title: Mechanical unfolding of covalently linked GroES: evidence of structural subunit intermediates.
abstract: It is difficult to determine the structural stability of the individual subunits or protomers of many proteins in the cell that exist in an oligomeric or complexed state. In this study, we used single-molecule force spectroscopy on seven subunits of covalently linked cochaperonin GroES (ESC7) to evaluate the structural stability of the subunit. A modified form of ESC7 was immobilized on a mica surface. The force-extension profile obtained from the mechanical unfolding of this ESC7 showed a distinctive sawtooth pattern that is typical for multimodular proteins. When analyzed according to the worm-like chain model, the contour lengths calculated from the peaks in the profile suggested that linked-GroES subunits unfold in distinct steps after the oligomeric ring structure of ESC7 is disrupted. The evidence that structured subunits of ESC7 withstand external force to some extent even after the perturbation of the oligomeric ring structure suggests that a stable monomeric intermediate is an important component of the equilibrium unfolding reaction of GroES.
authors.affiliation: Department of Chemistry and Biotechnology, Graduate School of Engineering, Tottori University, Japan.
authors.forename: Isao
authors.initials: I
authors.lastname: Sakane
authors.forename: Kunihiro
authors.initials: K
authors.lastname: Hongo
authors.forename: Tomohiro
authors.initials: T
authors.lastname: Mizobata
authors.forename: Yasushi
authors.initials: Y
authors.lastname: Kawata
mesh_terms: D018835:Chaperonin 10 / Q000737:chemistry* / Q000378:metabolism; D029968:Escherichia coli Proteins / Q000737:chemistry* / Q000378:metabolism; D055767:Immobilized Proteins / Q000737:chemistry; D018625:Microscopy, Atomic Force; D008958:Models, Molecular; D011489:Protein Denaturation; D017510:Protein Folding; D020836:Protein Structure, Quaternary
chemical_list: D018835:Chaperonin 10; D029968:Escherichia coli Proteins; D055767:Immobilized Proteins