Distinct Prion Domain Sequences Ensure Efficient Amyloid Propagation by Promoting Chaperone Binding or Processing In Vivo

Abstract

Prions are a group of proteins that can adopt a spectrum of metastable conformations in vivo. These alternative states change protein function and are self-replicating and transmissible, creating protein-based elements of inheritance and infectivity. Prion conformational flexibility is encoded in the amino acid composition and sequence of the protein, which dictate its ability not only to form an ordered aggregate known as amyloid but also to maintain and transmit this structure in vivo. But, while we can effectively predict amyloid propensity in vitro, the mechanism by which sequence elements promote prion propagation in vivo remains unclear. In yeast, propagation of the [PSI+] prion, the amyloid form of the Sup35 protein, has been linked to an oligopeptide repeat region of the protein. Here, we demonstrate that this region is composed of separable functional elements, the repeats themselves and a repeat proximal region, which are both required for efficient prion propagation. Changes in the numbers of these elements do not alter the physical properties of Sup35 amyloid, but their presence promotes amyloid fragmentation, and therefore maintenance, by molecular chaperones. Rather than acting redundantly, our observations suggest that these sequence elements make complementary contributions to prion propagation, with the repeat proximal region promoting chaperone binding to and the repeats promoting chaperone processing of Sup35 amyloid.

Prion Replication in the Mammalian Cytosol: Functional Regions within a Prion Domain Driving Induction, Propagation, and Inheritance

“…Instead, de novo NM aggregate induction, exogenous and endogenous NM seed-induced prion formation, and maintenance were preferentially driven by the last 2.5 repeats of the OPR and the CTN. Depending on the prion variant and/or genetic background of the host, the minimal region required for stable prion maintenance in S. cerevisiae varies but consistently includes the amino-terminal OPR ( 32 , 37 , 42 , 45 – 48 ) proposed to enhance fibril fragmentation by disaggregase Hsp104 ( 32 , 50 , 51 , 63 , 64 ). As Hsp104 has no homologue in the mammalian cytosol ( 65 ), NM seed multiplication in N2a cells must proceed by other means.…”

The [PSI +] yeast prion does not wildly affect proteome composition whereas selective pressure exerted on [PSI +] cells can promote aneuploidy

“…Interestingly, the N-terminal domain (prion domain) is abnormally rich in glutamine-asparagine (Q-N; residues ~1–40) and oligopeptide repeats (residues ~40–114) which facilitate the formation of amyloid-like aggregates and propagation of [ PSI + ] 6 – 9 . Translation termination therefore becomes impaired in cells that possess the [ PSI + ] prion as the amount of soluble Sup35 is diminished 10 .…”

A dominant-negative mutant inhibits multiple prion variants through a common mechanism

“…The G58D mutation lies in the second oligopeptide repeat of Sup35, a region of the protein that is essential for prion propagation [ 86 – 88 ] and that impacts the ability of the Hsp104 chaperone to thread monomers through its central pore during the fragmentation process [ 89 ]. Position 58 is located within the amyloid core of Sup35 in the [ PSI + ] Sc37 variant but is more accessible in the [ PSI + ] Sc4 variant [ 69 ].…”