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Molecular chaperones and the assembly of the prion Sup35p, an in vitro study

Joanna Krzewska1, Ronald Melki

  • 1Laboratoire d'Enzymologie et Biochimie Structurales, CNRS, Gif-sur-Yvette Cedex, France. krzewska@lebs.cnrs.gif.fr

The EMBO Journal
|February 10, 2006
PubMed

Insights

Molecular chaperones regulate prion formation. Hsp104p promotes Sup35p fibril assembly, while Hsp70-Hsp40 systems can inhibit it, revealing distinct chaperone roles in prion propagation.

Area of Science:

  • Biochemistry
  • Molecular Biology
  • Prion Biology

Background:

  • The protein Sup35 in Saccharomyces cerevisiae exhibits prion properties, forming the [PSI+] factor.
  • Molecular chaperones, including Hsp100, 70, and 40 families, are crucial for [PSI+] propagation, but their specific roles remain unclear.

Purpose of the Study:

  • To investigate the in vitro effects of specific molecular chaperones on the assembly of full-length Sup35 protein into fibrils.
  • To elucidate the distinct roles of Hsp104p and Hsp70-Hsp40 systems in Sup35p polymerization.

Main Methods:

  • Developed a reproducible in vitro system to study Sup35p assembly.
  • Assessed the impact of individual and combined chaperones (Hsp104p, Ydj1p, Hsp82p, Ssa1p, Sis1p, Hsp40 cochaperones) on Sup35p fibril formation.
  • Investigated ATP-dependent complex formation between chaperones and Sup35p oligomers.

Main Results:

  • Hsp104p significantly stimulates Sup35p fibril assembly.
  • Ydj1p inhibits Sup35p assembly; Hsp82p, Ssa1p, and Sis1p alone have no effect.
  • Ssa1p with Hsp40 cochaperones blocks Sup35p polymerization.
  • Ssa1p and Ydj1p or Sis1p counteract Hsp104p's effect by forming complexes with Sup35p oligomers in an ATP-dependent manner.

Conclusions:

  • Distinct functional mechanisms exist between Hsp104p and Hsp70-Hsp40 systems in Sup35p fibril assembly.
  • These findings provide new insights into how molecular chaperones modulate the propagation of the [PSI+] prion.

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