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

The objective of this research is to understand the interaction mechanism of β-amyloid (Aβ) with cell and were basically divided into two parts. The first part focused on the time-dependent structural changes of Aβ (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 Aβ (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 μm fibril after single day incubation. The driving force of kinetic interaction between Aβ and liposomes was revealed by SPR to be electrostatics. Further studies indicated that fresh Aβ has high GM1 affinity. Besides, addition of cholesterol to the liposome could alter membrane fluidity and affect the interactions of fresh Aβ with liposomes especially in the amount of Aβ absorbed and preserving the structure of liposome after adsorbing. Hydrophobicity was found to be the driving force leading to the interaction between Aβ fibrils and liposomes. These reactions are endothermic as supported by ITC measurements. When the composition of liposomes is zwitterionic lipids, the interaction of Aβ with liposomes is predominantly hydrophobic force. In contrast, the driving force of interaction of charged lipids with Aβ is electrostatic.