title: Diverse substrate recognition mechanism revealed by Thermotoga maritima Cel5A structures in complex with cellotetraose, cellobiose and mannotriose.
abstract: The hyperthermophilic endoglucanase Cel5A from Thermotoga maritima can find applications in lignocellulosic biofuel production, because it catalyzes the hydrolysis of glucan- and mannan-based polysaccharides. Here, we report the crystal structures in apo-form and in complex with three ligands, cellotetraose, cellobiose and mannotriose, at 1.29Å to 2.40Å resolution. The open carbohydrate-binding cavity which can accommodate oligosaccharide substrates with extensively branched chains explained the dual specificity of the enzyme. Combining our structural information and the previous kinetic data, it is suggested that this enzyme prefers β-glucosyl and β-mannosyl moieties at the reducing end and uses two conserved catalytic residues, E253 (nucleophile) and E136 (general acid/base), to hydrolyze the glycosidic bonds. Moreover, our results also suggest that the wide spectrum of Tm_Cel5A substrates might be due to the lack of steric hindrance around the C2-hydroxyl group of the glucose or mannose unit from active-site residues.
authors.affiliation: Institute of Biotechnology, National Taiwan University, Taipei, Taiwan.
authors.forename: Tzu-Hui
authors.initials: TH
authors.lastname: Wu
authors.forename: Chun-Hsiang
authors.initials: CH
authors.lastname: Huang
authors.forename: Tzu-Ping
authors.initials: TP
authors.lastname: Ko
authors.forename: Hui-Lin
authors.initials: HL
authors.lastname: Lai
authors.forename: Yanhe
authors.initials: Y
authors.lastname: Ma
authors.forename: Chun-Chi
authors.initials: CC
authors.lastname: Chen
authors.forename: Ya-Shan
authors.initials: YS
authors.lastname: Cheng
authors.forename: Je-Ruei
authors.initials: JR
authors.lastname: Liu
authors.forename: Rey-Ting
authors.initials: RT
authors.lastname: Guo
mesh_terms: D001665:Binding Sites / Q000235:genetics; D020134:Catalytic Domain / Q000235:genetics; D002475:Cellobiose / Q000737:chemistry / Q000378:metabolism*; D002480:Cellulase / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D002482:Cellulose / Q000031:analogs & derivatives* / Q000737:chemistry / Q000378:metabolism; D018360:Crystallography, X-Ray; D046911:Macromolecular Substances / Q000737:chemistry / Q000378:metabolism; D008958:Models, Molecular; D016297:Mutagenesis, Site-Directed; D011485:Protein Binding; D020836:Protein Structure, Quaternary; D013379:Substrate Specificity; D013780:Tetroses / Q000737:chemistry / Q000378:metabolism*; D020124:Thermotoga maritima / Q000201:enzymology* / Q000235:genetics / Q000378:metabolism; D014312:Trisaccharides / Q000737:chemistry / Q000378:metabolism*
chemical_list: D046911:Macromolecular Substances; D013780:Tetroses; D014312:Trisaccharides; D002475:Cellobiose; C048468:cellotetraose; C023872:mannotriose; D002482:Cellulose; C407024:endoglucanase Cel5A; D002480:Cellulase