title: Structural basis for ligand binding and processivity in cellobiohydrolase Cel6A from Humicola insolens.
abstract: The enzymatic digestion of cellulose entails intimate involvement of cellobiohydrolases, whose characteristic active-center tunnel contributes to a processive degradation of the polysaccharide. The cellobiohydrolase Cel6A displays an active site within a tunnel formed by two extended loops, which are known to open and close in response to ligand binding. Here we present five structures of wild-type and mutant forms of Cel6A from Humicola insolens in complex with nonhydrolyzable thio-oligosaccharides, at resolutions from 1.7-1.1 A, dissecting the structural accommodation of a processing substrate chain through the active center during hydrolysis. Movement of ligand is facilitated by extensive solvent-mediated interactions and through flexibility in the hydrophobic surfaces provided by a sheath of tryptophan residues.
authors.affiliation: Department of Chemistry, University of York, Heslington, Y010 5YW, York, United Kingdom.
authors.forename: Annabelle
authors.initials: A
authors.lastname: Varrot
authors.forename: Torben P
authors.initials: TP
authors.lastname: Frandsen
authors.forename: Ingemar
authors.initials: I
authors.lastname: von Ossowski
authors.forename: Viviane
authors.initials: V
authors.lastname: Boyer
authors.forename: Sylvain
authors.initials: S
authors.lastname: Cottaz
authors.forename: Hugues
authors.initials: H
authors.lastname: Driguez
authors.forename: Martin
authors.initials: M
authors.lastname: Schülein
authors.forename: Gideon J
authors.initials: GJ
authors.lastname: Davies
mesh_terms: D001203:Ascomycota / Q000201:enzymology*; D001483:Base Sequence; D002240:Carbohydrate Sequence; D020134:Catalytic Domain; D002482:Cellulose / Q000737:chemistry / Q000378:metabolism; D043366:Cellulose 1,4-beta-Cellobiosidase / Q000378:metabolism*; D003460:Crystallization; D017931:DNA Primers; D008024:Ligands; D008969:Molecular Sequence Data; D011485:Protein Binding
chemical_list: D017931:DNA Primers; D008024:Ligands; D002482:Cellulose; D043366:Cellulose 1,4-beta-Cellobiosidase