Fusion of phosphatidylserine and mixed phosphatidylserine-phosphatidylcholine vesicles Dependence on calcium concentration and temperature |
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Authors: | S.T. Sun C.C. Hsang E.P. Day J.T. Ho |
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Affiliation: | Department of Physics and Astronomy, State University of New York at Buffalo, Amherst, NY 14260 U.S.A. |
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Abstract: | Dynamic light scattering has been used to study the temperature dependence of Ca2+-induced fusion of phosphatidylserine vesicles and mixed vesicles containing phosphatidylserine and different phosphatidylcholines. The final vesicle size after Ca2+ and EDTA incubation serves as a measure of the extent of fusion. With phosphatidylserine vesicles, the extent of fusion shows a sharp maximum at an incubation temperature which depends on the Ca2+ concentration between 0.8 and 2 mM. The shift in the fusion peak temperature with Ca2+ concentration is similar to the typical shift in the phase transition temperature with divalent cation concentration in acidic phospholipids. The results suggest a direct correlation between the fusion peak temperature and the phase transition temperature in the presence of Ca2+ prior to fusion. With mixed vesicles containing up to 33% of a phosphatidylcholine in at least 2 mM Ca2+, the extent of fusion as a function of incubation temperature also shows a maximum. The fusion peak temperature is essentially independent of the quantity and type of phosphatidylcholine and the Ca2+ concentration, and identical to that with pure phosphatidylserine in excess Ca2+. The results imply that Ca2+-induced molecular segregation occurs first, and fusion subsequently takes place between pure phosphatidylserine domains. |
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Keywords: | Vesicle fusion Phosphatidylserine Phosphatidylcholine Temperature dependence (Dynamic light scattering) |
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