Improving catalytic efficiency of endo-β-1, 4-xylanase from Geobacillus stearothermophilus by directed evolution and H179 saturation mutagenesis

Engineering of xylanases for the development of biotechnologically important characteristics

Xylanases are the main biocatalysts used for the reduction of the xylan backbone from hemicellulose, randomly splitting off β-1,4-glycosidic linkages between xylopyranosyl residues. Xylanase market has been annually estimated at 500 million US Dollars and they are potentially used in broad industrial process ranges such as paper pulp biobleaching, xylo-oligosaccharide production, and biofuel manufacture from lignocellulose. The highly stable xylanases are preferred in the downstream procedure of industrial processes because they can tolerate severe conditions. Almost all native xylanases can not endure adverse conditions thus they are industrially not proper to be utilized. Protein engineering is a powerful technology for developing xylanases, which can effectively work in adverse conditions and can meet requirements for industrial processes. This study considered state-of-the-art strategies of protein engineering for creating the xylanase gene diversity, high-throughput screening systems toward upgraded traits of the xylanases, and the prediction and comprehensive analysis of the target mutations in xylanases by in silico methods. Also, key molecular factors have been elucidated for industrial characteristics (alkaliphilic enhancement, thermal stability, and catalytic performance) of GH11 family xylanases. The present review explores industrial characteristics improved by directed evolution, rational design, and semi-rational design as protein engineering approaches for pulp bleaching process, xylooligosaccharides production, and biorefinery & bioenergy production.

Improving the catalytic efficiency and substrate affinity of a novel esterase from marine Klebsiella aerogenes by random and site-directed mutation

A novel esterase (EstKa) from marine Klebsiella aerogenes was characterized with hydrolytic activity against p-nitrophenyl caprylate (pNPC, C₈) under optimum conditions (50 °C and pH 8.5). After two rounds of mutagenesis, two highly potential mutants (I6E9 and L7B11) were obtained with prominent activity, substrate affinity and thermostability. I6E9 (L90Q/P96T) and L7B11 (A37S/Q100L/S133G/R138C/Q156R) were 1.56- and 1.65-fold higher than EstKa in relative catalytic efficiency. The influence of each amino acid on enzyme activity was explored by site-directed mutation. The mutants Pro96Thr and Gln156Arg showed 1.29- and 1.48-fold increase in catalytic efficiency (Kcat/Km) and 54.4 and 36.2% decrease in substrate affinity (Km), respectively. The compound mutant Pro96Thr/Gln156Arg exhibited 68.9% decrease in Km and 1.41-fold increase in Kcat/Km relative to EstKa. Homology model structure analysis revealed that the replacement of Gln by hydrophilic Arg on the esterase surface improved the microenvironment stability and the activity. The replacement of Pro by Thr enabled the esterase enzyme to retain 90% relative activity after 3 h incubation at 45 °C. Structural analysis confirmed that the formation of a hydrogen bond leads to a notable increase of catalytic efficiency under high temperature conditions.

Enhancing the activity and thermal stability of a phthalate-degrading hydrolase by random mutagenesis

Our previous work has reported that EstJ6 was a phthalate-degrading hydrolase. In the study, a random mutant library was constructed by two rounds of error-prone PCR, three mutants (ET1.1, ET2.1, and ET2.2) with enhanced hydrolytic activity against dibutyl phthalate (DBP) were obtained. The best mutant ET2.2, accumulated three amino acid substitutions (Thr91Met, Ala67Val, and Val249Ile) and exhibited 2.8-fold increase enzyme activity and 2.3-fold higher expression level. Meanwhile, compared with EstJ6, ET2.2 showed over 50% improvement in thermostability (at 50 °C for 1 h) and 1.2-fold increase in 50% methanol tolerance. Kinetic parameters analysis revealed that the Km value for ET2.2 decreased by 60% and the kcat/Km value increased by 166%. The molecular docking indicated that the shortening of hydrogen bond between Ser146-OH and DBP-CO, which may led to an increase in enzyme activity and catalytic efficiency, the enhancement of hydrophobicity of hydrophobic pocket was related to the improvement of organic solvents tolerance, and three hydrophobic amino acid substitutions Thr91Met, Ala67Val, and Val249Ile facilitated to improve the thermal stability and organic solvents tolerance. These results confirmed that random mutagenesis was an effective tool for improving enzyme properties and lay a foundation for practical applications of phthalate-degrading hydrolase in biotechnology and industrial fields.

