3.3. Design of interfacial interactions
Double mutations of V137I-S314L, F306H-G311I, L134W-F310I were designed
to enhance the hydrogen bonds and salt bridges, which aim to promote
structure rigidity of enzyme. Calculation of mutation energy was carried
out by the webserver Calculate Mutation Energy of Discovery Studio 2016
Client. All mutation energy of double mutated enzymes was negative,
which indicated the enhanced thermostability. Therefore, positive
mutations were further combined and the designed enzymes DA06 to DA11
were obtained. None of mutated sites is located within active sites,
which would not arise activity change from binding substrate. Mutation
energy for the combined mutations indicated the cooperative effect on
the improvement of thermostability (Table 2).
Thermodynamic parameters of all designed enzymes were calculated by
Scoop and were listed in Table 3 [25]. Parameters such as change in
enthalpy (ΔHm), change in heat capacity
(ΔCp), melting temperature (Tm) and
difference in Gibbs free energy of stability (ΔGr), were
calculated. These thermodynamic parameters which have important
implications for enzyme thermostablility[26].