Gcn5p and Ubp8p Affect Protein Ubiquitylation and Cell Proliferation by Altering the Fermentative/Respiratory Flux Balance in Saccharomyces cerevisiae

Protein ubiquitylation regulates not only endocellular trafficking and
proteasomal degradation but also the catalytic activity of enzymes. In Saccharomyces
cerevisiae, we analyzed the composition of the ubiquitylated proteomes in strains
lacking acetyltransferase Gcn5p, Ub-protease Ubp8p, or both to understand their involvement in the regulation of protein ubiquitylation. We analyzed His6Ub proteins
with a proteomic approach coupling micro-liquid chromatography and tandem mass
spectrometry (LC-MS/MS) in gcn5?, ubp8? and ubp8? gcn5? strains. The Ub-proteome
altered in the absence of Gcn5p, Ubp8p, or both was characterized, showing that 43%
of the proteins was shared in all strains, suggesting their functional relationship. Remarkably, all major glycolytic enzymes showed increased ubiquitylation. Phosphofructokinase 1, the key enzyme of glycolytic flux, showed a higher and altered pattern of
ubiquitylation in gcn5? and ubp8? strains. Severe defects of growth in poor sugar
and altered glucose consumption confirmed a direct role of Gcn5p and Ubp8p in affecting the REDOX balance of the cell.
IMPORTANCE We propose a study showing a novel role of Gcn5p and Ubp8p in the
process of ubiquitylation of the yeast proteome which includes main glycolytic enzymes. Interestingly, in the absence of Gcn5p and Ubp8p glucose consumption and
redox balance were altered in yeast. We believe that these results and the role of
Gcn5p and Ubp8p in sugar metabolism might open new perspectives of research
leading to novel protocols for counteracting the enhanced glycolysis in tumors.