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

Simultaneous improvements of thermostability and activity of a Ca-independent -amylase from Bacillus subtilisCN7 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 -amylase, raised the turnover number by 35% and increased the thermostability in terms of half-life at 65 degrees C by threefold. A his(6)-tag fusion at either the C- or N-terminus of truncated -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.