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Biophysical Journal 87:1732-1740 (2004)
© 2004 The Biophysical Society

Insertion of Alzheimer's Aß40 Peptide into Lipid Monolayers

Canay Ege and Ka Yee C. Lee

Department of Chemistry, The Institute for Biophysical Dynamics, and the James Franck Institute, The University of Chicago, Chicago, Illinois

Correspondence: Address reprint requests to Ka Yee C. Lee, PhD, Dept. of Chemistry, The University of Chicago, 5735 S. Ellis Ave., Chicago, IL 60637. Tel: 773-702-7068; Fax: 773-702-0805; E-mail: kayeelee{at}uchicago.edu.

The amyloid beta (Aß) peptide is the major component found in the amyloid deposits in the brains of Alzheimer's disease patients. In vitro studies have demonstrated that the aggregation of Aß can take place at three orders of magnitude lower concentrations in the presence of phospholipid molecules compared to bulk peptide studies, suggesting that membrane lipids may mediate Aß toxicity. To understand the interaction of Aß with lipid membranes, we have examined Aß40 with anionic dipalmitoylphosphatidylglycerol (DPPG), zwitterionic dipalmitoylphosphatidylcholine (DPPC), and cationic dipalmitoyltrimethylammonium propane (DPTAP) monolayers under different subphase conditions. We have used a constant surface pressure insertion assay to assess the degree of peptide insertion into the lipids. Simultaneously, we monitored the surface morphology of the monolayers with fluorescence microscopy. We have also performed dual-probe fluorescence measurements where both the peptide and lipid are tagged with chromophores. Isotherm measurements show that Aß inserts into both DPTAP and DPPG monolayers under physiologically relevant conditions. Insertion into DPPC occurs at lipid densities below that found in a bilayer. The level of insertion is inversely proportional to the lipid packing density. Our results indicate that lipids need not be anionic to interact with Aß. Electrostatic effects involved in Aß40-lipid interaction are discussed.




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