Mutagenesis of Trp(54) and Trp(203) residues on Fibrobacter succinogenes 1,3-1,4-beta-D-glucanase significantly affects catalytic activities of the enzyme

A highly active beta-glucanase from a new strain of rumen fungus Orpinomyces sp.Y102 exhibits cellobiohydrolase and cellotriohydrolase activities

A new strain of rumen fungus was isolated from Bos taurus, identified and designated Orpinomyces sp.Y102. A clone, celC7, isolated from the cDNA library of Orpinomyces sp.Y102, was predicted to encode a protein containing a signal peptide (Residues 1-17), an N-terminal dockerin-containing domain, and a C-terminal cellobiohydrolase catalytic domain of glycoside hydrolase family 6. CelC7 was insoluble when expressed in Escherichia coli. Deletion of 17 or 105 residues from the N-terminus significantly improved its solubility. The resulting enzymes, CelC7(-17) and CelC7(-105), were highly active to β-glucan substrates and were stable between pH 5.0 and 11.0. CelC7(-105) worked as an exocellulase releasing cellobiose and cellotriose from acid-swollen Avicel and cellooligosaccharides, and displayed a Vmax of 6321.64μmole/min/mg and a Km of 2.18mg/ml to barley β-glucan. Further, the crude extract of CelC7(-105) facilitated ethanol fermentation from cellulose. Thus, CelC7(-105) is a good candidate for industrial applications such as biofuel production.

Purification, characterization, and heterologous expression of a thermostable β-1,3-1,4-glucanase from Bacillus altitudinis YC-9

Purification, characterization, gene cloning, and heterologous expression in Escherichia coli of a thermostable β-1,3-1,4-glucanase from Bacillus altitudinis YC-9 have been investigated in this paper. The donor strain B. altitudinis YC-9 was isolated from spring silt. The native enzyme was purified by ammonium sulfate precipitation, diethylaminoethyl-cellulose anion exchange chromatography, and Sephadex G-100 gel filtration. The purified β-1,3-1,4-glucanase was observed to be stable at 60 °C and retain more than 90% activity when incubated for 2 h at 60 °C and remain about 75% and 44% activity after incubating at 70 °C and 80 °C for 10 min, respectively. Acidity and temperature optimal for this enzyme was pH 6 and 65 °C. The open reading frame of the enzyme gene was measured to be 732 bp encoding 243 amino acids, with a predicted molecular weight of 27.47 kDa. The gene sequence of β-1,3-1,4-glucanase showed a homology of 98% with that of Bacillus licheniformis. After being expressed in E. coli BL21, active recombinant enzyme was detected both in the supernatants of the culture and the cell lysate, with the activity of 102.7 and 216.7 U/mL, respectively. The supernatants of the culture were used to purify the recombinant enzyme. The purified recombinant enzyme was characterized to show almost the same properties to the wild enzyme, except that the specific activity of the recombinant enzyme reached 5392.7 U/mg, which was higher than those ever reported β-1,3-1,4-glucanase from Bacillus strains. The thermal stability and high activity make this enzyme broad prospect for industry application. This is the first report on β-1,3-1,4-glucanase produced by B. altitudinis.

Structural modeling and further improvement in pH stability and activity of a highly-active xylanase from an uncultured rumen fungus

Rumen fungi are a rich source of enzymes degrading lignocelluloses. XynR8 is a glycosyl hydrolase family 11 xylanase previously cloned from unpurified rumen fungal cultures. Phylogenetic analysis suggested that xynR8 was obtained from a Neocallimastix species. Recombinant XynR8 expressed in Escherichia coli was highly active and stable between pH 3.0 and 11.0, and displayed a V(max) of 66,672μmolmin(-1)mg(-1), a k(cat) of 38,975s(-1), and a K(m) of 11.20mg/mL towards soluble oat spelt xylan. Based on molecular modeling, residues N41 and N58, important in stabilizing two loops and the structure of XynR8, were mutated to D. Both mutant enzymes showed higher tolerance to pH 2.0. The V(max), k(cat) and K(m) of the N41D and N58D mutant enzymes were 79,645μmolmin(-1)mg(-1), 46,493s(-1), 29.29mg/mL, and 96,689μmolmin(-1)mg(-1), 56,503s(-1), and 21.24mg/mL, respectively. Thus, they are good candidates for application, including biofuel production.

