Abstract
The differentiation of protein properties and biological functions arises from the variation in the primary and secondary structure. Specifically, in abnormal assemblies of protein, such as amyloid peptide, the secondary structure is closely correlated with the stable ensemble and the cytotoxicity. In this work, the early Aβ33‐42 aggregates forming the molecular monolayer at hydrophobic interface are investigated. The molecular monolayer of amyloid peptide Aβ33‐42 consisting of novel parallel β‐strand‐like structure is further revealed by means of a quantitative nanomechanical spectroscopy technique with force controlled in pico‐Newton range, combining with molecular dynamic simulation. The identified parallel β‐strand‐like structure of molecular monolayer is distinct from the antiparallel β‐strand structure of Aβ33‐42 amyloid fibril. This finding enriches the molecular structures of amyloid peptide aggregation, which could be closely related to the pathogenesis of amyloid disease.
Highlights
Aβ33-42 originates from residue 703–712 of the amyloid precursor protein (APP).[15]. This short peptide is a protein segment located in the transmembrane domain of APP that is an integral membrane protein that attaches to biological membranes.[16]
The short time incubation (30 min) of Aβ33-42 was determined to be typical β-strand secondary structure (Figure 1e) by using synchrotron radiation circular dichroism (SRCD) spectroscopy,[20] which is independent of the concentration from 200 to 50 × 10−6 M
It is of utmost significance to introduce the artificial surface to reveal the pathway of amyloid peptide assembly
Summary
The mediated self-assembled structure of Aβ33-42 was identified by quantitative nanomechanical mapping with force controlled in pN range.[14,21] The topography image (Figure 2a) reveals three components, including the fibrils, a few spherical oligomers, and the substrate. The fibrils and spherical oligomers are directly identified from their morphology, and they possess the lowest contrast in the stiffness map compared to the other species. The stiffness of the amyloid fibrils determined is consistent with the ones in the previous researches.[24] The newfound molecular monolayer structure is three times stiffer than. The coverage area of three different species (i = 5.2%; ii = 70.9%; iii = 23.9%) determined from Figure 2c demonstrates that the peptide molecular monolayer (ii) is the dominant nanostructure (70.9% surface coverage) in comparison with the spherical oligomers and fibrillary structures (total 5.2%, i).
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