Overexpression and characterization of TnCel12B, a hyperthermophilic GH12 endo-1,4-β-glucanase cloned from Thermotoga naphthophila RKU-10T

Enhancement of the catalytic activity of thermostable Endo-1,4-β-glucanase B (TnCelB) from Thermotoga neapolitana by error-prone PCR

Endo-1,4-β-glucanase plays a crucial role in converting cellulose from lignocellulosic biomass into fermentable sugars for biofuel production. However, its commercial utility is hindered by poor catalytic performance under extreme conditions. This study enhanced the catalytic activity of the endo-1,4-β-glucanase (TnCelB) from Thermotoga neapolitana through error-prone PCR directed evolution. After screening >4000 colonies, three mutants with enhanced activity were obtained. Mutants TnCelBY88F, TnCelBA233T, and TnCelBW219R displayed 52.14 U/mg, 44.90 U/mg, and 34.70 U/mg of specific activity on CMC, respectively, which is 1.9, 1.7, and 1.3 times higher than that of the wild-type (26.74 U/mg), correspondingly. Likewise, their enzyme activity on barley β-D-glucan increased by 3.5, 2.2, and 1.8 times, respectively. Notably, TnCelBY88F maintained over 90 % activity after 60 mins at high temperatures (80-100 °C), indicating an exceptional thermostability. Protein docking revealed that TnCelBY88F had higher binding affinity, aligned with kinetic studies. TnCelB was capble of released more non-oxidized sugars from the hydrolysis of regenerated amorphous cellulose (RAC) by synergy with auxiliary action family 10 (AA10), which is potential in development of efficient lignocellulosic saccharification. This study can provide useful insights for the future engineering of other endoglucanases in the glycoside hydrolases family 12.

Functional Characterization of a Highly Efficient Endoglucanase from Bacillus licheniformis BJ2022 and Its Application in the Preparation of Low-Molecular-Weight Konjac Glucomannan

Endoglucanases may not only act on β-1,4-linkages in β-glucan but also target d-glucose in glucomannan, which can expand their utility in the preparation of prebiotics. In this study, a highly efficient endoglucanase (BlGH5) from Bacillus licheniformis BJ2022 was expressed and characterized. BlGH5 exhibited the highest activity at pH 7.0 and 60 °C. It maintained over 80% activity at pH 4.0-7.0 and 30-60 °C. BlGH5 specifically cleaved β-1,4-glycosidic bonds linked to d-glucose. Site-directed mutagenesis results suggested that Arg91, Asn167, Glu168, Trp206, His228, Tyr230, Ser263, and Trp290 are key residues for its binding and catalytic activity. Moreover, BlGH5 displayed high activity against konjac glucomannan (KGM), indicating that BlGH5 could be used to prepare low-molecular-weight konjac glucomannan (KGM-L). Based on the physicochemical properties of KGM and KGM-L, KGM-L was characterized by reduced molecular weight and viscosity. Fecal fermentation experiments demonstrated that KGM and KGM-L could promote the production of short-chain fatty acids (SCFAs). Still, KGM-L was more conducive to the growth of the gut probiotics. In conclusion, we identified an endoglucanase for the degradation of KGM. Results indicated that KGM-L would have superior prebiotic effects. Thus, our study provides a basis for the future development and application of KGM-L as a prebiotic.

Biochemical characterization of the catalytic domain from a novel hyperthermophilic β-glucanase and its application for KOS production

Konjac oligosaccharide (KOS) exhibits various biological activities, and hyperthermophilic β-glucanases offer many advantages for KOS production from konjac glucanmannan (KGM). In this study, a novel β-glucanase, EG003, belonging to the glycosyl hydrolase (GH) subfamily 5_1, was predicted from the genome of the a Thermus strain. The recombinant EG003 and its catalytic domain, EG003A, were successfully expressed and characterized. EG003A displayed maximum activity at 95 °C and pH 8.0, with a specific activity of 1047.6 U/mg and retained approximately 50 % activity after 6 h at 90 °C. The enzyme exhibited both β-1,4-glucanase and β-1,3-1,4-glucanase activity with KGM and sodium carboxymethylcellulose (CMC), lichenan and oat β-glucan as substrates. Degree of polymerization (DP) 3 was the major oligosaccharide from the hydrolysis of KGM, while DP3 and DP4 were predominant products from the hydrolysis of oat β-glucan. Molecular docking analyses revealed that the catalytic mechanism of EG003A is consistent with those of other reported GH5_1 β-glucanases. Additionally, the viscosity of 500 mL solution of 1 % KGM decreased rapidly from 31,193 mPa.s to 4.50 mPa.s in 3 min with 30 U EG003A. This study provides an efficient hyperthermophilic β-glucanase with promising application for KOS production.

