Molecular cloning and functional characterization of an endo-β-1,3-glucanase from Streptomyces matensis ATCC 23935

Structural and functional analysis of SpGlu64A: a novel glycoside hydrolase family 64 laminaripentaose-producing β-1,3-glucanase from Streptomyces pratensis

Laminaripentaose (L5)-producing β-1,3-glucanases can preferentially cleave the triple-helix curdlan into β-1,3-glucooligosaccharides, especially L5. In this study, a newly identified member of the glycoside hydrolase family 64, β-1,3-glucanase from Streptomyces pratensis (SpGlu64A), was functionally and structurally characterized. SpGlu64A shared highest identity (30%) with a β-1,3-glucanase from Streptomyces matensis. The purified SpGlu64A showed maximal activity at pH 7.5 and 50 °C, and exhibited strict substrate specificity toward curdlan (83.1 U·mg-1). It efficiently hydrolyzed curdlan to produce L5 as the end product. The overall structure of SpGlu64A consisted of a barrel domain and a mixed (α/β) domain, which formed an unusually wide groove with a crescent-like structure. In the two complex structures (SpGlu64A-L3 and SpGlu64A-L4), two oligosaccharide chains were captured and the triple-helical structure was relatively compatible with the wide groove, which suggested the possibility of binding to the triple-helical β-1,3-glucan. A catalytic framework (β6-β9-β10) and the steric hindrance formed by the side chains of residues Y161, N163, and H393 in the catalytic groove were predicted to complete the exotype-like cleavage manner. On the basis of the structure, a fusion protein with the CBM56 domain (SpGlu64A-CBM) and a mutant (Y161F; by site-directed mutation) were obtained, with 1.2- and 1.7-fold increases in specific activity, respectively. Moreover, the combined expression of SpGlu64A-CBM and -Y161F improved the enzyme activity by 2.63-fold. The study will not only be helpful in understanding the reaction mechanism of β-1,3-glucanases but will also provide a basis for further enzyme engineering.

Novel Anti-Fungal d-Laminaripentaose-Releasing Endo-β-1,3-glucanase with a RICIN-like Domain from Cellulosimicrobium funkei HY-13

Endo-β-1,3-glucanase plays an essential role in the deconstruction of β-1,3-d-glucan polysaccharides through hydrolysis. The gene (1650-bp) encoding a novel, bi-modular glycoside hydrolase family 64 (GH64) endo-β-1,3-glucanase (GluY) with a ricin-type β-trefoil lectin domain (RICIN)-like domain from Cellulosimicrobium funkei HY-13 was identified and biocatalytically characterized. The recombinant enzyme (rGluY: 57.5 kDa) displayed the highest degradation activity for laminarin at pH 4.5 and 40 °C, while the polysaccharide was maximally decomposed by its C-terminal truncated mutant enzyme (rGluYΔRICIN: 42.0 kDa) at pH 5.5 and 45 °C. The specific activity (26.0 U/mg) of rGluY for laminarin was 2.6-fold higher than that (9.8 U/mg) of rGluYΔRICIN for the same polysaccharide. Moreover, deleting the C-terminal RICIN domain in the intact enzyme caused a significant decrease (>60%) of its ability to degrade β-1,3-d-glucans such as pachyman and curdlan. Biocatalytic degradation of β-1,3-d-glucans by inverting rGluY yielded predominantly d-laminaripentaose. rGluY exhibited stronger growth inhibition against Candida albicans in a dose-dependent manner than rGluYΔRICIN. The degree of growth inhibition of C. albicans by rGluY (approximately 1.8 μM) was approximately 80% of the fungal growth. The superior anti-fungal activity of rGluY suggests that it can potentially be exploited as a supplementary agent in the food and pharmaceutical industries.

