Molecular mechanisms used by chaperones to reduce the toxicity of aberrant protein oligomers.
Chaperones are the primary regulators of the proteostasis network and are known to facilitate protein folding, inhibit protein aggregation, and promote disaggregation and clearance of misfolded aggregates inside cells. We have tested the effects of five chaperones on the toxicity of misfolded oligomers preformed from three different proteins added extracellularly to cultured cells. All the chaperones were found to decrease oligomer toxicity significantly, even at very low chaperone/protein molar ratios, provided that they were added extracellularly rather than being overexpressed in the cytosol. Infrared spectroscopy and site-directed labeling experiments using pyrene ruled out structural reorganizations within the discrete oligomers. Rather, confocal microscopy, SDS-PAGE, and intrinsic fluorescence measurements indicated tight binding between oligomers and chaperones. Moreover, atomic force microscopy imaging indicated that larger assemblies of oligomers are formed in the presence of the chaperones. This suggests that the chaperones bind to the oligomers and promote their assembly into larger species, with consequent shielding of the reactive surfaces and a decrease in their diffusional mobility. Overall, the data indicate a generic ability of chaperones to neutralize extracellular misfolded oligomers efficiently and reveal that further assembly of protein oligomers into larger species can be an effective strategy to neutralize such extracellular species.
Department of Biochemical Sciences,  University of Florence, 50134 Florence,  Italy.
Benedetta
B
Mannini
Roberta
R
Cascella
Mariagioia
M
Zampagni
Maria
M
van Waarde-Verhagen
Sarah
S
Meehan
Cintia
C
Roodveldt
Silvia
S
Campioni
Matilde
M
Boninsegna
Amanda
A
Penco
Annalisa
A
Relini
Harm H
HH
Kampinga
Christopher M
CM
Dobson
Mark R
MR
Wilson
Cristina
C
Cecchi
Fabrizio
F
Chiti
D045744:Cell Line, Tumor; D006801:Humans; D018832:Molecular Chaperones / Q000235:genetics / Q000378:metabolism*; D017510:Protein Folding; D055503:Protein Multimerization
D018832:Molecular Chaperones