Vacuolar localization of oligomeric alpha-mannosidase requires the cytoplasm to vacuole targeting and autophagy pathway components in Saccharomyces cerevisiae
Mu. Hutchins et Dj. Klionsky, Vacuolar localization of oligomeric alpha-mannosidase requires the cytoplasm to vacuole targeting and autophagy pathway components in Saccharomyces cerevisiae, J BIOL CHEM, 276(23), 2001, pp. 20491-20498
One challenge facing eukaryotic cells is the posttranslational import of pr
oteins into organelles. This problem is exacerbated when the proteins assem
ble into large complexes. Aminopeptidase I (API) is a resident hydrolase of
the vacuole/lysosome in the yeast Saccharomyces cerevisiae. The precursor
form of API assembles into a dodecamer in the cytosol and maintains this ol
igomeric form during the import process. Vacuolar delivery of the precursor
form of API requires a vesicular mechanism termed the cytoplasm to vacuole
targeting (Cvt) pathway. Many components of the Cvt pathway are also used
in the degradative autophagy pathway. alpha -Mannosidase (Ams1) is another
resident hydrolase that enters the vacuole independent of the secretory pat
hway; however, its mechanism of vacuolar delivery has not been established.
We show vacuolar localization of Ams1 is blocked in mutants that are defec
tive in the Cvt and autophagy pathways. We have found that Ams1 forms an ol
igomer in the cytoplasm. The oligomeric form of Ams1 is also detected in su
bvacuolar vesicles in strains that are blocked in vesicle breakdown, indica
ting that it retains its oligomeric form during the import process. These r
esults identify Ams1 as a second biosynthetic cargo protein of the Cvt and
autophagy pathways.