Cyclodextrin glycosyltransferases (CGTase) (EC 2.4.1.19) are extracellular bacterial enzymes that generate cyclodextrins from starch. All known CGTases produce mixtures of alpha, beta, and gamma-cyclodextrins. A maltononaose inhibitor bound to the active site of the CGTase from Bacillus circulans strain 251 revealed sugar binding subsites, distant from the catalytic residues, which have been proposed to be involved in the cyclodextrin size specificity of these enzymes ...
Cyclodextrin glycosyltransferases (CGTase) (EC 2.4.1.19) are extracellular bacterial enzymes that generate cyclodextrins from starch. All known CGTases produce mixtures of alpha, beta, and gamma-cyclodextrins. A maltononaose inhibitor bound to the active site of the CGTase from Bacillus circulans strain 251 revealed sugar binding subsites, distant from the catalytic residues, which have been proposed to be involved in the cyclodextrin size specificity of these enzymes. To probe the importance of these distant substrate binding subsites for the alpha, beta, and gamma-cyclodextrin product ratios of the various CGTases, we have constructed three single and one double mutant, Y89G, Y89D, S146P and Y89D/S146P, using site-directed mutagenesis. The mutations affected the cyclization, coupling; disproportionation and hydrolyzing reactions of the enzyme. The double mutant Y89D/S146P showed a twofold increase in the production of alpha-cyclodextrin from starch. This mutant protein was crystallized and its X-ray structure, in a complex with a maltohexaose inhibitor, was determined at 2.4 A resolution. The bound maltohexaose molecule displayed a binding different from the maltononaose inhibitor, allowing rationalization of the observed change in product specificity. Hydrogen bonds (S146) and hydrophobic contacts (Y89) appear to contribute strongly to the size of cyclodextrin products formed and thus to CGTase product specificity. Changes in sugar binding subsites -3 and -7 thus result in mutant proteins with changed cyclodextrin production specificity.
Related Citations:
Engineering of Cyclodextrin Product Specificity and pH Optima of the Thermostable Cyclodextrin Glycosyltransferase from Thermoanaerobacterium thermosulfurigenes EM1 Wind, R.D., Uitdehaag, J.C.M., Buitelaar, R.M., Dijkstra, B.W., Dijkhuizen, L. (1998) J Biol Chem 273: 5771
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
Site Directed Mutagenesis in Tyrosine 195 of Cyclodextrin Glycosyltransferase from Bacillus circulans Strain 251 Affect Activity and Product Specificity Penninga, D., Strokopytov, B., Rozeboom, H.J., Lawson, C.L., Dijkstra, B.W., Bergsma, J., Dijkhuizen, L. (1995) Biochemistry 34: 3368
Organizational Affiliation:
Department of Microbiology Groningen Biomolecular Sciences and Biotechnology Institute (GBB), University of Groningen, Kerklaan 30, Haren, 9751 NN, The Netherlands.
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