The use of gel filtration to follow conformational changes in proteins. Conformational flexibility of bovine myelin basic protein

The hydrodynamic behavior of bovine myelin basic protein was studied by gel filtration through Sephadex G-100 under conditions which included variations in pH from 2 to 12, variations in ionic strength from 0.01 to 1.5 M at pH 2 and from 0.1 to 2 M at pH 7, and variations in guanidinium chloride concentration from 0 to 6 M. A number of well characterized compact globular proteins were subjected to the same conditions for comparison. Compact globular proteins showed major conformational transitions due to acid, alkali, and guanidinium chloride denaturation and, possibly, minor transitions as well. Myelin basic protein behaved like a flexible linear polyelectrolyte, expanding continuously between pH 11 and pH 2 to 3 at ionic strength 0.1 M and contracting continuously with increase in ionic strength at pH 2 and at pH 7 to the point of salting-out. Relatively low concentrations of guanidinium chloride (approximately 0.5 M) were sufficient to cause the basic protein to expand. With increasing concentration of the denaturant the molecule continued to expand, but in a noncooperative manner. These results demonstrated the lack of significant intramolecular stabilization in the protein.