Structure and biochemical characterization of glucose tolerant β-1,4 glucosidase (HtBgl) of family 1 glycoside hydrolase from Hungateiclostridium thermocellum

Expression of a thermostable glucose-stimulated β-glucosidase from a hot-spring metagenome and its promising application to produce gardenia blue

This study reports a thermostable glucose-stimulated β-glucosidase, BglY442, from hot-spring metagenomic data that was cloned and expressed in Escherichia coli BL21 (DE3). The molecular mass of recombinant BglY442 was 69.9 kDa and was used in the production of gardenia blue. The recombinant BglY442 showed its maximum activity at pH 6.0 and 75 °C, maintained 50 % activity at 70 °C for 36 h, presented over 90 % activity in a broad pH range and a wide range of pH stability. Moreover, BglY442 exhibited excellent tolerance toward methanol and ethanol. The specific activity of BglY442 was 235 U/mg at pH 6.0 and 75 °C with 10 mM pNPG as substrate. BglY442 activity increased by over fourfold with 2 M glucose or xylose. Specifically, the enzyme kinetics of BglY442 seem to be non-Michaelis-Menten kinetics or atypical kinetics because the Michaelis-Menten saturation kinetics were not observed with pNPG, oNPG or geniposide as substrates. Under optimum conditions, geniposide was dehydrated by BglY442 and reacted with nine amino acids respectively by the one-pot method. Only the Arg or Met derived pigments showed bright blue, and these two pigments had similar ultraviolet absorption spectra. The OD590 nm of GB was detected to be 1.06 after 24 h with the addition of Arg and 1.61 after 36 h with the addition of Met. The intermediate was elucidated and identified as ginipin. Molecular docking analysis indicated that the enzyme had a similar catalytic mechanism to the reported GH1 Bgls. BglY442 exhibited potential for gardenia blue production by the one-pot method. With outstanding thermostability and glucose tolerance, BglY442 should be considered a potential β-glucosidase in biotechnology applications.

Key roles of β-glucosidase BglA for the catabolism of both laminaribiose and cellobiose in the lignocellulolytic bacterium Clostridium thermocellum

The thermophilic bacterium Clostridium thermocellum efficiently degrades polysaccharides into oligosaccharides. The metabolism of β-1,4-linked cello-oligosaccharides is initiated by three enzymes, i.e., the cellodextrin phosphorylase (Cdp), the cellobiose phosphorylase (Cbp), and the β-glucosidase A (BglA), in C. thermocellum. In comparison, how the oligosaccharides containing other kinds of linkage are utilized is rarely understood. In this study, we found that BglA could hydrolyze the β-1,3-disaccharide laminaribiose with much higher activity than that against the β-1,4-disaccharide cellobiose. The structural basis of the substrate specificity was analyzed by crystal structure determination and molecular docking. Genetic deletions of BglA and Cbp, respectively, and enzymatic analysis of cell extracts demonstrated that BglA is the key enzyme responsible for laminaribiose metabolism. Furthermore, the deletion of BglA can suppress the expression of Cbp and the deletion of Cbp can up-regulate the expression of BglA, indicating that BglA and Cbp have cross-regulation and BglA is also critical for cellobiose metabolism. These insights pave the way for both a fundamental understanding of metabolism and regulation in C. thermocellum and emphasize the importance of the degradation and utilization of polysaccharides containing β-1,3-linked glycosidic bonds in lignocellulose biorefinery.

Structural and inflammatory characteristics of Maillard reaction products from litchi thaumatin-like protein and fructose

The structural characteristics and inflammatory activity of Maillard reaction products (MRPs) from fructose (Fru) and litchi thaumatin-like protein (LcTLP) with a pro-inflammatory activity were investigated. The structural changes of LcTLP-Fru MRPs were divided into two stages during the Maillard reaction. In 0-6 h, the unfolding and degradation of the LcTLP were dominant, resulting in a looser structure; the increase of β-sheets was 13.02%; the decrease of α-helices was 9.21%; and both the molecular weight and gyration radius R_g decreased. After 6 h, the enhanced glycosylation caused the molecular weight to increase, while R_g remained low, implying that the molecular structure became more compact. In addition, LcTLP-Fru MRPs reduced the inflammation response by significantly reducing the gene and protein expressions of tumor necrosis factor-α, interleukin-1β, and interleukin-6 compared with the LcTLP group in RAW264.7 macrophages. The findings provided a theoretical foundation for addressing the inflammatory response caused by litchi products consumption.

