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Identification and characterization of the putative human peroxisomal C-terminal targeting signal import receptor
M Fransen1, C Brees, E Baumgart
1Afdeling Farmakologie, Katholieke Universiteit Leuven, Belgium.
Abstract:
To identify proteins interacting with the C-terminal peroxisomal targeting signal (PTS1), we screened a human liver cDNA library by means of a Saccharomyces cerevisiae genetic system, known as the two-hybrid system. We isolated a cDNA encoding a protein that specifically bound the PTS1 topogenic signal in the intact yeast cell but also in vitro after bacterial expression and purification. Sequence analysis of the full-length cDNA revealed the presence of an open reading frame encoding a 70-kDa polypeptide that belongs to the tetratricopeptide repeat family and that is homologous to the PAS8 and PAS10 gene products, which are required for the formation of normal peroxisomes in yeast. Subcellular fractionation of human liver and immunofluorescence studies on HepG2 cells demonstrated that this PTS1-binding protein is present exclusively in peroxisomes and that the PTS1-binding domain is located to the cytosolic side of the peroxisomal membrane. All available evidence indicates that the PTS1-binding protein is part of the peroxisomal protein import machinery and most probably is the long sought after human PTS1 import receptor.
Insights
Researchers identified a novel protein that binds to the peroxisomal targeting signal (PTS1). This protein is crucial for peroxisomal protein import, acting as the human PTS1 import receptor.
Area of Science:
- Cell Biology
- Molecular Biology
- Biochemistry
Background:
- Peroxisomes are essential organelles involved in various metabolic processes.
- The import of proteins into peroxisomes is a complex process.
- The C-terminal peroxisomal targeting signal (PTS1) directs many proteins to peroxisomes.
Purpose of the Study:
- To identify proteins that interact with the PTS1.
- To characterize the function of the PTS1-binding protein in peroxisomal import.
Main Methods:
- Yeast two-hybrid system screening of a human liver cDNA library.
- In vitro binding assays after bacterial expression and purification.
- Subcellular fractionation of human liver cells.
- Immunofluorescence studies on HepG2 cells.
Main Results:
- A cDNA encoding a 70-kDa tetratricopeptide repeat protein was isolated.
- This protein specifically binds the PTS1 signal both in vivo and in vitro.
- The protein is localized exclusively to peroxisomes, with its binding domain on the cytosolic side of the membrane.
- It is homologous to yeast peroxisomal proteins PAS8 and PAS10.
Conclusions:
- The identified protein is a component of the peroxisomal protein import machinery.
- It is likely the human PTS1 import receptor, essential for peroxisome biogenesis and function.