Exponential decay kinetics in "downhill" protein folding

The observation of single‐exponential kinetic phases in early stages of protein folding is often interpreted as evidence that these phases are rate limited by significant energy or entropy barriers. However, although the existence of large barriers reliably implies exponential kinetics, the reverse...

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Bibliographic Details
Published in:Proteins, structure, function, and bioinformatics structure, function, and bioinformatics, 2003-01, Vol.50 (1), p.1-4
Main Author: Hagen, Stephen J.
Format: Article
Language:English
Subjects:
cytochrome c
diffusion
energy landscape
exponential
fluorescence
Fluorescence Resonance Energy Transfer
Kinetics
Models, Theoretical
Protein Folding
Protein Structure, Secondary
Proteins - chemistry
tryptophan
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Summary:The observation of single‐exponential kinetic phases in early stages of protein folding is often interpreted as evidence that these phases are rate limited by significant energy or entropy barriers. However, although the existence of large barriers reliably implies exponential kinetics, the reverse is not necessarily true. A simple model for the hydrophobic collapse of a chain molecule demonstrates that a barrierless or “downhill” diffusional relaxation can give rise to kinetics that are practically indistinguishable from a pure exponential. Within this model, even a highly nonlinear experimental probe such as resonance energy transfer (Förster transfer) could exhibit a large amplitude decay (greater than 90% in fluorescence) that deviates from a simple exponential by less than 0.5%. Only a detailed analysis of the dynamics is likely to reveal that a free energy barrier is absent. Proteins 2003;50:1–4. © 2002 Wiley‐Liss, Inc.
ISSN:0887-3585
1097-0134
DOI:10.1002/prot.10261