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Three-state analysis of sperm whale apomyoglobin folding
1Department of Biochemistry, Beckman Center, Stanford University Medical Center, California 94305.
Biochemistry
|April 13, 1993
Summary
This study quantitatively describes apomyoglobin unfolding using urea and acid. Results reveal an intermediate state (I) closer in stability to the unfolded state (U), highlighting the importance of side-chain packing for native protein structure.
Area of Science:
- Biochemistry
- Protein Folding
- Structural Biology
Background:
- Apomyoglobin is a key protein model for studying protein folding.
- Understanding protein transitions is crucial for comprehending biological function and disease.
- Environmental factors like pH and denaturants significantly influence protein stability.
Purpose of the Study:
- To quantitatively describe the urea- and acid-induced unfolding transitions of apomyoglobin.
- To derive and validate a three-state model for apomyoglobin conformations.
- To elucidate the thermodynamic and structural properties of native (N), intermediate (I), and unfolded (U) states.
Main Methods:
- Collected unfolding curves for apomyoglobin under varying urea concentrations and pH values.
- Applied a three-state equation to model the stability of N, I, and U conformations.
- Analyzed the sensitivity of equilibria to urea and pH to infer structural characteristics.
Main Results:
- A three-state equation accurately fits the experimental data for apomyoglobin unfolding.
- The intermediate state (I) is thermodynamically closer to the unfolded state (U) than the native state (N).
- Acid-induced unfolding involves the titration of two histidines with low pKa values in the native state.
Conclusions:
- Side-chain packing significantly contributes to the stability of native protein structure.
- The intermediate conformation (I) exhibits limited solvent accessibility.
- Under physiological conditions, the intermediate conformation is the most stable non-native state of apomyoglobin.
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