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Folding kinetics of a fluorescent variant of monomeric lambda repressor
S Ghaemmaghami1, J M Word, R E Burton
1Department of Biochemistry, Duke University Medical Center, Durham, North Carolina 27710, USA.
Biochemistry
|June 24, 1998
Summary
This study analyzed the folding kinetics of a lambda repressor variant using fluorescence stopped-flow and NMR. The protein folds rapidly, supporting a two-state folding model.
Area of Science:
- Protein Folding
- Biophysics
- Molecular Biology
Background:
- Understanding protein folding is crucial for molecular biology.
- Monomeric lambda repressor is a model system for studying protein folding.
- Tryptophan variants can be used to probe folding kinetics.
Purpose of the Study:
- To investigate the folding kinetics of a tryptophan-containing variant of monomeric lambda repressor.
- To compare folding kinetics under various denaturant conditions.
- To validate a two-state folding model.
Main Methods:
- Fluorescence stopped-flow spectroscopy.
- Nuclear Magnetic Resonance (NMR) spectroscopy.
- Circular Dichroism (CD) spectroscopy for equilibrium denaturation.
Main Results:
- Equilibrium denaturation curves from CD, fluorescence, and NMR were superimposable.
- Folding kinetics were analyzed at 20°C.
- The variant folds within 2 ms in 3.4 M urea and 1.8 M GdmCl.
- Extrapolated folding time in the absence of denaturants is 20 μs.
- All reactions exhibited monoexponential kinetics without burst-phases.
- Kinetic analysis yielded thermodynamic parameters consistent with equilibrium experiments.
Conclusions:
- The folding and unfolding kinetics of the lambda repressor variant are consistent across different methods.
- The results strongly support a two-state protein folding model (Denatured ⇌ Native).
- The study provides insights into the rapid folding mechanisms of proteins.