scholarly journals Homologous xylanases from Clostridium thermocellum: evidence for bi-functional activity, synergism between xylanase catalytic modules and the presence of xylan-binding domains in enzyme complexes

1999 ◽  
Vol 342 (1) ◽  
pp. 105-110 ◽  
Author(s):  
Ana C. FERNANDES ◽  
Carlos M. G. A. FONTES ◽  
Harry J. GILBERT ◽  
Geoffrey P. HAZLEWOOD ◽  
Tito H. FERNANDES ◽  
...  
Keyword(s):  
Clostridium Thermocellum ◽  
Plant Cell Wall ◽  
Catalytic Domain ◽  
Glycosyl Hydrolase ◽  
Biochemical Properties ◽  
Binding Domain ◽  
Binding Domains ◽  
A Cell ◽  
Cellulose Binding ◽  
Hydrolysis Of

Clostridium thermocellum produces a consortium of plant-cell-wall hydrolases that form a cell-bound multi-enzyme complex called the cellulosome. In the present study two similar xylanase genes, xynU and xynV, were cloned from C. thermocellum strain YS and sequenced. The deduced primary structures of both xylanases, xylanase U (XylU) and xylanase V (XylV), were homologous with the previously characterized xylanases from C. thermocellum strain F1. Truncated derivatives of XylV were produced and their biochemical properties were characterized. The xylanases were shown to be remarkably thermostable and resistant to proteolytic inactivation. The catalytic domains hydrolysed xylan by a typical endo-mode of action. The type VI cellulose-binding domain (CBD) homologue of XylV bound xylan and, to a smaller extent, Avicel and acid-swollen cellulose. Deletion of the CBD from XylV abolished the capacity of the enzymes to bind polysaccharides. The polysaccharide-binding domain was shown to have a key role in the hydrolysis of insoluble substrates by XylV. The C-terminal domain of XylV, which is absent from XylU, removed acetyl groups from acetylated xylan and acted in synergy with the glycosyl hydrolase catalytic domain of the enzyme to elicit the hydrolysis of acetylated xylan.

scholarly journals The Fibronectin Type 3-Like Repeat from the Clostridium thermocellum Cellobiohydrolase CbhA Promotes Hydrolysis of Cellulose by Modifying Its Surface

2002 ◽  
Vol 68 (9) ◽  
pp. 4292-4300 ◽  
Author(s):  
Irina A. Kataeva ◽  
Ronald D. Seidel ◽  
Ashit Shah ◽  
Larry T. West ◽  
Xin-Liang Li ◽  
...  
Keyword(s):  
Filter Paper ◽  
Clostridium Thermocellum ◽  
Catalytic Domain ◽  
Glycosyl Hydrolase ◽  
Binding Domain ◽  
Carbohydrate Binding ◽  
Hydrolysis Of Cellulose ◽  
Type 3 ◽  
Hydrolysis Of ◽  
Fibronectin Type

ABSTRACT Fibronectin type 3 homology domains (Fn3) as found in the cellobiohydrolase CbhA of Clostridium thermocellum are common among bacterial extracellular glycohydrolases. The function of these domains is not clear. CbhA is modular and composed of an N-terminal family IV carbohydrate-binding domain (CBDIV), an immunoglobulin-like domain, a family 9 glycosyl hydrolase catalytic domain (Gh9), two Fn3-like domains (Fn31,2), a family III carbohydrate-binding domain (CBDIII), and a dockerin domain. Efficiency of cellulose hydrolysis by truncated forms of CbhA increased in the following order: Gh9 (lowest efficiency), Gh9-Fn31,2 (more efficient), and Gh9-Fn31,2-CBDIII (greatest efficiency). Thermostability of the above constructs decreased in the following order: Gh9 (most stable), Gh9-Fn31,2, and then Gh9-Fn31,2-CBDIII (least stable). Mixing of Orpinomyces endoglucanase CelE with Fn31,2, or Fn31,2-CBDIII increased efficiency of hydrolysis of acid-swollen cellulose (ASC) and filter paper. Scanning electron microscopic studies of filter paper treated with Fn31,2, Fn31,2-CBDIII, or CBDIII showed that the surface of the cellulose fibers had been loosened up and crenellated by Fn31,2 and Fn31,2-CBDIII and to a lesser extent by CBDIII. X-ray diffraction analysis did not reveal changes in the crystallinity of the filter paper. CBDIII bound to ASC and filter paper with capacities of 2.45 and 0.73 μmoles g−1 and relative affinities (K r) of 1.12 and 2.13 liters g−1, respectively. Fn31,2 bound weakly to both celluloses. Fn31,2-CBD bound to ASC and filter paper with capacities of 3.22 and 0.81 μmoles g−1 and K rs of 1.14 and 1.98 liters g−1, respectively. Fn31,2 and CBDIII contained 2 and 1 mol of calcium per mol, respectively. The results suggest that Fn31,2 aids the hydrolysis of cellulose by modifying its surface. This effect is enhanced by the presence of CBDIII, which increases the concentration of Fn31,2 on the cellulose surface.

