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A polypeptide bound by the chaperonin groEL is localized within a central cavity
1Howard Hughes Medical Institute, Yale University School of Medicine, New Haven, CT 06510.
Summary
Chaperonins like E. coli groEL bind protein folding intermediates within internal ring cavities. This sequestration facilitates proper protein folding and prevents aggregation, ensuring cellular protein homeostasis.
Area of Science:
- Molecular Biology
- Structural Biology
- Biochemistry
Background:
- Chaperonins are essential protein complexes involved in ATP-dependent polypeptide folding.
- They prevent aggregation of folding intermediates and facilitate their maturation.
- Chaperonin complexes, like E. coli groEL, form cylindrical structures with central cavities.
Purpose of the Study:
- To identify the binding site of dihydrofolate reductase (DHFR) folding intermediates on the E. coli chaperonin groEL.
- To understand the spatial localization of protein folding within the chaperonin structure.
Main Methods:
- Utilized scanning transmission electron microscopy (STEM) to visualize groEL-DHFR complexes.
- Employed gold nanoparticles crosslinked to DHFR to pinpoint binding locations.
- Analyzed top and side views of the complexes to determine gold density positions.
Main Results:
- Gold densities, indicating bound DHFR, were observed in the central region in top views of groEL complexes.
- In side views, gold densities localized to the ends of the cylinders, within individual rings.
- Multiple binding sites within the central cavities were suggested by the presence of two gold densities in some complexes.
Conclusions:
- Protein folding intermediates bind within the central cavities of individual chaperonin rings.
- This sequestered location within groEL facilitates binding and proper folding of compact intermediates.
- Localization within the cavity may also aid in the rebinding of improperly folded structures.