Self-assemblies of amyloid beta peptides on glycolipid-embedded membranes

Abstract

Amyloid fibirl formation is a common phenomena of proteins obserbed on biomembranes. This phenomena is induced by a consecutive process of nucleation and elongation. The nucleation of proteins has been reported to occur on (bio)membranes. Of lipids in biosystem, glycolipids is an important species to predominate the accumulation and conformation change of proteins. Recently, beta-octyl-glucoside (b-CG), a derivative of cholesterol (Ch) that Ch is linked to glucose by a 1-4 glucoside bonding, played a role for a stress reponse of membrane surface against the heat and other environmental cahnges [1]. Such derivatives of lipids was embedded into lipid membranes to enhance the binding of amyloid beta peptides (Aβ) to membranes. Here, Aβis a causative protein of Alzheimer's disease. This was because glucoside cluster effect might promote the binding of peptides to membranes via a formation of hydgene bonding network.

Amyloid fibirl formation of Aβ was first examined in the presence and absence of b-CG-embedded DMPC liposomes. Unique self-assemblies of Aβ was observed, e.g. spherulitic fibrillar aggregates (spherulite) [2]. To clarify the mechanism of such self-assemblies, the kinetic analysis of fibril formation of Aβ. A concentration dependench of b-CG on nucleaton rate was observed.Alternatively, Aβ could interact with b-CG-embedded membranes in a manner of concentration dependency of b-CG.As a control, Ch-embedded membranes indicated the fibril formation propensity of Aβ different from that of b-CG-embedded membranes.Therefore, glucose group linked to Ch might act as the binding part with Aβ.This finding was supported by the peptide-adsorption experiment based on a quarzcrystal microbalance method and surface pressure measurement.

Alternatively, fluorescence probe-labelled Aβ was used to visualize how the lateral diffusion of Aβ was influenced by b-CG. First, b-CG was clearly seprarated from DMPC lipids, which was called b-CG rich domain. Next, we monitored the lateral diffusivity of labelled-Aβ with TIRFM and observed a localization of Aβ on the b-CG-rich domain. In addition, Aβ could be laterally diffused on DMPC and from DMPC to b-CG rich domain, whereas the lateral diffusion of amyloid beta peptiteds from b-CG rich domain to DMPC was not observed. These observations suggested that association process of Aβs occurred on b-CG rich domain rather than DMPC region. Lateral diffusivity of Aβ was determined by the orientation of Aβ into the surface of lipid membranes. As a cmparison, the orientation of Aβ into polymer membranes (polylactic acid, polymethyl methacrylate, and polyvinylpyrroridone) depended on the entanglement of Aβ with polymer membranes [3].

Further time-development of the associated Aβ formed the nuclei and fibrils. Finally, the self-assemblies of amyloid beta peptides on the b0CG embedded membranes induced the spherulitic fibrillar aggregate.

[1] H. Akiyama et al., J. Biol. Chem., 295, 5257-5277 (2020)

[2] T. Shimanouchi et al., Biophys. Biochim. Acta, 1870, 140816 (2022)

[3] T. Shimanoujchi et al., Appl. Sci., 11, 4480 (2021)