Investigation of amyloid-beta peptide interactions with membrane lipids

This thesis describes three investigations into the individual lipid mobility: A single molecule investigation into lipid mobility in model systems, a study of the interaction between lipids and the Amyloid-beta peptide and a study of the single molecule mobility in cell membranes.; Mobility of individual lipids in Langmuir monolayers was investigated. The mobility of lipids in monolayers was unaffected by changes to the area available per molecule. A novel trough was developed, comprising of a stage made of polydimethylsiloxane, with an inlet and outlet, where a sessile drop is formed. Using the inlet and outlet, the area available per molecule can be adjusted and materials can be introduced into the subphase without perturbing the interface. It was found that the area per molecule does not affect the mobility of the lipids in the monolayer.; The interactions between Amyloid-beta peptide and lipid monolayers and bilayers were studied. Neurons are special in that they have an extraordinarily large surface area to volume ratio. This feature makes them much more susceptible to interactions between membrane lipids and the Abeta peptide than other cells. It was seen that the peptide, when exposed to lipids, was fragmented into smaller aggregates. Both small soluble oligomers as well as large aggregates were fragmented to smaller entities. Fluorescence measurements showed that the smaller aggregates can pass through a bilayer membrane into the interior of giant vesicles. Monolayer exhibited domains with no motion at all, whereas other areas showed regular mobility.; The final part of this research focused on the interactions between lipids in cellular membranes and the Abeta peptide. Quantum dots were found to have an affinity for the cellular membrane which has not been reported previously, their diffusion coefficient was remarkably lower than reported in literature for organic fluorophores. The diffusion coefficient for this probe is equivalent to membrane proteins, about a tenth of the diffusion coefficient for a normal organic fluorophore attached to a lipid. When the cells are exposed to the Abeta peptide, very little change in mobility is observed. Cells die after exposure to the peptide for more than 12 hours.