A novel pathway for amyloids self-assembly in aggregates at nanomolar concentration mediated by the interaction with surfaces

Siddhartha Banerjee,Mohtadin Hashemi,Jean-Christophe Rochet,Sibaprasad Maity,Zhengjian Lv,Yuri L Lyubchenko

doi:10.1038/srep45592

Siddhartha Banerjee, Mohtadin Hashemi + Show 4 more

Open Access

https://doi.org/10.1038/srep45592

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Abstract

A limitation of the amyloid hypothesis in explaining the development of neurodegenerative diseases is that the level of amyloidogenic polypeptide in vivo is below the critical concentration required to form the aggregates observed in post-mortem brains. We discovered a novel, on-surface aggregation pathway of amyloidogenic polypeptide that eliminates this long-standing controversy. We applied atomic force microscope (AFM) to demonstrate directly that on-surface aggregation takes place at a concentration at which no aggregation in solution is observed. The experiments were performed with the full-size Aβ protein (Aβ42), a decapeptide Aβ(14-23) and α-synuclein; all three systems demonstrate a dramatic preference of the on-surface aggregation pathway compared to the aggregation in the bulk solution. Time-lapse AFM imaging, in solution, show that over time, oligomers increase in size and number and release in solution, suggesting that assembled aggregates can serve as nuclei for aggregation in bulk solution. Computational modeling performed with the all-atom MD simulations for Aβ(14-23) peptide shows that surface interactions induce conformational transitions of the monomer, which facilitate interactions with another monomer that undergoes conformational changes stabilizing the dimer assembly. Our findings suggest that interactions of amyloidogenic polypeptides with cellular surfaces play a major role in determining disease onset.

Highlights

Development of novel approaches[16,17] and have shown that at the very early aggregation stage, unstructured monomers form stable dimers due to structural transitions of monomers
The samples were prepared for incubation times 0 h, 24 h, 48 h and 72 h, and typical images are shown in Fig. 1B, plates i-iv, respectively
We have shown that the interaction of amyloid proteins with surfaces presents a unique opportunity to allow the protein to assemble into aggregates at concentrations that are non-permissive for aggregation in solution. This finding eliminates a major problem with understanding the spontaneous appearance of plaques in the Alzheimer’s disease (AD) brain due to the apparent gap between known extracellular Aβconcentrations in vivo and the concentration required for spontaneous aggregation in vitro

Summary

Introduction

Development of novel approaches[16,17] and have shown that at the very early aggregation stage, unstructured monomers form stable dimers due to structural transitions of monomers. We have found that dimers of α-synuclein (α-Syn) could be assembled at nanomolar concentrations, if the target monomer is tethered to a surface[20]. These data led us to hypothesize that binding to the surface can be a factor dramatically facilitating the aggregation process. This hypothesis is supported by recent studies in which the assembly of large α-Syn aggregates on a glass surface was observed with the protein concentration in the nanomolar range[21]. Given that the on-surface aggregates are oligomeric in nature, which are known to be the most neurotoxic species, we hypothesize that prevention of the on-surface aggregation should block the disease-prone process and can be considered a means for the development of future preventions and treatments for Alzheimer’s and similar neurodegenerative protein aggregation diseases

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