Somborac, T. | Search bioRxiv

bioRxiv2024

Ribosome-binding protein 1, RRBP1, maintains peroxisomal biogenesis

Peroxisomes are single membrane-bound organelles essential for human health, yet the mechanisms of peroxisome biogenesis are not fully understood. Here using a systematic double screening approach, we identified ribosome-binding protein 1, RRBP1, as a novel peroxisome biogenesis factor in human cells. Deletion of RRBP1 in HEK293T cells led to a reduction in both peroxisome number and peroxisomal protein levels as well as in defects in processing of peroxisomal matrix proteins, such as ACOX1 and thiolase. However, cell proliferation and protein translation were not altered in cells lacking RRBP1. RRBP1 depletion did not affect peroxisome-ER contact sites, and pexophagy did not contribute to the reduction of peroxisomes in RRBP1 KO cells. Instead, in the absence of RRBP1, peroxisomal proteins were processed by proteasomal degradation, suggesting that RRBP1 plays a role in the insertion of these proteins into ER membranes and their stabilization. Altogether our results showed that RRBP1 promotes peroxisome biogenesis in human cells highlighting the power of systematic approaches in discovering novel factors of organellar biogenesis.

cell biology↗

bioRxiv2023

Peroxisomal tail-anchored proteins do not reach peroxisomes via ER, instead mitochondria can be involved.

Peroxisomes are membrane-enclosed organelles with important roles in fatty acid breakdown, glycolysis, and biosynthesis of sterols and ether lipids. Defects in peroxisome biogenesis result in severe neurological diseases, such as Zellweger syndrome, neonatal adrenoleukodystrophy, infantile Refsum disease, and myelopathies. However, many aspects of peroxisomal biogenesis are not well understood. Here we investigated delivery of tail-anchored (TA) proteins to peroxisomes in mammalian cells. Using glycosylation assays we showed that peroxisomal TA proteins do not enter ER in both WT and peroxisome-lacking cells. We observed that in cells lacking the essential peroxisome biogenesis factor, PEX19, peroxisomal TA proteins localize mainly to mitochondria. However, in PEX3 KO cells, which lack peroxisomes as well, the endogenous TA protein, ACBD5, does not target mitochondria, suggesting that PEX3 plays an important role in targeting of peroxisomal TA proteins to mitochondria. Finally, to investigate peroxisomal TA protein targeting in cells with fully functional peroxisomes we used a proximity biotinylation approach. We showed that while ER-targeted TA construct was exclusively inserted into the endoplasmic reticulum (ER), peroxisome-targeted TA construct was inserted to both peroxisomes and mitochondria. Thus, in contrast to previous studies, our data suggest that peroxisomal TA proteins do not insert to the ER prior to their delivery to peroxisomes. Instead, mitochondria can play a role in the targeting of TA proteins to peroxisomes.

cell biology↗