A novel protease-resistant α-galactosidase with high hydrolytic activity from Gibberella sp. F75: gene cloning, expression, and enzymatic characterization

Comparative genomics predict specific genes in potential mucorales identification

Mucoralean fungi could cause mucormycosis in humans, particularly in immunodeficient individuals and those with diabetes mellitus or trauma. With plenty of species and genera, their molecular identification and pathogenicity have a large deviation. Reported cases of mucormycosis showed frequent occurrence in Rhizopus species, Mucor species, and Lichtheimia species. We analyzed the whole genome sequences of 25 species of the top 10 Mucorales genera, along with another 22 important pathogenic non-Mucorales species, to dig the target genes for monitoring Mucorales species and identify potential genomic imprints of virulence in them. Mucorales-specific genes have been found in various orthogroups extracted by Python script, while genus-specific genes were annotated covering cellular structure, biochemistry metabolism, molecular processing, and signal transduction. Proteins related to the virulence of Mucorales species varied with distinct significance in copy numbers, in which Orthofinder was conducted. Based on our fresh retrospective analysis of mucormycosis, a comparative genomic analysis of pathogenic Mucorales was conducted in more frequent pathogens. Specific orthologs between Mucorales and non-Mucoralean pathogenic fungi were discussed in detail. Referring to the previously reported virulence proteins, we included more frequent pathogenic Mucorales and compared them in Mucorales species and non-Mucorales species. Besides, more samples are needed to further verify the potential target genes.

Heterologous Expression of a Thermostable α-Galactosidase from Parageobacillus thermoglucosidasius Isolated from the Lignocellulolytic Microbial Consortium TMC7

α-Galactosidase is a debranching enzyme widely used in the food, feed, paper, and pharmaceuticals industries and plays an important role in hemicellulose degradation. Here, T26, an aerobic bacterial strain with thermostable α-galactosidase activity, was isolated from laboratory-preserved lignocellulolytic microbial consortium TMC7, and identified as Parageobacillus thermoglucosidasius. The α-galactosidase, called T26GAL and derived from the T26 culture supernatant, exhibited a maximum enzyme activity of 0.4976 IU/ml when cultured at 60°C and 180 rpm for 2 days. Bioinformatics analysis revealed that the α-galactosidase T26GAL belongs to the GH36 family. Subsequently, the pET-26 vector was used for the heterologous expression of the T26 α-galactosidase gene in Escherichia coli BL21 (DE3). The optimum pH for α-galactosidase T26GAL was determined to be 8.0, while the optimum temperature was 60°C. In addition, T26GAL demonstrated a remarkable thermostability with more than 93% enzyme activity, even at a high temperature of 90°C. Furthermore, Ca2+ and Mg2+ promoted the activity of T26GAL while Zn2+ and Cu2+ inhibited it. The substrate specificity studies revealed that T26GAL efficiently degraded raffinose, stachyose, and guar gum, but not locust bean gum. This study thus facilitated the discovery of an effective heat-resistant α-galactosidase with potent industrial application. Meanwhile, as part of our research on lignocellulose degradation by a microbial consortium, the present work provides an important basis for encouraging further investigation into this enzyme complex.

Intra-Laboratory Validation of Alpha-Galactosidase Activity Measurement in Dietary Supplements

INTRODUCTION

Alpha-galactosidase (α-Gal) is an enzyme responsible for the hydrolyzation of glycolipids and glycoprotein commonly found in dietary sources. More than 20% of the general population suffers from abdominal pain or discomfort caused by intestinal gas and by indigested or partially digested food residuals. Therefore, α-Gal is used in dietary supplements to reduce intestinal gases and help complex food digestion. Marketed enzyme-containing dietary supplements must be produced in accordance with the Food and Drug Administration (FDA) regulations for Current Good Manufacturing Practice (cGMPs).

AIM

in this work we illustrated the process used to develop and validate a spectrophotometric enzymatic assay for α-Gal activity quantification in dietary supplements.

METHODS

The validation workflow included an initial statistical-phase optimization of materials, reagents, and conditions, and subsequently a comparative study with another fluorimetric assay. A final validation of method performance in terms of specificity, linearity, accuracy, intermediate-precision repeatability, and system precision was then executed.