scholarly journals The type II and X cellulose-binding domains of Pseudomonas xylanase A potentiate catalytic activity against complex substrates by a common mechanism

1999 ◽  
Vol 342 (2) ◽  
pp. 473-480 ◽  
Author(s):  
Jaitinder GILL ◽  
Jane E. RIXON ◽  
David N. BOLAM ◽  
Simon MCQUEEN-MASON ◽  
Peter J. SIMPSON ◽  
...  
Keyword(s):  
Microcrystalline Cellulose ◽  
Plant Cell Wall ◽  
Catalytic Domain ◽  
Wall Material ◽  
Common Mechanism ◽  
Type Ii ◽  
Binding Domains ◽  
Covalently Linked ◽  
Cellulose Binding ◽  
Internal Domain

Xylanase A (Pf Xyn10A), in common with several other Pseudomonas fluorescens subsp. cellulosa polysaccharidases, consists of a Type II cellulose-binding domain (CBD), a catalytic domain (Pf Xyn10ACD) and an internal domain that exhibits homology to Type X CBDs. The Type X CBD of Pf Xyn10A, expressed as a discrete entity (CBDX) or fused to the catalytic domain (Pf Xyn10A′), bound to amorphous and bacterial microcrystalline cellulose with a Ka of 2.5×105 M-1. CBDX exhibited no affinity for soluble forms of cellulose or cello-oligosaccharides, suggesting that the domain interacts with multiple cellulose chains in the insoluble forms of the polysaccharide. Pf Xyn10A′ was 2-3 times more active against cellulose-hemicellulose complexes than Pf Xyn10ACD; however, Pf Xyn10A′ and Pf Xyn10ACD exhibited the same activity against soluble substrates. CBDX did not disrupt the structure of plant-cell-wall material or bacterial microcrystalline cellulose, and did not potentiate Pf Xyn10ACD when not covalently linked to the enzyme. There was no substantial difference in the affinity of full-length Pf Xyn10A and the enzyme's Type II CBD for cellulose. The activity of Pf Xyn10A against cellulose-hemicellulose complexes was similar to that of Pf Xyn10A′, and a derivative of Pf Xyn10A in which the Type II CBD is linked to the Pf Xyn10ACD via a serine-rich linker sequence [Bolam, Cireula, McQueen-Mason, Simpson, Williamson, Rixon, Boraston, Hazlewood and Gilbert (1998) Biochem J. 331, 775-781]. These data indicate that CBDX is functional in Pf Xyn10A and that no synergy, either in ligand binding or in the potentiation of catalysis, is evident between the Type II and X CBDs of the xylanase.

scholarly journals The structure of a glycoside hydrolase 29 family member from a rumen bacterium reveals unique, dual carbohydrate-binding domains

2016 ◽  
Vol 72 (10) ◽  
pp. 750-761 ◽  
Author(s):  
Emma L. Summers ◽  
Christina D. Moon ◽  
Renee Atua ◽  
Vickery L. Arcus
Keyword(s):  
Glycoside Hydrolase ◽  
Catalytic Domain ◽  
Binding Domain ◽  
Carbohydrate Binding ◽  
Catalytic Core ◽  
Binding Domains ◽  
Carbohydrate Binding Modules ◽  
Tim Barrel ◽  
Domain Arrangement ◽  
Hydrolysis Of

