6r3m
Family 11 Carbohydrate-Binding Module from Clostridium thermocellum in complex with beta-1,3-1,4-mixed-linked tetrasaccharide
Structural highlights
FunctionGUNH_ACET2 This enzyme catalyzes the endohydrolysis of 1,4-beta-glucosidic linkages in cellulose, lichenin and cereal beta-D-glucans. Publication Abstract from PubMedUnderstanding the specific molecular interactions between proteins and beta1,3-1,4-mixed-linked d-glucans is fundamental to harvest the full biological and biotechnological potential of these carbohydrates and of proteins that specifically recognize them. The family 11 carbohydrate-binding module from Clostridium thermocellum (CtCBM11) is known for its binding preference for beta1,3-1,4-mixed-linked over beta1,4-linked glucans. Despite the growing industrial interest of this protein for the biotransformation of lignocellulosic biomass, the molecular determinants of its ligand specificity are not well defined. In this report, a combined approach of methodologies was used to unravel, at a molecular level, the ligand recognition of CtCBM11. The analysis of the interaction by carbohydrate microarrays and NMR and the crystal structures of CtCBM11 bound to beta1,3-1,4-linked glucose oligosaccharides showed that both the chain length and the position of the beta1,3-linkage are important for recognition, and identified the tetrasaccharide Glcbeta1,4Glcbeta1,4Glcbeta1,3Glc sequence as a minimum epitope required for binding. The structural data, along with site-directed mutagenesis and ITC studies, demonstrated the specificity of CtCBM11 for the twisted conformation of beta1,3-1,4-mixed-linked glucans. This is mediated by a conformation-selection mechanism of the ligand in the binding cleft through CH-pi stacking and a hydrogen bonding network, which is dependent not only on ligand chain length, but also on the presence of a beta1,3-linkage at the reducing end and at specific positions along the beta1,4-linked glucan chain. The understanding of the detailed mechanism by which CtCBM11 can distinguish between linear and mixed-linked beta-glucans strengthens its exploitation for the design of new biomolecules with improved capabilities and applications in health and agriculture. DATABASE: Structural data are available in the Protein Data Bank under the accession codes 6R3M and 6R31. Molecular basis for the preferential recognition of beta1,3-1,4-glucans by the family 11 carbohydrate-binding module from Clostridium thermocellum.,Ribeiro DO, Viegas A, Pires VMR, Medeiros-Silva J, Bule P, Chai W, Marcelo F, Fontes CMGA, Cabrita EJ, Palma AS, Carvalho AL FEBS J. 2019 Dec 3. doi: 10.1111/febs.15162. PMID:31794092[1] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. See AlsoReferences
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