Enzymatic characterization of a novel thermostable and alkaline tolerant GH10 xylanase and activity improvement by multiple rational mutagenesis strategies

Thermo-alkaline xylanases are widely applied in paper pulping industry. In this study, a novel thermostable and alkaline tolerant GH10 xylanase (Xyn30Y5) gene from alkaliphilic Bacillus sp. 30Y5 was cloned and the surface-layer homology (SLH) domains truncated enzyme (Xyn30Y5-SLH) was expressed in Escherichia coli. The purified Xyn30Y5-SLH was most active at 70 °C and pH 7.0 and showed the highest specific activity of 349.4 U mg^-1. It retained more than 90% activity between pH 6.0 to 9.5 and was stable at pH 6.0-10.0. To improve the activity, 47 mutants were designed based on eight rational strategies and 21 mutants showed higher activity. By combinatorial mutagenesis, the best mutant 3B demonstrated specific activity of 1016.8 U mg^-1 with a doubled catalytic efficiency (k_cat/K_m) and RA60_1/2h value, accompanied by optimal pH shift to 8.0. The molecular dynamics simulation analysis indicated that the increase of flexibility of α5 helix and loop7 located near to the catalytic residues is likely responsible for its activity improvement. And the decrease of flexibility of the most unstable regions is vital for the thermostablity improvement. This work provided not only a novel thermostable and alkaline tolerant xylanase with industrial application potential but also an effective mutagenesis strategy for xylanase activity improvement.

Improving the catalytic activity of thermostable xylanase from Thermotoga maritima via mutagenesis of non-catalytic residues at glycone subsites

Endo-β-1,4-xylanase from Thermotoga maritima, TmxB, is an industrially attractive enzyme due to its extreme thermostability. To improve its application value, four variants were designed on the basis of multiple sequence and three-dimensional structure alignments. Wild-type TmxB (wt-TmxB) and its mutants were produced via a Pichia pastoris expression system. Among four single-site mutants, the tyrosine substitution of a threonine residue (T74Y) at putative -3/-4 subsite led to a 1.3-fold increase in specific activity at 40 °C - 100 °C and pH 5 for 5 min, with beechwood xylan as the substrate. T74Y had an improved catalytic efficiency (k_cat/K_m), being 1.6 times that of wt-TmxB. Variants DY (two amino acid insertions) and N68Q displayed a slight increase (1.2 fold) and dramatic decline (1.7 fold) in catalytic efficiency, respectively. Mutant E67Y was totally inactive under all test conditions. Structural modeling and docking simulation elucidated structural insights into the molecular mechanism of activity changes for these TmxB variants. This study helps in further understanding the roles of the non-catalytic amino acids at the glycone subsites of xylanases from glycoside hydrolase family 10.

Improving the catalytic efficiency of thermostable Geobacillus stearothermophilus xylanase XT6 by single-amino acid substitution

