Hansenula polymorpha Vam7p is required for macropexophagy.
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.
Stevens
Patricia
P
Eukaryotic Microbiology, Groningen Biomolecular Sciences and Biotechnology Institute (GBB), University of Groningen, P.O. Box 14, 9751 AA Haren, The Netherlands.
Monastyrska
Iryna
I
Leão-Helder
Adriana N
AN
van der Klei
Ida J
IJ
Veenhuis
Marten
M
Kiel
Jan A K W
JA
D008969:Molecular Sequence Data; D015388:Organelles / Q000502:physiology; D020675:Peroxisomes / Q000378:metabolism*; D010843:Pichia / Q000737:chemistry*; D050765:Qa-SNARE Proteins; D050767:Qc-SNARE Proteins / Q000502:physiology; D050600:SNARE Proteins / Q000502:physiology; D029701:Saccharomyces cerevisiae Proteins / Q000502:physiology; D050825:Synaptosomal-Associated Protein 25; D014617:Vacuoles / Q000502:physiology* / Q000648:ultrastructure
D050765:Qa-SNARE Proteins; D050767:Qc-SNARE Proteins; D050600:SNARE Proteins; D029701:Saccharomyces cerevisiae Proteins; D050825:Synaptosomal-Associated Protein 25; C107706:VAM3 protein, S cerevisiae; C494205:VAM7 protein, S cerevisiae