Rational design to improve thermostability and specific activity of the truncated Fibrobacter succinogenes 1,3-1,4-β-D-glucanase

1,3-1,4-β-D-Glucanase has been widely used as a feed additive to help non-ruminant animals digest plant fibers, with potential in increasing nutrition turnover rate and reducing sanitary problems. Engineering of enzymes for better thermostability is of great importance because it not only can broaden their industrial applications, but also facilitate exploring the mechanism of enzyme stability from structural point of view. To obtain enzyme with higher thermostability and specific activity, structure-based rational design was carried out in this study. Eleven mutants of Fibrobacter succinogenes 1,3-1,4-β-D-glucanase were constructed in attempt to improve the enzyme properties. In particular, the crude proteins expressed in Pichia pastoris were examined firstly to ensure that the protein productions meet the need for industrial fermentation. The crude protein of V18Y mutant showed a 2 °C increment of Tm and W203Y showed ∼30% increment of the specific activity. To further investigate the structure-function relationship, some mutants were expressed and purified from P. pastoris and Escherichia coli. Notably, the specific activity of purified W203Y which was expressed in E. coli was 63% higher than the wild-type protein. The double mutant V18Y/W203Y showed the same increments of Tm and specific activity as the single mutants did. When expressed and purified from E. coli, V18Y/W203Y showed similar pattern of thermostability increment and 75% higher specific activity. Furthermore, the apo-form and substrate complex structures of V18Y/W203Y were solved by X-ray crystallography. Analyzing protein structure of V18Y/W203Y helps elucidate how the mutations could enhance the protein stability and enzyme activity.

Structural modeling of glucanase-substrate complexes suggests a conserved tyrosine is involved in carbohydrate recognition in plant 1,3-1,4-beta-D-glucanases

Glycosyl hydrolase family 16 (GHF16) truncated Fibrobacter succinogenes (TFs) and GHF17 barley 1,3-1,4-beta-D-glucanases (beta-glucanases) possess different structural folds, beta-jellyroll and (beta/alpha)8, although they both catalyze the specific hydrolysis of beta-1,4 glycosidic bonds adjacent to beta-1,3 linkages in mixed beta-1,3 and beta-1,4 beta-D-glucans or lichenan. Differences in the active site region residues of TFs beta-glucanase and barley beta-glucanase create binding site topographies that require different substrate conformations. In contrast to barley beta-glucanase, TFs beta-glucanase possesses a unique and compact active site. The structural analysis results suggest that the tyrosine residue, which is conserved in all known 1,3-1,4-beta-D-glucanases, is involved in the recognition of mixed beta-1,3 and beta-1,4 linked polysaccharide.

A Galactolipid Possesses Novel Cancer Chemopreventive Effects by Suppressing Inflammatory Mediators and Mouse B16 Melanoma

Crassocephalum rabens (Asteraceae) is a popular anti-inflammatory folk medicine and food supplement. We investigated the cancer chemopreventive bioactivity of C. rabens phytocompounds in vitro and in vivo using cell- and gene-based bioassays and a mouse B16 melanoma model. The bioactive glyceroglycolipid 1,2-di-O-alpha-linolenoyl-3-O-beta-galactopyranosyl-sn-glycerol (dLGG) that was identified from C. rabens was found in vitro and in vivo to be a potent nitric oxide (NO) scavenger. dLGG treatment inhibited both mRNA and protein expression of inducible NO synthase and cyclooxygenase-2 (COX-2) in murine macrophages and inhibited COX-2 gene transcription in 12-O-tetradecanoylphorbol-13-acetate (TPA)-treated B16 cells. In immunohistochemical studies, dLGG inhibited TPA-induced expression of COX-2 and nitration of proteins in mouse skin. dLGG could also significantly inhibit lipopolysaccharide-induced prostaglandin E(2) production in murine macrophages. Furthermore, dLGG prevented nuclear translocation of cytoplasmic nuclear factor-kappaB (NF-kappaB) by suppressing IkappaBalpha phosphorylation and degradation. Structure-activity relationship study by electrophoretic mobility shift assay indicated that the dilinolenoylglycerol moiety in dLGG is the essential structural feature preventing NF-kappaB.DNA complex formation. A dLGG-enriched extract from C. rabens (10 mg/kg) markedly suppressed B16 melanoma growth in C57BL/6J mice following i.p. administration, an effect comparable with that of cisplatin, a cancer chemotherapeutic drug. This study shows the detailed molecular mechanism(s) underlying the anti-inflammatory and tumor-suppressive effects of a natural galactolipid.

