Article

A chaperone pathway in protein disaggregation: HSP26 alteks the nature of protein aggregates to facilitate reactivation by HSP104

Whitehead Institute for Biomedical Research, Cambridge, Massachusetts 02143, USA.
Journal of Biological Chemistry (Impact Factor: 4.57). 07/2005; 280(25):23869-75. DOI: 10.1074/jbc.M502854200
Source: PubMed

ABSTRACT Cellular protein folding is challenged by environmental stress and aging, which lead to aberrant protein conformations and
aggregation. One way to antagonize the detrimental consequences of protein misfolding is to reactivate vital proteins from
aggregates. In the yeast Saccharomyces cerevisiae, Hsp104 facilitates disaggregation and reactivates aggregated proteins with assistance from Hsp70 (Ssa1) and Hsp40 (Ydj1).
The small heat shock proteins, Hsp26 and Hsp42, also function in the recovery of misfolded proteins and prevent aggregation
in vitro, but their in vivo roles in protein homeostasis remain elusive. We observed that after a sublethal heat shock, a majority of Hsp26 becomes insoluble.
Its return to the soluble state during recovery depends on the presence of Hsp104. Further, cells lacking Hsp26 are impaired
in the disaggregation of an easily assayed heat-aggregated reporter protein, luciferase. In vitro, Hsp104, Ssa1, and Ydj1 reactivate luciferase:Hsp26 co-aggregates 20-fold more efficiently than luciferase aggregates alone.
Small Hsps also facilitate the Hsp104-mediated solubilization of polyglutamine in yeast. Thus, Hsp26 renders aggregates more
accessible to Hsp104/Ssa1/Ydj1. Small Hsps partially suppress toxicity, even in the absence of Hsp104, potentially by sequestering
polyglutamine from toxic interactions with other proteins. Hence, Hsp26 plays an important role in pathways that defend cells
against environmental stress and the types of protein misfolding seen in neurodegenerative disease.

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