Abstract
BackgroundThe aggregation of the baker's yeast prion Ure2p is at the origin of the [URE3] trait. The Q- and N-rich N-terminal part of the protein is believed to drive Ure2p assembly into fibrils of amyloid nature and the fibrillar forms of full-length Ure2p and its N-terminal part generated in vitro have been shown to induce [URE3] occurrence when introduced into yeast cells. This has led to the view that the fibrillar form of the N-terminal part of the protein is sufficient for the recruitment of constitutive Ure2p and that it imprints its amyloid structure to full-length Ure2p.ResultsHere we generate a set of Ure2p N-terminal fragments, document their assembly and structural properties and compare them to that of full-length Ure2p. We identify the minimal region critical for the assembly of Ure2p N-terminal part into amyloids and show that such fibrils are unable to seed the assembly of full length Ure2p unlike fibrils made of intact Ure2p.ConclusionOur results clearly indicate that fibrillar Ure2p shares no structural similarities with the amyloid fibrils made of Ure2p N-terminal part. Our results further suggest that the induction of [URE3] by fibrils made of full-length Ure2p is likely the consequence of fibrils growth by depletion of cytosolic Ure2p while it is the consequence of de novo formation of prion particles following, for example, titration within the cells of a specific set of molecular chaperones when fibrils made of Ure2p N-terminal domain are introduced within the cytoplasm.
Highlights
Prions are infectious proteins [1]
GST-Ure2p 1–42, 42–79, 1–79, 1–93 (Ure2p1– 42, 43–79, 1–79 and 1–93 correspond to Ure2p N-terminal fragments spanning amino acid residues 1 to 42, 43 to 79, 1 to 79 and 1–93, respectively) and glutathione S-transferase (GST) alone exhibit similar far UV circular dichroism (CD) spectra (Figure 1B)
Comparison of the assembly kinetics of free Ure2p 42–79, 1–79 and 1–93 and fulllength Ure2p show that the free N-terminal fragments of Ure2p assemble much faster that the authentic protein, while GST-Ure2p 42–79, 1–79 and 1–93 assemble slower than fulllength Ure2p
Summary
Prions are infectious proteins [1]. In the baker’s yeast Saccharomyces cerevisiae they are at the origin of the occurrence, maintenance, transmission in a non-mendelian manner and propagation of 3 traits, the [URE3], [PSI+] and [PIN+] phenotypes [2,3,4]. The Q- and N-rich Nterminal part of the protein is believed to drive Ure2p assembly into fibrils of amyloid nature and the fibrillar forms of fulllength Ure2p and its N-terminal part generated in vitro have been shown to induce [URE3] occurrence when introduced into yeast cells. This has led to the view that the fibrillar form of the N-terminal part of the protein is sufficient for the recruitment of constitutive Ure2p and that it imprints its amyloid structure to full-length Ure2p
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