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.
Department of Molecular Bioscience, Faculty of Life Sciences, Kyoto Sangyo University, Kyoto, Japan.
Fumihiro
F
Motojima
Masasuke
M
Yoshida
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