The enzyme cyclodextrin glycosyltransferase is closely related to alpha-amylases but has the unique ability to produce cyclodextrins (circular alpha(1-->4)-linked glucoses) from starch. To characterize this specificity we determined a 1.8-A structure of an E257Q/D229N mutant cyclodextrin glycosyltransferase in complex with its product gamma-cyclodextrin, which reveals for the first time how cyclodextrin is competently bound ...
The enzyme cyclodextrin glycosyltransferase is closely related to alpha-amylases but has the unique ability to produce cyclodextrins (circular alpha(1-->4)-linked glucoses) from starch. To characterize this specificity we determined a 1.8-A structure of an E257Q/D229N mutant cyclodextrin glycosyltransferase in complex with its product gamma-cyclodextrin, which reveals for the first time how cyclodextrin is competently bound. Across subsites -2, -1, and +1, the cyclodextrin ring binds in a twisted mode similar to linear sugars, giving rise to deformation of its circular symmetry. At subsites -3 and +2, the cyclodextrin binds in a manner different from linear sugars. Sequence comparisons and site-directed mutagenesis experiments support the conclusion that subsites -3 and +2 confer the cyclization activity in addition to subsite -6 and Tyr-195. On this basis, a role of the individual residues during the cyclization reaction cycle is proposed.
Related Citations:
X-ray Structures Along the Reaction Pathway of Cyclodextrin Glycosyltransferase Elucidate Catalysis in the Alpha-amylase Family Uitdehaag, J.C.M., Mosi, R., Kalk, K.H., van der Veen, B.A., Dijkhuizen, L., Withers, S.G., Dijkstra, B.W. (1999) Nat Struct Biol 6: 432
Crystallographic Studies of the Interaction of Cyclodextrin Glycosyltransferase from Bacillus Circulans Strain 251 with Natural Substrates and Products Knegtel, R.M., Strokopytov, B., Penninga, D., Faber, O.G., Rozeboom, H.J., Kalk, K.H., Dijkhuizen, L., Dijkstra, B.W. (1995) J Biol Chem 270: 29256
Structure of Cyclodextrin Glycosyltransferase Complexed with a Maltononaose Inhibitor at 2.6 Angstrom Resolution. Implications for Product Specificity Strokopytov, B., Knegtel, R.M., Penninga, D., Rozeboom, H.J., Kalk, K.H., Dijkhuizen, L., Dijkstra, B.W. (1996) Biochemistry 35: 4241
Organizational Affiliation:
BIOSON Research Institute, Laboratory of Biophysical Chemistry, Groningen Biomolecular Sciences, University of Groningen, Nijenborgh 4, 9747AG Groningen, the Netherlands.
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