Research Interests
The major focus of our laboratory is to understand the role of compartmentation of enzymes and metabolites in biological regulation. The organellar localization of metabolic pathways requires considerable expenditure of metabolic energy for protein targeting, organelle assembly, and movement of substrates and products across intracellular membranes. Such expenditures must result in biological efficiencies commensurate with the investment of biological resources. However, it is not always clear what advantages are conferred by such compartmentation. We have focused our attention on arginine metabolism in Neurospora crassa because it encompasses many of the compartmental features characteristic of eukaryotic cells. Biosynthesis of arginine originates in the mitochondria but culminates in the cytosol. Intermediates and arginine cross both mitochondrial membranes. More than 95% of the intramycelial pool of arginine is sequestered in the vacuoles. Our hypothesis is that these compartmentation features play a significant role in the biology of the organism. We are investigating the metabolic consequences of relocating the arginine biosynthetic enzymes from the mitochondrial matrix to the cytosol: structural genes are being altered so that their products are no longer translocated into the mitochondria; the physiological consequences of such enzyme mislocation is being examined. We are also examining how variations in cytosolic arginine concentrations are communicated across the mitochondrial membranes to coordinately inhibit two enzymes of arginine biosynthesis: cell biology techniques are being used to identify and characterize transport systems in intracellular (organellar) membranes and molecular techniques are being used to construct mutants defective in the movement of metabolites across intracellular membranes. Control of arginine degradation is being examined by characterizing the expression, structure and properties of arginase, the initial catabolic enzyme. Initial results suggest the existence of multiple promoters and products from a single gene which are expressed under different conditions. The results of these research projects will provide insight into the function of enzyme and amino acid compartmentation in eukaryotic cells.