Confinement of Aβ1−40 Peptides in Liposome for Structural Characterization by Solid-State NMR

Abstract

One of the hallmarks of the Alzheimer’s disease (AD) is the amyloid plaques consisting of β-amyloid (Aβ) fibrils. Aβ oligomers have been considered as an important intermediate in the pathway of fibrillization, and are suggested to be the primary pathological species of AD. However, little is known about the molecular structure of Aβ oligomers because of their structural heterogeneity and transient nature. Therefore, we attempt to use liposomes to limit the fibrillization process by providing a confined space for Aβ1−40 in order to obtain stabilized oligomers, for which solid-state NMR technique can be utilized to identify the molecular structure. In this work, liposomes containing approximately 14% of Aβ1−40 monomers are synthesized with the reverse-phase evaporation method, which is more efficient than the thin-film liposome preparation method. However, instead of being confined by liposomes, the peptides form fibrils at a surprisingly low concentration of 3 μM. We propose that the liposomes may maintain a high local concentration of peptides, and may act as two-dimensional templates to accelerate the fibrillization of Aβ1−40. Solid-state NMR spectra reveal that the fibrils possess β-sheet secondary structure which is structurally different from oligomers prepared in buffer solution at 4 degrees Celsius. The chemical shift data of our fibril sample show significant difference from those reported for Tycko’s fibrils incubated in bulk solution. Additional experiments are required to confirm whether or not the structural distinction of our fibril sample is due to the modulation effect of liposomes.