title: Structure of cyclodextrin glycosyltransferase complexed with a maltononaose inhibitor at 2.6 angstrom resolution. Implications for product specificity.
abstract: Crystals of the Y195F mutant of cyclodextrin glycosyltransferase from Bacillus circulans strain 251 were subjected to a double soaking procedure, in which they were first soaked in a solution containing the inhibitor acarbose and subsequently in a solution containing maltohexaose. The refined structure of the resulting protein-carbohydrate complex has final crystallographic and free R-factors for data in the 8-2.6 angstrom resolution range of 15.0% and 21.5%, respectively, and reveals that a new inhibitor, composed of nine saccharide residues, is bound in the active site. The first four residues correspond to acarbose and occupy the same subsites near the catalytic residues as observed in the previously reported acarbose-enzyme complex [Strokopytov et al. (1995) Biochemistry 34, 2234-2240]. An oliogosaccharide consisting of five glucose residues has been coupled to the nonreducing end of acarbose. At the fifth residue the polysaccharide chain makes a sharp turn, allowing it to interact with residues Tyr89, Phe195, and Asn193 and a flexible loop formed by residues 145-148. On the basis of the refined model of the complex an explanation is given for the product specificity of CGTases.
authors.affiliation: BIOSON Research Institute and Laboratory of Biophysical Chemistry, Groningen Biomolecular Sciences and Biotechnology Institute, University of Groningen, The Netherlands.
authors.forename: B
authors.initials: B
authors.lastname: Strokopytov
authors.forename: R M
authors.initials: RM
authors.lastname: Knegtel
authors.forename: D
authors.initials: D
authors.lastname: Penninga
authors.forename: H J
authors.initials: HJ
authors.lastname: Rozeboom
authors.forename: K H
authors.initials: KH
authors.lastname: Kalk
authors.forename: L
authors.initials: L
authors.lastname: Dijkhuizen
authors.forename: B W
authors.initials: BW
authors.lastname: Dijkstra
mesh_terms: D000595:Amino Acid Sequence; D001407:Bacillus / Q000201:enzymology; D001665:Binding Sites; D002236:Carbohydrate Conformation; D002240:Carbohydrate Sequence; D018360:Crystallography, X-Ray; D004791:Enzyme Inhibitors / Q000737:chemistry / Q000378:metabolism* / Q000494:pharmacology; D005964:Glucosyltransferases / Q000037:antagonists & inhibitors / Q000737:chemistry* / Q000378:metabolism*; D006860:Hydrogen Bonding; D008024:Ligands; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009844:Oligosaccharides / Q000737:chemistry* / Q000378:metabolism* / Q000494:pharmacology; D013379:Substrate Specificity
chemical_list: D004791:Enzyme Inhibitors; D008024:Ligands; D009844:Oligosaccharides; C021705:maltooligosaccharides; D005964:Glucosyltransferases; C019963:cyclomaltodextrin glucanotransferase