Metabolomics analysis reveals novel aspects of 2-hydroxyglutarate homeostasis and links citramalate to branched chain amino acid metabolism

Cells produce a wide variety of metabolic products. Many of these metabolites have annotated functions in supporting the life of a cell or organism, but many others whose functions are unknown or unclear are considered errors in metabolism. It is well established that cell metabolism changes based on the type and quantity of the nutrients available. The work presented herein explores how growth on different nutrient types affects the metabolism of two compounds with incompletely defined roles: citramalate and 2-hydroxyglutarate (2-HG). I leverage the genetic and metabolic tools available for the yeast Saccharomyces cerevisiae to examine the metabolism of these two isomeric compounds. I demonstrate that citramalate is a product of pyruvate and acetyl-CoA whose synthesis is catalyzed by leucine biosynthesis enzyme Leu4. I show that citramalate is produced when cells adapt to mitochondrial dysfunction and propose that citramalate synthesis is an alternate, energetically conservative path to isoleucine biosynthesis. The findings described here expand our understanding of branched chain amino acid biosynthesis. The oncometabolite D-2-HG is believed to be the product of metabolic error because it is produced from the readily available compound α-ketoglutarate by a variety of enzymes with other, already well established functions. In the yeast Saccharomyces cerevisiae D-2-HG is produced by the first enzyme in serine biosynthesis, phosphoglycerate dehydrogenase. I show that D-2-HG metabolism may contribute to mitochondrial electron transport and is also regulated by mitochondrial health. I show there are two metabolic pathways in yeast for the turnover of D-2-HG that occur in different sub-cellular compartments. The work presented in this thesis shows that "off-target" catalysis by metabolic enzymes can be means for cells to adapt to changing nutrient availability.Ph.D.2020-07-11 00:00:0