Coexistence of ribbon and helical fibrils originating from hIAPP _20–29 revealed by quantitative nanomechanical atomic force microscopy

Abstract

Uncontrolled misfolding of proteins leading to the formation of amyloid deposits is associated with more than 40 types of diseases, such as neurodegenerative diseases and type-2 diabetes. These irreversible amyloid fibrils typically assemble in distinct stages. Transitions among the various intermediate stages are the subject of many studies but are not yet fully elucidated. Here, we combine high-resolution atomic force microscopy and quantitative nanomechanical mapping to determine the self-assembled structures of the decapeptide hIAPP [20][21][22][23][24][25][26][27][28][29] , which is considered to be the fibrillating core fragment of the human islet amyloid polypeptide (hIAPP) involved in type-2 diabetes. We successfully follow the evolution of hIAPP 20-29 nanostructures over time, calculate the average thickening speed of small ribbon-like structures, and provide evidence of the coexistence of ribbon and helical fibrils, highlighting a key step within the self-assembly model. In addition, the mutations of individual side chains of wide-type hIAPP 20-29 shift this balance and destabilize the helical fibrils sufficiently relative to the twisted ribbons to lead to their complete elimination. We combine atomic force microscopy structures, mechanical properties, and solid-state NMR structural information to build a molecular model containing β sheets in cross-β motifs as the basis of selfassembled amyloids.μFS | mutants | nanomechanical map | self-assembly nanostructure P rotein aggregation and amyloid deposits (1, 2) are associated with more than 40 different diseases (3) ranging from neurodegenerative diseases such as Alzheimer's disease (4) and Parkinson disease (5) to systemic amyloidosis, such as type-2 diabetes mellitus (T2D) (6). Over the last few decades, amyloid structures and amyloid assembly have been extensively studied using a variety of diffraction techniques such as X-ray scattering and electron diffraction. However, these methods only provide average structures (7). Many structures have also been resolved in great detail by solid-state NMR spectroscopy (8, 9), which mainly represents end-point structures and, unless specifically trapping intermediates, typically does not provide a clear picture of the transient structures formed during the fibrillation process. However, it is very important to resolve the dynamics of the nanostructures of amyloids at various steps during self-assembly to understand the mechanics behind amyloid initialization, formation, growth, and maturation as well as for the design of potential drugs. Atomic force microscopy (AFM) is capable of obtaining nanoscale resolution of individual molecules or supermolecular structures. This method also allows for the analysis of the selfassembly mechanism and the driving force of aggregation (10-14). Importantly, AFM, furthermore, provides the possibility to follow the dynamics to obtain a detailed picture of the amyloid assembly process (15).In the case of T2D, amyloid deposits, composed mainly of human islet amyloid polypeptide (hIA...

Microfluidic Synthesis of Hybrid Nanoparticles with Controlled Lipid Layers: Understanding Flexibility-Regulated Cell–Nanoparticle Interaction

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“…These dyes interact with amyloid peptide in the aggregation process, which interferes with in situ measurements, for example Congo Red and Thioflavin T (ThT) . Herein, we combined label‐free quartz crystal microbalance (QCM), atomic force microscopy (AFM), and circular dichroism (CD) spectra, to quantitatively explore the modulating effect of MoS 2 on the fibrillization of two amyloid peptides, Aβ (33–42), a key hydrophobic fragment of amyloid protein Aβ (1–42), and amylin (20–29), the fibrillating core fragment of the human islet amyloid polypeptide (hIAPP) involved in type‐II diabetes …”

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