Amyloid particles facilitate surface-catalyzed cross-seeding by acting as promiscuous nanoparticles

Abstract

Amyloid seeds are nanometre-sized protein particles that accelerate amyloid assembly, as well as propagate and transmit the amyloid protein conformation associated with a wide range of protein misfolding diseases. However, seeded amyloid growth through templated elongation at fibril ends cannot explain the full range of molecular behaviours observed during cross-seeded formation of amyloid by heterologous seeds. Here, we demonstrate that amyloid seeds can accelerate amyloid formation via a surface catalysis mechanism without propagating the specific amyloid conformation associated with the seeds. This type of seeding mechanism is demonstrated through quantitative characterisation of the cross-seeded assembly reactions involving two non-homologous and unrelated proteins: the human Aβ42 peptide and the yeast prion-forming protein Sup35NM. Our results suggest experimental approaches to differentiate seeding by templated elongation from non-templated amyloid seeding, and rationalise the molecular mechanism of the cross-seeding phenomenon as a manifestation of the aberrant surface activities presented by amyloid seeds as nanoparticles.

Co-aggregation and secondary nucleation in the life cycle of human prolactin/galanin functional amyloids

“…This is further supported as the structure of PRL seeded GAL fibril showed similar fibrils morphology and secondary structure as of GAL fibrils formed alone (Fig 3). This is a typical property of surface-mediated secondary nucleation that produce fibrils 56 . Further the PRL seeding to GAL fibril formation was more efficient as compared to homo-seeding of GAL further support surface mediated secondary nucleation 53,56 (Fig 3).…”

“…This is a typical property of surface-mediated secondary nucleation that produce fibrils 56 . Further the PRL seeding to GAL fibril formation was more efficient as compared to homo-seeding of GAL further support surface mediated secondary nucleation 53,56 (Fig 3).…”

“…Important to note that these homotypic and heterotypic seeding studies were done in the absence of any helper molecules of GAGs. When lag times were compared, the heterotypic seeding rate was significantly higher than homotypic seeding for GAL aggregation suggesting surface-mediated secondary nucleation might be triggering GAL aggregation in the presence of PRL seeds 56…”

“…The median and mean fibril diameter analysis also suggests that GAL fibril formed in presence of PRL seed (median and mean diameter 12.35 nm) is very similar compared to GAL fibrils formed in presence of GAL seed (median and mean diameter 12 nm) as well as GAL fibrils formed in presence of heparin (median and mean diameter 11.20 nm) (Fig 3g, right panel, Supplementary Figure 6). This means that the incorporation of GAL monomers does not happen to the PRL fibril end (elongation) 25,51,57,58 , rather, GAL monomers use PRL seeds as surface and form amyloid fibrils via secondary (or surface) nucleation 26,52,53,56 mechanism. This was further confirmed with the FTIR study, which suggested that GAL-Hep and GAL in the presence of PRL seed possessed identical FTIR spectral signature, which was substantially different from the PRL fibril spectrum (Fig 3h).…”

Secondary Nucleation and the Conservation of Structural Characteristics of Amyloid Fibril Strains

“…Indeed, secondary nucleation might only be a special case of general surface nucleation (Buell, 2017). It has been shown that fibrils of one protein can nucleate from monomer on the surface of fibrils of another protein, while the same proteins are unable to elongate each others fibrils (Koloteva-Levine et al, 2020;Vaneyck et al, 2021). This difference suggests that cross-surface nucleation has much lower requirements for sequence similarity than cross-elongation.…”