Glycoside hydrolase (GH) family 29 consists solely of α-L-fucosidases. These enzymes catalyse the hydrolysis of glycosidic bonds. Here, the structure of GH29_0940, a protein cloned from metagenomic DNA from the rumen of a cow, has been solved, which reveals a multi-domain arrangement that has only recently been identified in bacterial GH29 enzymes. The microbial species that provided the source of this enzyme is unknown. This enzyme contains a second carbohydrate-binding domain at its C-terminal end in addition to the typical N-terminal catalytic domain and carbohydrate-binding domain arrangement of GH29-family proteins. GH29_0940 is a monomer and its overall structure consists of an N-terminal TIM-barrel-like domain, a central β-sandwich domain and a C-terminal β-sandwich domain. The TIM-barrel-like catalytic domain exhibits a (β/α)8/7arrangement in the core instead of the typical (β/α)8topology, with the `missing' α-helix replaced by a long meandering loop that `closes' the barrel structure and suggests a high degree of structural flexibility in the catalytic core. This feature was also noted in all six other structures of GH29 enzymes that have been deposited in the PDB. Based on sequence and structural similarity, the residues Asp162 and Glu220 are proposed to serve as the catalytic nucleophile and the proton donor, respectively. Like other GH29 enzymes, the GH29_0940 structure shows five strictly conserved residues in the catalytic pocket. The structure shows two glycerol molecules in the active site, which have also been observed in other GH29 structures, suggesting that the enzyme catalyses the hydrolysis of small carbohydrates. The two binding domains are classed as family 32 carbohydrate-binding modules (CBM32). These domains have residues involved in ligand binding in the loop regions at the edge of the β-sandwich. The predicted substrate-binding residues differ between the modules, suggesting that different modules bind to different groups on the substrate(s). Enzymes that possess multiple copies of CBMs are thought to have a complex mechanism of ligand recognition. Defined electron density identifying a long 20-amino-acid hydrophilic loop separating the two CBMs was observed. This suggests that the additional C-terminal domain may have a dynamic range of movement enabled by the loop, allowing a unique mode of action for a GH29 enzyme that has not been identified previously.

scholarly journals The non-catalytic C-terminal region of endoglucanase E from Clostridium thermocellum contains a cellulose-binding domain

1991 ◽  
Vol 273 (2) ◽  
pp. 289-293 ◽  
Author(s):  
A J Durrant ◽  
J Hall ◽  
G P Hazlewood ◽  
H J Gilbert
Keyword(s):  
Amino Acids ◽  
Clostridium Thermocellum ◽  
Catalytic Domain ◽  
Specific Activity ◽  
Binding Domain ◽  
Full Length ◽  
Crystalline Cellulose ◽  
Cellulose Binding Domain ◽  
Beta Glucan ◽  
Cellulose Binding

Mature endoglucanase E (EGE) from Clostridium thermocellum consists of 780 amino acid residues and has an Mr of 84,016. The N-terminal 334 amino acids comprise a functional catalytic domain. Full-length EGE bound to crystalline cellulose (Avicel) but not to xylan. Bound enzyme could be eluted with distilled water. The capacity of truncated derivatives of the enzyme to bind cellulose was investigated. EGE lacking 109 C-terminal residues (EGEd) or a derivative in which residues 367-432 of the mature form of the enzyme had been deleted (EGEb), bound to Avicel, whereas EGEa and EGEc, which lack 416 and 246 C-terminal residues respectively, did not. The specific activity of EGEa, consisting of the N-terminal 364 amino acids, was 4-fold higher than that of the full-length enzyme. The truncated derivative also exhibited lower affinity for the substrate beta-glucan than the full-length enzyme. It is concluded that EGE contains a cellulose-binding domain, located between residues 432 and 671, that is distinct from the active site. The role of this substrate-binding domain is discussed.

scholarly journals Pseudomonas cellulose-binding domains mediate their effects by increasing enzyme substrate proximity

1998 ◽  
Vol 331 (3) ◽  
pp. 775-781 ◽  
Author(s):  
David N. BOLAM ◽  
Antonio CIRUELA ◽  
Simon McQUEEN-MASON ◽  
Peter SIMPSON ◽  
Michael P. WILLIAMSON ◽  
...  
Keyword(s):  
Plant Cell ◽  
Mode Of Action ◽  
Plant Cell Wall ◽  
Catalytic Domain ◽  
Cellulase Activity ◽  
Type Ii ◽  
Binding Domains ◽  
Enzyme Substrate ◽  
Tryptophan Residues ◽  
Cellulose Binding

