PEX1G843D remains functional in peroxisome biogenesis but is rapidly degraded by the proteasome.

Abstract

The PEX1/PEX6 AAA-ATPase is required for the biogenesis and maintenance of peroxisomes. Mutations in HsPEX1 and HsPEX6 disrupt peroxisomal matrix protein import and are the leading cause of Peroxisome Biogenesis Disorders (PBDs). The most common disease-causing mutation in PEX1 is the HsPEX1^G843D allele, which results in a reduction of peroxisomal protein import. Here we demonstrate that in vitro the homologous yeast mutant, ScPex1^G700D, reduces the stability of Pex1's active D2 ATPase domain and impairs assembly with Pex6, but can still form an active AAA-ATPase motor. In vivo, ScPex1^G700D exhibits only a slight defect in peroxisome import. We generated model human HsPEX1^G843D cell lines and show that PEX1^G843D is rapidly degraded by the proteasome, but that induced overexpression of PEX1^G843D can restore peroxisome import. Additionally, we found that the G843D mutation reduces PEX1's affinity for PEX6, and that impaired assembly is sufficient to induce degradation of PEX1^WT. Lastly, we found that fusing a deubiquitinase to PEX1^G843D significantly hinders its degradation in mammalian cells. Altogether, our findings suggest a novel regulatory mechanism for PEX1/PEX6 hexamer assembly and highlight the potential of protein stabilization as a therapeutic strategy for PBDs arising from the G843D mutation and other PEX1 hypomorphs.