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

Abstract

Spontaneous aggregation of misfolded proteins typically results in the formation of morphologically and structurally different amyloid fibrils, protein aggregates that are strongly associated with various neurodegenerative disorders. Elucidation of the structural organization of amyloid aggregates is crucial to understanding their role in the onset and progression of these diseases. Using atomic force microscopy–infrared spectroscopy (AFM‐IR), we investigated the structural organization of insulin fibrils. We found that insulin aggregation results in the formation of two structurally different fibril polymorphs. One polymorph has a β‐sheet core surrounded by primarily unordered protein secondary structure. This polymorph has β‐sheet‐rich surface, whereas the surface of the other fibril polymorph is primarily composed of unordered protein. Using AFM‐IR, we also revealed the structural organization of the insulin oligomers. Finally, we discovered a new pathway for amyloid fibril formation that is based on a fusion of several oligomers into a single fibril structure.

The degree of unsaturation of fatty acids in phosphatidylserine alters the rate of insulin aggregation and the structure and toxicity of amyloid aggregates

“…High-speed AFM (HS-AFM) [12,13] atomic force microscopy infrared (AFM-IR) [14][15][16][17][18] and tipenhanced Raman spectroscopy [19][20][21][22][23] are scanning probe methods that can be utilized to unravel nanoscale structural organization of amyloid oligomers.…”

Nanoscale Hyperspectral Imaging of Amyloid Secondary Structures in Liquid

“…TERS also gave insight into the secondary structure of insulin [5] or amyloid‐β (Aβ 1‐42 ) [6, 7] aggregates as well as the insulin aggregates influenced by several aggregation inhibitors during aggregation [8] . Simultaneously, infrared nano‐spectroscopy has been increasingly used for the nanoscale investigation of amyloids such as Josephin, [9] insulin, [10] and to study the interaction between Aβ 1‐42 and lipids [11] …”

“…[4] TERS also gave insight into the secondary structure of insulin [5] or amyloid-b (Ab 1-42 ) [6,7] aggregates as well as the insulin aggregates influenced by several aggregation inhibitors during aggregation. [8] Simultaneously, infrared nano-spectroscopy has been increasingly used for the nanoscale investigation of amyloids such as Josephin, [9] insulin, [10] and to study the interaction between Ab 1-42 and lipids. [11] The secondary structure of delicate biological samples, including amyloids, should be studied under physiological conditions (i.e., in solvent), because upon drying they may change their conformation, which is essential for their stability and biochemical activity.…”

Molecular Spectroscopic Markers of Abnormal Protein Aggregation

“…In the presence of the Nt17 domain, the IR spectra of fibrils revealed the peak characteristic for β-turn rich secondary structure at 1684 cm −1 while the lack of this domain changed the secondary structure of fibrils which displayed antiparallel β-sheet structure. Rizevsky et al [68] studied insulin fibrils using AFM-IR. In the following work, the formation of two different types of fibers was described.…”