Cloning, expression, and characterization of β-glucosidase from Exiguobacterium sp. DAU5 and transglycosylation activity

A Novel Neutral and Mesophilic β-Glucosidase from Coral Microorganisms for Efficient Preparation of Gentiooligosaccharides

β-glucosidases can produce gentiooligosaccharides that are lucrative and promising for the prebiotic and alternative food industries. However, the commercial production of gentiooligosaccharides using β-glucosidase is challenging, as this process is limited by the need for high thermal energy and increasing demand for the enzyme. Here, a putative β-glucosidase gene, selected from the coral microbial metagenome, was expressed in Escherichia coli. Reverse hydrolysis of glucose by Blg163 at pH 7.0 and 40 °C achieved a gentiooligosaccharide yield of 43.02 ± 3.20 g·L⁻¹ at a conversion rate of 5.38 ± 0.40%. Transglycosylation of mixed substrates, glucose and cellobiose, by Blg163 consumed 21.6 U/0.5 g glucose/g cellobiose, achieving a gentiooligosaccharide yield of 70.34 ± 2.20 g·L⁻¹ at a conversion rate of 15.63%, which is close to the highest yield reported in previous findings. Blg163-mediated synthesis of gentiooligosaccharides is the mildest reaction and the lowest β-glucosidase consumption reported to date.

Directional bioconversion and optimization of stevioside into rubusoside by Lelliottia sp. LST-1

AIMS

The present study aimed to specifically transform stevioside (ST) into rubusoside (RS) through bioconversion with high efficiency, seeking to endow steviol glycosides (SGs) with subtle flavours for commercial acceptability.

METHODS AND RESULTS

An endophytic bacterium named Lelliottia LST-1 was screened and confirmed to specifically convert ST into RS, reaching a conversion rate of 75.4% after response surface optimization. Phylogenetic analysis combined with complete genome sequencing demonstrated that LST-1 was also presumed to be a new species. To further explore the principle and process of biological transformation, the potential beta-glucosidases GH3-1, GH3-2, GH3-3 and GH3-4 were expressed, purified and reacted with SGs. High-performance liquid chromatography revealed that all enzymes hydrolysed ST and generated RS, but substrate specificity analysis indicated that GH3-2 had the highest substrate specificity towards STs and the highest enzyme activity.

CONCLUSION

The potential β-glucosidase GH3-2 in Lelliottia sp. LST-1 was found to specifically and efficiently convert ST to RS.

SIGNIFICANCE AND IMPACT OF STUDY

The efficient biotransformation of ST into RS will be beneficial to its large-scale production and extensive application in the food and pharmaceutical industries.

Cloning, expression, biochemical characterization, and molecular docking studies of a novel glucose tolerant β-glucosidase from Saccharomonospora sp. NB11

Most of the presently known β-glucosidases are sensitive to end-product inhibition by glucose, restricting their potential use in many industrial applications. Identification of novel glucose tolerant β-glucosidase can prove a pivotal solution to eliminate end-product inhibition and enhance the overall lignocellulosic saccharification process. In this study, a novel gene encoding β-glucosidase BglNB11 of 1405bp was identified in the genome of Saccharomonospora sp. NB11 and was successfully cloned and heterologously expressed in E. coli BL21 (DE3).The presence of conserved amino acids; NEPW and TENG indicated that BglNB11 belonged to GH1 β-glucosidases. The recombinant enzyme was purified using a Ni-NTA column, with the molecular mass of 51 kDa, using SDS-PAGE analysis. BglNB11 showed optimum activity at 40 °C and pH 7 and did not require any tested co-factors for activation. The kinetic values, K_m, V_max, k_cat, and k_cat/K_m of purified enzyme were 0.4037 mM, 5735.8 μmol/min/mg, 5042.16 s^-1 and 12487.71 s^-1 mM^-1, respectively. The enzyme was not inhibited by glucose to a concentration of 4 M but was slightly stimulated in the presence of glucose. Molecular docking of BglNB11 with glucose suggested that the relative binding position of glucose in the active site channel might be responsible for modulating end product tolerance and stimulation. β-glucosidase from BglNB11 is an excellent enzyme with high catalytic efficiency and enhanced glucose tolerance compared to many known glucose tolerant β-glucosidases. These unique properties of BglNB11 make it a prime candidate to be utilized in many biotechnological applications.