Characterization of the GH16 and GH17 laminarinases from Vibrio breoganii 1C10

Laminarin is an abundant glucose polymer used as an energy reserve by micro- and macroalgae. Bacteria digest and consume laminarin with laminarinases. Their genomes frequently contain multiple homologs; however, the biological role for this replication remains unclear. We investigated the four laminarinases of glycoside hydrolase families GH16 and GH17 from the marine bacterium Vibrio breoganii 1C10, which can use laminarin as its sole carbon source. All four laminarinases employ an endolytic mechanism and specifically cleave the β-1,3-glycosidic bond. Two primarily produce low-molecular weight laminarin oligomers (DP 3-4) whereas the others primarily produce high-molecular weight oligomers (DP > 8), which suggests that these enzymes sequentially degrade laminarin. The results from this work provide an overview of the laminarinases from a single marine bacterium and also provide insights regarding how multiple laminarinases are used to degrade laminarin.

Curdlan conformation change during its hydrolysis by multi-domain β-1,3-glucanases

Enzymatic curdlan hydrolysis is gaining more attention for the value of oligo-β-glucans in many aspects. Currently, the triple-helical conformation of curdlan fiber was imposed to the structure of β-1,3-glucanase as its substrate without experimental evidence. Here, solution conformation of differently treated curdlan and each hydrolysis rate by a variety of β-1,3-glucanases were systematically examined. Results showed that different enzymes exhibited preferences over the trajectories of pH change that curdlan solution went through, and all enzymes hydrolyzed heat treated curdlan solution at their maximum rates where most of the higher ordered helices were diminished. Combined with molecular docking studies, a multi-step hydrolysis process was proposed. Recognition of triple-helical curdlan by their ancillary region of β-1,3-glucanase occurred before its unwinding into single- and double-helical forms, and the later ones fitted better to the catalytic cavity of the enzyme where the polysaccharides chain eventually got hydrolyzed into oligo-β-glucans.

Expression and biochemical characterization of a multifunctional glycosidase from the thermophilic Bacillus licheniformis SR01

A gene (gkdA) (741 bp) encoding a putative protein of 247 amino acids was cloned from the Bacillus licheniformis SR01. The protein was expressed in Escherichia coli BL21 with a molecular mass estimated by SDS-PAGE of approximately 28.03 kDa and showed a calculating isoelectric point (pI) of 6.42. Structure analysis and function identification showed that the enzyme was a multifunctional glycosidase. Its specific activity was 0.013 U/μg. The recombinant glycosidase showed a maximum activity at 50°C and pH 7.0. It was very stable below 90°C and may have heat activation at higher temperatures. The relative residual activity was still more than 80% after 120 min at pH 5.0-10.0. The enzyme activity was inhibited by Cu²⁺, Fe²⁺, Ca²⁺, Mg²⁺, Co²⁺, Li⁺, SDS and EDTA, activated by Ca²⁺, and not affected by Mn²⁺ and K⁺. Under simulated stomach, and in vitro intestine, conditions, the enzyme retained 80%, and more than 100%, activity, respectively, after incubation for 90 min. The excellent properties of this enzyme, specifically its thermal stability and multifunctional abilities, give it potential application in the field of feed processing and other high-temperature processing industries.

Modulating the function of a β-1,3-glucanosyltransferase to that of an endo-β-1,3-glucanase by structure-based protein engineering

A glycoside hydrolase (GH) family 17 β-1,3-glucanosyltransferase (RmBgt17A) from Rhizomucor miehei CAU432 (CGMCC No. 4967) shared very low sequence homology (∼20 % identity) with that of other β-1,3-glucanases,despite their similar structural folds. Structural comparison and sequence alignment between RmBgt17A and GH family 17 β-1,3-glucanases suggested important roles for three residues (Tyr102, Trp157, and Glu158) located in the substrate-binding cleft of RmBgt17A in transglycosylation activity. A series of site-directed mutagenesis studies indicated that a single Glu-to-Ala mutation (E158A) modulates the function of RmBgt17A to that of a β-1,3-glucanase. Mutant E158A exhibited high hydrolytic activity (39.95 U/mg) toward reduced laminarin, 348.5-fold higher than the wild type. Optimal pH and temperature of the purified RmBgt17A-E158A were 4.5 and 55 °C, respectively. TLC analysis suggested that RmBgt17A-E158A is an endo-β-1,3-glucanase. Our study provides novel insight into protein engineering of the substrate-binding cleft of glycoside hydrolases to modulate the function of transglycosylation and hydrolysis.