Hydrolysis of ionic liquid-treated substrate with an Iocasia fonsfrigidae strain SP3-1 endoglucanase

Recently, we reported the discovery of a novel endoglucanase of the glycoside hydrolase family 12 (GH12), designated IfCelS12A, from the haloalkaliphilic anaerobic bacterium Iocasia fonsfrigidae strain SP3-1, which was isolated from a hypersaline pond in the Samut Sakhon province of Thailand (ca. 2017). IfCelS12A exhibits high substrate specificity on carboxymethyl cellulose and amorphous cellulose but low substrate specificity on b-1,3;1,4-glucan. Unlike some endoglucanases of the GH12 family, IfCelS12A does not exhibit hydrolytic activity on crystalline cellulose (i.e., Avicel™). High-Pressure Liquid Chromatography (HPLC) and Thin Layer Chromatography (TLC) analyses of products resulting from IfCelS12-mediated hydrolysis indicate mode of action for this enzyme. Notably, IfCelS12A preferentially hydrolyzes cellotetraoses, cellopentaoses, and cellohexaoses with negligible activity on cellobiose or cellotriose. Kinetic analysis with cellopentaose and barely b-D-glucan as cellulosic substrates were conducted. On cellopentaose, IfCelS12A demonstrates a 16-fold increase in activity (KM = 0.27 mM; kcat = 0.36 s-1; kcat/KM = 1.34 mM-1 s-1) compared to the enzymatic hydrolysis of barley b-D-glucan (KM: 0.04 mM, kcat: 0.51 s-1, kcat/KM = 0.08 mM-1 s-1). Moreover, IfCelS12A enzymatic efficacy is stable in hypersaline sodium chlorids (NaCl) solutions (up to 10% NaCl). Specifically, IfCel12A retains notable activity after 24 h at 2M NaCl (10% saline solution). IfCelS12A used as a cocktail component with other cellulolytic enzymes and in conjunction with mobile sequestration platform technology offers additional options for deconstruction of ionic liquid-pretreated cellulosic feedstock. KEY POINTS: • IfCelS12A from an anaerobic alkaliphile Iocasia fronsfrigidae shows salt tolerance • IfCelS12A in cocktails with other enzymes efficiently degrades cellulosic biomass • IfCelS12A used with mobile enzyme sequestration platforms enhances hydrolysis.

Gene cloning, IPTG-independent auto-induction and characterization of a novel hyperstable S9 prolyl oligopeptidase having lipolytic activity from Thermotoga naphthophila RKU-10T with applications

