The ides of MARCH5: The E3 ligase essential for peroxisome degradation by pexophagy

A recent study by Zheng et al. (2021. J. Cell Biol.https://doi.org/10.1083/jcb.202103156) identifies the ubiquitin-protein ligase (E3) MARCH5 as a dual-organelle localized protein that not only targets to mitochondria but also to peroxisomes in a PEX19-mediated manner. Moreover, the authors demonstrate that the Torin1-dependent induction of pexophagy is executed by the MARCH5-catalyzed ubiquitination of the peroxisomal membrane protein PMP70.

The importomer is a peroxisomal membrane protein translocase

ABSTRACTThree sites of membrane protein biogenesis (the endoplasmic reticulum, mitochondria and chloroplasts) receive unfolded substrates from organelle-specific protein targeting factors, then integrate them using separate translocation channels. Peroxisomes also receive membrane proteins from known targeting factors, but whether a separate translocase is needed for integration remains unknown. Here, using a novel genetic screening strategy, we reveal that the importomer–known for matrix protein import–integrates the peroxisomal membrane protein Pex14. In importomer mutants, Pex14 is arrested in a pre-integrated state on the peroxisome surface. To undergo integration, a Pex14 translocation signal binds the importomer’s substrate receptor Pex5 at a distinct site from matrix proteins. En bloc translocation of an engineered protein complex with Pex14’s luminal region argues that integration occurs without substrate unfolding. Our work shows that the handling of membrane protein targeting and integration by discrete machineries is a fundamental principle shared by diverse membrane protein biogenesis pathways.

Pex24 and Pex32 tether peroxisomes to the ER for organelle biogenesis, positioning and segregation

We analyzed all four Pex23 family proteins of the yeast Hansenula polymorpha, which localize to the ER. Of these Pex24 and Pex32, but not Pex23 and Pex29, accumulate at peroxisome-ER contacts, where they are important for normal peroxisome biogenesis and proliferation and contribute to organelle positioning and segregation.Upon deletion of PEX24 and PEX32 - and to a lesser extent of PEX23 and PEX29 - peroxisome-ER contacts are disrupted, concomitant with peroxisomal defects. These defects are suppressed upon introduction of an artificial peroxisome-ER tether.Accumulation of Pex32 at peroxisomes-ER contacts is lost in the absence of the peroxisomal membrane protein Pex11. At the same time peroxisome-ER contacts are disrupted, indicating that Pex11 contributes to Pex32-dependent peroxisome-ER contact formation.Summarizing, our data indicate that H. polymorpha Pex24 and Pex32 are tethers at peroxisome-ER contacts that are important for normal peroxisome biogenesis and dynamics.SummaryTwo Hansenula polymorpha ER proteins, Pex24 and Pex32, are tethers at peroxisome-ER contacts and function together with the peroxisomal protein Pex11. Their absence disturbs these contacts leading to multiple peroxisomal defects, which can be restored by an artificial tether.

The membrane remodeling protein Pex11p activates the GTPase Dnm1p during peroxisomal fission

The initial phase of peroxisomal fission requires the peroxisomal membrane protein Peroxin 11 (Pex11p), which remodels the membrane, resulting in organelle elongation. Here, we identify an additional function for Pex11p, demonstrating that Pex11p also plays a crucial role in the final step of peroxisomal fission: dynamin-like protein (DLP)-mediated membrane scission. First, we demonstrate that yeast Pex11p is necessary for the function of the GTPase Dynamin-related 1 (Dnm1p) in vivo. In addition, our data indicate that Pex11p physically interacts with Dnm1p and that inhibiting this interaction compromises peroxisomal fission. Finally, we demonstrate that Pex11p functions as a GTPase activating protein (GAP) for Dnm1p in vitro. Similar observations were made for mammalian Pex11β and the corresponding DLP Drp1, indicating that DLP activation by Pex11p is conserved. Our work identifies a previously unknown requirement for a GAP in DLP function.