A Novel Glycoside Hydrolase Family 5 β-1,3-1,6-Endoglucanase from Saccharophagus degradans 2-40T and Its Transglycosylase Activity

In this study, we characterized Gly5M, originating from a marine bacterium, as a novel β-1,3-1,6-endoglucanase in glycoside hydrolase family 5 (GH5) in the Carbohydrate-Active enZyme database. The gly5M gene encodes Gly5M, a newly characterized enzyme from GH5 subfamily 47 (GH5_47) in Saccharophagus degradans 2-40(T) The gly5M gene was cloned and overexpressed in Escherichia coli Through analysis of the enzymatic reaction products by thin-layer chromatography, high-performance liquid chromatography, and matrix-assisted laser desorption ionization-tandem time of flight mass spectrometry, Gly5M was identified as a novel β-1,3-endoglucanase (EC 3.2.1.39) and bacterial β-1,6-glucanase (EC 3.2.1.75) in GH5. The β-1,3-endoglucanase and β-1,6-endoglucanase activities were detected by using laminarin (a β-1,3-glucan with β-1,6-glycosidic linkages derived from brown macroalgae) and pustulan (a β-1,6-glucan derived from fungal cell walls) as the substrates, respectively. This enzyme also showed transglycosylase activity toward β-1,3-oligosaccharides when laminarioligosaccharides were used as the substrates. Since laminarin is the major form of glucan storage in brown macroalgae, Gly5M could be used to produce glucose and laminarioligosaccharides, using brown macroalgae, for industrial purposes.

IMPORTANCE

In this study, we have discovered a novel β-1,3-1,6-endoglucanase with a unique transglycosylase activity, namely, Gly5M, from a marine bacterium, Saccharophagus degradans 2-40(T) Gly5M was identified as the newly found β-1,3-endoglucanase and bacterial β-1,6-glucanase in GH5. Gly5M is capable of cleaving glycosidic linkages of both β-1,3-glucans and β-1,6-glucans. Gly5M also possesses a transglycosylase activity toward β-1,3-oligosacchrides. Due to the broad specificity of Gly5M, this enzyme can be used to produce glucose or high-value β-1,3- and/or β-1,6-oligosaccharides.

High-level production of β-1,3-1,4-glucanase by Rhizomucor miehei under solid-state fermentation and its potential application in the brewing industry

AIMS

To improve the β-1,3-1,4-glucanase production by Rhizomucor miehei under solid-state fermentation (SSF) for industrial application.

METHODS AND RESULTS

The fermentation conditions for β-1,3-1,4-glucanase production by R. miehei CAU432 under SSF were optimized using a 'one-factor-at-a-time' method. Under the optimized fermentation conditions, viz. oatmeal (0·45-0·9 mm) as sole carbon source, 5% (w/w) peptone as sole nitrogen source, initial moisture of 80% (w/w), initial culture pH of 5·0, incubation temperature of 50°C and incubation time of 6 days, the highest β-1,3-1,4-glucanase activity of 20,025 U g(-1) dry substrate was achieved, which represents the highest yield for β-1,3-1,4-glucanase production ever reported. The crude enzyme was extracted and purified to homogeneity with a purification fold of 4·6 and a recovery yield of 9·0%. The addition of the purified β-1,3-1,4-glucanase in mash obviously reduced its filtration time (24·6%) and viscosity (2·61%).

CONCLUSIONS

The optimal fermentation conditions for maximal β-1,3-1,4-glucanase production under SSF was obtained, and the enzyme was suitable for application in the malting process.

SIGNIFICANCE AND IMPACT OF THE STUDY

The high production yield and excellent capability of the enzyme may enable it great potential in industries, especially in brewing industry.