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Updated: Aug 15, 2026
Monitoring Stub1-Mediated Pexophagy
Published on: May 12, 2023
Hansenula polymorpha Vam7p is required for macropexophagy
Patricia Stevens1, Iryna Monastyrska, Adriana N Leão-Helder
1Eukaryotic Microbiology, Groningen Biomolecular Sciences and Biotechnology Institute (GBB), University of Groningen, P.O. Box 14, 9751 AA Haren, The Netherlands.
Abstract:
We have analyzed the functions of two vacuolar t-SNAREs, Vam3p and Vam7p, in peroxisome degradation in the methylotrophic yeast Hansenula polymorpha. A Hp-vam7 mutant was strongly affected in peroxisome degradation by selective macropexophagy as well as non-selective microautophagy. Deletion of Hp-Vam3p function had only a minor effect on peroxisome degradation processes. Both proteins were located at the vacuolar membrane, with Hp-Vam7p also having a partially cytosolic location. Previously, in baker's yeast Vam3p and Vam7p have been demonstrated to be components of a t-SNARE complex essential for vacuole biogenesis. We speculate that the function of this complex in macropexophagy includes a role in membrane fusion processes between the outer membrane layer of sequestered peroxisomes and the vacuolar membrane. Our data suggest that Hp-Vam3p may be functionally redundant in peroxisome degradation. Remarkably, deletion of Hp-VAM7 also significantly affected peroxisome biogenesis and resulted in organelles with multiple, membrane-enclosed compartments. These morphological defects became first visible in cells that were in the mid-exponential growth phase of cultivation on methanol, and were correlated with accumulation of electron-dense extensions that were connected to mitochondria.
Insights
In Hansenula polymorpha yeast, Vam7p is crucial for peroxisome degradation, while Vam3p plays a minor role. Vam7p deficiency also impairs peroxisome biogenesis, causing abnormal organelle structures.
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.
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