Thermal stability and activity improvements of a Ca-independent a-amylase from Bacillus subtilis CN7 by C-terminal truncation and hexahistidine-tag fusion

摘要

Simultaneous improvements of thermostability and activity of a Ca-independent a-amylase from Bacillus subtilis CN7 were achieved by C-terminal truncation and his_6-tag fusion. C-terminal truncation, which eliminates C-terminal 194-amino-acid residues from the intact mature a-amylase, raised the turnover munber by 35% and increased the thermostability in terms of half-life at 65℃ by threefold. A his_6-tag fusion at either the C or N-terminus of truncated a-amylase further enhanced its turnover number by 59% and 37%, respectively. Molecular modeling revealed that these improvements could be attributed to structural rearrangement and reorientation of the catalytic residues.