Alkaline pretreatment and response surface methodology based recombinant enzymatic saccharification and fermentation of sugarcane tops

In present study, the water-soluble extractives removal prior to alkali pretreatment of sugarcane tops (SCT) was carried out. The solid alkali pretreated SCT (apSCT) recovered on Field-emission scanning electron microscopy (FE-SEM) analysis showed exposure of cellulosic fibres as compared with raw SCT. The analyses of apSCT by Fourier Transform Infrared (FT-IR) Spectroscopy, X-ray diffraction (XRD) and High performance liquid chromatography (HPLC) analysis also confirmed the enhanced cellulose content in apSCT. Optimum conditions for response surface methodology based saccharification of apSCT at 40 °C, 150 rpm were 2.14% (w/v) apSCT loading in citrate-phosphate buffer (50 mM, pH 6.0), recombinant hydrolytic enzymes (from Clostridium/Hungateiclostridium thermocellum) loading for endo-1,4-β-glucanase (CtCel8A) = 213.2 U/g, cellobiohydrolase (CtCBH5A) = 272.5 U/g and β-glucosidase (HtBg1) = 299.8 U/g for 49.2 h. Under optimized saccharification conditions, the total reducing sugar yield was 265 mg/g (glucose 214 mg/g) of apSCT. Fermentation of produced glucose by S. cerevisiae gave 0.19 g/g glucose of bioethanol.

Structural and Catalytic Characterization of TsBGL, a β-Glucosidase From Thermofilum sp. ex4484_79

Beta-glucosidase is an enzyme that catalyzes the hydrolysis of the glycosidic bonds of cellobiose, resulting in the production of glucose, which is an important step for the effective utilization of cellulose. In the present study, a thermostable β-glucosidase was isolated and purified from the Thermoprotei Thermofilum sp. ex4484_79 and subjected to enzymatic and structural characterization. The purified β-glucosidase (TsBGL) exhibited maximum activity at 90°C and pH 5.0 and displayed maximum specific activity of 139.2μmol/min/mg_zne against p-nitrophenyl β-D-glucopyranoside (pNPGlc) and 24.3μmol/min/mg_zen against cellobiose. Furthermore, TsBGL exhibited a relatively high thermostability, retaining 84 and 47% of its activity after incubation at 85°C for 1.5h and 90°C for 1.5h, respectively. The crystal structure of TsBGL was resolved at a resolution of 2.14Å, which revealed a classical (α/β)₈-barrel catalytic domain. A structural comparison of TsBGL with other homologous proteins revealed that its catalytic sites included Glu210 and Glu414. We provide the molecular structure of TsBGL and the possibility of improving its characteristics for potential applications in industries.

VqBGH40a isolated from Chinese wild Vitis quinquangularis degrades trans-piceid and enhances trans-resveratrol

Resveratrol (3,5,4'-trihydroxy-stilbene) is a phytoalexin that can prevent plants from pathogen attacks. Piceid is the glycosylation product of resveratrol and the main storage form of stilbenes in grapevines. Here, we reported the function of a β-glycoside hydrolase gene, VqBGH40a, from the Chinese wild grapevine Vitis quinquangularis accession Danfeng-2 in the regulation of plant resistance to powdery mildew (Uncinula necator). VqBGH40a belonging to β-glycoside hydrolase family 1 encoded 506 amino acids and was located on the cytomembrane. Its optimal induction condition was 28 or 30℃, for 4 h, with 0.1 mM IPTG in a prokaryotic expression system. Enzyme activity detection showed that purified VqBGH40a could hydrolyze trans-piceid to form trans-resveratrol in vitro. VqBGH40a was transiently overexpressed in Danfeng-2 leaves and then artificially inoculated with powdery mildew showed that VqBGH40a protein could hydrolyze trans-piceid in vivo. Additionally, a comparative family analysis between VqBGH40a and 38 VviBGHs was performed. Overall, these results demonstrate that VqBGH40a can hydrolyze trans-piceid, enhance trans-resveratrol content, and participate in the defense mechanism of grapevine against powdery mildew.

