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Chandran, Suchismita

Biology

2004

M.S.

Lipid rafts are membrane domains that are enriched in glycosphingolipids and cholesterol. They serve as platforms for organizing signal transduction components such as GPI anchored proteins for axon guidance and T cell activation, G proteins (large and small), serpentine receptors, receptor and non-receptor tyrosine kinases. We find that Paramecium surface membranes can be separated in Optiprep/sucrose gradients into fractions by density, which correlate with ganglioside and cholesterol levels. Proteins, such as the GPI - anchored putative folate chemoreceptor and surface antigens, and the plasma membrane calcium pumps separate into the light density fractions, therefore supporting the existence of lipid rafts that organize these proteins in signaling. We use cholera toxin to localize gangliosides as a marker of rafts on the cell surface. We have shown that ganglioside Gm₁ is associated with the low density lipid raft fractions. In order to understand the structure of Paramecium lipid rafts further, we have studied some affects of removal of cholesterol from the plasma membrane of the organism and its implications to chemoresponse and the distribution of signaling proteins in sucrose gradients and on the cell surface.