Chiral Selectivity of Secondary Nucleation in Amyloid Fibril Propagation

Abstract

Chirality is a fundamental feature of asymmetric molecules and of critical importance for intermolecular interactions. The growth of amyloid fibrils displays a strong enantioselectivity, which is manifested as elongation through the addition of monomers of the same, but not opposite, chirality as the parent aggregate. Here we ask whether also secondary nucleation on the surface of amyloid fibrils, of relevance for toxicity, is governed by the chirality of the nucleating monomers. We use short amyloid peptides (Ab20-34 and IAPP20-29) with all residues as L-or all D-enantiomer in self and cross-seeding experiments with low enough seed concentration that any acceleration of fibril formation is dominated by secondary nucleation. We find a strong enantiospecificity of this auto-catalytic process with secondary nucleation being observed in the self-seeding experiments only. The results highlight a role of secondary nucleation in strain propagation.

Molecular Scale Structure and Kinetics of Layer-by-Layer Peptide Self-Organization at Atomically Flat Solid Surfaces

“…The suitable high resolution is necessary both in spatial and temporal observations to capture and identify critical phenomena taking place during the various stages of self-organization and formation, including, e.g., incubation, nanowire nucleation, and domain growth, as we discuss below. Toward this end, although studies have been undertaken, for example, using ex situ atomic force microscopy (AFM) 31 and transmission electron microscopy (TEM), 32 such as in protein assembly and fibril formation, they, however, provide incomplete data, limiting qualitative analysis of the formation processes. Furthermore, molecular self-assembly processes can be highly dynamic and complex, multiple phenomena happening simultaneously, e.g., involving diffusion, nucleation, and growth and, therefore, require in situ techniques to quantitatively record kinetics of the surface phenomena taking place in the natural aqueous environment over a short and long-time scales.…”

Role of Hydrophobicity at the N-Terminal Region of Aβ42 in Secondary Nucleation

“…Secondary nucleation was found to be a dominating route of Aβ42 aggregation regardless of these hydrophobic residues; however, the replacement of some residues, most prominently V18, with polar ones led to the formation of an alternatively folded fibril structure that failed to catalyze the nucleation of monomers lacking this substitution . Other examples of failed cross-catalysis has been observed for Aβ40 versus Aβ42, and for all-L versus all-D Aβ20-34, in both cases related to different fibrillar structures of peptide variants. , However, if the fibrils are totally different, formed from different proteins, some systems display an effect that can be explained as heterogeneous primary nucleation akin to the catalysis of primary nucleation on nanoparticle surfaces …”

“…20 Other examples of failed cross-catalysis has been observed for Aβ40 versus Aβ42, and for all-L versus all-D Aβ20-34, in both cases related to different fibrillar structures of peptide variants. 21,22 However, if the fibrils are totally different, formed from different proteins, some systems display an effect that can be explained as heterogeneous primary nucleation akin to the catalysis of primary nucleation on nanoparticle surfaces. 23 In the present study, we investigate the role of the hydrophobic residues of the N-terminal region of Aβ42 in secondary nucleation by creating mutants with altered hydrophobicity or hydrophilic character.…”