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AKB: Biologische Physik

AKB 50: Poster Session "Biological Physics"

AKB 50.106: Poster

Freitag, 12. März 2004, 10:30–13:00, B

Are there lipid rafts? — •Heiko Heerklotz — Biozentrum Basel, Klingelbergstr. 70, CH-4056 Basel

Functional domains in biological membranes and the role of lipids in the formation of such structures are still not unequivocally clarified. A classical definition of the term lipid rafts refers to large, long-lived domains in native cellular membranes that are formed by a spontaneous de-mixing of a liquid ordered phase rich in sphingomyelin (SM) and cholesterol (Cho) from the fluid, phosphatidylcholine (PC)-rich matrix. Rafts have been believed to accumulate large numbers of proteins and it has been assumed that rafts can be isolated from membranes as so-called detergent resistant membrane fragments (DRMs). Our investigations have revealed however that these common assumptions are inconsistent. Putative lipid rafts having stability properties similar to liquid ordered domains in a PC-SM-Cho mixture cannot be isolated by detergent without changing their properties substantially. We came to this conclusion on the basis of studies of the stability of domains and intermolecular interactions between lipids (POPC-SM-Cho) and detergents (Triton X-100 and others) by various microcalorimetric techniques (isothermal titration calorimetry, differential scanning calorimetry, pressure perturbation calorimetry) and solid-state NMR. A simple thermodynamic model based on the enthalpy and entropy of the interactions of different lipids with the detergent explains the phenomena.