RESULTS AND CONCLUSIONS

The proven method achieved good performance in the quantitative determination of α-Gal activity in commercial food supplements in accordance with the International Council for Harmonisation of Technical Requirements for Pharmaceuticals (ICH) guidelines and is suitable as a rapid in-house quality control test.

Engineering a Trypsin-Resistant Thermophilic α-Galactosidase to Enhance Pepsin Resistance, Acidic Tolerance, Catalytic Performance, and Potential in the Food and Feed Industry

α-Galactosidase has potential applications, and attempts to improve proteolytic resistance of enzymes have important values. We use a novel strategy for genetic manipulation of a pepsin-sensitive region specific for a pepsin-sensitive but trypsin-resistant high-temperature-active Gal27B from Neosartorya fischeri to screen mutants with enhanced pepsin resistance. All enzymes were produced in Pichia pastoris to identify the roles of loop 4 (Gal27B-A23) and its key residue at position 156 (Gly156Arg/Pro/His) in pepsin resistance. Gal27B-A23 and Gly156Arg/Pro/His elevated pepsin resistance, thermostability, stability at low pH, activity toward raffinose (5.3-6.9-fold) and stachyose (about 1.3-fold), and catalytic efficiencies (up to 4.9-fold). Replacing the pepsin cleavage site Glu155 with Gly improved pepsin resistance but had no effect on pepsin resistance when Arg/Pro/His was at position 156. Thus, pepsin resistance could appear to occur through steric hindrance between the residue at the altered site and neighboring pepsin active site. In the presence of pepsin or trypsin, all mutations increased the ability of Gal27B to hydrolyze galactosaccharides in soybean flour (up to 9.6- and 4.3-fold, respectively) and promoted apparent metabolizable energy and nutrient digestibility in soybean meal for broilers (1.3-1.8-fold). The high activity and tolerance to heat, low pH, and protease benefit food and feed industry in a cost-effective way.

Characterization of a protease-resistant α-galactosidase from Aspergillus oryzae YZ1 and its application in hydrolysis of raffinose family oligosaccharides from soymilk

The α-galactosidase gene (galC) was cloned from Aspergillus oryzae YZ1 and expressed in Pichia pastoris. The galC (2319 bp) containing two introns encoded a protein of 726 amino acids. The activity of the α-galactosidase (GalC) increased 1-fold after coding sequence optimization. Purified GalC exhibited a single protein band (100 kDa) in SDS-PAGE. The optimum pH and temperature of GalC were pH 4.66 and 50 °C, respectively. Like many GH36 family α-galactosidases, GalC displayed its activities towards raffinose and stachyose. The Km values for pNPG, raffinose and stachyose were 2.16, 4.63 and 8.54 mM, respectively. The GalC retained about 90% activity within the pH range 3.0-8.0. The activity of GalC was inhibited by Cu2+, while Ca2+ increased the enzyme activity. Different concentrations of glucose, mannose, galactose, xylose and sucrose slightly affected the activity of GalC. The GalC displayed strong resistance to trypsin, α-chymotrypsin, and proteinase K. Under simulated gastric conditions, GalC maintained most of its native activity after pepsin treatment for 3 h. The GalC could also effectively degrade raffinose and stachyose in soymilk. The GalC with high hydrolysis efficiency towards raffinose family oligosaccharides (RFOs) and strong resistance to proteases is considered to have great potential in food and feed industries.

A thermophilic fungal GH36 α-galactosidase from Lichtheimia ramosa and its synergistic hydrolysis of locust bean gum

A novel GH36 α-galactosidase gene (LrAgal36A) from Lichtheimia ramosa was synthesized and highly expressed in Pichia pastoris. The enzyme titer and protein yield for high-density fermentation in a 5 L fermentor were up to 953.6 U mL^-1 and 4.36 g L^-1. Purified recombinant LrAgal36A showed the maximum activity at pH 6.0 and 65 °C and was thermostable with a half-life of 70 min at 60 °C. LrAgal36A displayed the highest specific activity (353.17 ± 4.19 U mg^-1) toward p-nitrophenyl-α-d-galactopyranoside (pNPGal) followed by galacto-oligosaccharides and could act slightly on galactomannans. The K_m and catalytic efficiency (k_cat/K_m) of LrAgal36A for pNPGal were 0.33 mM and 1569.50 mM^-1 s^-1, respectively. LrAgal36A and GH5 β-mannanase from L. ramosa showed a significant synergistic effect on the degradation of locust bean gum (LBG), resulting in release more reducing sugars (1.56 folds) and galactose (7.6 folds) by simultaneous or sequential reactions. Due to its hydrolysis properties, LrAgal36A might have potential applications in the area of pulp biobleaching, feed and food processing.

