Hansenula polymorpha Vam7p is required for macropexophagy

Area of Science:

• Cell Biology
• Molecular Biology
• Yeast Genetics

Background:

• Peroxisome degradation is essential for cellular homeostasis.
• Vacuolar t-SNAREs (Vam3p, Vam7p) are known to be involved in vacuole biogenesis in yeast.
• The specific roles of these proteins in peroxisome turnover remain to be fully elucidated.

Purpose of the Study:

• To investigate the functions of vacuolar t-SNAREs Vam3p and Vam7p in peroxisome degradation in Hansenula polymorpha.
• To analyze the impact of mutations in these proteins on peroxisome biogenesis and morphology.

Main Methods:

• Genetic analysis of Vam3p and Vam7p deletion mutants in Hansenula polymorpha.
• Microscopy techniques to observe peroxisome degradation (macropexophagy, microautophagy) and peroxisome morphology.
• Subcellular localization studies of Vam3p and Vam7p.

Main Results:

• A mutant lacking Vam7p (Hp-vam7) showed severe defects in both selective macropexophagy and non-selective microautophagy.
• Deletion of Hp-Vam3p function had minimal impact on peroxisome degradation.
• Hp-Vam7p localized to the vacuolar membrane and cytosol, while Hp-Vam3p was primarily at the vacuolar membrane.
• Hp-VAM7 deletion also disrupted peroxisome biogenesis, leading to multi-compartment organelles and mitochondrial association.

Conclusions:

• Vam7p is a key regulator of peroxisome degradation pathways in Hansenula polymorpha.
• Vam3p appears to be functionally redundant in peroxisome degradation in this yeast.
• The t-SNARE complex involving Vam3p and Vam7p likely plays a role in membrane fusion events during macropexophagy.
• Vam7p is also essential for proper peroxisome biogenesis, and its absence causes significant morphological abnormalities.