Vid28 Protein Is Required for the Association of Vacuole Import and Degradation (Vid) Vesicles with Actin Patches and the Retention of Vid Vesicle Proteins in the Intracellular Fraction

Abstract

Gluconeogenic enzymes are induced when Saccharomyces cerevisiae are starved of glucose. However, when glucose is added to prolonged starved cells, these enzymes are degraded in the vacuole via the vacuole import and degradation (Vid) pathway. The Vid pathway is linked to the nonclassical secretory and internalizing pathways. In prolonged starved cells, substantial amounts of the key gluconeogenic enzyme fructose-1,6-bisphosphatase (FBPase) are in the extracellular fraction (periplasm). However, when glucose is added to glucose-starved cells, levels of extracellular FBPase decrease rapidly. Ultrastructural studies indicate that FBPase is in Vid/endosomes following glucose addition, suggesting that FBPase is internalized in response to glucose refeeding. Under the same conditions, the majority of Vid vesicle proteins are in the intracellular fraction. In yeast, actin polymerization is involved in endocytosis. Vid vesicles associate with actin patches initially, and they dissociate later. Here, we show that VID28 plays a critical role in the association of Vid vesicles with actin patches and the retention of Vid vesicle proteins in the intracellular fraction. Vid28p was distributed to Vid vesicles and interacted with other Vid vesicle proteins. Vid28p contains an Armadillo (ARM) domain required for FBPase degradation. When VID28 was deleted or when the ARM domain was mutated, Vid vesicles failed to co-localize with actin patches, and Vid vesicle proteins appeared in the extracellular fraction. We suggest that the ARM domain is required for the association of Vid vesicles with actin patches and the retention of Vid vesicle proteins in the intracellular fraction.