Cloning of beta-1,3-1,4-glucanase gene from Bacillus licheniformis EGW039 (CGMCC 0635) and its expression in Escherichia coli BL21 (DE3)

Beta-1,3-1,4-glucanase has been applied in the brewing and animal feed additive industry. It can effectively improve digestibility of barley-based diets and reduce enteritis. It also reduces viscosity during mashing for high-quality brewers malt. The aim of this work is to clone beta-1,3-1,4-glucanase-encoding gene and express it heterogeneously. The gene was amplified by polymerase chain reaction using Bacillus licheniformis genomic DNA as the template and ligated into the expression vector pET28a. The recombinant vector was transformed into Escherichia coli. The estimated molecular weight of the recombinant enzyme with a six-His tag at the N terminus was about 28 kDa, and its activities in cell lysate supernatant were 1,286 and 986 U ml(-1) for 1% (w/v) barley beta-glucan and 1% (w/v) lichenan, respectively. Accordingly, the specific activities were 2,479 and 1,906 U mg(-1) for these two substrates. The expression level of recombinant beta-1,3-1,4-glucanase was about 60.9% of the total protein and about 12.5% of the total soluble protein in crude cell lysate supernatant. Acidity and temperature optimal for this recombinant enzyme was pH 5.6 and 40 degrees C, respectively.

Structural basis for the substrate specificity of a Bacillus 1,3-1,4-beta-glucanase

Depolymerization of polysaccharides is catalyzed by highly specific enzymes that promote hydrolysis of the scissile glycosidic bond by an activated water molecule. 1,3-1,4-beta-Glucanases selectively cleave beta-1,4 glycosidic bonds in 3-O-substituted glucopyranosyl units within polysaccharides with mixed linkage. The reaction follows a double-displacement mechanism by which the configuration of the anomeric C(1)-atom of the glucosyl unit in subsite -I is retained. Here we report the high-resolution crystal structure of the hybrid 1,3-1,4-beta-glucanase H(A16-M)(E105Q/E109Q) in complex with a beta-glucan tetrasaccharide. The structure shows four beta-d-glucosyl moieties bound to the substrate-binding cleft covering subsites -IV to -I, thus corresponding to the reaction product. The ten active-site residues Asn26, Glu63, Arg65, Phe92, Tyr94, Glu105, Asp107, Glu109, Asn182 and Trp184 form a network of hydrogen bonds and hydrophobic stacking interactions with the substrate. These residues were previously identified by mutational analysis as significant for stabilization of the enzyme-carbohydrate complex, with Glu105 and Glu109 being the catalytic residues. Compared to the Michaelis complex model, the tetrasaccharide moiety is slightly shifted toward that part of the cleft binding the non-reducing end of the substrate, but shows previously unanticipated strong stacking interactions with Phe92 in subsite -I. A number of specific hydrogen-bond contacts between the enzyme and the equatorial O(2), O(3) and O(6) hydroxyl groups of the glucosyl residues in subsites -I, -II and -III are the structural basis for the observed substrate specificity of 1,3-1,4-beta-glucanases. Kinetic analysis of enzyme variants with the all beta-1,3 linked polysaccharide laminarin identified key residues mediating substrate specificity in good agreement with the structural data. The comparison with structures of the apo-enzyme H(A16-M) and a covalent enzyme-inhibitor (E.I) complex, together with kinetic and mutagenesis data, yields new insights into the structural requirements for substrate binding and catalysis. A detailed view of enzyme-carbohydrate interactions is presented and mechanistic implications are discussed.

