Study on the Relationship between CGTase´s Thermostability and Electrostatic Energy by Molecular Dynamics Simulation

Cyclodextrin glycosyltransferase (CGTase) (EC 2.4.1.19) is an important industrial enzyme for the production of cyclodextrins. As we know, thermophilic CGTase is more usefully than mesophilic CGTase in industry. There are many factors that affect CGTase thermostability. In all the cases studied, electrostatic interactions are more favorable in the hyperthermophilic proteins. The electrostatic free energy is found not only to be correlated with the number of ionizable amino acid residues, saltbridges or saltbridge networks in a protein, but also depends on the location of these groups within the protein structure. Taken together, electrostatic contributions to the energy of wildtype CGTase and its mutant are calculated. The dynamics of a mutant CGTase in a water environment, as studied by performing molecular dynamics (MD) simulations at various temperatures, is compared to the dynamical behavior of a homologous wildtype protein simulated under identical conditions. Our results suggest that mutant protein enhances electrostatic interactions through mutation of amino acids within the time scale of the simulations. Regime saltbridge interactions provide a stabilizing contribution in particular in the mutant protein in the high temperature. Optimization of electrostatic interactions offers a simple means of enhancing stability without disrupting the core residues characteristic of different protein families. This leads to the conclusion that electrostatic interactions play an important role in determining the stability of protein at high temperatures.