The Nature of Non-Arrhenius Kinetics in the Heat Denaturation of Proteins

The nature of non-Arrhenius kinetics of protein unfolding is investigated in this study. Free-energy profiles along the reaction coordinate of protein unfolding are built in a wide temperature interval. These profiles reveal the temperature-dependent contribution of the intermediate assigned to be the dry molten globule (DMG) state, stabilized by the entropy gain provided by the loose framework of extended hydrogen bonds. The revealed DMG state with a loose pseudo-secondary structure of protein provides a funnel-shaped free-energy landscape, which is a central point of the folding mechanism, rationalizing Levinthal's paradox. The rate constants of the elementary steps of the unfolding process are calculated according to Transition State Theory. The strong temperature dependence of the Arrhenius parameters for the rate constants of the elementary steps of the unfolding process, and the negative activation energy of the folding process are explained. The main factor influencing the non-Arrhenius behavior of the rate constants is the strong temperature-dependent shift in the location of the DMG and Transition State along the reaction coordinate. The Arrhenius plot for the calculated rate constant for heat denaturation of the protein in a wide temperature range (270-600 K) is built. Its "convex" shape and the sharp drop in the values of the Arrhenius parameters at high temperatures are in very good agreement with the experimentally observed dependencies.