Whole Conversion of Soybean Molasses into Isomaltulose and Ethanol by Combining Enzymatic Hydrolysis and Successive Selective Fermentations

Isomaltulose is mainly produced from sucrose by microbial fermentation, when the utilization of sucrose contributes a high production cost. To achieve a low-cost isomaltulose production, soy molasses was introduced as an alternative substrate. Firstly, α-galactosidase gene from Rhizomucor miehei was expressed in Yarrowia lipolytica, which then showed a galactosidase activity of 121.6 U/mL. Under the effects of the recombinant α-galactosidase, most of the raffinose-family oligosaccharides in soy molasses were hydrolyzed into sucrose. Then the soy molasses hydrolysate with high sucrose content (22.04%, w/w) was supplemented into the medium, with an isomaltulose production of 209.4 g/L, and the yield of 0.95 g/g. Finally, by virtue of the bioremoval process using Pichia stipitis, sugar byproducts in broth were transformed into ethanol at the end of fermentation, thus resulting in high isomaltulose purity (97.8%). The bioprocess employed in this study provides a novel strategy for low-cost and efficient isomaltulose production from soybean molasses.

Purification and characterization of a novel -glucosidase from Aspergillus flavus and its application in saccharification of soybean meal

Aspergillus flavus has been regarded as a potential candidate for its production of industrial enzymes, but the details of β-glucosidase from this strain is very limited. In herein, we first reported a novel β-glucosidase (AfBglA) with the molecular mass of 94.2 kDa from A. flavus. AfBglA was optimally active at pH 4.5 and 60 °C and is stable between pH 3.5 and 9.0 and at a temperature of up to 55 °C for 30 min remaining more than 90% of its initial activity. It showed an excellent tolerance to Trypsin, Pepsin, Compound Protease, and Flavourzyme and its activity was not inhibited by specific certain cations. AfBglA displayed broad substrate specificity, it acted on all tested pNP-glycosides and barley glucan, indicating this novel β-glucosidase exhibited a β-1, 3-1, 4-glucanase activity. Moreover, the AfBglA could effectively hydrolyze the soybean meal suspension into glucose and exhibit a strong tolerance to the inhibition of glucose at a concentration of 20.0 g/L during the saccharification. The maximum amount of the glucose obtained by AfBglA corresponded to 67.0 g/kg soybean meal. All of these properties mentioned above indicated that the AfBglA possibly attractive for food and feed industry and saccharification of cellulolytic materials.

In vitro fermentation of raffinose by the human gut bacteria

Raffinose has become a major focus of research interest and recent studies have shown that besides beneficial bifidobacteria and lactobacilli, Escherichia coli, Enterococcus faecium and Streptococcus pneumoniae can also utilize raffinose and raffinose might lead to flatulence in some hosts. Therefore, it is required to find out the raffinose-metabolizing bacteria in the gut and the bacteria responsible for the flatulence. The BLASTP search results showed that the homologous proteins of glycosidases related to raffinose utilization are widely distributed in 196 of the 528 gut bacterial strains. Fifty-nine bacterial strains belonging to nine species of five genera were isolated from human feces and were found to be capable of utilizing raffinose; of these species, Enterococcus avium and Streptococcus salivarius were reported for the first time. High-performance liquid chromatography (HPLC) analysis of the supernatants of the nine species revealed that the bacteria could utilize raffinose in different manners. Glucose and melibiose were detected in the supernatants of Enterococcus avium E5 and Streptococcus salivarius B5, respectively. However, no resulting saccharides of raffinose degradation were detected in the supernatants of other seven strains, indicating that they had different raffinose utilization types from Enterococcus avium E5 and Streptococcus salivarius B5. Gas was produced with raffinose utilization by Escherichia coli, Enterococcus faecium, Streptococcus macedonicus, Streptococcus pasteurianus and Enterococcus avium. Thus, more attention should be paid to the raffinose-utilizing bacteria besides bifidobacteria and further studies are required to reveal the mechanisms of raffinose utilization to clarify the relationship between raffinose and gut bacteria.

