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Exponential decay kinetics in "downhill" protein folding.
1Physics Department, University of Florida, Gainesville 32611-8440, USA. sjhagen@ufl.edu
Proteins
|December 10, 2002
Summary
Protein folding kinetics may appear exponential due to barriers, but downhill relaxation can mimic this. Detailed analysis is needed to detect barrierless protein folding dynamics.
Area of Science:
- Biophysics
- Chemical Kinetics
- Computational Biology
Background:
- Single-exponential kinetic phases in protein folding are typically attributed to significant energy or entropy barriers.
- However, exponential kinetics do not exclusively indicate the presence of large free energy barriers.
Purpose of the Study:
- To investigate if barrierless processes can produce kinetics indistinguishable from exponential decay.
- To model the hydrophobic collapse of a chain molecule and its kinetic implications.
Main Methods:
- Development of a simple model for hydrophobic collapse of a chain molecule.
- Simulation of kinetics using this model, including analysis of a nonlinear experimental probe (resonance energy transfer).
Main Results:
- A barrierless, downhill diffusional relaxation can generate kinetics practically identical to pure exponential decay.
- Even a nonlinear probe like Förster transfer can show over 90% fluorescence decay deviating less than 0.5% from a simple exponential.
Conclusions:
- The presence of significant free energy barriers in protein folding cannot be definitively concluded from single-exponential kinetics alone.
- Detailed dynamic analysis is crucial to differentiate between barrier-limited and barrierless folding pathways.