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Conformational transitions provoked by organic solvents in beta-lactoglobulin: can a molten globule like intermediate
V N Uversky1, N V Narizhneva, S O Kirschstein
1Institute of Protein Research, Russian Academy of Sciences, Pushchino, Moscow Region, Russia.
Folding & Design
|January 1, 1997
Summary
Organic solvents induce a compact, denatured intermediate state in beta-lactoglobulin by decreasing the dielectric constant. This molten globule-like state exhibits significant secondary structure and binds hydrophobic probes, confirming its unique properties.
Area of Science:
- Protein chemistry
- Biophysical chemistry
- Molecular biology
Background:
- Nonnative protein states occur in cells and are involved in physiological processes.
- Membrane surfaces can denature proteins due to negative charges and decreased water dielectric constant.
- Previous data lacked confirmation for the role of dielectric constant in protein denaturation.
Purpose of the Study:
- To investigate the conformational transitions of beta-lactoglobulin induced by organic solvents.
- To confirm the role of the dielectric constant in protein denaturation.
- To characterize the intermediate denatured state.
Main Methods:
- Near and far UV circular dichroism spectroscopy.
- Steady-state and time-resolved fluorescence spectroscopy using 8-anilinonaphthalene-1-sulfonate (8-ANS).
- Analysis of conformational transitions in response to varying dielectric constants.
Main Results:
- Five organic solvents (methanol, ethanol, isopropanol, DMF, dioxane) induced at least two cooperative conformational transitions in beta-lactoglobulin.
- These transitions involve disruption of tertiary structure and formation of expanded helical structures.
- The dielectric constant was identified as a key factor, with transitions aligning across different solvents.
Conclusions:
- A decrease in solvent dielectric constant induces an equilibrium intermediate state in beta-lactoglobulin.
- This denatured intermediate state is compact, possesses pronounced secondary structure, and binds 8-ANS.
- The observed properties align with the characteristics of a molten globule intermediate state.