To investigate the mode of action of cellulose-binding domains (CBDs), the Type II CBD from Pseudomonas fluorescenssubsp. cellulosaxylanase A (XYLACBD) and cellulase E (CELECBD) were expressed as individual entities or fused to the catalytic domain of a Clostridium thermocellumendoglucanase (EGE). The two CBDs exhibited similar Ka values for bacterial microcrystalline cellulose (CELECBD, 1.62×106 M-1; XYLACBD, 1.83×106 M-1) and acid-swollen cellulose (CELECBD, 1.66×106 M-1; XYLACBD, 1.73×106 M-1). NMR spectra of XYLACBD titrated with cello-oligosaccharides showed that the environment of three tryptophan residues was affected when the CBD bound cellohexaose, cellopentaose or cellotetraose. The Ka values of the XYLACBD for C6, C5 and C4 cello-oligosaccharides were estimated to be 3.3×102, 1.4×102 and 4.0×101 M-1 respectively, suggesting that the CBD can accommodate at least six glucose molecules and has a much higher affinity for insoluble cellulose than soluble oligosaccharides. Fusion of either the CELECBD or XYLACBD to the catalytic domain of EGE potentiated the activity of the enzyme against insoluble forms of cellulose but not against carboxymethylcellulose. The increase in cellulase activity was not observed when the CBDs were incubated with the catalytic domain of either EGE or XYLA, with insoluble cellulose and a cellulose/hemicellulose complex respectively as the substrates. PseudomonasCBDs did not induce the extension of isolated plant cell walls nor weaken cellulose paper strips in the same way as a class of plant cell wall proteins called expansins. The XYLACBD and CELECBD did not release small particles from the surface of cotton. The significance of these results in relation to the mode of action of Type II CBDs is discussed.

scholarly journals Novel cellulose-binding domains, NodB homologues and conserved modular architecture in xylanases from the aerobic soil bacteria Pseudomonas fluorescens subsp. cellulosa and Cellvibrio mixtus

1995 ◽  
Vol 312 (1) ◽  
pp. 39-48 ◽  
Author(s):  
S J Millward-Sadler ◽  
K Davidson ◽  
G P Hazlewood ◽  
G W Black ◽  
H J Gilbert ◽  
...  
Keyword(s):  
Pseudomonas Fluorescens ◽  
Soil Bacteria ◽  
Catalytic Domain ◽  
Glycosyl Hydrolase ◽  
Glycosyl Hydrolase Family ◽  
Sequence Identity ◽  
Binding Domains ◽  
N Terminus ◽  
Cellulose Binding ◽  
Hydrolase Family

To test the hypothesis that selective pressure has led to the retention of cellulose-binding domains (CBDs) by hemicellulase enzymes from aerobic bacteria, four new xylanase (xyn) genes from two cellulolytic soil bacteria, Pseudomonas fluorescens subsp. cellulosa and Cellvibrio mixtus, have been isolated and sequenced. Pseudomonas genes xynE and xynF encoded modular xylanases (XYLE and XYLF) with predicted M(r) values of 68,600 and 65000 respectively. XYLE contained a glycosyl hydrolase family 11 catalytic domain at its N-terminus, followed by three other domains; the second of these exhibited sequence identity with NodB from rhizobia. The C-terminal domain (40 residues) exhibited significant sequence identity with a non-catalytic domain of previously unknown function, conserved in all the cellulases and one of the hemicellulases previously characterized from the pseudomonad, and was shown to function as a CBD when fused to the reporter protein glutathione-S-transferase. XYLF contained a C-terminal glycosyl hydrolase family 10 catalytic domain and a novel CBD at its N-terminus. C. mixtus genes xynA and xynB exhibited substantial sequence identity with xynE and xynF respectively, and encoded modular xylanases with the same molecular architecture and, by inference, the same functional properties. In the absence of extensive cross-hybridization between other multiple cel (cellulase) and xyn genes from P. fluorescens subsp. cellulosa and genomic DNA from C. mixtus, similarity between the two pairs of xylanases may indicate a recent transfer of genes between the two bacteria.

scholarly journals Arabinanase A from Pseudomonas fluorescens subsp. cellulosa exhibits both an endo- and an exo- mode of action

