RUI: Tetrahymena: A Model for Eukaryotic Phospholipid Metabolism

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This research will continue to develop the use of the ciliate protozoan Tetrahymena thermophila as a model system for the study of eukaryotic phospholipid metabolism. The research focuses on the interrelationships between the pathways of phosphatidylethanolamine and phosphatidylcholine biosynthesis, with particular emphasis on elaborating the newly-discovered cross-regulation between ethanolamine kinase and choline kinase in which choline phosphate has been shown to activate ethanolamine kinase. The possible role of this regulation in vivo will be investigated by examining levels of the intermediates in the pathways (ethanolamine, ethanolamine phosphate, CDP-ethanolamine, choline, choline phosphate and CDP- choline) under normal growth conditions and under conditions in which the levels of these intermediates may be perturbed (by using analogs of choline and ethanolamine.) The results will elaborate the potential for metabolic channelling of intermediates in the phospholipid biosynthetic pathways. Enzymes from bovine liver, such as the ethanolamine kinase and choline kinase will also be examined in order to elaborate similarities and differences in phospholipid biosynthesis between Tetrahymena and higher eukaryotes. The role of lipids in the structure and function of biological membranes has been of major interest for a considerable period of time. Modifications of the physical state of lipids and of the types of lipids in a given membrane have led to some understanding of requirements for membrane fluidity, surface charge and polar head groups. All of these aspects appear to be important to normal operation of a given membrane system. The phospholipid composition of eukaryotes varies from tissue to tissue, from cell type to cell type within a given tissue and even between membrane types with in a given cell. How these differences in phospholipid composition in eukaryotes arise has been of considerable interest and relates to such clinical problems as defects in formation of the surfactant dipalmitoylphosphatidylcholine in the human lung. This research explores the first reactions in phospholipid biosynthesis (ethanolamine and choline kinases) which exhibit great variability in structure and properties between various tissues and between organisms. These differences suggest possible additional regulation at this step in the phospholipid biosynthetic pathways in some tissues. This possiblity will be examined in Tetrahymena (a unicellular eukaryote) whose pathways for pospholipid biosynthesis are the same as those in mammals. The research will extensively involve undergraduates and will expose them to the intensive laboratory experience which they will encournter in their funther scientific careers.