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A mobile loop order–disorder transition modulates the speed of chaperonin cycling
Author(s) -
Shewmaker Frank,
Kerner Michael J.,
HayerHartl Manajit,
Klein Gracjana,
Georgopoulos Costa,
Landry Samuel J.
Publication year - 2004
Publication title -
protein science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.353
H-Index - 175
eISSN - 1469-896X
pISSN - 0961-8368
DOI - 10.1110/ps.04773204
Subject(s) - chaperonin , groel , groes , biophysics , protein folding , mutant , atp hydrolysis , conformational change , chemistry , biochemistry , crystallography , biology , enzyme , escherichia coli , atpase , gene
Abstract Molecular machines order and disorder polypeptides as they form and dissolve large intermolecular interfaces, but the biological significance of coupled ordering and binding has been established in few, if any, macromolecular systems. The ordering and binding of GroES co‐chaperonin mobile loops accompany an ATP‐dependent conformational change in the GroEL chaperonin that promotes client protein folding. Following ATP hydrolysis, disordering of the mobile loops accompanies co‐chaperonin dissociation, reversal of the GroEL conformational change, and release of the client protein. “High‐affinity” GroEL mutants were identified by their compatibility with “low‐affinity” co‐chaperonin mutants and incompatibility with high‐affinity co‐chaperonin mutants. Analysis of binding kinetics using the intrinsic fluorescence of tryptophan‐containing co‐chaperonin variants revealed that excessive affinity causes the chaperonin to stall in a conformation that forms in the presence of ATP. Destabilizing the β‐hairpins formed by the mobile loops restores the normal rate of dissociation. Thus, the free energy of mobile‐loop ordering and disordering acts like the inertia of an engine's flywheel by modulating the speed of chaperonin conformational changes.