Structure and function of the peroxisomal ubiquitin ligase complex

Peroxisomes are essential organelles that perform diverse metabolic functions, including fatty acid oxidation and reactive oxygen species detoxification. While many peroxisomal enzymes are synthesized in the cytosol and imported into the organelle, the process of receptor recycling remains poorly understood. Prior research has shown that peroxisomal import receptors must return to the cytosol after delivering cargo. This gap motivated investigations into the mechanisms that regulate receptor turnover. No prior work had resolved how ubiquitination is used to control receptor fate. Understanding this process is important for addressing peroxisomal biogenesis disorders like the Zellweger spectrum. Researchers have long sought to clarify how ubiquitin ligases function in this context. The role of RING finger proteins in ubiquitination is well established, but their specific contributions to receptor recycling remain unclear. This paper explores the structural and functional basis of receptor ubiquitination in peroxisomes.

The aim of this study is to investigate the structure and function of the peroxisomal ubiquitin ligase complex. This complex is composed of PEX2, PEX10, and PEX12, which are RING finger domain-containing proteins. The study seeks to clarify how these proteins facilitate receptor recycling after import into peroxisomes. The researchers propose that the complex acts as a retro-translocation channel. Understanding this mechanism is essential for elucidating how peroxisomal import receptors are returned to the cytosol. The study also explores how monoubiquitination and polyubiquitination differ in their roles. The researchers aim to determine how each subunit contributes to the overall structure of the complex. This work may provide insight into the molecular basis of peroxisomal biogenesis disorders.

The researchers used cryo-electron microscopy to determine the structure of the ubiquitin ligase complex. They analyzed the arrangement of transmembrane segments contributed by each subunit. The study included functional assays to assess how the complex interacts with peroxisomal import receptors. The researchers examined the role of each RING finger domain in ubiquitination. They tested whether the complex forms an open channel for retro-translocation. The study also involved measuring receptor ubiquitination under different conditions. The researchers used biochemical techniques to confirm the localization of ubiquitinated receptors. The results were compared to prior knowledge of ubiquitin ligase function in other organelles.

The cryo-EM structure revealed that the ubiquitin ligase complex forms an open channel with five transmembrane segments per subunit. The N terminus of the receptor is likely inserted into the pore from the lumenal side of the peroxisome. Monoubiquitination by one RING finger domain enables receptor extraction into the cytosol. If receptor recycling is compromised, polyubiquitination occurs via the other two RING finger domains. The complex functions as a retro-translocation channel for peroxisomal import receptors. The structure suggests that the channel is open on both sides of the membrane. The findings indicate that each subunit contributes equally to channel formation. The study provides the first detailed structural model of this ubiquitin ligase complex.

The study provides mechanistic insight into peroxisomal protein import and receptor recycling. The ubiquitin ligase complex functions as a retro-translocation channel, as proposed by the authors. Each subunit contributes five transmembrane segments to form an open pore. Monoubiquitination by one RING finger domain enables receptor extraction. Polyubiquitination by the other two domains leads to receptor degradation. The findings clarify how receptor fate is regulated by ubiquitination status. The structure supports the hypothesis that the complex is essential for receptor turnover. The authors suggest that these findings may inform future studies on peroxisomal biogenesis disorders.