The oligomeric structure of GroEL/GroES is required for biologically significant chaperonin function in protein folding.
Two models are being considered for the mechanism of chaperonin-assisted protein folding in E. coli: (i) GroEL/GroES act primarily by enclosing substrate polypeptide in a folding cage in which aggregation is prevented during folding. (ii) GroEL mediates the repetitive unfolding of misfolded polypeptides, returning them onto a productive folding track. Both models are not mutually exclusive, but studies with the polypeptide-binding domain of GroEL have suggested that unfolding is the primary mechanism, enclosure being unnecessary. Here we investigate the capacity of the isolated apical polypeptide-binding domain to functionally replace the complete GroEL/GroES system. We show that the apical domain binds aggregation-sensitive polypeptides but cannot significantly assist their refolding in vitro and fails to replace the groEL gene or to complement defects of groEL mutants in vivo. A single-ring version of GroEL cannot substitute for GroEL. These results strongly support the view that sequestration of aggregation-prone intermediates in a folding cage is an important element of the chaperonin mechanism.
Weber
F
F
Max-Planck-Institut für Biochemie, Martinsried, Germany.
Keppel
F
F
Georgopoulos
C
C
Hayer-Hartl
M K
MK
Hartl
F U
FU
D000818:Animals; D002417:Cattle; D018835:Chaperonin 10 / Q000737:chemistry* / Q000502:physiology; D018834:Chaperonin 60 / Q000737:chemistry* / Q000235:genetics / Q000502:physiology; D002942:Circular Dichroism; D002950:Citrate (si)-Synthase / Q000737:chemistry; D004926:Escherichia coli / Q000737:chemistry; D005816:Genetic Complementation Test; D008291:Malate Dehydrogenase / Q000737:chemistry; D008958:Models, Molecular; D011487:Protein Conformation; D017510:Protein Folding; D011993:Recombinant Fusion Proteins; D017384:Sequence Deletion; D013762:Tetrahydrofolate Dehydrogenase / Q000737:chemistry; D013884:Thiosulfate Sulfurtransferase / Q000737:chemistry
D018835:Chaperonin 10; D018834:Chaperonin 60; D011993:Recombinant Fusion Proteins; D008291:Malate Dehydrogenase; D013762:Tetrahydrofolate Dehydrogenase; D002950:Citrate (si)-Synthase; D013884:Thiosulfate Sulfurtransferase