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A new alternative method to quantify residual structure in 'unfolded' proteins
1Institut für Physikalische Chemie der Westfälischen Wilhelms-Universität Münster, Germany.
Biochimica Et Biophysica Acta
|September 27, 2000
Summary
Researchers studied pig and human calpastatin domain 1 proteins to understand protein denaturation. They found residual structure in unfolded proteins leads to suboptimal hydration, confirmed by heat capacity and circular dichroism measurements.
Area of Science:
- Biophysics
- Protein Chemistry
- Structural Biology
Background:
- Calpastatin domain 1 (CSD1) proteins from pigs (pCSD1) and humans (hCSD1) were investigated.
- Previous studies suggested pCSD1 is unstructured in water at room temperature.
- Preliminary spectroscopic data indicated hCSD1 might share similar unstructured features.
Purpose of the Study:
- To characterize common features of the denatured state of pCSD1 and hCSD1 proteins.
- To quantitatively estimate residual structure in the unfolded state of these proteins.
- To investigate the degree of hydration in unfolded polypeptide chains.
Main Methods:
- Differential scanning calorimetry (DSC) heat capacity measurements were performed between 10-80°C.
- Circular dichroism (CD) spectroscopy was used to assess protein structure.
- The effect of guanidinium hydrochloride (GdnHCl) on unfolding was studied at selected temperatures.
Main Results:
- Experimental heat capacity data were compared with theoretical values from a new increment system.
- A quantitative estimate of residual structure was obtained, consistent between DSC and CD measurements.
- Unfolded pCSD1 and hCSD1 chains showed lower heat capacity than calculated, indicating suboptimal hydration.
Conclusions:
- The heat capacity approach provides insight into the hydration of unfolded polypeptide chains.
- Suboptimal hydration in unfolded pCSD1 and hCSD1 is attributed to residual structure.
- This residual structure affects the hydration of residues compared to oligopeptides.