Degradation of the Gluconeogenic Enzyme Fructose-1, 6-Bisphosphatase is Dependent on the Vacuolar ATPase.
The key gluconeogenic enzyme fructose-1,6-bisphosphatase (FBPase) is induced during glucose starvation. After the addition of glucose, inactivated FBPase is selectively targeted to Vid (vacuolar import and degradation) vesicles and then to the vacuole for degradation. To identify proteins involved in this pathway, we screened various libraries for mutants that failed to degrade FBPase. Via these approaches, subunits of the vacuolar- H(+)-ATPase (V-ATPase) have been identified repeatedly. The V-ATPase has established roles in endocytosis, sorting of carboxypeptidase Y and homotypic vacuole fusion. Here, we show that mutants lacking Stv1p, Vph1p, and other subunits of the V-ATPase are defective for FBPase degradation. FBPase was detected in Vid vesicles. However, most FBPase was resistant to proteinase K digestion in the Deltavph1 or vma mutants, whereas the majority of FBPase was sensitive to proteinase K digestion in the Deltastv1 mutant. Therefore, STV1 and VPH1 have distinct functions in FBPase degradation. In cells lacking V(0) genes, Vma2p and Vma5p were still detected on Vid vesicles and vacuoles, suggesting that the distribution of V(1) proteins is independent of V(0) genes. The V(0) and V(1) domains are assembled following a glucose shift and the assembly is not regulated by protein kinase A and RAV genes. Assembly of the V(0) complex is necessary for FBPase trafficking, since mutants that block the assembly and transport of V(0) out of the ER were defective in FBPase degradation.[1]References
- Degradation of the Gluconeogenic Enzyme Fructose-1, 6-Bisphosphatase is Dependent on the Vacuolar ATPase. Liu, J., Brown, C.R., Chiang, H.L. Autophagy. (2005) [Pubmed]
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