piñero, Kathrin Lemke, Elena Rugarli, Thomas Langer.

Mitochondria dynamically adapt to cellular stress to ensure cell survival. The stress-regulated mitochondrial peptidase OMA1 orchestrates these adaptive responses, which limit mitochondrial fusion and promote mitochondrial stress signaling and metabolic rewiring. Here, we show that cellular stress adaptation involves OMA1-mediated regulation of mitochondrial protein import and OXPHOS biogenesis. OMA1 cleaves the mitochondrial chaperone DNAJC15 and promotes its degradation by the m-AAA protease AFG3L2. Loss of DNAJC15 impairs mitochondrial protein import and restricts OXPHOS biogenesis under conditions of mitochondrial dysfunction. Non-imported mitochondrial preproteins accumulate at the endoplasmic reticulum, inducing an unfolded protein response. Our results demonstrate stress-dependent changes in mitochondrial protein import as part of the OMA1-mediated mitochondrial stress response and highlight the interdependence of proteostasis regulation between different organelles.

DOI: https://doi.org/10.1038/s41594-026-01756-0

Nat Cell Biol. 2026 Feb 26.

Mitochondria contact lipid droplets through the mitochondrial import complex binding to lipid metabolism enzyme Ayr1.

Mitochondria play central roles in the energetics and metabolism of eukaryotic cells. Their outer membrane is essential for protein transport, membrane dynamics, signalling and metabolic exchange with other cellular compartments. The mitochondrial import (MIM) complex functions as main translocase for importing the precursors of more than 90% of integral outer-membrane proteins. Here we report that the MIM complex performs a second major function in lipid-droplet homeostasis. Lipid droplets are crucial in cellular lipid metabolism and as storage organelles for neutral lipids. The lipid metabolism enzyme Ayr1 captures the MIM complex, promoting the formation of mitochondria-lipid droplet contact sites. MIM and Ayr1 enhance the lipid droplet number in cells. Ayr1 binds to MIM via its single hydrophobic segment in a substrate-mimicry mechanism but remains bound and is not released into the outer membrane. The functional diversity is mediated by different MIM complexes: MIM-Ayr1 for recruiting lipid droplets and MIM-preprotein for protein insertion into the outer membrane. Our work uncovers translocase capture as a mechanism for functional conversion of a membrane protein complex from protein insertion to lipid metabolism.

DOI: https://doi.org/10.1038/s41556-026-01890-3

Curr Biol. 2026 Feb 24. pii: S0960-9822(26)00134-X. [Epub ahead of print]

Regulation of mitophagy by Fis1 and Fascin1-organized actin.

Shintaro Nakajima, Ting-Yu Wang, Tsui-Fen Chou, Yogaditya Chakrabarty, David C Chan.

Mitophagy, the autophagic degradation of mitochondria, plays a central role in controlling the quality and quantity of mitochondria, thereby ensuring cellular health. The mitochondrial outer membrane protein Fis1 is important for several types of mitophagy, but its mechanism of action remains unclear. F-actin is recruited to autophagic cargo and is important for autophagic progression, but the mechanism for its recruitment is poorly understood. To address the molecular function of Fis1, we performed affinity purification of Fis1 and mass spectrometry and identified the actin-bundling protein Fascin1 as a physical interactor. We demonstrate that Fis1 is required for recruitment of Fascin1 as well as F-actin to mitochondria under stress conditions, including mitochondrial depolarization and iron chelation. Iron chelation also triggers mitophagy that is independent of the Parkinson's associated gene Parkin, and we show that Fis1 enables recruitment of Fascin1-organized F-actin to facilitate proper morphogenesis of autophagosomes and the ensuing mitochondrial degradation. In contrast, although Parkin-mediated mitophagy also relies on Fis1, it is unaffected by loss of Fascin1 or F-actin recruitment. These findings indicate that Fis1 has distinct modes of action in mitophagy, depending on the triggering cellular stress. They establish Fis1 as a key driver of Fascin1 and F-actin recruitment to mitochondria, events that are critical for autophagosome morphogenesis during iron-chelation-induced mitophagy.

Keywords: Fascin1; Fis1; actin; autophagy; mitochondria; mitophagy

DOI: https://doi.org/10.1016/j.cub.2026.01.062

J Biol Chem. 2026 Feb 25. pii: S0021-9258(26)00196-1. [Epub ahead of print] 111326

The AAA-ATPase Yta4 inhibits the interaction between Ppa2 and Atg43 to promote Atg43 phosphorylation and mitophagy.

Ke Liu, Jiajia He, Yifan Wu, Chenhui Zhao, Shuaijie Yan, Fangyuan Xiong, Xing Liu, Xuebiao Yao, Chuanhai Fu.

AAA-ATPase Yta4/Msp1/ATAD1 is a well-known quality control factor that clears mistargeted tail-anchored proteins and precursor proteins on mitochondria. However, whether Yta4 preserves mitochondrial homeostasis through alternate pathways remains unclear. Traditionally, mitophagy has been recognized as a crucial pathway for eliminating dysfunctional mitochondria, thereby ensuring the maintenance of mitochondrial homeostasis. In this study, we unveil a novel role for Yta4 in sustaining mitochondrial homeostasis by facilitating mitophagy in fission yeast. The absence of Yta4 delays the phosphorylation of the mitophagy receptor Atg43 and specifically inhibits mitophagy. Additionally, Atg43 phosphorylation sites Ser32, Ser35, and Ser36, which are crucial for mitophagy, were identified. We further found that the phosphatase Ppa2 plays a major role in Atg43 dephosphorylation and inhibits excessive mitophagy. Yta4 physically interacts with both Atg43 and Ppa2, and coordinates with Ppa2 to modulate Atg43 phosphorylation and mitophagy. Moreover, Yta4 and Ppa2 bind to the same cytosolic region of Atg43, and Yta4 inhibits the interaction between Atg43 and Ppa2. Collectively, our findings suggest that Yta4 promotes mitophagy by ensuring the effectiveness of Atg43 phosphorylation. Thus, our findings reveal the novel function of Yta4 in regulating mitophagy and expand the understanding of the molecular mechanisms underlying mitophagy in fission yeast.

Keywords: ATAD1; PP2A; fission yeast; mitochondria; phosphatase; phosphorylation

DOI: https://doi.org/10.1016/j.jbc.2026.111326