A hyperstable lipase from Thermotoga naphthophila (TnLip) was cloned and overexpressed as a soluble and active monomeric protein in an effectual mesophilic host system. Sequence study revealed that TnLip is a peptidase S9 prolyl oligopeptidase domain (acetyl esterase/lipase-like protein), belongs to alpha/beta (α/β)-hydrolase superfamily containing a well-conserved α/β-hydrolase fold and penta-peptide (GLSAG) motif. Various cultivation and induction strategies were applied to improve the heterologous expression and bacterial biomass, but TnLip intracellular activity was enhanced by 14.25- fold with IPTG-independent auto-induction approach after 16 h (26 °C, 150 rev min-1) incubation. Purified TnLip (35 kDa) showed peak activity at 85 °C in McIlvaine buffer (pH 7.0-8.0), and has great stability over a broad range of pH (5.0-10.0), and temperature (40-85 °C) for 8 h. TnLip exhibited prodigious resistance toward various commercial detergents, chemical additives, and salt. TnLip activity was improved by 170.51 %, 130.67 %, 127.42 %, 126.54 %, 126.61 %, 120.32 %, and 116.31 % with 50 % (v/v) of methanol, ethanol, n-butanol, isopropanol, acetone, glycerol, and acetic acid, respectively. Moreover, with 3.0 M of NaCl, and 10 mM of Ca2+, Mn2+, and Mg2+ TnLip activity was augmented by 210 %, 185.64 %, 152.03 %, and 116.26 %, respectively. TnLip has an affinity with various substrates (p-nitrophenyl ester and natural oils) but maximal hydrolytic activity was perceived with p-nitrophenyl palmitate (pNPP, 3600 U mg-1) and olive oil (1182.05 U mg-1). The values of Km (0.576 mM), Vmax (4216 μmol mg-1 min-1), VmaxKm-1 (7319.44 min-1), kcat (1106.74 s-1), and kcatKm-1 (1921.42 mM-1 s-1) were calculated using pNPP substrate. Additionally, TnLip degraded animals' fats and removed oil stains within 3 h and 5 min, respectively. All these features make halo-alkali-thermophilic TnLip as an auspicious contender for laundry detergents (cleaning bio-additive), fat degradation, wastewater treatment and endorse eco-friendly stewardship along with various other biotechnological applications.

Auto-induction, biochemical characterization and application of a novel thermo-alkaline and detergent-stable lipase (S9 peptidase domain) from Thermotoga petrophila as cleaning additive and degrading oil/fat wastes

A peptidase S9 prolyl oligopeptidase domain from Thermotoga petrophila RKU-1T (TpS9) was over-expressed as an active, soluble and hyperstable lipolytic enzyme in the mesophilic host system. The sequence analysis demonstrated, TpS9 is an esterase/lipase-like protein belongs to alpha/beta (α/β)-hydrolase superfamily with a well-conserved penta-peptide (GLSAG) motif and α/β-hydrolase fold. Various approaches (induction and cultivation) were employed to enrich TpS9 production, 6.04- and 7.26-fold increment was observed with IPTG (0.4 mM) and lactose (200 mM) in the modified 4ZB medium (pH 7.0), but with IPTG-independent auto-induction strategy 9.02-fold augmentation was achieved after 16 h incubation at 24 °C (150 rev min-1). Purified TpS9 showed optimal activity in McIlvaine buffer (pH 6.5) at 80-85 °C, and revealed great thermal (30-85 °C) and pH (6.0-9.0) for 8 h. No obvious constraint was perceived with various metal ions, surfactants, commercial laundry detergents, and chemical modulators. Whereas, TpS9 activity was improved with Ca2+, Mn2+, and Mg2+ by 210 %, 142.5 %, and 134.3 %, respectively. With 2.5 M NaCl (215 %), 50 % (v/v) methanol (140 %), 50 % (v/v) ethanol (126.6 %), 50 % (v/v) n-butanol (122.3 %), 50 % (v/v) isopropanol (120.4 %), 50 % (v/v) acetone (118.6 %) and 50 % (v/v) glycerol (113.2 %) TpS9 activity was also enriched. TpS9 demonstrated great affinity toward natural oils and p-nitrophenyl ester substrates, but showed peak activity with p-nitrophenyl palmitate (3160 U mg-1). Km, Vmax, kcat, Vmax Km-1 and kcat Km-1 of TpS9 with pNPP were 0.421 mM, 4015 µmol mg-1 min-1, 906.4 s-1, 9536.8 min-1, and 2152.96 mM-1 s-1, respectively. Moreover, TPS9 has notable ability to clean stains (5 min) and degrade the animals' fat (3 h). Hence, TpS9 is a favorable candidate as cleaning bio-additive in detergent formulation, fat degradation and various other applications.

