Chaperonin-Mediated Folding in the Eukaryotic Cytosol Proceeds through Rounds of Release of Native and Nonnative Forms

The eukaryotic cytosolic chaperonin, CCT, plays an essential role in mediating ATP-dependent folding of actin and tubulin. There is debate about whether it mediates folding through a single round of association followed by release of native forms, or through cycles of binding and full release in whi...

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Bibliographic Details
Published in:Cell 1997-06, Vol.89 (6), p.927-937
Main Authors: Farr, George W, Scharl, Elizabeth C, Schumacher, Robert J, Sondek, Stacey, Horwich, Arthur L
Format: Article
Language:English
Subjects:
Actins - biosynthesis
Actins - chemistry
Actins - metabolism
Animals
Cattle
Chaperonin 60 - chemistry
Chaperonin 60 - genetics
Chaperonin 60 - metabolism
Chaperonins - chemistry
Chaperonins - genetics
Chaperonins - metabolism
Cross-Linking Reagents - pharmacology
Cytosol - chemistry
Cytosol - metabolism
Eukaryotic Cells - chemistry
Eukaryotic Cells - physiology
Female
Humans
Microinjections
Mutagenesis - physiology
Oocytes - physiology
Protein Folding
Protein Synthesis Inhibitors - pharmacology
Recombinant Proteins - pharmacology
Reticulocytes - physiology
Transducin - chemistry
Transducin - metabolism
Tubulin - biosynthesis
Tubulin - chemistry
Tubulin - metabolism
Xenopus laevis
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Summary:The eukaryotic cytosolic chaperonin, CCT, plays an essential role in mediating ATP-dependent folding of actin and tubulin. There is debate about whether it mediates folding through a single round of association followed by release of native forms, or through cycles of binding and full release in which only a fraction of released molecules reaches native form in any cycle. We examine the fate of newly synthesized substrate proteins bound to CCT in reticulocyte lysate or intact Xenopus oocytes. When a chaperonin “trap,” able to bind but not release substrate protein, is introduced, production of the native state is strongly inhibited, associated with transfer to trap. While predominantly nonnative forms of actin, tubulin, and a newly identified substrate, Gα-transducin, are released from CCT, a small fraction reaches native form with each round of release, inaccessible to trap. This overall mechanism resembles that of the bacterial chaperonin, GroEL.
ISSN:0092-8674
1097-4172
DOI:10.1016/S0092-8674(00)80278-0