PEX5, the Shuttling Import Receptor for Peroxisomal Matrix Proteins, Is a Redox‐Sensitive Protein

• Published in: Traffic (Copenhagen, Denmark) Vol. 15; no. 1; pp. 94 - 103
• Main Authors: Apanasets, Oksana, Grou, Cláudia P., Van Veldhoven, Paul P., Brees, Chantal, Wang, Bo, Nordgren, Marcus, Dodt, Gabriele, Azevedo, Jorge E., Fransen, Marc
• Format: Journal Article
• Language: English
• Published: Former Munksgaard John Wiley & Sons A/S 01.01.2014; Wiley Subscription Services, Inc
• Subjects: Cell Line; Cysteine - genetics; Cysteine - metabolism; Cytosol - metabolism; Glutathione - metabolism; Humans; monoubiquitination; Oxidation-Reduction; Oxidative Stress; Peroxisome-Targeting Signal 1 Receptor; peroxisomes; Peroxisomes - metabolism; PEX5; protein import; Protein Sorting Signals; Protein Transport; Proteins; PTS1; Receptors, Cytoplasmic and Nuclear - chemistry; Receptors, Cytoplasmic and Nuclear - genetics; Receptors, Cytoplasmic and Nuclear - metabolism; redox switch; Ubiquitination; PEX5; PTS1; redox switch; peroxisomes; protein import; monoubiquitination; oxidative stress
• ISSN: 1398-9219; 1600-0854
• DOI: 10.1111/tra.12129

Mounting evidence suggests that oxidative stress impairs peroxisomal matrix protein import. This study provides direct evidence that the import of PTS1 matrix proteins into peroxisomes is indeed a redox‐regulated process, and that this redox‐sensitivity is mediated by PEX5, the shuttling receptor for PTS1 proteins. In addition, it demonstrates that Cys11 of human PEX5 functions as a redox switch that modulates PEX5 activity in response to intracellular oxidative stress, most likely by modulating its monoubiquitination at the peroxisomal membrane. Peroxisome maintenance depends on the import of nuclear‐encoded proteins from the cytosol. The vast majority of these proteins is destined for the peroxisomal lumen and contains a C‐terminal peroxisomal targeting signal, called PTS1. This targeting signal is recognized in the cytosol by the receptor PEX5. After docking at the peroxisomal membrane and release of the cargo into the organelle matrix, PEX5 is recycled to the cytosol through a process requiring monoubiquitination of an N‐terminal, cytosolically exposed cysteine residue (Cys11 in the human protein). At present, the reason why a cysteine, and not a lysine residue, is the target of ubiquitination remains unclear. Here, we provide evidence that PTS1 protein import into human fibroblasts is a redox‐sensitive process. We also demonstrate that Cys11 in human PEX5 functions as a redox switch that regulates PEX5 activity in response to intracellular oxidative stress. Finally, we show that exposure of human PEX5 to oxidized glutathione results in a ubiquitination‐deficient PEX5 molecule, and that substitution of Cys11 by a lysine can counteract this effect. In summary, these findings reveal that the activity of PEX5, and hence PTS1 import, is controlled by the redox state of the cytosol. The potential physiological implications of these findings are discussed.