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Why are Lipid Rafts a Major Research Topic in Molecular Biophysics? Lessons from Yeast Cells and Supported Lipid Bilayers

By: Rodrigo Almeida
From: FCUL, Univ. Lisboa
At: Instituto de Investigação Interdisciplinar, Anfiteatro
[2010-12-09] 11:30

At present, cellular membranes are considered to be organized in different hierarchical levels, and lipids play a crucial role in the regulation of such complex organization. They are responsible for the formation of membrane domains, including the sphingolipid- and sterol-enriched lipid rafts, which are crucial in cellular physiology and pathology. Accordingly, lipid therapy, i.e. tackling human diseases through manipulation of membrane lipid domains, is emerging. In the past, binary and ternary lipid phase diagrams, which are models for lipid rafts, were obtained from a combination of spectroscopic and imaging techniques. Fluorescence anisotropy, excited-state lifetimes and resonance energy transfer allow determining several biophysical properties of the lipid phases. This paved the way to characterize lipid domains in cellular membranes. Recently, we have found a new type of lipid raft in the plasma membrane of Saccharomyces cerevisiae, which is sphingolipid-enriched but ergosterol-depleted. These solid ordered domains were considered absent in eukaryotic cells under physiological conditions, but our findings suggest an important physiological role in regulating membrane order, signaling and trafficking. We also prepare lipid membranes deposited on solid supports and characterize them with high spatial resolution using atomic force microscopy. We found that the effects of ethanol in lipid membranes are intimately related with membrane domains. Currently, we study lipid rafts formed on gold surfaces due to their potential biosensing applications. The presence of rippled structures throughout these fluid membranes suggests that the interaction with the solid surface may induce a long range order that is usually associated to non-fluid bilayers.