Direct observation of secondary nucleation along the fibril surface of the amyloid β 42 peptide

Abstract

Alzheimer’s disease is a neurodegenerative condition which involves heavy neuronal cell death linked to oligomers formed during the aggregation process of the amyloid β peptide 42 (A β 42). The aggregation of A β 42 involves both primary and secondary nucleation. Secondary nucleation dominates the generation of oligomers and involves the formation of new aggregates from monomers on catalytic fibril surfaces. Understanding the molecular mechanism of secondary nucleation may be crucial in developing a targeted cure. Here, the self-seeded aggregation of WT A β 42 is studied using direct stochastic optical reconstruction microscopy (dSTORM) with separate fluorophores in seed fibrils and monomers. Seeded aggregation proceeds faster than nonseeded reactions because the fibrils act as catalysts. The dSTORM experiments show that monomers grow into relatively large aggregates on fibril surfaces along the length of fibrils before detaching, thus providing a direct observation of secondary nucleation and growth along the sides of fibrils. The experiments were repeated for cross-seeded reactions of the WT A β 42 monomer with mutant A β 42 fibrils that do not catalyze the nucleation of WT monomers. While the monomers are observed by dSTORM to interact with noncognate fibril surfaces, we fail to notice any growth along such fibril surfaces. This implies that the failure to nucleate on the cognate seeds is not a lack of monomer association but more likely a lack of structural conversion. Our findings support a templating role for secondary nucleation, which can only take place if the monomers can copy the underlying parent structure without steric clashes or other repulsive interactions between nucleating monomers.

Redox-Regulated In Situ Seed-Induced Assembly of Peptides

“…Reduction of EIM SeO to EIM Se by TCEP led to the formation of bundled nanoribbons with a width ranging from 12.8 to 30.6 nm (Figure C), distinct from the dispersed nanoribbons formed by the original co-assemblies. The formation of the bundled nanoribbons is potentially attributed to the nanofibril surface-nucleated assembly of peptides, which has been observed in the fibrillation of amyloid β-42 peptides. , The morphologies of the co-assemblies, oxidized co-assemblies, and reduced co-assemblies were also confirmed by AFM studies, in which the dispersed nanoribbons, short nanoribbons, and bundled nanoribbons were also detected in the corresponding images (Figure S23).…”

“…The mechanism for the accelerated assembly is potentially induced via the association between the reduced peptide with the surface of EIL n seeds, analogous to the accelerated secondary nucleation along the nanofibril surface of the amyloid β-42 peptide. 49,50 It is worth noting that no significant difference between the time t 1/2 and apparent rate constants accelerated by the exogenous and endogenous EIL n seeds is observed. The phenomenon implies an identical mechanism for accelerating the reductioninduced assembly of EIM SeO by both exogenous and endogenous seeds.…”

“…The apparent rate constants for the reduction-induced assembly of EIM SeO accelerated by the exogenous and endogenous EIL n seeds are in the order of k 100 > k 50 > k 30 > k 0 (Table S1), indicating an increase of the assembly kinetics upon improving the seed concentration. The mechanism for the accelerated assembly is potentially induced via the association between the reduced peptide with the surface of EIL n seeds, analogous to the accelerated secondary nucleation along the nanofibril surface of the amyloid β-42 peptide. , It is worth noting that no significant difference between the time t 1/2 and apparent rate constants accelerated by the exogenous and endogenous EIL n seeds is observed. The phenomenon implies an identical mechanism for accelerating the reduction-induced assembly of EIM SeO by both exogenous and endogenous seeds.…”

“…Owing to the excellent biocompatibility and reliable noncovalent interactions of peptides, self-assembly of peptides into nanostructures has been demonstrated as a versatile approach for development of biomaterials. − In this context, we developed different morphology-transformable self-assembly systems applicable to living systems via rational design of peptide monomers. − The functionality of peptide assemblies could be further tailored through co-assembly of different monomers, due to the robust co-assembly behavior of different peptides. − Accelerating the morphological transformation is critical for preventing peptide degradation and rapidly creating functional structures. Recent studies have shown the significant role of the surface-catalyzed secondary nucleation process in amyloid fibrillation responsible for Alzheimer’s disease. , To facilitate the application of morphology-transformational assembly systems toward biomedicines in living systems, we here reported redox-regulated in situ seed-induced assembly of peptides via design of two peptides, including one seed monomer EIL n IL n IE (EIL n ) and one redox-responsive monomer EIM Se IM Se IE (EIM Se ) (Scheme ). On the basis of the robust assembling propensity of bola-amphiphiles − and our previous experience on sorted or co-assembled peptides, we designed and synthesized the two bola-amphiphilic peptide monomers EIL n and EIM Se .…”

Comparing brute force to transition path sampling for gas hydrate nucleation with a flat interface: comments on time reversal symmetry

“…Experiments can investigate trends in homogeneous (not influenced by any surface, other than perhaps the fluid–fluid interface if the resulting solid is comprised of 2 immiscible formers) and heterogeneous (influenced by an external surface such as a vessel wall, surrounding geologic material, sand or atmospheric dust) nucleation rates and ensuing growth rates, and recent advances in time-resolved experimental capacity give insights into the molecular mechanisms of nucleation in important systems. 10,46–48 Still, nucleation's nanoscale nature in time and space is an obstacle to gaining mechanistic understanding from experiments. Molecular dynamics (MD) simulation is often used to study solid formation because its ability to track the fates of individual atoms and molecules during phase change (subject to the assumptions of the simulation model and setup).…”