Correlated dynamics, reactive conformations and non-Arrhenius behaviour in the temperature-dependence of enzyme activity: triosephosphate isomerase

Abstract

Heat capacity changes are increasingly recognised as crucial for understanding the temperature dependence of enzyme-catalysed reaction rates. Here, we combine experiments and molecular dynamics simulations to investigate triosephosphate isomerase (TIM, TPI) from psychrophilic, mesophilic and thermophilic organisms. Kinetic data show clear curvature in rate-temperature plots, particularly for the cold-adapted enzyme, independent of unfolding. This non-Arrhenius behaviour is accounted for by Macromolecular Rate Theory (MMRT), implying an activation heat capacity, largest for the psychrophile. Simulations reveal the molecular origins of these differences, showing significant conformational and dynamical changes between reactant and transition states in the cold-adapted enzyme, with a smaller activation heat capacity in the mesophilic enzyme, and near-zero for the thermophile. Transition-state-like conformations and reorganized correlated dynamics underlie these adaptations. These results demonstrate that dynamical differences between crucial states along the reaction pathway play a key role in determining the optimum temperature of activity for this archetypal enzyme.