Molecular Structure of B. stearothermophilus Cyclodextrin Glucanotransferase and Analysis of Substrate Binding Site

The 3-dimensional X-ray crystallographic structure of cyclodextrin glucanotransferase (CGT-ase) from B. stearothermophilus showed that the CGTase molecule fold into four globular domains, A, B, C and D. The N-terminal domains, A and B, are similar to those of Taka-amylase. The C and D domains, which are unique to this enzyme, both consist of antiparallel β-barrel structure. With a substrate binding analysis in the crystal, two binding sites have been found on the enzyme molecule, one in a cleft of the A-domain and the other in the D-domain. The first one is considered to be related to the enzyme activity in a same manner with a-amylase and the second to the raw starch binding activity of the CGTase.