title: GroEL-mediated protein folding proceeds by multiple rounds of binding and release of nonnative forms.
abstract: The chaperonin GroEL is a ribosome-sized double-ring structure that assists in folding a diverse set of polypeptides. We have examined the fate of a polypeptide during a chaperonin-mediated folding reaction. Strikingly, we find that, upon addition of ATP and the cochaperonin GroES, polypeptide is released rapidly from GroEL in a predominantly nonnative conformation that can be trapped by mutant forms of GroEL that are capable of binding but not releasing substrate. Released polypeptide undergoes kinetic partitioning: a fraction completes folding while the remainder is rebound rapidly by other GroEL molecules. Folding appears to occur in an all-or-none manner, as proteolysis and tryptophan fluorescence indicate that after rebinding, polypeptide has the same structure as in the original complex. These observations suggest that GroEL functions by carrying out multiple rounds of binding aggregation-prone or kinetically trapped intermediates, maintaining them in an unfolded state, and releasing them to attempt to fold in solution.
authors.affiliation: Howard Hughes Medical Institute, Department of Genetics, Yale University School of Medicine, New Haven, Connecticut 06510.
authors.forename: J S
authors.initials: JS
authors.lastname: Weissman
authors.forename: Y
authors.initials: Y
authors.lastname: Kashi
authors.forename: W A
authors.initials: WA
authors.lastname: Fenton
authors.forename: A L
authors.initials: AL
authors.lastname: Horwich
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D018835:Chaperonin 10; D018834:Chaperonin 60; D003432:Cross-Linking Reagents; D006360:Heat-Shock Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D007700:Kinetics; D008956:Models, Chemical; D009954:Ornithine Carbamoyltransferase / Q000737:chemistry / Q000378:metabolism; D011485:Protein Binding; D011487:Protein Conformation; D017510:Protein Folding; D013884:Thiosulfate Sulfurtransferase / Q000737:chemistry / Q000378:metabolism
chemical_list: D001426:Bacterial Proteins; D018835:Chaperonin 10; D018834:Chaperonin 60; D003432:Cross-Linking Reagents; D006360:Heat-Shock Proteins; D009954:Ornithine Carbamoyltransferase; D013884:Thiosulfate Sulfurtransferase