Polypeptide in the chaperonin cage partly protrudes out and then folds inside or escapes outside.
The current mechanistic model of chaperonin-assisted protein folding assumes that the substrate protein in the cage, formed by GroEL central cavity capped with GroES, is isolated from outside and exists as a free polypeptide. However, using ATPase-deficient GroEL mutants that keep GroES bound, we found that, in the rate-limiting intermediate of a chaperonin reaction, the unfolded polypeptide in the cage partly protrudes through a narrow space near the GroEL/GroES interface. Then, the entire polypeptide is released either into the cage or to the outside medium. The former adopts a native structure very rapidly and the latter undergoes spontaneous folding. Partition of the in-cage folding and the escape varies among substrate proteins and is affected by hydrophobic interaction between the polypeptide and GroEL cavity wall. The ATPase-active GroEL with decreased in-cage folding produced less of a native model substrate protein in Escherichia coli cells. Thus, the polypeptide in the critical GroEL-GroES complex is neither free nor completely confined in the cage, but it is interacting with GroEL's apical region, partly protruding to outside.
Motojima
Fumihiro
F
Department of Molecular Bioscience, Faculty of Life Sciences, Kyoto Sangyo University, Kyoto, Japan.
Yoshida
Masasuke
M
D000818:Animals; D018835:Chaperonin 10 / Q000378:metabolism*; D018834:Chaperonin 60 / Q000235:genetics / Q000378:metabolism*; D018833:Chaperonins / Q000378:metabolism; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism*; D029968:Escherichia coli Proteins / Q000235:genetics / Q000378:metabolism*; D015870:Gene Expression; D057927:Hydrophobic and Hydrophilic Interactions; D051379:Mice; D008958:Models, Molecular; D009154:Mutation; D010455:Peptides / Q000378:metabolism*; D011489:Protein Denaturation; D017510:Protein Folding; D012273:Ribulose-Bisphosphate Carboxylase / Q000378:metabolism; D013762:Tetrahydrofolate Dehydrogenase / Q000378:metabolism; D013884:Thiosulfate Sulfurtransferase / Q000378:metabolism
D018835:Chaperonin 10; D018834:Chaperonin 60; D029968:Escherichia coli Proteins; D010455:Peptides; D013762:Tetrahydrofolate Dehydrogenase; D013884:Thiosulfate Sulfurtransferase; D018833:Chaperonins; D012273:Ribulose-Bisphosphate Carboxylase