Single-molecule studies of amyloid proteins: from biophysical properties to diagnostic perspectives

Abstract

In neurodegenerative diseases, a wide range of amyloid proteins or peptides such as amyloid-beta and α-synuclein fail to keep native functional conformations, followed by misfolding and self-assembling into a diverse array of aggregates. The aggregates further exert toxicity leading to the dysfunction, degeneration and loss of cells in the affected organs. Due to the disordered structure of the amyloid proteins, endogenous molecules, such as lipids, are prone to interact with amyloid proteins at a low concentration and influence amyloid cytotoxicity. The heterogeneity of amyloid proteinscomplicates the understanding of the amyloid cytotoxicity when relying only on conventional bulk and ensemble techniques. As complementary tools, single-molecule techniques (SMTs) provide novel insights into the different subpopulations of a heterogeneous amyloid mixture as well as the cytotoxicity, in particular as involved in lipid membranes. This review focuses on the recent advances of a series of SMTs, including single-molecule fluorescence imaging, single-molecule force spectroscopy and single-nanopore electrical recording, for the understanding of the amyloid molecular mechanism. The working principles, benefits and limitations of each technique are discussed and compared in amyloid protein related studies.. We also discuss why SMTs show great potential and are worthy of further investigation with feasibility studies as diagnostic tools of neurodegenerative diseases and which limitations are to be addressed.

The channel activities of the full-length prion and truncated proteins

“…Soluble low-molecular weight PrP oligomers are much more infectious and neurotoxic than insoluble PrP Sc fibrils in vitro and in vivo (5,6). This supports the common mechanism 'toxic oligomer hypothesis' (7) for neurodegeneration where the oligomers emerge as the most neurotoxic species (8) through permeabilizing cellular membranes and causing cell dysfunction (9,10).…”

Amyloid-beta–copper interaction studied by simultaneous nitrogen K and copper L2,3-edge soft X-ray absorption spectroscopy

“…Ab is cleaved from intramembrane proteolytic processing of amyloid precursor protein (APP) by b-/g-secretase (Selkoe and Hardy, 2016). The Ab peptides may aggregate into transient and on-pathway oligomers, and eventually deposit as insoluble fibrils within the plaques (Luo et al, 2014) (Wu et al, 2020(Wu et al, , 2021. Among these aggregates, on-pathway oligomers are assumed in many studies to induce the neuronal dysfunction (Glabe, 2008).…”

Cross interactions between Apolipoprotein E and amyloid proteins in neurodegenerative diseases

“…The basic structure of all amyloids is the fibril, which is built up by twisted protofilaments that are stacks of protein layers in a β-sheet structure [4] . Amyloid proteins can convert stepwise from soluble monomers into oligomers and then into the insoluble β-sheet fibrils [5] . There are several functional and pathological amyloids.…”