title: The N-Terminal GH10 Domain of a Multimodular Protein from Caldicellulosiruptor bescii Is a Versatile Xylanase/β-Glucanase That Can Degrade Crystalline Cellulose.
abstract: The genome of the thermophilic bacterium Caldicellulosiruptor bescii encodes three multimodular enzymes with identical C-terminal domain organizations containing two consecutive CBM3b modules and one glycoside hydrolase (GH) family 48 (GH48) catalytic module. However, the three proteins differ much in their N termini. Among these proteins, CelA (or C. bescii Cel9A [CbCel9A]/Cel48A) with a GH9/CBM3c binary partner in the N terminus has been shown to use a novel strategy to degrade crystalline cellulose, which leads to its outstanding cellulose-cleaving activity. Here we show that C. bescii Xyn10C (CbXyn10C), the N-terminal GH10 domain from CbXyn10C/Cel48B, can also degrade crystalline cellulose, in addition to heterogeneous xylans and barley β-glucan. The data from substrate competition assays, mutational studies, molecular modeling, and docking point analyses point to the existence of only one catalytic center in the bifunctional xylanase/β-glucanase. The specific activities of the recombinant CbXyn10C on Avicel and filter paper were comparable to those of GH9/CBM3c of the robust CelA expressed in Escherichia coli. Appending one or two cellulose-binding CBM3bs enhanced the activities of CbXyn10C in degrading crystalline celluloses, which were again comparable to those of the GH9/CBM3c-CBM3b-CBM3b truncation mutant of CelA. Since CbXyn10C/Cel48B and CelA have similar domain organizations and high sequence homology, the endocellulase activity observed in CbXyn10C leads us to speculate that CbXyn10C/Cel48B may use the same strategy that CelA uses to hydrolyze crystalline cellulose, thus helping the excellent crystalline cellulose degrader C. bescii acquire energy from the environment. In addition, we also demonstrate that CbXyn10C may be an interesting candidate enzyme for biotechnology due to its versatility in hydrolyzing multiple substrates with different glycosidic linkages.
authors.affiliation: Key Laboratory for Feed Biotechnology of the Ministry of Agriculture, Feed Research Institute, Chinese Academy of Agricultural Sciences, Beijing, People's Republic of China.
authors.forename: Xianli
authors.initials: X
authors.lastname: Xue
authors.affiliation: Key Laboratory for Feed Biotechnology of the Ministry of Agriculture, Feed Research Institute, Chinese Academy of Agricultural Sciences, Beijing, People's Republic of China College of Life Sciences, Shanxi University, Taiyuan, People's Republic of China.
authors.forename: Rong
authors.initials: R
authors.lastname: Wang
authors.affiliation: Key Laboratory for Feed Biotechnology of the Ministry of Agriculture, Feed Research Institute, Chinese Academy of Agricultural Sciences, Beijing, People's Republic of China.
authors.forename: Tao
authors.initials: T
authors.lastname: Tu
authors.affiliation: Key Laboratory for Feed Biotechnology of the Ministry of Agriculture, Feed Research Institute, Chinese Academy of Agricultural Sciences, Beijing, People's Republic of China.
authors.forename: Pengjun
authors.initials: P
authors.lastname: Shi
authors.affiliation: Key Laboratory for Feed Biotechnology of the Ministry of Agriculture, Feed Research Institute, Chinese Academy of Agricultural Sciences, Beijing, People's Republic of China.
authors.forename: Rui
authors.initials: R
authors.lastname: Ma
authors.affiliation: Key Laboratory for Feed Biotechnology of the Ministry of Agriculture, Feed Research Institute, Chinese Academy of Agricultural Sciences, Beijing, People's Republic of China.
authors.forename: Huiying
authors.initials: H
authors.lastname: Luo
authors.affiliation: Key Laboratory for Feed Biotechnology of the Ministry of Agriculture, Feed Research Institute, Chinese Academy of Agricultural Sciences, Beijing, People's Republic of China binyao@caas.cn suxiaoyun@caas.cn.
authors.forename: Bin
authors.initials: B
authors.lastname: Yao
authors.affiliation: Key Laboratory for Feed Biotechnology of the Ministry of Agriculture, Feed Research Institute, Chinese Academy of Agricultural Sciences, Beijing, People's Republic of China binyao@caas.cn suxiaoyun@caas.cn.
authors.forename: Xiaoyun
authors.initials: X
authors.lastname: Su
mesh_terms: D020134:Catalytic Domain; D002482:Cellulose / Q000378:metabolism*; D000068536:Bacillota / Q000201:enzymology* / Q000235:genetics; D006026:Glycoside Hydrolases / Q000235:genetics / Q000378:metabolism*; D006868:Hydrolysis; D017434:Protein Structure, Tertiary; D017386:Sequence Homology, Amino Acid
chemical_list: D002482:Cellulose; D006026:Glycoside Hydrolases
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