title: Identification of a novel family of carbohydrate-binding modules with broad ligand specificity.
abstract: Most enzymes that act on carbohydrates include non-catalytic carbohydrate-binding modules (CBMs) that recognize and target carbohydrates. CBMs bring their appended catalytic modules into close proximity with the target substrate and increase the hydrolytic rate of enzymes acting on insoluble substrates. We previously identified a novel CBM (CBMC5614-1) at the C-terminus of endoglucanase C5614-1 from an uncultured microorganism present in buffalo rumen. In the present study, that the functional region of CBMC5614-1 involved in ligand binding was localized to 134 amino acids. Two representative homologs of CBMC5614-1, sharing the same ligand binding profile, targeted a range of β-linked polysaccharides that adopt very different conformations. Targeted substrates included soluble and insoluble cellulose, β-1,3/1,4-mixed linked glucans, xylan, and mannan. Mutagenesis revealed that three conserved aromatic residues (Trp-380, Tyr-411, and Trp-423) play an important role in ligand recognition and targeting. These results suggest that CBMC5614-1 and its homologs form a novel CBM family (CBM72) with a broad ligand-binding specificity. CBM72 members can provide new insight into CBM-ligand interactions and may have potential in protein engineering and biocatalysis.
authors.affiliation: State Key Laboratory for Conservation and Utilization of Subtropical Agro-bioresources, The Key Laboratory of Ministry of Education for Microbial and Plant Genetic Engineering, and College of Life Science and Technology, Guangxi University, 100 Daxue Road, Nanning, Guangxi, 530004, China.
authors.forename: Cheng-Jie
authors.initials: CJ
authors.lastname: Duan
authors.affiliation: State Key Laboratory for Conservation and Utilization of Subtropical Agro-bioresources, The Key Laboratory of Ministry of Education for Microbial and Plant Genetic Engineering, and College of Life Science and Technology, Guangxi University, 100 Daxue Road, Nanning, Guangxi, 530004, China.
authors.forename: Yu-Liang
authors.initials: YL
authors.lastname: Feng
authors.affiliation: State Key Laboratory for Conservation and Utilization of Subtropical Agro-bioresources, The Key Laboratory of Ministry of Education for Microbial and Plant Genetic Engineering, and College of Life Science and Technology, Guangxi University, 100 Daxue Road, Nanning, Guangxi, 530004, China.
authors.forename: Qi-Long
authors.initials: QL
authors.lastname: Cao
authors.affiliation: State Key Laboratory for Conservation and Utilization of Subtropical Agro-bioresources, The Key Laboratory of Ministry of Education for Microbial and Plant Genetic Engineering, and College of Life Science and Technology, Guangxi University, 100 Daxue Road, Nanning, Guangxi, 530004, China.
authors.forename: Ming-Yue
authors.initials: MY
authors.lastname: Huang
authors.affiliation: State Key Laboratory for Conservation and Utilization of Subtropical Agro-bioresources, The Key Laboratory of Ministry of Education for Microbial and Plant Genetic Engineering, and College of Life Science and Technology, Guangxi University, 100 Daxue Road, Nanning, Guangxi, 530004, China.
authors.forename: Jia-Xun
authors.initials: JX
authors.lastname: Feng
mesh_terms: D000595:Amino Acid Sequence; D001665:Binding Sites; D050260:Carbohydrate Metabolism; D002241:Carbohydrates / Q000737:chemistry*; D017124:Conserved Sequence; D004798:Enzymes / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D007527:Isoenzymes; D008024:Ligands; D005810:Multigene Family; D011134:Polysaccharides / Q000737:chemistry / Q000378:metabolism; D011485:Protein Binding; D000072756:Protein Conformation, alpha-Helical; D054730:Protein Interaction Domains and Motifs; D012995:Solubility; D013379:Substrate Specificity
chemical_list: D002241:Carbohydrates; D004798:Enzymes; D007527:Isoenzymes; D008024:Ligands; D011134:Polysaccharides