Structure and dynamics analysis of multi-domain putative β-1,4-glucosidase of family 3 glycoside hydrolase (PsGH3) from Pseudopedobacter saltans

Structure and conformational behaviour of a putative β-1,4-glucosidase of glycoside hydrolase family 3 (PsGH3) from Pseudopedobacter saltans was predicted by using in-silico tools. PsGH3 modeled structure constructed using Phyre2 displayed multidomain architecture comprising an N-terminal (β/α)₈-fold domain followed by (α/β)₆-sandwich domain, PA14 domain, and a C-terminal domain resembling an immunoglobulin fold. Ramachandran plot displayed 99.3% of amino acids in the allowed region and 0.7% residues in the disallowed region. Multiple sequence alignment (MSA) and structure superposition of PsGH3 with other homologues from GH3 family revealed the conserved residues, Asp274 and Glu624 present in loops LA and LB, respectively originating from N-terminal domain act as catalytic residues. The volume and area calculated for PsGH3 displayed a deep active-site conformation comparable with its homologues, β-1,4-glucosidases (GH3) of Kluyveromyces marxianus and Streptomyces venezuelae. Molecular dynamic (MD) simulation of PsGH3 structure for 80 ns suggested stable and compact structure. Molecular docking studies revealed deeper active site conformation of PsGH3 that could house larger cellooligosaccharides up to 7° of polymerization (DP7). The amino acid residues, Ala86, Leu88, Cys275, Pro483, Phe493, Asn417, Asn491, Pro492, and Leu495 created a binding pocket near the catalytic cleft, crucial for ligand binding. MD simulation of PsGH3 in the presence of cellooligosaccharides, viz., cellobiose and celloheptaose showed stability in terms of RMSD, R_g, and SASA values till 80 ns. The calculation of average number of hydrogen bond (H-bond), interaction energy, and binding free energy confirmed the stronger binding affinity of the larger cellooligosaccharides such as celloheptaose in the binding cavity of PsGH3.

A novel β-glucosidase from a hot-spring metagenome shows elevated thermal stability and tolerance to glucose and ethanol

β-glucosidase causes hydrolysis of β-1,4-glycosidic bond in glycosides and oligosaccharides. It is an industrially important enzyme owing to its potential in biomass processing applications. In this study, computational screening of an extreme temperature aquatic habitat metagenomic resource was done, leading to the identification of a novel gene, bgl_M, encoding a β-glucosidase. The comparative protein sequence and homology structure analyses designated it as a GH1 family β-glucosidase. The bgl_M gene was expressed in a heterologous host, Escherichia coli. The purified protein, Bgl_M, was biochemically characterized for β-glucosidase activity. Bgl_M exhibited noteworthy hydrolytic potential towards cellobiose and lactose. Bgl_M, showed substantial catalytic activity in the pH range of 5.0-7.0 and at the temperature 40 °C-70 °C. The enzyme was found quite stable at 50 °C with a loss of hardly 20% after 40 h of heat exposure. Furthermore, any drastically negative effect was not observed on the enzyme's activity in the presence of metal ions, non-ionic surfactants, metal chelating, and denaturing agents. A significantly high glucose tolerance, retaining 80% relative activity at 1 M, and 40% at 5 M glucose, and ethanol tolerance, exhibiting 80% relative activity in 10% ethanol, enrolled Bgl_M as a promising enzyme for cellulose saccharification. Furthermore, its ability to catalyze the hydrolysis of daidzin and polydatin ascertained it as an admirably suited biocatalyst for enhancement of nutritional values in soya and wine industries.