Directed evolution using error-prone polymerase chain reaction was employed in the current study to enhance the catalytic efficiency of a thermostable Geobacillus stearothermophilus xylanase XT6 parent. High-throughput screening identified two variants with enhanced activity. Sequencing analysis revealed the presence of a single-amino acid substitution (P209L or V161L) in each variant. The maximum activity of mutant V161L and P209L was at 85°C and 70°C, respectively. Both mutants exhibited maximum activity at pH 7. The thermal and alkaline tolerance of mutant V161L only were markedly improved. The two mutants were more resistant to ethanol inhibition than the parent. Substrate specificity of the two mutants was shifted from beechwood xylan to birchwood xylan. The potential of the two mutants to hydrolyze rice straw and sugarcane bagasse increased. Both turnover number (kcat) and catalytic efficiency (kcat/kM) increased 12.2- and 5.7-folds for variant P209L and 13- and 6.5-folds for variant V161L, respectively, towards birchwood xylan. Based on the previously published crystal structure of extracellular G. stearothermophilus xylanase XT6, V161L and P209L mutation locate on βα-loops. Conformational changes of the respective loops could potentiate the loop swinging, product release and consequently result in enhancement of the catalytic performance.

Improvement in catalytic activity and thermostability of a GH10 xylanase and its synergistic degradation of biomass with cellulase

BACKGROUND

Xylanase is one of the most extensively used biocatalysts for biomass degradation. However, its low catalytic efficiency and poor thermostability limit its applications. Therefore, improving the properties of xylanases to enable synergistic degradation of lignocellulosic biomass with cellulase is of considerable significance in the field of bioenergy.

RESULTS

Using fragment replacement, we improved the catalytic performance and thermostability of a GH10 xylanase, XylE. Of the ten hybrid enzymes obtained, seven showed xylanase activity. Substitution of fragments, M3, M6, M9, and their combinations enhanced the catalytic efficiency (by 2.4- to fourfold) as well as the specific activity (by 1.2- to 3.3-fold) of XylE. The hybrids, XylE-M3, XylE-M3/M6, XylE-M3/M9, and XylE-M3/M6/M9, showed enhanced thermostability, as observed by the increase in the T ₅₀ (3-4.7 °C) and T _m (1.1-4.7 °C), and extended t _1/2 (by 1.8-2.3 h). In addition, the synergistic effect of the mutant xylanase and cellulase on the degradation of mulberry bark showed that treatment with both XylE-M3/M6 and cellulase exhibited the highest synergistic effect. In this case, the degree of synergy reached 1.3, and the reducing sugar production and dry matter reduction increased by 148% and 185%, respectively, compared to treatment with only cellulase.

CONCLUSIONS

This study provides a successful strategy to improve the catalytic properties and thermostability of enzymes. We identified several xylanase candidates for applications in bioenergy and biorefinery. Synergistic degradation experiments elucidated a possible mechanism of cellulase inhibition by xylan and xylo-oligomers.

Laboratory Evolution of GH11 Endoxylanase Through DNA Shuffling: Effects of Distal Residue Substitution on Catalytic Activity and Active Site Architecture

Endoxylanase with high specific activity, thermostability, and broad pH adaptability is in huge demand. The mutant library of GH11 endoxylanase was constructed via DNA shuffling by using the catalytic domain of Bacillus amyloliquefaciens xylanase A (BaxA) and Thermomonospora fusca TF xylanase A (TfxA) as parents. A total of 2,250 colonies were collected and 756 of them were sequenced. Three novel mutants (DS153: N29S, DS241: S31R and DS428: I51V) were identified and characterized in detail. For these mutants, three residues of BaxA were substituted by the corresponding one of TfxA_CD. The specific activity of DS153, DS241, and DS428 in the optimal condition was 4.54, 4.35, and 3.9 times compared with the recombinant BaxA (reBaxA), respectively. The optimum temperature of the three mutants was 50°C. The optimum pH for DS153, DS241, and DS428 was 6.0, 7.0, and 6.0, respectively. The catalytic efficiency of DS153, DS241, and DS428 enhanced as well, while their sensitivity to recombinant rice xylanase inhibitor (RIXI) was lower than that of reBaxA. Three mutants have identical hydrolytic function as reBaxA, which released xylobiose–xylopentaose from oat spelt, birchwood, and beechwood xylan. Furthermore, molecular dynamics simulations were performed on BaxA and three mutants to explore the precise impact of gain-of-function on xylanase activity. The tertiary structure of BaxA was not altered under the substitution of distal residues (N29S, S31R, and I51V); it induced slightly changes in active site architecture. The distal impact rescued the BaxA from native conformation (“closed state”) through weakening interactions between “gate” residues (R112, N35 in DS241 and DS428; W9, P116 in DS153) and active site residues (E78, E172, Y69, and Y80), favoring conformations with an “open state” and providing improved activity. The current findings would provide a better and more in-depth understanding of how distal single residue substitution improved the catalytic activity of xylanase at the atomic level.