Homology analysis of 35 β-glucosidases in Oenococcus oeni and biochemical characterization of a novel β-glucosidase BGL0224

β-Glucosidases play an important role in food industry. Oenococcus oeni are typical lactic acid bacteria that initiate malolactic fermentation of wines. 35 β-glucosidases from O. oeni were selected and their conserved domains and evolutionary relationships were further explored in this study. The homology analysis results indicated that 35 β-glucosidases were basically derived from GH1 and GH3 family. A novel β-glucosidase was successfully expressed and characterized. The recombinant protein, referred to as BGL0224, consisted of a total 480 amino acids with an apparent molecular weight of 55.15 kDa and was classified as GH1 family. It achieved the highest activity at pH 5.0 and 50 °C. The activity and stability were significantly increased when 12% ethanol was supplemented to the enzyme. Using p-NPG as substrate, the K_m, V_max and K_cat of BGL0224 were 0.34 mM, 382.81 U/mg and 351.88 s^-1, respectively. In all, BGL0224 has good application prospects in food industry.

Purification and characterization of a novel GH1 beta-glucosidase from Jeotgalibacillus malaysiensis

Beta-glucosidase (BGL) is an important industrial enzyme for food, waste and biofuel processing. Jeotgalibacillus is an understudied halophilic genus, and no beta-glucosidase from this genus has been reported. A novel beta-glucosidase gene (1344 bp) from J. malaysiensis DSM 28777^T was cloned and expressed in E. coli. The recombinant protein, referred to as BglD5, consists of a total 447 amino acids. BglD5 purified using a Ni-NTA column has an apparent molecular mass of 52 kDa. It achieved the highest activity at pH 7 and 65 °C. The activity and stability were increased when CaCl₂ was supplemented to the enzyme. The enzyme efficiently hydrolyzed salicin and (1 → 4)-beta-glycosidic linkages such as in cellobiose, cellotriose, cellotetraose, cellopentose, and cellohexanose. Similar to many BGLs, BglD5 was not active towards polysaccharides such as Avicel, carboxymethyl cellulose, Sigmacell cellulose 101, alpha-cellulose and xylan. When BglD5 blended with Cellic® Ctec2, the total sugars saccharified from oil palm empty fruit bunches (OPEFB) was enhanced by 4.5%. Based on sequence signatures and tree analyses, BglD5 belongs to the Glycoside Hydrolase family 1. This enzyme is a novel beta-glucosidase attributable to its relatively low sequence similarity with currently known beta-glucosidases, where the closest characterized enzyme is the DT-Bgl from Anoxybacillus sp. DT3-1.

Preparation of gentiooligosaccharides using Trichoderma viride β-glucosidase

The recombinant plasmid pPIC9K-bgl1 containing β-glucosidase bgl1 from Trichoderma viride was constructed by overlapping PCR and integrated into Pichia pastoris KM71. In order to assist the formation of disulfide bonds and thus improve protein folding efficiency, protein disulfide isomerase pdi was co-expressed in the P. pastoris KM71/pPIC9K-bgl1/pPICZ-A-pdi strain, and fermentation in flasks resulted in enzyme activity of 143 U/ml. The enzyme activity of β-glucosidase reached 1402 U/ml following optimisation of fermentation conditions in a 3.6 l bioreactor. With 80% glucose as substrate, gentiooligosaccharides were synthesised by β-glucosidase-based reverse hydrolysis. A yield of 130 g/l was achieved with a conversion rate of 16.25%. With 20% glucose and 40% cellobiose as substrates, gentiooligosaccharides were synthesised by transglycosylation with a yield of 116 g/l and a conversion rate of 19.4%.

Light induced expression of β-glucosidase in Escherichia coli with autolysis of cell

Background

β-Glucosidase has attracted substantial attention in the scientific community because of its pivotal role in cellulose degradation, glycoside transformation and many other industrial processes. However, the tedious and costly expression and purification procedures have severely thwarted the industrial applications of β-glucosidase. Thus development of new strategies to express β-glucosidases with cost-effective and simple procedure to meet the increasing demands on enzymes for biocatalysis is of paramount importance.

