Regulation of glucose metabolism by P21-Activated Kinases (PAKs), Ste20 and Cla4: using the budding yeast Saccharomyces cerevisiae as a model organism

Abstract

Glucose, an important macromolecule, serves as a major source of energy in most organisms. Its regulation is a vital process mediated by a number of enzymes including protein kinases such as the p-21-activated kinases, PAKs. PAKs are highly conserved serine/threonine kinases that are involved in a wide range of biological functions including including glucose homeostasis. In S.cerevisiae, two of these kinases, Ste20 and Cla4, are well characterised. In this study, the interaction between these kinases and the enzymes involved in glycolysis, gluconeogenesis, pentose phosphate pathway and glycerol synthesis from glycolysis were tested and identified by the split ubiquitin system. furthermore, the effect of Ste20 and Cla4 were investigated in the expression level and phosphorylation of Gpd1p – an enzyme that catalyse the rate limiting step in the synthesis of glycerol- under various conditions mediated by these kinases including optimal growth condition, hyperosmotic stress and glucose response. Data obtained showed that levels of Gpd1p and its phosphorylation status were significantly reduced when both kinases are mutated but remained unchanged in single deletion strains. finally, the reduced levels of Gpd1 observed in double mutant strain of STE20 and CLA4 had no effect on the accumulation of glycerol. These results demonstrate that Ste20 and Cla4 contribute to protein stability of Gpd1.