Improvements of thermophilic enzymes: From genetic modifications to applications

Thermozymes (from thermophiles or hyperthermophiles) offer obvious advantages due to their excellent thermostability, broad pH adaptation, and hydrolysis ability, resulting in diverse industrial applications including food, paper, and textile processing, biofuel production. However, natural thermozymes with low yield and poor adaptability severely hinder their large-scale applications. Extensive studies demonstrated that using genetic modifications such as directed evolution, semi-rational design, and rational design, expression regulations and chemical modifications effectively improved enzyme's yield, thermostability and catalytic efficiency. However, mechanism-based techniques for thermozymes improvements and applications need more attention. In this review, stabilizing mechanisms of thermozymes are summarized for thermozymes improvements, and these improved thermozymes eventually have large-scale industrial applications.

Site-Directed Mutagenesis of a β-Glycoside Hydrolase from Lentinula Edodes

The β-glycoside hydrolases (LXYL-P1-1 and LXYL-P1-2) from Lentinula edodes (strain M95.33) can specifically hydrolyze 7-β-xylosyl-10-deacetyltaxol (XDT) to form 10-deacetyltaxol for the semi-synthesis of Taxol. Our previous study showed that both the I368T mutation in LXYL-P1-1 and the T368E mutation in LXYL-P1-2 could increase the enzyme activity, which prompted us to investigate the effect of the I368E mutation on LXYL-P1-1 activity. In this study, the β-xylosidase and β-glucosidase activities of LXYL-P1-1I368E were 1.5 and 2.2 times higher than those of LXYL-P1-1. Most importantly, combination of I368E and V91S exerted the cumulative effects on the improvement of the enzyme activities and catalytic efficiency. The β-xylosidase and β-glucosidase activities of the double mutant LXYL-P1-1V91S/I368E were 3.2 and 1.7-fold higher than those of LXYL-P1-1I368E. Similarly, the catalytic efficiency of LXYL-P1-1V91S/I368E on 7-β-xylosyl-10-deacetyltaxol was 1.8-fold higher than that of LXYL-P1-1I368E due to the dramatic increase in the substrate affinity. Molecular docking results suggest that the V91S and I368E mutation might positively promote the interaction between enzyme and substrate through altering the loop conformation near XDT and increasing the hydrogen bonds among Ser91, Trp301, and XDT. This study lays the foundation for exploring the relationship between the structure and function of the β-glycoside hydrolases.

Insight into the functional roles of Glu175 in the hyperthermostable xylanase XYL10C-ΔN through structural analysis and site-saturation mutagenesis

BACKGROUND

Improving the hydrolytic performance of hemicellulases to degrade lignocellulosic biomass is of considerable importance for second-generation biorefinery. Xylanase, as the crucial hemicellulase, must be thermostable and have high activity for its potential use in the bioethanol industry. To obtain excellent xylanase candidates, it is necessary to understand the structure-function relationships to provide a meaningful reference to improve the enzyme properties. This study aimed to investigate the catalytic mechanism of a highly active hyperthermophilic xylanase variant, XYL10C-ΔN, for hemicellulose degradation.

