Thermodynamic and kinetic stabilities of hen-egg lysozyme and its chemically modified derivatives: Analysis of the transition state of the protein unfolding

For the stabilization of a protein against irreversible denaturation caused by rapid reaction of the unfolded form of the protein (kinetic stabilization), the free energy change of activation for unfolding should be increased. First, we demonstrated that this strategy was effective to stabilize a protein against protease digestion. For kinetic stabilization, it is important to stabilize a protein at a site where the local structures are largely unfolded in the transition state for unfolding. We developed a method to find such sites by comparison of the thermodynamic stabilities and the unfolding rate constants between unmodified and modified proteins. Application of this method to analyze the transition state of hen-egg lysozyme using some chemically modified derivatives is also described. Moreover, it was confirmed that the protease digestion method is superior to the relaxation method for estimation of the unfolding rate constant. Namely, the protease digestion method may be useful in analyzing the transition state of protein unfolding.