Kinetics and enthalpy measurements of interaction between beta-amyloid and liposomes by surface plasmon resonance and isothermal titration microcalorimetry.

The objective of this research is to understand the interaction mechanism of beta-amyloid (Abeta) with cell and were basically divided into two parts. The first part focused on the time-dependent structural changes of Abeta (1-40) by circular dichroism (CD) spectroscopy, thioflavin T (ThT) fluorescence assay, and atomic force microscopy (AFM). The second part emphasized the kinetics and enthalpy of interaction between Abeta (1-40) and liposome by surface plasmon resonance (SPR) and isothermal titration microcalorimetry (ITC). Results obtained from CD, ThT and AFM confirmed the formation of 1 microm fibril after single day incubation. The driving force of kinetic interaction between Abeta and liposomes was revealed by SPR to be electrostatics. Further studies indicated that fresh Abeta has high GM1 affinity. Besides, addition of cholesterol to the liposome could alter membrane fluidity and affect the interactions of fresh Abeta with liposomes especially in the amount of Abeta absorbed and preserving the structure of liposome after adsorbing. Hydrophobicity was found to be the driving force leading to the interaction between Abeta fibrils and liposomes. These reactions are endothermic as supported by ITC measurements. When the composition of liposomes is zwitterionic lipids, the interaction of Abeta with liposomes is predominantly hydrophobic force. In contrast, the driving force of interaction of charged lipids with Abeta is electrostatic.