RESULTS

By removing the N-terminal 66 amino acids, the variant XYL10C-ΔN showed a 1.8-fold improvement in catalytic efficiency and could hydrolyze corn stover more efficiently in hydrolysis of corn stover; however, it retained similar thermostability to the wild-type XYL10C. Based on the crystal structures of XYL10C-ΔN and its complex with xylobiose, Glu175 located on loop 3 was found to be specific to GH10 xylanases and probably accounts for the excellent enzyme properties by interacting with Lys135 and Met137 on loop 2. Site-saturation mutagenesis confirmed that XYL10C-ΔN with glutamate acid at position 175 had the highest catalytic efficiency, specific activity, and the broadest pH-activity profile. The functional roles of Glu175 were also verified in the mutants of another two GH10 xylanases, XylE and XynE2, which showed increased catalytic efficiencies and wider pH-activity profiles.

CONCLUSIONS

XYL10C-ΔN, with excellent thermostability, high catalytic efficiency, and great lignocellulose-degrading capability, is a valuable candidate xylanase for the biofuel industry. The mechanism underlying improved activity of XYN10C-ΔN was thus investigated through structural analysis and functional verification, and Glu175 was identified to play the key role in the improved catalytic efficiency. This study revealed the importance of a key residue (Glu175) in XYN10C-ΔN and provides a reference to modify GH10 xylanases for improved catalytic performance.

Dynamic Management of Codon Compression for Saturation Mutagenesis

Saturation mutagenesis is conveniently located between the two extremes of protein engineering, namely random mutagenesis, and rational design. It involves mutating a confined number of target residues to other amino acids, and hence requires knowledge regarding the sites for mutagenesis, but not their final identity. There are many different strategies for performing and designing such experiments, ranging from simple single degenerate codons to codon collections that code for distinct sets of amino acids. Here, we provide detailed information on the Dynamic Management for Codon Compression (DYNAMCC) approaches that allow us to precisely define the desired amino acid composition to be introduced to a specific target site. DYNAMCC allows us to set usage thresholds and to eliminate undesirable stop and wild-type codons, thus allowing us to control library size and subsequently downstream screening efforts. The DYNAMCC algorithms are free of charge and are implemented in a website for easy access and usage: www.dynamcc.com .

Improvement of the catalytic efficiency of a hyperthermophilic xylanase from Bispora sp. MEY-1

Extremophilic xylanases have attracted great scientific and industrial interest. In this study, a GH10 xylanase-encoding gene, Xyl10E, was cloned from Bispora sp. MEY-1 and expressed in Pichia pastoris GS115. Deduced Xyl10E shares the highest identities of 62% and 57% with characterized family GH10 xylanases from Talaromyces leycettanus and Penicillium canescens (structure 4F8X), respectively. Xyl10E was most active at 93 to 95°C and pH 4.0, retained more than 75% or 48% of the initial activity when heated at 80°C or 90°C for 30 min, respectively, and hardly lost activity at pH 1.0 to 7.0, but was completely inhibited by SDS. Two residues, A160 and A161, located on loop 4, were identified to play roles in catalysis. Mutants A160D/E demonstrated higher affinity to substrate with lower K_m values, while mutants A161D/E mainly displayed elevated V_max values. All of these mutants had significantly improved catalytic efficiency. According to the molecular dynamics simulation, the mutation of A160E was able to affect the important substrate binding site Y204 and then improve the substrate affinity, and the mutation of A161D was capable of forming a hydrogen bond with the substrate to promote the substrate binding or accelerate the product release. This study introduces a highly thermophilic fungal xylanase and reveals the importance of loop 4 for catalytic efficiency.

Improving the Catalytic Property of the Glycoside Hydrolase LXYL-P1-2 by Directed Evolution

