Koloteva-Levine, N. | bioRxiv Science

bioRxiv2026

Structural evolution of a yeast amyloid in vivo is shaped by chaperones

Cryo-electron microscopy (cryo-EM) studies of amyloid fibrils have revealed endpoint structures of disease-relevant filaments and polymorphic intermediates formed during in vitro assembly of prion-like proteins. However, how transmissible prion or prion-like amyloids evolve during de novo formation and maturation in living cells remains unknown. Here, using the yeast prion [PSI+] as a model, we isolated Sup35NM amyloid fibrils from successive stages of [PSI+] maturation in Saccharomyces cerevisiae and characterised their near-atomic structures and population-level structural diversity by combining cryo-EM and atomic force microscopy. We show that intermediate and mature states differ in predominant fibril structure and the regions of the Sup35 sequence incorporated into the core, and that structural diversity decreases during maturation. Curing of [PSI+] at the mature state by guanidine hydrochloride (GdnHCl), which selectively inhibits ATPase activity of the chaperone Hsp104, restored both the predominant intermediate amyloid structure and the broader structural diversity characteristic of the intermediate state. In addition, Hsp104, Ssa1 (Hsp70) and Sis1 (Hsp40) associate differently with fibrils from the two states. Together, these findings provide direct structural evidence for amyloid evolution in vivo and support a chaperone-mediated mechanism of conformer selection within a polymorphic amyloid population.

molecular biology↗

bioRxiv2020

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

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 A{beta}42 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.

biochemistry↗