Structures of maltohexaose and maltoheptaose bound at the donor sites of cyclodextrin glycosyltransferase give insight into the mechanisms of transglycosylation activity and cyclodextrin size specificity.
Primary Citation of Related Structures: 1EO7, 1EO5
PubMed Abstract:
The enzymes from the alpha-amylase family all share a similar alpha-retaining catalytic mechanism but can have different reaction and product specificities. One family member, cyclodextrin glycosyltransferase (CGTase), has an uncommonly high transgly ...
The enzymes from the alpha-amylase family all share a similar alpha-retaining catalytic mechanism but can have different reaction and product specificities. One family member, cyclodextrin glycosyltransferase (CGTase), has an uncommonly high transglycosylation activity and is able to form cyclodextrins. We have determined the 2.0 and 2.5 A X-ray structures of E257A/D229A CGTase in complex with maltoheptaose and maltohexaose. Both sugars are bound at the donor subsites of the active site and the acceptor subsites are empty. These structures mimic a reaction stage in which a covalent enzyme-sugar intermediate awaits binding of an acceptor molecule. Comparison of these structures with CGTase-substrate and CGTase-product complexes reveals three different conformational states for the CGTase active site that are characterized by different orientations of the centrally located residue Tyr 195. In the maltoheptaose and maltohexaose-complexed conformation, CGTase hinders binding of an acceptor sugar at subsite +1, which suggests an induced-fit mechanism that could explain the transglycosylation activity of CGTase. In addition, the maltoheptaose and maltohexaose complexes give insight into the cyclodextrin size specificity of CGTases, since they precede alpha-cyclodextrin (six glucoses) and beta-cyclodextrin (seven glucoses) formation, respectively. Both ligands show conformational differences at specific sugar binding subsites, suggesting that these determine cyclodextrin product size specificity, which is confirmed by site-directed mutagenesis experiments.
Related Citations:
The Cyclization Mechanism of Cyclodextrin Glycosyltransferase (CGTase) as Revealed by a Gamma-Cyclodextrin-Cgtase Complex at 1.8 Angstrom Resolution Uitdehaag, J.C.M., Kalk, K.H., Van Der Veen, B.A., Dijkhuizen, L., Dijkstra, B.W. (1999) J Biol Chem 274: 34868
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.A., 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.A., Penninga, D., Rozeboom, H.J., Kalk, K.H., Dijkhuizen, L., Dijkstra, B.W. (1996) Biochemistry 35: 4241
Organizational Affiliation:
Center for Carbohydrate Bioengineering and Laboratory of Biophysical Chemistry, University of Groningen, Nijenborgh 4, 9747 AG Groningen, The Netherlands.
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