The glycoside hydrolase LXYL-P1–2 from Lentinula edodes can specifically hydrolyze 7-β-xylosyltaxanes to form 7-β-hydroxyltaxanes for the semi-synthesis of paclitaxel. In order to improve the catalytic properties of the enzyme, we performed error-prone PCR to construct the random mutant library of LXYL-P1–2 and used the methanol-induced plate method to screen the mutants with improved catalytic properties. Two variants, LXYL-P1–2-EP1 (EP1, S91D mutation) and LXYL-P1–2-EP2 (EP2, T368E mutation), were obtained from the library and exhibited 17% and 47% increases in their catalytic efficiencies on 7-β-xylosyl-10-deacetyltaxol. Meanwhile, compared with LXYL-P1–2, EP1 and EP2 showed elevated stabilities in the range of pH ≥ 6 conditions. After treatment at pH 12 for 48 h, EP1 and EP2 retained 77% and 63% activities, respectively, while the wild-type only retained 33% activity under the same condition. Molecular docking results revealed that the S91D mutation led to a shorter distance between the R-chain and the substrate, while the T368E mutation increased negative charge at the surface of the enzyme, and may introduce alterations of the loop near the active pocket, both of which may result in improved stabilities and catalytic activities of enzymes. This study provides a practical directed evolution method for exploring catalytically improved glycoside hydrolase.

Enzyme engineering: reaching the maximal catalytic efficiency peak

The practical need for highly efficient enzymes presents new challenges in enzyme engineering, in particular, the need to improve catalytic turnover (k_cat) or efficiency (k_cat/K_M) by several orders of magnitude. However, optimizing catalysis demands navigation through complex and rugged fitness landscapes, with optimization trajectories often leading to strong diminishing returns and dead-ends. When no further improvements are observed in library screens or selections, it remains unclear whether the maximal catalytic efficiency of the enzyme (the catalytic 'fitness peak') has been reached; or perhaps, an alternative combination of mutations exists that could yield additional improvements. Here, we discuss fundamental aspects of the process of catalytic optimization, and offer practical solutions with respect to overcoming optimization plateaus.

Improvement of the catalytic performance of a hyperthermostable GH10 xylanase from Talaromyces leycettanus JCM12802

A xylanase gene of GH 10, Tlxyn10A, was cloned from Talaromyces leycettanus JCM12802 and expressed in Pichia pastoris. Purified recombinant TlXyn10A was acidic and hyperthermophilic, and retained stable over the pH range of 2.0-6.0 and at 90°C. Sequence analysis of TlXyn10A identified seven residues probably involved in substrate contacting. Three mutants (TlXyn10A_P, _N and _C) were then constructed by substituting some or all of the residues with corresponding ones of hyperthermal Xyl10C from Bispora sp. MEY-1. TlXyn10A_P with mutations at subsites +2 to +4 exhibited improved specific activity (by 0.44-fold) and pH stability (2.0-10.0). Molecular dynamics simulation analysis indicated that mutations E229I and F232E probably weaken the substrate affinity at subsites +3 to +4, and G149D may introduce a new hydrogen bond. These modifications altogether account for the improved performance of TlXyn10A_P. Moreover, TlXyn10A_P was able to hydrolyze wheat straw persistently, and has the application potentials in various industries.

A trehalase from Zunongwangia sp.: characterization and improving catalytic efficiency by directed evolution

BACKGROUND

Trehalases have potential applications in several fields, including food additives, insecticide development, and transgenic plant. In the present study, we focused on a trehalase from the marine bacterium Zunongwangia sp., which hydrolyzes trehalose to glucose.

RESULTS

A novel gene, treZ (1590 bp) encoding an α, α-trehalase of 529 amino acids was cloned from Zunongwangia sp., and TreZ was found to have an optimal activity at 50 °C and pH 6. The activity of TreZ was increased by the presence of NaCl, showing the highest activity (136 %) at 1 M NaCl. A variant C4 with improved catalytic activity was obtained by error-prone PCR and followed by a 96-well plate high-throughput screening. The variant C4 with two altered sites (Y227H, and R442G) displayed a 3.3 fold increase in catalytic efficiency (k cat/K m, 1143.40 mmol(-1) s(-1)) compared with the wild type enzyme (265.91 mmol(-1) s(-1)). In order to explore the contribution of the mutations found in variant C4 to the increased catalytic activity, two mutants Y227H and R442G were constructed by site-directed mutagenesis. The results showed that the catalytic efficiencies of Y227H and R442G were 416.78 mmol(-1) s(-1) and 740.97 mmol(-1) s(-1), respectively, indicating that both mutations contributed to the increased catalytic efficiency of variant C4. The structure modeling and substrate docking revealed that the substitution Y227H enlarged the shape of the binding pocket, to improve the binding of the substrate and the release of the products; while the substitution R442G reduced the size of the side chain and decreased the steric hindrance, which contributed to channel the substrate into the active cavity easier and promote the release of the product.

