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<p>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.</p>

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

  • 期刊论文

  • 发表日期：

    2026年2月26日

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  • Sandra Heinen,
  • Vitasta Tiku,
  • Alexander Grevel,
  • Marie Hugenroth,
  • Lars Ellenrieder,
  • Isabelle Steymans,
  • Mariya Licheva,
  • Sara Bonini,
  • Silke Oeljeklaus,
  • Nicole Okon,
  • Jessica Lambertz,
  • Sylvia Poppe,
  • Jiyao Song,
  • Lars Fester,
  • Chris Meisinger,
  • Bettina Warscheid,
  • Matthias Eckhardt,
  • Nils Wiedemann,
  • Dominic Winter,
  • Claudine Kraft,
  • Fabian den Brave,
  • Maria Bohnert,
  • Nikolaus Pfanner,
  • Thomas Becker

摘要

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.