Decrease of dielectric constant transforms the protein molecule into the molten globule state

The effect of organic solvents of different nature (alcohols, amides, and cyclic ethers) on the structural properties of beta-lactoglobulin was studied by circular dichroism and fluorescence spectroscopy. It is shown that the protein molecule undergoes at least two consecutive conformational transitions upon increase of the organic solvent concentration. Denaturation of the protein molecule occurs in the first step and a transition into the highly helical non-compact state in the second. In other words, under such conditions a compact denatured intermediate state is formed with a pronounced secondary structure, i.e., a molten globule-like state. It is shown that decrease of the dielectric constant of the media is responsible for structural changes of the protein molecule.