Analysis of the catalytic center of cyclomaltodextrinase from Thermoanaerobacter ethanolicus 39E

The amino acid sequences of cyclomaltodextrinase (CDase) from Thermoanaerobacter ethanolicus 39E (formerly Clostridium thermohydrosulfuricum 39E) and other amylolytic enzymes were compared by using linear alignment and hydrophobic cluster analysis. Two Asp and one Glu residue, which were considered to be the catalytic residues of the compared enzymes according to crystallographic or protein engineering experiments, were also conserved in CDase. Asp325, Asp421 and Glu354 of the CDase were individually replaced by means of site-directed mutagenesis. The mutant enzymes completely lost activity, suggesting that these residues play an important role in catalysis.