1997 ◽  
Vol 323 (2) ◽  
pp. 547-555 ◽  
Author(s):  
Vincent A. McKIE ◽  
Gary W. BLACK ◽  
Sarah J. MILLWARD-SADLER ◽  
Geoffrey P. HAZLEWOOD ◽  
Judith I. LAURIE ◽  
...  
Keyword(s):  
Pseudomonas Fluorescens ◽  
Mode Of Action ◽  
Plant Cell Wall ◽  
Catalytic Domain ◽  
Genomic Library ◽  
Glycosyl Hydrolase ◽  
Single Copy ◽  
Terminal Sequence ◽  
Reading Frame ◽  
Significant Release

Pseudomonas fluorescens subsp. cellulosa expressed arabinanase activity when grown on media supplemented with arabinan or arabinose. Arabinanase activity was not induced by the inclusion of other plant structural polysaccharides, and was repressed by the addition of glucose. The majority of the Pseudomonas arabinanase activity was extracellular. Screening of a genomic library of P. fluorescens subsp. cellulosa DNA constructed in Lambda ZAPII, for recombinants that hydrolysed Red-dyed arabinan, identified five arabinan-degrading plaques. Each of the phage contained the same Pseudomonas arabinanase gene, designated arbA, which was present as a single copy in the Pseudomonas genome. The nucleotide sequence of arbA revealed an open reading frame of 1041 bp encoding a protein, designated arabinanase A (ArbA), of Mr 39438. The N-terminal sequence of ArbA exhibited features typical of a prokaryotic signal peptide. Analysis of the primary structure of ArbA indicated that, unlike most Pseudomonas plant cell wall hydrolases, it did not contain linker sequences or have a modular structure, but consisted of a single catalytic domain. Sequence comparison between the Pseudomonas arabinanase and proteins in the SWISS-PROT database showed that ArbA exhibits greatest sequence identity with arabinanase A from Aspergillus niger, placing the enzyme in glycosyl hydrolase Family 43. The significance of the differing substrate specificities of enzymes in Family 43 is discussed. ArbA purifed from a recombinant strain of Escherichia coli had an Mr of 34000 and an N-terminal sequence identical to residues 32–51 of the deduced sequence of ArbA, and hydrolysed linear arabinan, carboxymethylarabinan and arabino-oligosaccharides. The enzyme displayed no activity against other plant structural polysaccharides, including branched sugar beet arabinan. ArbA produced almost exclusively arabinotriose from linear arabinan and appeared to hydrolyse arabino-oligosaccharides by successively releasing arabinotriose. ArbA and the Aspergillus arabinanase mediated a decrease in the viscosity of linear arabinan that was associated with a significant release of reducing sugar. We propose that ArbA is an arabinanase that exhibits both an endo- and an exo- mode of action.

scholarly journals Feruloyl Esterase Activity of the Clostridium thermocellum Cellulosome Can Be Attributed to Previously Unknown Domains of XynY and XynZ

2000 ◽  
Vol 182 (5) ◽  
pp. 1346-1351 ◽  
Author(s):  
David L. Blum ◽  
Irina A. Kataeva ◽  
Xin-Liang Li ◽  
Lars G. Ljungdahl
Keyword(s):  
Ferulic Acid ◽  
Esterase Activity ◽  
Clostridium Thermocellum ◽  
Plant Cell Wall ◽  
Feruloyl Esterase ◽  
Lower Amount ◽  
Acetyl Xylan Esterase ◽  
Hydrolytic Activities ◽  
C And N ◽  
Cellulose Binding