Results

Light activated cassette YF1/FixJ and the SRRz lysis system were successfully constructed to produce Bgl1A(A24S/F297Y), a mutant β-glucosidase tolerant to both glucose and ethanol. By optimizing the parameters for light induction, Bgl1A(A24S/F297Y) activity reached 33.22 ± 2.0 U/mL and 249.92 ± 12.25 U/mL in 250-mL flask and 3-L fermentation tank, respectively, comparable to the controls of 34.02 ± 1.96 U/mL and 322.21 ± 10.16 U/mL under similar culture conditions with IPTG induction. To further simplify the production of our target protein, the SRRz lysis gene cassette from bacteriophage Lambda was introduced to trigger cell autolysis. As high as 84.53 ± 6.79% and 77.21 ± 4.79% of the total β-glucosidase were released into the lysate after cell autolysis in 250 mL flasks and 3-L scale fermentation with lactose as inducer of SRRz. In order to reduce the cost of protein purification, a cellulose-binding module (CBM) from Clostridium thermocellum was fused into the C-terminal of Bgl1A(A24S/F297Y) and cellulose was used as an economic material to adsorb the fusion enzyme from the lysate. The yield of the fusion protein could reach 92.20 ± 2.27% after one-hour adsorption at 25 °C.

Conclusions

We have developed an efficient and inexpensive way to produce β-glucosidase for potential industrial applications by using the combination of light induction, cell autolysis, and CBM purification strategy.

Electronic supplementary material

The online version of this article (10.1186/s12896-017-0402-1) contains supplementary material, which is available to authorized users.

Screening, production, optimization and characterization of β-glucosidase using microbes from shellfish waste

An extracellular β-glucosidase was isolated from Proteus mirabilis VIT117 found to be growing on prawn shells. The enzyme production was found to be enhanced (14.58 U/ml) when the culture was maintained at pH 9 and provided with sorbitol as carbon source, yeast extract as nitrogen source and incubated at 37 °C for approximately 72 h. Statistical methods like Plackett–Burman and RSM were also applied here to study the effects of different combinations of growth parameters for the bacteria, where the most significant parameters were found to be inoculum size, pH, yeast extract, incubation time and sorbitol. The optimum concentrations of inoculum size, pH and yeast extract determined by RSM were 2 %, 9 and 2 %, respectively. Partial purification of the protein was done by ammonium sulfate precipitation, followed by dialysis, gel filtration chromatography and SDS-PAGE. The enzyme was found to have a molecular weight of approximately 50 kDa and was observed to be most active at 37 °C in pH 9, with a sharp decline in the enzyme activity when temperature or the pH was increased. Enzyme kinetics study was performed to understand the catalytic behavior of the enzyme and it was found that our β-glucosidase had 5.613 U/ml and 0.082 mM as V_max and K_m values, respectively.

Catalytic properties, functional attributes and industrial applications of β-glucosidases

β-Glucosidases are diverse group of enzymes with great functional importance to biological systems. These are grouped in multiple glycoside hydrolase families based on their catalytic and sequence characteristics. Most studies carried out on β-glucosidases are focused on their industrial applications rather than their endogenous function in the target organisms. β-Glucosidases performed many functions in bacteria as they are components of large complexes called cellulosomes and are responsible for the hydrolysis of short chain oligosaccharides and cellobiose. In plants, β-glucosidases are involved in processes like formation of required intermediates for cell wall lignification, degradation of endosperm’s cell wall during germination and in plant defense against biotic stresses. Mammalian β-glucosidases are thought to play roles in metabolism of glycolipids and dietary glucosides, and signaling functions. These enzymes have diverse biotechnological applications in food, surfactant, biofuel, and agricultural industries. The search for novel and improved β-glucosidase is still continued to fulfills demand of an industrially suitable enzyme. In this review, a comprehensive overview on detailed functional roles of β-glucosidases in different organisms, their industrial applications, and recent cloning and expression studies with biochemical characterization of such enzymes is presented for the better understanding and efficient use of diverse β-glucosidases.

