Hansenula polymorpha Pex1p and Pex6p are peroxisome-associated AAA proteins that functionally and physically...

Area of Science:

• Cell Biology
• Molecular Biology
• Biochemistry

Background:

• Peroxisome biogenesis is essential for cellular function.
• Peroxins are proteins involved in peroxisome assembly.
• Defects in peroxisome formation lead to disease.

Purpose of the Study:

• To clone and characterize the Hansenula polymorpha PEX1 and PEX6 genes.
• To investigate the function and interaction of HpPex1p and HpPex6p in peroxisome assembly.
• To understand the role of these proteins in peroxisomal matrix protein import.

Main Methods:

• Functional complementation of peroxisome-deficient mutants.
• Gene cloning and characterization.
• Cell fractionation and co-sedimentation assays.
• Protein interaction studies (in vivo).
• Overexpression studies.

Main Results:

• HpPex1p and HpPex6p are ATPases belonging to the AAA protein family.
• Deletion mutants (Deltapex1, Deltapex6) show impaired peroxisome formation with matrix proteins in the cytosol.
• HpPex1p and HpPex6p are loosely membrane-bound, face the cytosol, and interact physically and functionally.
• Overexpression of PEX6 causes import defects, rescued by PEX1 co-overproduction.
• Overproduced proteins are membrane-bound but show partial co-localization with HpPex3p.

Conclusions:

• HpPex1p and HpPex6p form a complex associated with the peroxisomal membrane.
• This complex is vital for peroxisomal matrix protein import.
• Mislocalized HpPex6p can interfere with HpPex1p function, disrupting peroxisome assembly.