Crystal Structure of Truncated Fibrobacter succinogenes 1,3-1,4-β-d-Glucanase in Complex with β-1,3-1,4-Cellotriose

Fibrobacter succinogenes 1,3-1,4-beta-D-glucanase (Fsbeta-glucanase) catalyzes the specific hydrolysis of beta-1,4 glycosidic bonds adjacent to beta-1,3 linkages in beta-D-glucans or lichenan. This is the first report to elucidate the crystal structure of a truncated Fsbeta-glucanase (TFsbeta-glucanase) in complex with beta-1,3-1,4-cellotriose, a major product of the enzyme reaction. The crystal structures, at a resolution of 2.3 angstroms, reveal that the overall fold of TFsbeta-glucanase remains virtually unchanged upon sugar binding. The enzyme accommodates five glucose residues, forming a concave active cleft. The beta-1,3-1,4-cellotriose with subsites -3 to -1 bound to the active cleft of TFsbeta-glucanase with its reducing end subsite -1 close to the key catalytic residues Glu56 and Glu60. All three subsites of the beta-1,3-1,4-cellotriose adopted a relaxed C(1)4 conformation, with a beta-1,3 glycosidic linkage between subsites -2 and -1, and a beta-1,4 glycosidic linkage between subsites -3 and -2. On the basis of the enzyme-product complex structure observed in this study, a catalytic mechanism and substrate binding conformation of the active site of TFsbeta-glucanase is proposed.

A Truncated Fibrobacter succinogenes 1,3−1,4-β-d-Glucanase with Improved Enzymatic Activity and Thermotolerance

As an approach to improving Fibrobacter succinogenes 1,3-1,4-beta-d-glucanase (Fsbeta-glucanase) for use in industry and to studying the structure-function relationship of the C-terminus in the enzyme, a C-terminally truncated ( approximately 10 kDa) Fsbeta-glucanase was generated using a PCR-based gene truncation method and then overexpressed in either Escherichia coli BL21(DE3) or Pichia pastoris strain X-33 host cells. The initial rate kinetics, protein folding, and thermostability of the wild-type and truncated glucanases were characterized. The truncated enzyme expressed in Pichia cells was found to be glycosylated and composed of two dominant polypeptide bands as judged by SDS-PAGE. An approximate 3-4-fold increase in the turnover rate (k(cat)), relative to that of the full-length enzyme, was detected for the purified truncated glucanases produced in E. coli (designated TF-glucanase) or Pichia host cells (designated glycosylated TF-glucanase). The glycosylated TF-glucanase is the most active known 1,3-1,4-beta-d-glucanase, with a specific activity of 10 800 +/- 200 units/mg. Similar binding affinities for lichenan (K(m) = 2.5-2.89 mg/mL) were detected for the full-length enzyme, TF-glucanase, and glycosylated TF-glucanase. Both forms of truncated glucanase retained more than 80% of their original enzymatic activity after a 10 min incubation at 90 degrees C, whereas the full-length enzyme possessed only 30% of its original enzymatic activity after the same treatment. This report demonstrates that deletion of the C-terminal region ( approximately 10 kDa) in Fsbeta-glucanase, consisting of serine-rich repeats and a basic terminal domain rich in positively charged amino acids, significantly increases the catalytic efficiency and thermotolerance of the enzyme.

Crystal structure of a natural circularly permuted jellyroll protein: 1,3-1,4-beta-D-glucanase from Fibrobacter succinogenes

The 1,3-1,4-beta-D-glucanase from Fibrobacter succinogenes (Fsbeta-glucanase) is classified as one of the family 16 glycosyl hydrolases. It hydrolyzes the glycosidic bond in the mixed-linked glucans containing beta-1,3- and beta-1,4-glycosidic linkages. We constructed a truncated form of recombinant Fsbeta-glucanase containing the catalytic domain from amino acid residues 1-258, which exhibited a higher thermal stability and enzymatic activity than the full-length enzyme. The crystal structure of the truncated Fsbeta-glucanase was solved at a resolution of 1.7A by the multiple wavelength anomalous dispersion (MAD) method using the anomalous signals from the seleno-methionine-labeled protein. The overall topology of the truncated Fsbeta-glucanase consists mainly of two eight-stranded anti-parallel beta-sheets arranged in a jellyroll beta-sandwich, similar to the fold of many glycosyl hydrolases and carbohydrate-binding modules. Sequence comparison with other bacterial glucanases showed that Fsbeta-glucanase is the only naturally occurring circularly permuted beta-glucanase with reversed sequences. Structural comparison shows that the engineered circular-permuted Bacillus enzymes are more similar to their parent enzymes with which they share approximately 70% sequence identity, than to the naturally occurring Fsbeta-glucanase of similar topology with 30% identity. This result suggests that protein structure relies more on sequence identity than topology. The high-resolution structure of Fsbeta-glucanase provides a structural rationale for the different activities obtained from a series of mutant glucanases and a basis for the development of engineered enzymes with increased activity and structural stability.