Hansenula polymorpha Vam7p is required for macropexophagy |
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Authors: | Stevens Patricia Monastyrska Iryna Leão-Helder Adriana N van der Klei Ida J Veenhuis Marten Kiel Jan A K W |
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Institution: | Eukaryotic Microbiology, Groningen Biomolecular Sciences and Biotechnology Institute (GBB), University of Groningen, P.O. Box 14, 9751 AA Haren, The Netherlands. |
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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. |
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Keywords: | Autophagy Peroxisome Pexophagy Selective organelle degradation SNARE Yeast |
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