Directed evolution of Aspergillus niger glucoamylase to increase thermostability.
Bottom Line: Irreversible inactivation tests indicated that CR2-1 increases the free energy of thermoinactivation at 80°C by 10 kJ mol(-1) compared with that of wild-type GA.Thus, CR2-1 is more thermostable (by 5 kJ mol(-1) at 80°C) than the most thermostable A. niger GA variant previously described, THS8.In addition, Val59Ala and Glu408Lys were shown to individually increase the thermostability in GA variants by 1 and 2 kJ mol(-1), respectively, at 80°C.
Affiliation: Department of Food Science and Human Nutrition, Iowa State University, Ames, IA 50011, USA.Show MeSH
Mentions: Figure 4 is an irreversible thermoinactivation plot showing the effect of temperatures between 65°C and 87.5°C on the thermoinactivation constant (kd) of RE15, CR1‐1, CR2‐1 and wild‐type GAs. The results show that at all temperatures, each of the mutant GAs is substantially more thermostable than wild‐type GA, with CR2‐1 being the most thermostable. Figure 5 shows the effect of temperature on the kd values of SRE15+V59A versus SRE15 as a control, and RE5+E408K versus RE5 as a control. The results show that at every temperature tested, SRE15+V59A and RE5+E408K are more thermostable than SRE15 and RE5 respectively.
Affiliation: Department of Food Science and Human Nutrition, Iowa State University, Ames, IA 50011, USA.