AFM-Based Single Molecule Techniques: Unraveling the Amyloid Pathogenic Species

Abstract

BackgroundA wide class of human diseases and neurodegenerative disorders, such as Alzheimer’s disease, is due to the failure of a specific peptide or protein to keep its native functional conformational state and to undergo a conformational change into a misfolded state, triggering the formation of fibrillar cross-β sheet amyloid aggregates. During the fibrillization, several coexisting species are formed, giving rise to a highly heterogeneous mixture. Despite its fundamental role in biological function and malfunction, the mechanism of protein self-assembly and the fundamental origins of the connection between aggregation, cellular toxicity and the biochemistry of neurodegeneration remains challenging to elucidate in molecular detail. In particular, the nature of the specific state of proteins that is most prone to cause cytotoxicity is not established.Methods:In the present review, we present the latest advances obtained by Atomic Force Microscopy (AFM) based techniques to unravel the biophysical properties of amyloid aggregates at the nanoscale. Unraveling amyloid single species biophysical properties still represents a formidable experimental challenge, mainly because of their nanoscale dimensions and heterogeneous nature. Bulk techniques, such as circular dichroism or infrared spectroscopy, are not able to characterize the heterogeneity and inner properties of amyloid aggregates at the single species level, preventing a profound investigation of the correlation between the biophysical properties and toxicity of the individual species.Conclusion:The information delivered by AFM based techniques could be central to study the aggregation pathway of proteins and to design molecules that could interfere with amyloid aggregation delaying the onset of misfolding diseases.

Studies for Improving a Rat Model of Alzheimer’s Disease: Icv Administration of Well-Characterized β-Amyloid 1-42 Oligomers Induce Dysfunction in Spatial Memory

“…The main problem is the heterogeneous nature and the nanoscale dimensions of the amyloid assemblies. Circular dichroism and infrared spectroscopy are bulk techniques and cannot characterize the inner properties of the aggregates at the single species level [ 57 ].…”

“…The crucial problem of the application of Aβ in rat models is the heterogeneity of the peptide samples [ 57 ]. Aβ exists in vitro and in vivo as a continuum of different oligomeric states, none of which are particularly stable.…”

Oligomerization and Conformational Change Turn Monomeric β-Amyloid and Tau Proteins Toxic: Their Role in Alzheimer’s Pathogenesis

“…The determination of fAβ structure has been a challenge owing to its structural polymorphism. Several physicochemical, spectroscopic, and biochemical techniques (solid-state NMR, high-speed atomic force microscopy [66], transition microscopy, Raman and 2D infrared spectroscopy [67], X-ray fiber diffraction, small angle neutron scattering [68,69], cryo-EM) [70] have been used for structural analysis of AβOs and fibrils. Computational studies have also been used for studying conformational dynamics and stability of different Aβ assemblies [71,72].…”

β-Amyloid and the Pathomechanisms of Alzheimer’s Disease: A Comprehensive View

“…Not only might the size of Aβ-aggregates be important for toxicity, but also the peptide conformation. A formidable experimental challenge is the analysis of the biophysical properties and conformation of a single Aβ-species (e.g., Aβ 1-42), mainly because of their nanoscale dimensions and heterogeneous nature [ 54 ]. Bulk techniques (CD or IR spectroscopy) are not able to characterize the heterogeneity and inner conformational properties of amyloid aggregates at the single species level.…”