Interaction Of The Supported Planar Lipid Bilayer And The Amyloid-β

Alzheimer’s disease(AD) is the most common form of neurodegenerative disorder, which is manifested through loss of memory, disorientation and performing daily tasks. The number of people suffering AD increases every year. In recent years, there has been great interests and progresses in the development of molecular level strategies to target steps in the pathogenesis of AD. Though various strategies for the diagnosis of AD have been proposed, the pathogenesis of AD is still in quest eagerly. Studies have shown that one of the primary pathological hallmarks of AD is the presence of insoluble neuritic plaques composed of amyloid-β peptides(Aβs) primarily, which contains both Aβ(1-40) and Aβ(1-42). Many reports suggest that the aggregation of toxic Aβ(1-40) peptides occurs on membrane containing GM1-ganglioside(GM1). GM1 are abundant in the neuronal system and play a key role in the aggregation of Aβ.Supported planar lipid bilayers(SPBs) have been usually used as cell membrane systems in vitro for studying lipid-protein and cell-cell interactions. They have potential applications in medical implants, programmed drug delivery, as well as the production of catalytic interfaces and biosensors. Raman spectroscopy has been a powerful analytical tool providing molecular-structural information. It is very useful for studying biomolecules in a native aqueous environment since the Raman scattering cross section of water molecule is very small. Recently, a rapid increase of applications of Raman spectroscopy in particular to address biomedical question has gotten many attention. Raman spectra provide extensive information at the molecular level based on intrinsic molecular vibrations arising from specific components in the physic-chemical makeup of a material. And it has the potential to offer detailed chemical and structural analysis of SPBs. However, Raman scattering is a weak effect and easily swamp by competing photophysical processes. Especially, it is difficult to obtain the molecular structure information of SPBs since the Raman signal of SPBs is very weak with the only 5-6 nm thickness. Previously, a Raman microspectroscopy system for studying SPBs has been developed, which combined a Raman spectrometer, microscope and confocal system to provide high spatial resolution and signal collection from small sample volumes.In this paper, we investigate the interaction between Aβ(1-40) and the SPBs containing GM1 by several methods. The SPBs are prepared on the solid substrates mica and SiO2. By performing Fluorescence microscope and Raman microscopy, we obtained the morphology and molecular vibrations of SPBs composed of GM1, SM and Chol. The effects of materials on the conformation of SPBs and the interaction between Aβ(1-40) and SPbs. We instert Aβ(1-40) for different time. According to the Raman spectra at different time, the adhesion process and the interaction between Aβ(1-40) peptides with the SPBs containing GM1 have been analyzed in detail. It is demonstrated that the formed the SPBs on mica are in a liquid-crystalline state and the increasing amount of ganglioside GM1 can decrease the lateral interaction between and the order of the acyl chains of the SPBs. The ν(C-C) vibration in the ring of N-Acetylneuraminic acid(Neu5Ac) of ganglioside-GM1 head group has been observed. The Aβ(1-40) has been found to interact initially with the galactose ring of ganglioside-GM1 head group, leading to its binding and gradual aggregation onto the membrane surface. The obvious change of Raman spectroscopy in the ν(C–H) region confirms that the hydrophobic C-terminal of Aβ(1-40) inserts itself into the SPBs and affects the hydrophobic acyl chains. The Raman data indicate that α-helix and β-sheet structures of Aβ(1-40) increase and coexist over longer time frames, and the vibration of aromatic residues Phenylalanine(Phe) and Tyrosine(Tyr), components of Aβ(1-40) peptides, have also been detected. On the basis of these results, a model has been proposed to describe the mechanism of the conformation transition and the aggregation of Aβ(1-40) mediated by lipid bilayers containing ganglioside-GM1. We also investigate the insulation and stability of SPBs( GM1/SM/Chol) formed on gold electrode. The electrochemical properties of Aβ(1-40) on the SPBs and the effects of Aβ(1-40) on the SPBs are studied by cyclic voltammetry and electrochemical impedance spectroscopy.It is found that Aβ(1-40) can defect the SPBs.