title: Oligosaccharide substrate binding in Escherichia coli maltodextrin phosphorylase.
abstract: The crystal structure of E. coli maltodextrin phosphorylase co-crystallized with an oligosaccharide has been solved at 3.0 A resolution, providing the first structure of an oligosaccharide bound at the catalytic site of an alpha-glucan phosphorylase. An induced fit mechanism brings together two domains across the catalytic site tunnel. A stacking interaction between the glucosyl residue and the aromatic group of a tyrosine residue at a sub-site remote (8 A) from the catalytic site provides a key element in substrate recognition; mutation of this residue to Ala decreases the Kcat/Km by 10(4). Extrapolation of the results to substrate binding across the site of attack by phosphorolysis indicates a likely alteration in the glycosidic torsion angles from their preferred values, an alteration that appears to be important for the catalytic mechanism.
authors.affiliation: Laboratory of Molecular Biophysics, University of Oxford.
authors.forename: M
authors.initials: M
authors.lastname: O'Reilly
authors.forename: K A
authors.initials: KA
authors.lastname: Watson
authors.forename: R
authors.initials: R
authors.lastname: Schinzel
authors.forename: D
authors.initials: D
authors.lastname: Palm
authors.forename: L N
authors.initials: LN
authors.lastname: Johnson
mesh_terms: D003460:Crystallization; D018360:Crystallography, X-Ray; D004926:Escherichia coli / Q000201:enzymology*; D005936:Glucans / Q000737:chemistry / Q000378:metabolism; D005964:Glucosyltransferases / Q000737:chemistry* / Q000378:metabolism; D007700:Kinetics; D008958:Models, Molecular; D009844:Oligosaccharides / Q000737:chemistry* / Q000378:metabolism; D011485:Protein Binding; D011487:Protein Conformation; D014443:Tyrosine / Q000502:physiology
chemical_list: D005936:Glucans; D009844:Oligosaccharides; C016549:maltohexaose; C031146:maltoheptaose; D014443:Tyrosine; D005964:Glucosyltransferases; C033938:maltodextrin phosphorylase