Cloning, expression and purification of cellobiohydrolase gene from Caldicellulosiruptor bescii for efficient saccharification of plant biomass

Anthropogenic activities have led to a drastic shift from natural fuels to alternative renewable energy reserves that demand heat-stable cellulases. Cellobiohydrolase is an indispensable member of cellulases that play a critical role in the degradation of cellulosic biomass. This article details the process of cloning the cellobiohydrolase gene from the thermophilic bacterium Caldicellulosiruptor bescii and expressing it in Escherichia coli (BL21) CondonPlus DE3-(RIPL) using the pET-21a(+) expression vector. Multi-alignments and structural modeling studies reveal that recombinant CbCBH contained a conserved cellulose binding domain III. The enzyme's catalytic site included Asp-372 and Glu-620, which are either involved in substrate or metal binding. The purified CbCBH, with a molecular weight of 91.8 kDa, displayed peak activity against pNPC (167.93 U/mg) at 65°C and pH 6.0. Moreover, it demonstrated remarkable stability across a broad temperature range (60-80°C) for 8 h. Additionally, the Plackett-Burman experimental model was employed to assess the saccharification of pretreated sugarcane bagasse with CbCBH, aiming to evaluate the cultivation conditions. The optimized parameters, including a pH of 6.0, a temperature of 55°C, a 24-hour incubation period, a substrate concentration of 1.5% (w/v), and enzyme activity of 120 U, resulted in an observed saccharification efficiency of 28.45%. This discovery indicates that the recombinant CbCBH holds promising potential for biofuel sector.

Insights into the transcriptomic mechanism and characterization of endoglucanases from Aspergillus terreus in cellulose degradation

Filamentous fungi are the main industrial source of cellulases which are important in the process of converting cellulose to fermentable sugars. In this study, transcriptome analysis was conducted on Aspergillus terreus NEAU-7 cultivated using corn stover and glucose as carbon sources. Four putative endoglucanases (EG5A, EG7A, EG12A, and EG12C) from A. terreus NEAU-7 were efficiently expressed in Pichia pastoris. Among them, EG7A exhibited the highest enzyme activity (75.17 U/mg) with an optimal temperature of 40 °C and pH 5.0. EG5A and EG12A displayed specific activities of 19.92 U/mg and 14.62 U/mg, respectively, at 50 °C. EG12C showed acidophilic characteristics with an optimal pH of 3.0 and a specific activity of 12.21 U/mg at 40 °C. With CMC-Na as the substrate, the Km value of EG5A, EG7A, EG12A or, EG12C was, 11.08 ± 0.87 mg/mL, 6.82 ± 0.74 mg/mL, 7.26 ± 0.64 mg/mL, and 9.88 ± 0.86 mg/mL, with Vmax values of 1258.23 ± 51.62 μmol∙min-1∙mg-1, 842.65 ± 41.53 μmol∙min-1∙mg-1, 499.38 ± 20.42 μmol∙min-1∙mg-1, and 681.41 ± 30.08 μmol∙min-1∙mg-1, respectively. The co-treatment of EG7A with the commercial cellulase increased the yield of reducing sugar by 155.77 % (filter paper) and 130.49 % (corn stover). Molecular docking assay showed the interaction energy of EG7A with cellotetraose at -10.50 kcal/mol, surpassing EG12A (-10.43 kcal/mol), EG12C (-10.28 kcal/mol), and EG5A (-9.00 kcal/mol). Root Mean Square Deviation (RMSD) and Solvent Accessible Surface Area (SASA) values revealed that the presence of cellotetraose stabilized the molecular dynamics simulation of the cellotetraose-protein complex over a 100 ns time scale. This study provides valuable insights for developing recombinant enzymes and biomass degradation technologies.

Discovery of two bifunctional/multifunctional cellulases by functional metagenomics

Cellulases are widely used in industry, and the usage in bioconversion of biofuels makes cellulases more valuable. In this study, two tandem genes that encoded cellulases ZF994-1 and ZF994-2, respectively, were identified on a cosmid from a soil metagenomic library. Phylogenetic analysis indicated that ZF994-1 and ZF994-2 belonged to glycoside hydrolase family 12 (GH12), and GH3, respectively. Based on the substrate specificity analysis, the recombinant ZF994-1 exhibited weak endoglucanase activity, moderate β-1,3-glucanase and β-1,4-mannanase activities, and strong β-glucosidase activity, while the recombinant ZF994-2 exhibited moderate endoglucanase activity and strong β-glucosidase activity. More than 45% β-glucosidase activity of the recombinant ZF994-1 retained in the buffer containing 3 M glucose, indicating the good tolerance against glucose. The recombinant ZF994-2 showed high activity in the presence of metal ions and organic reagents, exhibiting potential industrial applications.