ABSTRACT The cellulosome of Clostridium thermocellum is a multiprotein complex with endo- and exocellulase, xylanase, β-glucanase, and acetyl xylan esterase activities. XynY and XynZ, components of the cellulosome, are composed of several domains including xylanase domains and domains of unknown function (UDs). Database searches revealed that the C- and N-terminal UDs of XynY and XynZ, respectively, have sequence homology with the sequence of a feruloyl esterase of strain PC-2 of the anaerobic fungusOrpinomyces. Purified cellulosomes from C. thermocellum were found to hydrolyze FAXX (O-{5-O-[(E)-feruloyl]-α-l-arabinofuranosyl}-(1→3)-O-β-d-xylopyranosyl-(1→4)-d-xylopyranose) and FAX3(5-O-[(E)-feruloyl]-[O-β-d-xylopyranosyl-(1→2)]-O-α-l-arabinofuranosyl-[1→3]}-O-β-d-xylopyranosyl-(1→4)-d-xylopyranose), yielding ferulic acid as a product, indicating that they have feruloyl esterase activity. Nucleotide sequences corresponding to the UDs of XynY and XynZ were cloned into Escherichia coli, and the expressed proteins hydrolyzed FAXX and FAX3. The recombinant feruloyl esterase domain of XynZ alone (FAEXynZ) and with the adjacent cellulose binding domain (FAE-CBDXynZ) were characterized. FAE-CBDXynZhad a molecular mass of 45 kDa that corresponded to the expected product of the 1,203-bp gene. Km andV max values for FAX3 were 5 mM and 12.5 U/mg, respectively, at pH 6.0 and 60°C. PAX3, a substrate similar to FAX3 but with ap-coumaroyl group instead of a feruloyl moiety was hydrolyzed at a rate 10 times slower. The recombinant enzyme was active between pH 3 to 10 with an optimum between pH 4 to 7 and at temperatures up to 70°C. Treatment of Coastal Bermuda grass with the enzyme released mainly ferulic acid and a lower amount ofp-coumaric acid. FAEXynZ had similar properties. Removal of the 40 C-terminal amino acids, residues 247 to 286, of FAEXynZ resulted in protein without activity. Feruloyl esterases are believed to aid in a release of lignin from hemicellulose and may be involved in lignin solubilization. The presence of feruloyl esterase in the C. thermocellumcellulosome together with its other hydrolytic activities demonstrates a powerful enzymatic potential of this organelle in plant cell wall decomposition.

scholarly journals Properties and Mutation Analysis of the CelK Cellulose-Binding Domain from the Clostridium thermocellum Cellulosome

2001 ◽  
Vol 183 (5) ◽  
pp. 1552-1559 ◽  
Author(s):  
Irina A. Kataeva ◽  
Ronald D. Seidel ◽  
Xin-Liang Li ◽  
Lars G. Ljungdahl
Keyword(s):  
Amino Acids ◽  
Calcium Binding ◽  
Clostridium Thermocellum ◽  
Binding Capacity ◽  
Binding Domain ◽  
Cellulose Binding Domain ◽  
Calcium Binding Site ◽  
Aromatic Residues ◽  
Cellulose Binding ◽  
Family Iv

ABSTRACT The family IV cellulose-binding domain of Clostridium thermocellum CelK (CBDCelK) was expressed inEscherichia coli and purified. It binds to acid-swollen cellulose (ASC) and bacterial microcrystalline cellulose (BMCC) with capacities of 16.03 and 3.95 μmol/g of cellulose and relative affinities (K r) of 2.33 and 9.87 liters/g, respectively. The CBDCelK is the first representative of family IV CBDs to exhibit an affinity for BMCC. The CBDCelKalso binds to the soluble polysaccharides lichenin, glucomannan, and barley β-glucan, which are substrates for CelK. It does not bind to xylan, galactomannan, and carboxymethyl cellulose. The CBDCelK contains 1 mol of calcium per mol. The CBDCelK has three thiol groups and one disulfide, reduction of which results in total loss of cellulose-binding ability. To reveal amino acid residues important for biological function of the domain and to investigate the role of calcium in the CBDCelK four highly conserved aromatic residues (Trp56, Trp94, Tyr111, and Tyr136) and Asp192 were mutated into alanines, giving the mutants W56A, W94A, Y111A, Y136A, and D192A. In addition 14 N-terminal amino acids were deleted, giving the CBD-NCelK. The CBD-NCelK and D192A retained binding parameters close to that of the intact CBDCelK, W56A and W94A totally lost the ability to bind to cellulose, Y136A bound to both ASC and BMCC but with significantly reduced binding capacity and K rand Y111A bound weakly to ASC and did not bind to BMCC. Mutations of the aromatic residues in the CBDCelK led to structural changes revealed by studying solubility, circular-dichroism spectra, dimer formation, and aggregation. Calcium content was drastically decreased in D192A. The results suggest that Asp192 is in the calcium-binding site of the CBDCelK and that calcium does not affect binding to cellulose. The 14 amino acids from the N terminus of the CBDCelK are not important for binding. Tyr136, corresponding to Cellulomonas fimi CenC CBDN1Y85, located near the binding cleft, might be involved in the formation of the binding surface, while Y111, W56A, and W94A are essential for the binding process by keeping the CBDCelK correctly folded.

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