CONCLUSION

In this study, a novel trehalase was cloned, purified, characterized, and engineered. A variant C4 with dramatically improved catalytic activity was obtained by directed evolution, and the mutation sites Y227H and R442G were found to play a significant role in the catalytic efficiency. The overall results provide useful information about the structure and function of trehalase.

Improvement of glycine oxidase by DNA shuffling, and site-saturation mutagenesis of F247 residue

Glyphosate is a broad spectrum herbicide widely used throughout the world, and it could be degraded by glycine oxidase (GO) through CN bond cleavage. For a better understanding of the structure-function relationship and improving the activity of B3S1 (GO from Bacillus cereus), DNA shuffling was performed. A mutant B4S7 (The Km, Vmax, kcat and kcat/Km values on glyphosate were 0.1 mM, 0.002401 mM min(-1), 3.62 min(-1) and 36.2 mM(-1) min(-1), respectively. The four parameters on glycine were 50.34 mM, 0.001983 mM min(-1), 2.18 min(-1) and 0.04 mM(-1) min(-1), respectively) was obtained from 10,000 clones, which presented a 3.9-fold increase of the specificity constant (the kcat/Km ratio between glyphosate and glycine) compared with B3S1. Especially, the Km value of B4S7 to glyphosate was much less than those of the reported GO. Structure modeling and molecular docking indicated that the novel mutation point F247S was close to the active site of the enzyme. To identify the role of the site, the remaining 19 amino acids were introduced into the site by site-saturation mutagenesis. The result showed that compared with B3S1, the specificity constant of mutant F247S and F247R increased 0.64-fold and 1.04-fold, respectively. While the specificity constant of mutant F247E decreased 2.01-fold. Therefore, the site 247 plays a crucial role in regulating the substrate specificity. This study provides new information on the structure-function relationship of glycine oxidase and the development of glyphosate-tolerant crops.

Calcium alginate matrix increases the stability and recycling capability of immobilized endo-β-1,4-xylanase from Geobacillus stearothermophilus KIBGE-IB29

Exploration of microbial pool from extremely diversified ecosystem is significantly important for various industrial applications. Bacterial communities from extreme habitats including volcanic vents, hot springs, and industrial sectors are eagerly explored for the isolation of thermophiles. Geobacillus stearothermophilus KIBGE-IB29, isolated from blast furnace site of a steel processing industry, is capable of producing thermostable endo-β-1,4-xylanase. In the current study, this enzyme was immobilized within calcium alginate beads using entrapment technique. Amalgamation of sodium alginate (40.0 gL(-1)) and calcium chloride (0.4 M) was used for the formation of immobilized beads. It was observed that temperature (50 °C) and pH (7.0) optima of immobilized enzyme remained same, but enzyme-substrate reaction time increased from 5.0 to 30.0 min as compared to free enzyme. Diffusion limit of high molecular weight xylan (corncob) caused a decline in V max of immobilized enzyme from 4773 to 203.7 U min(-1), whereas K m value increased from 0.5074 to 0.5722 mg ml(-1) with reference to free enzyme. Immobilized endo-β-1,4-xylanase showed its stability even at high temperatures as compared to free enzyme and retained 18 and 9 % residual activity at 70 and 80 °C, respectively. Immobilized enzyme also exhibited sufficient recycling efficiency up to five reaction cycles which indicated that this enzyme can be a plausible candidate in paper and pulp industry.