title: Crystal structure of truncated Fibrobacter succinogenes 1,3-1,4-beta-D-glucanase in complex with beta-1,3-1,4-cellotriose.
abstract: Fibrobacter succinogenes 1,3-1,4-beta-D-glucanase (Fsbeta-glucanase) catalyzes the specific hydrolysis of beta-1,4 glycosidic bonds adjacent to beta-1,3 linkages in beta-D-glucans or lichenan. This is the first report to elucidate the crystal structure of a truncated Fsbeta-glucanase (TFsbeta-glucanase) in complex with beta-1,3-1,4-cellotriose, a major product of the enzyme reaction. The crystal structures, at a resolution of 2.3 angstroms, reveal that the overall fold of TFsbeta-glucanase remains virtually unchanged upon sugar binding. The enzyme accommodates five glucose residues, forming a concave active cleft. The beta-1,3-1,4-cellotriose with subsites -3 to -1 bound to the active cleft of TFsbeta-glucanase with its reducing end subsite -1 close to the key catalytic residues Glu56 and Glu60. All three subsites of the beta-1,3-1,4-cellotriose adopted a relaxed C(1)4 conformation, with a beta-1,3 glycosidic linkage between subsites -2 and -1, and a beta-1,4 glycosidic linkage between subsites -3 and -2. On the basis of the enzyme-product complex structure observed in this study, a catalytic mechanism and substrate binding conformation of the active site of TFsbeta-glucanase is proposed.
authors.affiliation: Department of Molecular Science and Engineering, National Taipei University of Technology, Taipei 10608, Taiwan. lichu@ntut.edu.tw
authors.forename: Li-Chu
authors.initials: LC
authors.lastname: Tsai
authors.forename: Lie-Fen
authors.initials: LF
authors.lastname: Shyur
authors.forename: Yi-Sheng
authors.initials: YS
authors.lastname: Cheng
authors.forename: Shu-Hua
authors.initials: SH
authors.lastname: Lee
mesh_terms: D002482:Cellulose / Q000737:chemistry / Q000378:metabolism*; D018360:Crystallography, X-Ray; D044644:Endo-1,3(4)-beta-Glucanase / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D045848:Fibrobacter / Q000201:enzymology* / Q000235:genetics; D008958:Models, Molecular; D009844:Oligosaccharides / Q000737:chemistry* / Q000378:metabolism*; D020836:Protein Structure, Quaternary; D017434:Protein Structure, Tertiary; D013379:Substrate Specificity; D014306:Trioses / Q000737:chemistry / Q000378:metabolism*
chemical_list: D009844:Oligosaccharides; D014306:Trioses; C506455:beta-1,3-1,4-cellotriose; D002482:Cellulose; D044644:Endo-1,3(4)-beta-Glucanase