Recent progress in key lignocellulosic enzymes: Enzyme discovery, molecular modifications, production, and enzymatic biomass saccharification

Lignocellulose, the most prevalent biomass on earth, can be enzymatically converted into carbohydrates for bioethanol production and other uses. Among lignocellulosic enzymes, endoglucanase, xylanase, and laccase are the key enzymes, owing to their ability to disrupt the main structure of lignocellulose. Recently, new discovery methods have been established to obtain key lignocellulosic enzymes with excellent enzymatic properties. Molecular modification of enzymes to modulate their thermostability, catalytic activity, and substrate specificity has been performed with protein engineering technology. In addition, the enzyme expression has been effectively improved through expression element screening and host modification, as well as fermentation optimization. Immobilization of enzymes, use of surfactants, synergistic degradation, and optimization of reaction conditions have addressed the inefficiency of enzymatic saccharification. In this review, recent advances in key lignocellulosic enzymes are summarized, along with future prospects for the development of super-engineered strains and integrative technologies for enzymatic biomass saccharification.

Genus Thermotoga: A valuable home of multifunctional glycoside hydrolases (GHs) for industrial sustainability

Nature is a dexterous and prolific chemist for cataloging a number of hostile niches that are the ideal residence of various thermophiles. Apart from having other species, these subsurface environments are considered a throne of bacterial genus Thermotoga. The genome sequence of Thermotogales encodes complex and incongruent clusters of glycoside hydrolases (GHs), which are superior to their mesophilic counterparts and play a prominent role in various applications due to their extreme intrinsic stability. They have a tremendous capacity to use a wide variety of simple and multifaceted carbohydrates through GHs, formulate fermentative hydrogen and bioethanol at extraordinary yield, and catalyze high-temperature reactions for various biotechnological applications. Nevertheless, no stringent rules exist for the thermo-stabilization of biocatalysts present in the genus Thermotoga. These enzymes endure immense attraction in fundamental aspects of how these polypeptides attain and stabilize their distinctive three-dimensional (3D) structures to accomplish their physiological roles. Moreover, numerous genome sequences from Thermotoga species have revealed a significant fraction of genes most closely related to those of archaeal species, thus firming a staunch belief of lateral gene transfer mechanism. However, the question of its magnitude is still in its infancy. In addition to GHs, this genus is a paragon of encapsulins which carry pharmacological and industrial significance in the field of life sciences. This review highlights an intricate balance between the genomic organizations, factors inducing the thermostability, and pharmacological and industrial applications of GHs isolated from genus Thermotoga.

Thermostable Cellulases / Xylanases From Thermophilic and Hyperthermophilic Microorganisms: Current Perspective

The bioconversion of lignocellulose into monosaccharides is critical for ensuring the continual manufacturing of biofuels and value-added bioproducts. Enzymatic degradation, which has a high yield, low energy consumption, and enhanced selectivity, could be the most efficient and environmentally friendly technique for converting complex lignocellulose polymers to fermentable monosaccharides, and it is expected to make cellulases and xylanases the most demanded industrial enzymes. The widespread nature of thermophilic microorganisms allows them to proliferate on a variety of substrates and release substantial quantities of cellulases and xylanases, which makes them a great source of thermostable enzymes. The most significant breakthrough of lignocellulolytic enzymes lies in lignocellulose-deconstruction by enzymatic depolymerization of holocellulose into simple monosaccharides. However, commercially valuable thermostable cellulases and xylanases are challenging to produce in high enough quantities. Thus, the present review aims at giving an overview of the most recent thermostable cellulases and xylanases isolated from thermophilic and hyperthermophilic microbes. The emphasis is on recent advancements in manufacturing these enzymes in other mesophilic host and enhancement of catalytic activity as well as thermostability of thermophilic cellulases and xylanases, using genetic engineering as a promising and efficient technology for its economic production. Additionally, the biotechnological applications of thermostable cellulases and xylanases of thermophiles were also discussed.