[Denatured transitions of the molecular chaperone GroEL from Escherichia coli]

Conformational changes of oligomeric particle of GroEL chaperone from E. coli in solution were studied, which proceed during its denaturation upon the action of elevated urea concentration, temperature, and extremal pH values by the methods of CD, light scattering, scanning microcalorimetry, hydrophobic probe binding, and ATPase activity measurements. The ranges of changing the external conditions; within which GroEL retains its structure and functions, were determined. Denaturation transitions were found to be cooperative, pronounced, and irreversible. In the pH range from 6.0 to 9.6, the three-step change of the ATPase activity of GroEL was shown to occur with half-transition pH1/2 of 6.3, 8.5, and 9.3. It does not result in any essential structural changes and is probably associated with a protonation/deprotonation of amino acid residues important for the GroEL ATPase activity.