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A thermodynamic coupling mechanism for GroEL-mediated unfolding
S Walter1, G H Lorimer, F X Schmid
1Laboratorium für Biochemie, Universität Bayreuth, Germany.
Summary
Chaperonins like E. coli GroEL prevent protein aggregation. GroEL unfolds misfolded proteins not by catalysis, but by binding to unfolded states, shifting the equilibrium.
Area of Science:
- Biochemistry
- Molecular Biology
- Protein Folding
Background:
- Chaperonins, such as E. coli GroEL, are crucial for preventing protein aggregation.
- It was hypothesized that GroEL catalyzes the unfolding of misfolded protein intermediates.
Purpose of the Study:
- To investigate the kinetic mechanism of GroEL-mediated protein unfolding.
- To determine if GroEL catalyzes the unfolding of misfolded protein intermediates.
Main Methods:
- Utilized a reduced and carbamidomethylated variant of RNase T1 (RCAM-T1) as a model for non-native protein states.
- Analyzed the effect of GroEL on the microscopic unfolding rate constant of RCAM-T1.
Main Results:
- GroEL binding to RCAM-T1 induced unfolding, but did not alter the microscopic unfolding rate constant.
- GroEL demonstrated high-affinity binding to the unfolded state of RCAM-T1, shifting the equilibrium towards unfolding.
Conclusions:
- GroEL does not catalyze protein unfolding; instead, it promotes unfolding via a thermodynamic coupling mechanism.
- This mechanism is effective when GroEL's binding free energy exceeds the intermediate's conformational stability and unfolding rate.