Oligomerization as a strategy for cold adaptation: Structure and dynamics of the GH1 β-glucosidase from Exiguobacterium antarcticum B7

Psychrophilic enzymes evolved from a plethora of structural scaffolds via multiple molecular pathways. Elucidating their adaptive strategies is instrumental to understand how life can thrive in cold ecosystems and to tailor enzymes for biotechnological applications at low temperatures. In this work, we used X-ray crystallography, in solution studies and molecular dynamics simulations to reveal the structural basis for cold adaptation of the GH1 β-glucosidase from Exiguobacterium antarcticum B7. We discovered that the selective pressure of low temperatures favored mutations that redesigned the protein surface, reduced the number of salt bridges, exposed more hydrophobic regions to the solvent and gave rise to a tetrameric arrangement not found in mesophilic and thermophilic homologues. As a result, some solvent-exposed regions became more flexible in the cold-adapted tetramer, likely contributing to enhance enzymatic activity at cold environments. The tetramer stabilizes the native conformation of the enzyme, leading to a 10-fold higher activity compared to the disassembled monomers. According to phylogenetic analysis, diverse adaptive strategies to cold environments emerged in the GH1 family, being tetramerization an alternative, not a rule. These findings reveal a novel strategy for enzyme cold adaptation and provide a framework for the semi-rational engineering of β-glucosidases aiming at cold industrial processes.

Hydrolysis of isoflavone glycoside by immobilization of β-glucosidase on a chitosan-carbon in two-phase system

We explored a method to examine the hydrolysis of isoflavone glycoside by immobilizing β-glucosidase on chitosan-carbon beads in an aqueous-organic two-phase system. The chitosan-carbon beads were cross-linked with glutaraldehyde to immobilize β-glucosidase from Exiguobacterium sp. DAU5. The optimal pH and temperature were 9.0 and 55 °C, respectively. Under the optimized conditions, crude and purified enzymes immobilized onto chitosan-carbon beads gave yields of 16.7% and 60%, respectively. The specific activities of immobilized crude and purified enzymes were 4.3 U/g and 6 U/g, respectively. The immobilized enzyme retained more than 80% of its maximum activity at pH 7.0-11.0, while temperature was more influential (80% activity after 40 °C for 1.5 h, but only 40% activity after 55 °C for 0.5 h, respectively. The immobilized enzyme was able to hydrolyze isoflavone glycoside in an aqueous-organic two-phase system, and the hydrolyzed products were enriched in the organic phase, making it easy to recover the products, i.e., genistein and daidein from the reaction system. These results suggest that immobilized β-glucosidase may be applicable for the industrial-scale hydrolysis of isoflavone glycoside.

Molecular cloning and characterization of active truncated dextransucrase from Leuconostoc mesenteroides B-1299CB4

The open reading frame of dsrE563, a dextransucrase gene obtained from a constitutive mutant (CB4-BF563) of Leuconostoc mesenteroides B-1299, consists of 8,511 bp encoding 2,836 amino acid residues. DsrE563 contains two catalytic domains (CD1 and CD2). Two truncated derivative mutants DsrE563ΔCD2ΔGBD (DsrE563-1) and DsrE563ΔCD2ΔVR (DsrE563-2) of DsrE563 were constructed and expressed using the pRSETC vector in Escherichia coli. The derivatives DsrE563-1 (deletion of 1,620 amino acids from the C-terminus) and DsrE563-2 (deletion of 1,258 amino acids from the C-terminus and 349 amino acids from the N-terminus) were expressed as active enzymes. Both enzymes synthesized less-soluble dextran, mainly containing α-1,6 glucosidic linkage. The synthesized less-soluble dextran also had a branched α-1,3 linkage. DsrE563-2 showed 4.5-fold higher dextransucrase activity than that of DsrE563-1 and showed higher acceptor reaction efficiency than that of dextransucrase from L. mesenteroides 512 FMCM when various mono or disaccharides were used as acceptors. Thus, the glucan-binding domain was important for both enzyme expression and dextransucrase activity.