aFinnish-Russian Joint Biotechnology Laboratory, University of Turku, SF-20500 Turku, Finland
bTurku Center for Biotechnology, Tykistkatu 6, BioCity, SF-20520 Turku, Finland
cEuropean Molecular Biology Laboratory, Postfach 10.2209, Meyerhofstrae 1, 6900 Heidelberg, Germany
The Ca coordinates of the crystallographic structure of Bacillus circulans cyclomaltodextrin glucanotransferase (CGTase) has been used as a template for the construction of the three-dimensional structure of the Bacillus circulans var. alkalophilus CGTase. Comparison of the modeled structure with a-amylase revealed that the catalytic and the structure-forming residues of both enzymes maintain their positions and functional role, making the active site geometry strikingly similar. We have calculated the electrostatic potential field of the CGTase by numerically solving the Poisson-Boltzmann equation and have made PKa estimates for the catalytic residues. We have found that in the catalytic dyad, Glu257 is more protonated than Asp328 and therefore acts as a general acid in the catalytic mechanism of the enzyme.
In ``Stability and Stabilization of Enzymes''
Eds. van der Tweel,W.J.J., Harder,A. and Buitelaar,R.M.
Elsevier, Netherlands. (1993) pp291-298.