1DTU: Bacillus Circulans Strain 251 Cyclodextrin Glycosyltransferase: A Mutant Y89d/s146p Complexed To An Hexasaccharide Inhibitor

Cyclodextrin glycosyltransferases (CGTase) (EC 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.
PDB ID: 1DTUDownload
MMDB ID: 12622
PDB Deposition Date: 2000/1/13
Updated in MMDB: 2017/11
Experimental Method:
x-ray diffraction
Resolution: 2.4  Å
Source Organism:
Similar Structures:
Biological Unit for 1DTU: monomeric; determined by author
Molecular Components in 1DTU
Label Count Molecule
Protein (1 molecule)
Protein (Cyclodextrin Glycosyltransferase)
Molecule annotation
Chemicals (18 molecules)
* Click molecule labels to explore molecular sequence information.

Citing MMDB