Structural analysis of rice Os4BGlu18 monolignol β-glucosidase

Monolignol glucosides are storage forms of monolignols, which are polymerized to lignin to strengthen plant cell walls. The conversion of monolignol glucosides to monolignols is catalyzed by monolignol β-glucosidases. Rice Os4BGlu18 β-glucosidase catalyzes hydrolysis of the monolignol glucosides, coniferin, syringin, and p-coumaryl alcohol glucoside more efficiently than other natural substrates. To understand more clearly the basis for substrate specificity of a monolignol β-glucosidase, the structure of Os4BGlu18 was determined by X-ray crystallography. Crystals of Os4BGlu18 and its complex with δ-gluconolactone diffracted to 1.7 and 2.1 Å resolution, respectively. Two protein molecules were found in the asymmetric unit of the P212121 space group of their isomorphous crystals. The Os4BGlu18 structure exhibited the typical (β/α)8 TIM barrel of glycoside hydrolase family 1 (GH1), but the four variable loops and two disulfide bonds appeared significantly different from other known structures of GH1 β-glucosidases. Molecular docking studies of the Os4BGlu18 structure with monolignol substrate ligands placed the glycone in a similar position to the δ-gluconolactone in the complex structure and revealed the interactions between protein and ligands. Molecular docking, multiple sequence alignment, and homology modeling identified amino acid residues at the aglycone-binding site involved in substrate specificity for monolignol β-glucosides. Thus, the structural basis of substrate recognition and hydrolysis by monolignol β-glucosidases was elucidated.

Combined SAXS and computational approaches for structure determination and binding characteristics of Chimera (CtGH1-L1-CtGH5-F194A) generated by assembling β-glucosidase (CtGH1) and a mutant endoglucanase (CtGH5-F194A) from Clostridium thermocellum

Chimera (CtGH1-L1-CtGH5-F194A) developed by fusing β-glucosidase (CtGH1) at N-terminal and endoglucanase (CtGH5-F194A) at C-terminal was structurally characterized. Its secondary structure analysis by CD showed 38% α-helix, 9.3% β-sheets and 52.7% random coils corroborating with prediction. In-silico modeled structure of Chimera comprised two modules, CtGH1 and CtGH5-F194A displaying (α/β)8 fold. Ramachandran plot of Chimera showed 99.9% residues in allowed region. Binding interaction of Chimera with cello-oligosaccharides suggested active forms of CtGH1 and CtGH5-F194A and their involvement in catalysis. MD simulation of cellohexaose bound endoglucanase module of Chimera showed favourable flexibility in loops, LA with H-bond formation with Asn510 and in loop LC relocation of Tyr687 away from active site efficiently releasing the product after catalysis. Higher short range interaction energy of Chimera, -383 kJ/mol than the individual endoglucanase, 254 kJ/mol against cellohexaose suggested higher efficient catalysis by Chimera. β-Glucosidase module of Chimera showed fluctuations in outer loops suggesting conformational changes that might be contributing to improved hydrolysis. SAXS analysis of Chimera displayed monodispersed state. Guinier analysis of Chimera showed globular shape (Rg= 3.15 ± 0.10 nm). Kratky plot confirmed fully folded and flexible behaviour in solution. Gasbor modeled structure of Chimera displayed an elongated structure with two modules having shape similar to bean-bag contour.

Peptide-Mediated Immobilization on Magnetoferritin for Enzyme Recycling

Ferritin possess favorable properties because its exterior and interior surface can be applied to generate functional nanomaterials, which make them possible for enzyme immobilization and recycling. Here, we report the noncovalent immobilization of a genetically modified β-glucosidase onto the outer surface of synthetic magnetoferritin through the electrostatic interaction of a heterodimeric coiled-coil protein formed by coils containing lysine residues (K-coils) and coils containing glutamic acid (E-coils). The immobilized enzyme was characterized, and its enzymatic properties were evaluated. Furthermore, reusability of immobilized enzyme was demonstrated in aqueous solution under an applied magnetic field. The results showed that magnetoferritin was successfully prepared and it was an excellent support for enzyme immobilization. After three times usages, the retention rates were 93.75%, 82.5%, and 56.25%, respectively, demonstrating that immobilized enzyme possessed good retention efficiency and could be used as potential carrier for other biomolecules. The strategy of enzyme immobilization developed in this work can be applied, in general, to many other target molecules.