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Thermodynamics of Membrane Protein Folding Measured by Fluorescence Spectroscopy
Published on: April 28, 2011
The cytochrome c folding landscape revealed by electron-transfer kinetics
Jennifer C Lee1, I-Jy Chang, Harry B Gray
1Beckman Institute, California Institute of Technology, Pasadena, CA 91125, USA.
Journal of Molecular Biology
|June 25, 2002
Summary
Investigating cytochrome c folding revealed that collapsed structures are not more stable than extended ones. Most folding energy is released when compact structures form the native fold, impacting protein stability studies.
Area of Science:
- Biochemistry
- Protein Folding Dynamics
- Electron Transfer Kinetics
Background:
- Cytochrome c is a crucial protein involved in cellular respiration.
- Understanding protein folding energy landscapes is vital for comprehending protein function and dysfunction.
- Electron transfer (ET) reactions are fundamental to many biological processes.
Purpose of the Study:
- To investigate the folding energy landscape of cytochrome c.
- To correlate electron transfer (ET) reactivities with protein structural changes during folding.
- To elucidate the stability of intermediate structures during the folding process.
Main Methods:
- Utilized Zn(II)-substituted cytochrome c (Zn-cyt c) with distinct electron-transfer reactivities for buried and exposed hemes.
- Measured ET kinetics of Zn-cyt c in guanidine hydrochloride denaturant and during refolding.
- Analyzed the kinetics of ruthenium(III) hexaammine reduction by electronically excited Zn-porphyrin.
Main Results:
- Denatured Zn-cyt c showed a ~10-fold faster ET rate compared to folded Zn-cyt c.
- A folding intermediate was observed with distinct populations exhibiting fast and slow ET kinetics.
- Collapsed non-native structures were found to be not substantially more stable than extended conformations.
Conclusions:
- The folding energy landscape of cytochrome c is characterized by rapid interconversion between collapsed and extended conformations.
- Significant folding free energy is released during the transition from compact structures to the native fold.
- Electron transfer kinetics serve as a sensitive probe for structural dynamics during protein folding.
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