Spatially resolved spectroscopic differentiation of hydrophilic and hydrophobic domains on individual insulin amyloid fibrils

Abstract

The formation of insoluble β-sheet-rich protein structures known as amyloid fibrils is associated with numerous neurodegenerative diseases, such as Alzheimer’s and Parkinson’s disease. A detailed understanding of the molecular structure of the fibril surface is of interest as the first contact with the physiological environment in vivo and plays a decisive role in biological activity and associated toxicity. Recent studies reveal that the inherent sensitivity and specificity of tip-enhanced Raman scattering (TERS) renders this technique a compelling method for fibril surface analysis at the single-particle level. Here, the reproducibility of TERS is demonstrated, indicating its relevance for detecting molecular variations. Consequently, individual fibrils are systematically investigated at nanometer spatial resolution. Spectral parameters were obtained by band-fitting, particularly focusing on the identification of the secondary structure via the amide III band and the differentiation of hydrophobic and hydrophilic domains on the surface. In addition multivariate data analysis, specifically the N-FINDR procedure, was employed to generate structure-specific maps. The ability of TERS to localize specific structural domains on fibril surfaces shows promise to the development of new fibril dissection strategies and can be generally applied to any (bio)chemical surface when structural variations at the nanometer level are of interest.

Nanoscale Structural Organization of Insulin Fibril Polymorphs Revealed by Atomic Force Microscopy–Infrared Spectroscopy (AFM‐IR)

“…Therefore, the fibril surface of this polymorph is coated by a thin layer of α‐helical/ unordered protein. It should also be noted that this fibril polymorph was previously observed by Deckert‐Gaudig and co‐workers using TERS …”

“…They found that the fibril surface is heterogeneous from the viewpoint of both protein secondary structure and amino acid composition. Using TERS, Deckert‐Gaudig and co‐workers showed that unordered protein secondary structure dominates on the fibril surface, whereas the fibril core is composed of β‐sheets . The Zenobi group demonstrated that amyloid β 1–42 fibrils have sophisticated structures with turns, unstructured coils, and β‐sheets simultaneously present on the fibril surface .…”

High resolution spectroscopy reveals fibrillation inhibition pathways of insulin

“…Data were not further analysed regarding the amino acid distribution; however, if required, such an analysis is certainly possible, as we have reported elsewhere. See for instance refs 16 and 38.…”

Atomic Force Microscopy Meets Biophysics, Bioengineering, Chemistry, and Materials Science

“…[44] Therefore, the combination of AFM (which can be operated in liquid conditions) with Raman spectroscopy can be usefult oi nvestigate both topographical and chemicalc hanges at the nanoscale for aw ide range of (biological) samples, such as fibril proteins, [45] carbon nanotubes, [46] DNA, [47] and cells. [44] Therefore, the combination of AFM (which can be operated in liquid conditions) with Raman spectroscopy can be usefult oi nvestigate both topographical and chemicalc hanges at the nanoscale for aw ide range of (biological) samples, such as fibril proteins, [45] carbon nanotubes, [46] DNA, [47] and cells.…”