Functional relationships between cyclodextrin glucanotransferase from an alkalophilic Bacillus and α-amylases Site-directed mutagenesis of the conserved two Asp and one Glu residues

摘要: Comparison of the amino acid sequences cyclodextrin glucanotransferases (CGTases) with those α-amylases revealed that two Asp and one Glu residues, which are considered to be catalytic residues in α-amylases, were also conserved CGTases. To analyze function three CGTases, site-directed mutagenesis was carried out. The mutant Asp229, Glu257 Asp328 individually replaced by Asn or Gln, completely lost both their starch-degrading β-cyclodextrin-forming activities, whereas another CGTase, Glu264 retained these activities. inactive enzymes ability bound starch. These results suggest play an important role enzymatic reaction catalyzed CGTase a similar mechanism is present CGTases α-amylases.