Activation parameters for the spontaneous and pressure-induced phases of the dissociation of single-ring GroEL (SR1) chaperonin

We investigated the dissociation of single-ring heptameric GroEL (SR1) by high hydrostatic pressure in the range 0.5-3.0 kbar. The kinetics were studied as a function of temperature in the range 15-35 °C. The dissociation processes at each pressure and temperature showed biphasic behavior. The slower rate (k_1,obs) was confirmed to be the self-dissociation of SR1 at any specific temperature at atmospheric pressure. This dissociation was pressure independent and followed concentration-dependent first-order kinetics. The self-dissociation rates followed normal Eyring plots (ln k_1,obs/T vs. 1/T) from which the free energy of activation (ΔG‡ = 22 ± 0.3 kcal mol^-1), enthalpy of activation (ΔH‡ = 18 ± 0.5 kcal mol^-1), and entropy of activation (ΔS‡ = -15 ± 1 kcal mol^-1) were evaluated. The effect of pressure on the dissociation rates resulted in nonlinear behavior (ln k_2,obs vs. pressure) at all the temperatures studied indicating that the activation volumes were pressure dependent. Activation volumes at zero pressure (V‡_o) and compressibility factors (β‡) for the dissociation rates at the specific temperatures were calculated. This is the first systematic study where the self-dissociation of an oligomeric chaperonin as well as its activation parameters are reported.