Kinetics and enthalpy measurements of interaction between P-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 (A beta) with cell and were basically divided into two parts. The first part focused on the time-dependent structural changes of A beta (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 A beta (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 mu m fibril after single day incubation. The driving force of kinetic interaction between A beta and liposomes was revealed by SPR to be electrostatics. Further studies indicated that fresh A beta has high GM1 affinity. Besides, addition of cholesterol to the liposome could alter membrane fluidity and affect the interactions of fresh A beta with liposomes especially in the amount of A beta absorbed and preserving the structure of liposome after adsorbing. Hydrophobicity was found to be the driving force leading to the interaction between A beta fibrils and liposomes. These reactions are endothermic as supported by ITC measurements. When the composition of liposomes is zwitterionic lipids, the interaction of A beta with liposomes is predominantly hydrophobic force. In contrast, the driving force of interaction of charged lipids with A beta is electrostatic. (C) 2007 Elsevier B.V. All rights reserved.