Variant‐specific and reciprocal Hsp40 functions in Hsp104‐mediated prion elimination

• Published in: Molecular microbiology Vol. 109; no. 1; pp. 41 - 62
• Main Authors: Astor, Michael T., Kamiya, Erina, Sporn, Zachary A., Berger, Scott E., Hines, Justin K.
• Format: Journal Article
• Language: English
• Published: England Blackwell Publishing Ltd 01.07.2018; John Wiley and Sons Inc
• Subjects: Baking yeast; Chaperones; Cures; Curing; Hsp40 protein; Hsp70 protein; Molecular chains; Prion protein; Prions; Protein folding; Proteins; Saccharomyces cerevisiae; Well construction; Yeast
• ISSN: 0950-382X; 1365-2958; 1365-2958
• DOI: 10.1111/mmi.13966

Summary The amyloid‐based prions of Saccharomyces cerevisiae are heritable aggregates of misfolded proteins, passed to daughter cells following fragmentation by molecular chaperones including the J‐protein Sis1, Hsp70 and Hsp104. Overexpression of Hsp104 efficiently cures cell populations of the prion [PSI+] by an alternative Sis1‐dependent mechanism that is currently the subject of significant debate. Here, we broadly investigate the role of J‐proteins in this process by determining the impact of amyloid polymorphisms (prion variants) on the ability of well‐studied Sis1 constructs to compensate for Sis1 and ask whether any other S. cerevisiae cytosolic J‐proteins are also required for this process. Our comprehensive screen, examining all 13 members of the yeast cytosolic/nuclear J‐protein complement, uncovered significant variant‐dependent genetic evidence for a role of Apj1 (antiprion DnaJ) in this process. For strong, but not weak [PSI+] variants, depletion of Apj1 inhibits Hsp104‐mediated curing. Overexpression of either Apj1 or Sis1 enhances curing, while overexpression of Ydj1 completely blocks it. We also demonstrated that Sis1 was the only J‐protein necessary for the propagation of at least two weak [PSI+] variants and no J‐protein alteration, or even combination of alterations, affected the curing of weak [PSI+] variants, suggesting the possibility of biochemically distinct, variant‐specific Hsp104‐mediated curing mechanisms. Yeast prions are aggregates of misfolded proteins that are inherited when cells divide while chaperone proteins, which normally work to prevent protein misfolding, fragment yeast prions, inadvertently creating additional pieces, which can be passed on to subsequent cell generations. In one case, the overproduction of the chaperone Hsp104, capable of dissolving protein aggregates, causes the complete elimination of one prion from cell populations but the mechanism by which this occurs is debated. Here, we show that prion structural variations drastically affect the need for chaperone proteins in prion elimination, indicating the possibility of biochemically distinct, variant‐specific Hsp104‐mediated prion elimination mechanisms.