PEX1^G843D remains functional in peroxisome biogenesis but is rapidly degraded by the proteasome

Area of Science:

• Cell Biology
• Molecular Biology
• Genetics

Background:

• Peroxisome biogenesis disorders (PBDs) are severe genetic diseases caused by defects in peroxisome assembly.
• Mutations in PEX1 and PEX6, which encode AAA-ATPases essential for peroxisomal matrix protein import, are the most frequent cause of PBDs.
• The HsPEX1^G843D mutation is the most common PEX1 pathogenic allele, leading to reduced protein import.

Purpose of the Study:

• To investigate the molecular mechanisms underlying the HsPEX1^G843D mutation's impact on peroxisome biogenesis.
• To explore the role of PEX1/PEX6 assembly and stability in PBDs.
• To assess the therapeutic potential of protein stabilization for PEX1-related PBDs.

Main Methods:

• Comparative analysis of yeast (ScPex1^G700D) and human (HsPEX1^G843D) PEX1 mutants.
• In vitro studies of ATPase activity and Pex1/Pex6 assembly.
• Generation and analysis of human cell lines expressing HsPEX1^G843D.
• Investigation of protein degradation pathways (proteasome).
• Functional studies involving deubiquitinase fusion to PEX1^G843D.

Main Results:

• The yeast ScPex1^G700D mutant showed reduced stability and impaired Pex6 assembly but retained ATPase activity, with only minor in vivo import defects.
• Human HsPEX1^G843D was rapidly degraded by the proteasome in cell lines, but overexpression could restore peroxisome import.
• The G843D mutation decreased PEX1's affinity for PEX6, and impaired assembly induced degradation of wild-type PEX1.
• Fusing a deubiquitinase to PEX1^G843D reduced its degradation in mammalian cells.

Conclusions:

• The PEX1 G843D mutation destabilizes the PEX1/PEX6 complex, leading to PEX1 degradation and impaired peroxisome function.
• Impaired PEX1/PEX6 assembly is a key factor triggering PEX1 degradation.
• Stabilizing PEX1 protein presents a promising therapeutic strategy for PBDs caused by PEX1 hypomorphic mutations.