Figure 4.

In S. cerevisiae, gluconeogenic enzymes undergo distinct glucose-induced, GID complex-dependent degradation mechanisms. Left: 1. In cells starved of glucose for 24 hours, glucose replenishment triggers Gid4 induction. 2. Gid4 associates with the GID complex via Gid5 and recruits gluconeogenic enzymes to the complex. 3. Gluconeogenic enzymes are ubiquitinated by the GID complex via the E2 enzyme Ubc8. This requires the Hsp70 chaperone Ssa1. 4. Polyubiquitinated gluconeogenic enzymes are delivered to the proteasome, which involves cdc48, Dsk2, and Rad23. 5. Gluconeogenic enzymes are degraded. Right: During long-term glucose starvation, gluconeogenic enzymes are secreted as extracellular vesicles in the periplasm (*). 1. Upon glucose replenishment, the gluconeogenic enzymes undergo endocytosis and localize at actin patches, which requires End3 and PI3 kinase Vps34. At the same time, Gid4 expression is induced. 2. At actin patches, 30–50 nm membrane-bound vesicles (named Vid vesicles) are formed with the gluconeogenic enzyme in the lumen and the Gid1–Gid4–Gid5–Sec28 complex on the periphery. Importing the gluconeogenic enzyme substrate into the lumen requires Ssa2. 3. The Vid vesicles aggregate and form endosome-like clusters of varying size that disassociate from actin. 4. The vesicles are delivered to the vacuole, which requires cAMP signaling. 5. The gluconeogenic enzymes are degraded in the vacuole, but other Vid vesicle proteins are returned to the cytosol. In both mechanisms, cells adapt back to a normal state of glycolysis. Created with Biorender.com (accessed on 21 April 2022).