SUP35 and SUP45 Genes Code for Ribosome-Bound Proteins Involved in the Control of Translational Fidelity in Yeast

Prions are self-perpetuating and, in most cases, aggregation-prone protein isoforms that transmit neurodegenerative diseases in mammals and control heritable traits in yeast. Prion conversion requires a very high level of identity of the interacting protein sequences. Decreased transmission of the prion state between divergent proteins is termed ''species barrier'' and was thought to occur because of the inability of divergent prion proteins to coaggregate. Species barrier can be overcome in cross-species infections, e.g., from ''mad cows'' to humans. We studied the counterparts of yeast prion protein Sup35, originated from three different species of the Saccharomyces sensu stricto group and exhibiting the range of prion domain divergence that overlaps with the range of divergence observed among distant mammalian species. All three proteins were capable of forming a prion in Saccharomyces cerevisiae, although prions formed by heterologous proteins were usually less stable than the endogenous S. cerevisiae prion. Heterologous Sup35 proteins coaggregated in the S. cerevisiae cells. However, in vivo cross-species prion conversion was decreased and in vitro polymerization was cross-inhibited in at least some heterologous combinations, thus demonstrating the existence of prion species barrier. Moreover, the barrier between the S. cerevisiae protein and its Saccharomyces paradoxus and Saccharomyces bayanus counterparts was asymmetric both in vivo and in vitro. Our data show that a decreased cross-species prion transmission does not necessarily correlate with a lack of crossspecies coaggregation, suggesting that species-specificity of prion transmission is controlled at the level of conformational transition rather than coaggregation.amyloid ͉ Saccharomyces bayanus ͉ Saccharomyces cerevisiae ͉ Saccharomyces paradoxus ͉ Sup35

Section: Resultsmentioning

confidence: 99%

Prion species barrier between the closely related yeast proteins is detected despite coaggregation

Chen

Newnam²,

Chernoff³

2007

“…The density of the GNNQQNY microcrystals was determined to be 1.39 Ϯ 0.02 g͞cm 3 . The number of water molecules per unit cell (14) follows directly from our measurements of the unit cell volume (V ϭ 4.30 ϫ 10 3 Å 3 ) and crystal density ( ϭ 1.39 Ϯ 0.02 g͞cm 3 ), the molecular mass M (836.7 Da) and knowing that the liquid of crystallization is pure water. This follows from the well-known relationship, X P ϭ (nM)͞(NV ), where X P is the weight fraction of protein in the crystals and N is Avogadro's number.…”

Section: Characterization Of Microcrystalsmentioning

confidence: 99%

“…The first 123 residues constitute the prion-determining domain (PrD) (13), which contains a series of nine-residue repeats with consensus sequence PQGGYQQYN, similar to the human prion protein repeats (PHGGGWGQ). The PrD is sufficient for [PSI ϩ ] propagation (14) and readily forms amyloid fibrils in vitro (15,16). The ability of the PrD to seed amyloid formation is highly species-dependent and hence sequence-specific (17).…”

mentioning

confidence: 99%

An amyloid-forming peptide from the yeast prion Sup35 reveals a dehydrated β-sheet structure for amyloid

Balbirnie

Grothe²,

Eisenberg³

2001

375

367

X-ray diffraction and other biophysical tools reveal features of the atomic structure of an amyloid-like crystal. Sup35, a prion-like protein in yeast, forms fibrillar amyloid assemblies intrinsic to its prion function. We have identified a polar peptide from the N-terminal prion-determining domain of Sup35 that exhibits the amyloid properties of full-length Sup35, including cooperative kinetics of aggregation, fibril formation, binding of the dye Congo red, and the characteristic cross-␤ x-ray diffraction pattern. Microcrystals of this peptide also share the principal properties of the fibrillar amyloid, including a highly stable, ␤-sheet-rich structure and the binding of Congo red. The x-ray powder pattern of the microcrystals, extending to 0.9-Å resolution, yields the unit cell dimensions of the well-ordered structure. These dimensions restrict possible atomic models of this amyloid-like structure and demonstrate that it forms packed, parallel-stranded ␤-sheets. The unusually high density of the crystals shows that the packed ␤-sheets are dehydrated, despite the polar character of the side chains. These results suggest that amyloid is a highly intermolecularly bonded, dehydrated array of densely packed ␤-sheets. This dry ␤-sheet could form as Sup35 partially unfolds to expose the peptide, permitting it to hydrogen-bond to the same peptide of other Sup35 molecules. The implication is that amyloid-forming units may be short segments of proteins, exposed for interactions by partial unfolding.

“…Ure2p and Sup35p are each composed of an N-terminal prion domain (PD) that is dispensable for function and a C-terminal functional domain (7)(8)(9)(10)(11). The Sup35p PD is composed of residues 1-114, whereas that of Ure2p is generally described as amino acids 1-89 or 1-65.…”

mentioning

confidence: 99%

Primary sequence independence for prion formation

Ross

Edskes

Terry

et al. 2005

199

223

Many proteins can adopt self-propagating ␤-sheet-rich structures, termed amyloid fibrils. The [URE3] and [PSI ؉ ] prions of Saccharomyces cerevisiae are infectious amyloid forms of the proteins Ure2p and Sup35p, respectively. Ure2p forms prions primarily as a result of its sequence composition, as versions of Ure2p with the prion domain amino acids shuffled are still able to form prions. Here we show that prion induction by both Ure2p and Ure2-21p, one of the scrambled versions of Ure2p, is clearly dependent on the length of the inducing fragment. For Ure2-21p, no single sequence is found in all of the inducing fragments, highlighting the sequence independence of prion formation. Furthermore, the sequence of the Sup35p prion domain can also be randomized without blocking prion formation. Indeed, a single shuffled sequence could give rise to several prion variants. These results suggest that [PSI ؉ ] formation is driven primarily by the amino acid composition of the Sup35p prion domain, and that the Sup35p oligopeptide repeats are not required for prion maintenance.[PSI ϩ ] ͉ amyloid ͉ Sup35