MITOL regulates phosphatidic acid-binding activity of RMDN3/PTPIP51

The transfer of phospholipids from the endoplasmic reticulum (ER) to mitochondria via the mitochondria-ER contact site (MERCS) is essential for maintaining mitochondrial function and integrity. Here, we identified RMDN3/PTPIP51, possessing phosphatidic acid (PA)-transfer activity, as a neighbouring protein of the mitochondrial E3 ubiquitin ligase MITOL/MARCH5 by proximity-dependent biotin labelling using APEX2. We found that MITOL interacts with and ubiquitinates RMDN3. Mutational analysis identified lysine residue 89 in RMDN3 as a site of ubiquitination by MITOL. Loss of MITOL or the substitution of lysine 89 to arginine in RMDN3 significantly reduced the PA-binding activity of RMDN3, suggesting that MITOL regulates the transport of PA to mitochondria by activating RMDN3. Our findings imply that ubiquitin signalling regulates phospholipid transport at the MERCS.

Automated summary

The study identifies a mechanism by which ubiquitin signaling regulates phospholipid transport at the mitochondria-ER contact site (MERCS). It demonstrates that MITOL interacts with RMDN3 and ubiquitinates it to modulate phospholipid transfer. This sheds light on the role of ubiquitin signaling in maintaining mitochondrial function and integrity.