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Toward a better understanding of protein folding pathways
1Medical Research Council, Laboratory of Molecular Biology, Cambridge, England.
Summary
Protein refolding experiments challenge common theories, revealing a rapid pre-folding equilibrium that favors compact structures. Most proteins refold through a single, late-stage transition state, not multiple pathways or nucleation events.
Area of Science:
- Biochemistry
- Physical Chemistry
- Molecular Biology
Background:
- Protein folding is crucial for biological function.
- Existing theories propose diverse folding mechanisms.
- Experimental data offers a contrasting perspective.
Purpose of the Study:
- To reconcile experimental observations with protein folding theories.
- To elucidate the general scheme of protein refolding.
- To address specific proposed alternative folding mechanisms.
Main Methods:
- Analysis of experimental data on protein refolding kinetics.
- Consideration of conformational equilibrium in unfolded states.
- Evaluation of transition state models for folding.
- Critique of specific proposed folding pathways (e.g., Scheraga et al.).
Main Results:
- Unfolded proteins rapidly equilibrate into compact conformations before refolding.
- A single, high-energy transition state governs the rate-limiting step of folding.
- Protein folding does not typically initiate via nucleation followed by growth.
- Disulfide bond formation pathways align with general folding principles.
Conclusions:
- Protein refolding follows a general scheme characterized by early equilibrium and a late transition state.
- Popular theories suggesting multiple pathways or nucleation-initiated folding are inconsistent with experimental evidence.
- A previously proposed exceptional folding mechanism is attributed to experimental and analytical limitations.