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Setting the chaperonin timer: a two-stroke, two-speed, protein machine.
John P Grason1, Jennifer S Gresham, George H Lorimer
1Department of Chemistry and Biochemistry, Center for Biological Structure and Organization, University of Maryland, College Park, MD 20742, USA.
The chaperonin cycle speed is controlled by the trans ring
Area of Science:
- Molecular biology
- Biochemistry
- Protein folding
Background:
- Chaperonins are essential molecular machines that assist protein folding.
- The timing mechanism of chaperonin function is crucial for cellular processes.
- GroEL and GroES form a chaperonin complex regulating protein folding cycles.
Purpose of the Study:
- To elucidate the timing mechanism of the chaperonin nanomachine.
- To determine the factors governing the hemicycle time (HCT) of chaperonin function.
- To understand the role of allosteric interactions in regulating chaperonin cycle speed.
Main Methods:
- Kinetic analysis of chaperonin activity.
- Investigating the effect of various ligands on chaperonin cycle parameters.
- Studying the conformational states of GroEL and GroES.
Main Results:
- Hemicycle time (HCT) is determined by the mean residence time (MRT) of GroES on the cis ring of GroEL.
- Allosteric interactions within the trans ring of GroEL govern the MRT.
- Ligands stabilizing the R state (ADP, K+) extend HCT, while ligands stabilizing the T state (unfolded substrate protein, SP) decrease HCT.
Conclusions:
- The conformational state of the trans ring of GroEL dictates the speed of the chaperonin cycle.
- Substrate protein binding accelerates the chaperonin machine towards its maximum speed.
- Understanding these regulatory mechanisms is key to comprehending protein homeostasis.

