Characterization of Amyloid Cores in Prion Domains

Abstract

Amyloids consist of repetitions of a specific polypeptide chain in a regular cross-β-sheet conformation. Amyloid propensity is largely determined by the protein sequence, the aggregation process being nucleated by specific and short segments. Prions are special amyloids that become self-perpetuating after aggregation. Prions are responsible for neuropathology in mammals, but they can also be functional, as in yeast prions. The conversion of these last proteins to the prion state is driven by prion forming domains (PFDs), which are generally large, intrinsically disordered, enriched in glutamines/asparagines and depleted in hydrophobic residues. The self-assembly of PFDs has been thought to rely mostly on their particular amino acid composition, rather than on their sequence. Instead, we have recently proposed that specific amyloid-prone sequences within PFDs might be key to their prion behaviour. Here, we demonstrate experimentally the existence of these amyloid stretches inside the PFDs of the canonical Sup35, Swi1, Mot3 and Ure2 prions. These sequences self-assemble efficiently into highly ordered amyloid fibrils, that are functionally competent, being able to promote the PFD amyloid conversion in vitro and in vivo. Computational analyses indicate that these kind of amyloid stretches may act as typical nucleating signals in a number of different prion domains.

Novel Variations in Native Ethiopian Goat breeds PRNP Gene and Their Potential Effect on Prion Protein Stability

“…The variation in amino acid sequence found to determine the propensity of amyloid formation 38,39 . In the present study, three consecutive novel polymorphic sites were identified in the first octapeptide repeat of the goat prion gene.…”

“…PHGGSRD (0.008) was predicted to have lower amyloidogenicity propensity than the wild type sequence PHGGGWG (0.096). As some proportion of amino acid sequence balance intrinsic amyloid formation and unwanted nucleation, these variants may create favourable conditions in the avoidance of non-physiologic folding 36,38 .Hotspot sequences with the H159 variant exhibited higher amyloidogenicity propensity than the wild type. The relatively higher destabilizing effect of H159 could be the potential reason why heptapeptides that included H159 had higher amyloidogenicity than other novel variants.…”

Reversible, functional amyloids: towards an understanding of their regulation in yeast and humans

“…Studies in yeast also allowed us to get a first glimpse on how physiological aggregation is regulated. We now know that functional aggregation generally depends on the presence of a prion-like, glutamine/ asparagine-rich domain, or a region of low compositional complexity (LCR), which interestingly are often found also in pathological aggregates [53,54]. Indeed, several proteins able to undergo reversible aggregation in yeast were shown to contain a predicted LCR, which likely triggers aggregate formation.…”

Characterization of Soft Amyloid Cores in Human Prion-Like Proteins

“…We wanted to test whether the soft amyloid cores predicted inside the PrLDs of these putative human prion-like proteins could spontaneously self-assemble into amyloid-like conformations and propagate their aggregated state, as we observed before for yeast prions 30 and the prion-like C. botulinum Rho factor 31 . We focused on nucleic acid-binding proteins, both because this molecular function is enriched in our dataset and because most of the experimentally validated yeast prions act in translational or transcriptional regulation.…”

“…This notion was implemented in pWALTZ, an algorithm that predicts the 21-residues long sequence stretch with the highest average amyloid potential in PrLDs 14 , 15 . This concept was further validated experimentally by demonstrating the existence of such soft amyloid stretches in the prion domains of four of the best characterized yeast prions 30 , as well as in the predicted PrLD of the Rho termination factor of Clostridium botulinum 31 , which later led to the discovery of the first bacterial prion-like protein 32 .…”