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Quantification of -Synuclein Binding to Lipid Vesicles Using Fluorescence Correlation Spectroscopy

Elizabeth Rhoades ^*, Trudy F. Ramlall , Watt W. Webb ^* and David Eliezer 

^* Applied and Engineering Physics, Cornell University, Ithaca, New York; and Department of Biochemistry and Program in Structural Biology, Weill Medical College of Cornell University, New York, New York

Correspondence: Address reprint requests to David Eliezer, Weill Medical College of Cornell University, Dept. of Biochemistry, 1300 York Ave., New York, NY 10021. Tel.: 212-746-6557; E-mail: dae2005{at}med.cornell.edu; or to Watt W. Webb, Cornell University, School of Applied & Engineering Physics, 212 Clark Hall, Ithaca, NY 14853-2501. Tel.: 607-255-3331; E-mail: www2{at}cornell.edu.

-Synuclein (S) is a soluble synaptic protein that is the major proteinaceous component of insoluble fibrillar Lewy body deposits that are the hallmark of Parkinson's disease. The interaction of S with synaptic vesicles is thought to be critical both to its normal function as well as to its pathological role in Parkinson's disease. We demonstrate the use of fluorescence correlation spectroscopy as a tool for rapid and quantitative analysis of the binding of S to large unilamellar vesicles of various lipid compositions. We find that S binds preferentially to vesicles containing acidic lipids, and that this interaction can be blocked by increasing the concentration of NaCl in solution. Negative charge is not the only factor determining binding, as we clearly observe binding to vesicles composed entirely of zwitterionic lipids. Additionally, we find enhanced binding to lipids with less bulky headgroups. Quantification of the protein-to-lipid ratio required for binding to different lipid compositions, combined with other data in the literature, yields an upper bound estimate for the number of lipid molecules required to bind each individual molecule of S. Our results demonstrate that fluorescence correlation spectroscopy provides a powerful tool for the quantitative characterization of S-lipid interactions.

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