Background: Pex20 recycling and degradation depend on its ubiquitination. Results: Ubiquitination of Pex20 and the roles of the E2 enzyme Pex4, the RING peroxins (Pex2/Pex10/Pex12), and Pex7 in Pex20 ubiquitination were determined in vivo. Conclusion: The RING peroxins and Pex4 are required for Pex20 mono/polyubiquitination, whereas Pex7 is only required for its polyubiquitination. Significance: This novel mechanism of ubiquitination is not used by other PTS receptors.

Peroxisomes are essential organelles responsible for many metabolic reactions, such as the oxidation of very long chain and branched fatty acids, D-amino acids and polyamines, as well as the production and turnover of hydrogen peroxide. They comprise a class of organelles called microbodies, including glycosomes, glyoxysomes and Woronin bodies. Dysfunction of human peroxisomes causes severe and often fatal peroxisome biogenesis disorders (PBDs). Peroxisomal matrix protein import is mediated by receptors that shuttle between the cytosol and peroxisomal matrix using ubiquitination/deubiquitination reactions and ATP hydrolysis for receptor recycling. We focus on the machinery involved in the peroxisomal matrix protein import cycle, highlighting recent advances in peroxisomal matrix protein import, cargo release and receptor recycling/degradation.