title: Atomic (0.94 A) resolution structure of an inverting glycosidase in complex with substrate.
abstract: The crystal structure of Clostridium thermocellum endoglucanase CelA in complex with cellopentaose has been determined at 0.94 A resolution. The oligosaccharide occupies six D-glucosyl-binding subsites, three on either side of the scissile glycosidic linkage. The substrate and product of the reaction occupy different positions at the reducing end of the cleft, where an extended array of hydrogen-bonding interactions with water molecules fosters the departure of the leaving group. Severe torsional strain upon the bound substrate forces a distorted boat(2,5) B conformation for the glucosyl residue bound at subsite -1, which facilitates the formation of an oxocarbenium ion intermediate and might favor the breakage of the sugar ring concomitant with catalysis.
authors.affiliation: Unité de Biochimie Structurale, CNRS URA 2185, Institut Pasteur, 25 rue du Dr. Roux, 75724 Paris cédex 15, France.
authors.forename: Diego M A
authors.initials: DM
authors.lastname: Guérin
authors.forename: Marie-Bernard
authors.initials: MB
authors.lastname: Lascombe
authors.forename: Marcelo
authors.initials: M
authors.lastname: Costabel
authors.forename: Hélène
authors.initials: H
authors.lastname: Souchon
authors.forename: Victor
authors.initials: V
authors.lastname: Lamzin
authors.forename: Pierre
authors.initials: P
authors.lastname: Béguin
authors.forename: Pedro M
authors.initials: PM
authors.lastname: Alzari
mesh_terms: D001665:Binding Sites; D002480:Cellulase / Q000737:chemistry* / Q000378:metabolism*; D003013:Clostridium / Q000201:enzymology*; D018360:Crystallography, X-Ray; D006860:Hydrogen Bonding; D008024:Ligands; D008958:Models, Molecular; D009844:Oligosaccharides / Q000378:metabolism*; D011485:Protein Binding; D011487:Protein Conformation; D014867:Water / Q000378:metabolism
chemical_list: D008024:Ligands; D009844:Oligosaccharides; D014867:Water; C019193:maltopentaose; C074775:CelA endoglucanase; D002480:Cellulase