Purification and characterization of a novel protease-resistant GH27 α-galactosidase from Hericium erinaceus

A novel 57-kDa acidic α-galactosidase designated as HEG has been purified from the dry fruiting bodies of Hericium erinaceus. The isolation protocol involved ion-exchange chromatography and gel filtration on a Superdex75 column. The purification fold and specific activity were 1251 and 46 units/mg, respectively. A BLAST search of internal peptide sequences obtained by liquid chromatography-tandem mass spectrometry (LC-MS/MS) analysis suggested that the enzyme belonged to the GH27 family. The activity of the enzyme reached its maximum at a pH of 6.0 or at 60 °C. The enzyme was stable within an acidic pH range of 2.2-7.0 and in a narrow temperature range. The enzyme was strongly inhibited by Zn²⁺, Fe³⁺, Ag⁺ ions and SDS. The Lineweaver-Burk plot suggested that the mode of inhibition by galactose and melibiose were of a mixed type. N-bromosuccinimide drastically decreased the activity of the enzyme, whereas diethylpyrocarbonate and carbodiimide strengthened the activity slightly. Moreover, the isolated enzyme displayed remarkable resistance to acid proteases, neutral proteases and pepsin. The enzyme could also hydrolyse oligosaccharides and polysaccharides. In addition, acidic protease promoted the hydrolysis of RFOs by HEG. The K_m values of the enzyme towards pNPGal, raffinose and stachyose were 0.36 mM, 40.07 mM and 54.71 mM, respectively. These favourable properties increase the potential of the enzyme in the food industry and animal feed applications.

A novel α-galactosidase from the thermophilic probiotic Bacillus coagulans with remarkable protease-resistance and high hydrolytic activity

A novel α-galactosidase of glycoside hydrolase family 36 was cloned from Bacillus coagulans, overexpressed in Escherichia coli, and characterized. The purified enzyme Aga-BC7050 was 85 kDa according to SDS-PAGE and 168 kDa according to gel filtration, indicating that its native structure is a dimer. With p-nitrophenyl-α-d- galactopyranoside (pNPGal) as the substrate, optimal temperature and pH were 55 °C and 6.0, respectively. At 60 °C for 30 min, it retained > 50% of its activity. It was stable at pH 5.0–10.0, and showed remarkable resistance to proteinase K, subtilisin A, α-chymotrypsin, and trypsin. Its activity was not inhibited by glucose, sucrose, xylose, or fructose, but was slightly inhibited at galactose concentrations up to 100 mM. Aga-BC7050 was highly active toward pNPGal, melibiose, raffinose, and stachyose. It completely hydrolyzed melibiose, raffinose, and stachyose in < 30 min. These characteristics suggest that Aga-BC7050 could be used in feed and food industries and sugar processing.

Characterization of a long-chain α-galactosidase from Papiliotrema flavescens

α-Galactosidases are assigned to the class of hydrolases and the subclass of glycoside hydrolases (GHs). They belong to six GH families and include the only characterized α-galactosidases from yeasts (GH 27, Saccharomyces cerevisiae). The present study focuses on an investigation of the lactose-inducible α-galactosidase produced by Papiliotrema flavescens. The enzyme was present on the surface of cells and in the cytosol. Its temperature optimum was about 60 °C and the pH optimum was 4.8; the pH stability ranged from 3.2 to 6.6. This α-galactosidase also exhibited transglycosylation activity. The cytosol α-galactosidase with a molecular weight about 110 kDa, was purified using a combination of liquid chromatography techniques. Three intramolecular peptides were determined by the partial structural analysis of the sequences of the protein isolated, using MALDI-TOF/TOF mass spectrometry. The data obtained recognized the first yeast α-galactosidase, which belongs to the GH 36 family. The bioinformatics analysis and homology modeling of a 210 amino acids long C-terminal sequence (derived from cDNA) confirmed the correctness of these findings. The study was also supplemented by the screening of capsular cryptococcal yeasts, which produce the surface lactose-inducible α- and β-galactosidases. The production of the lactose-inducible α-galactosidases was not found to be a general feature within the yeast strains examined and, therefore, the existing hypothesis on the general function of this enzyme in cryptococcal capsule rearrangement cannot be confirmed.

Production of a Highly Protease-Resistant Fungal α-Galactosidase in Transgenic Maize Seeds for Simplified Feed Processing

Raffinose-family oligosaccharide (RFO) in soybeans is one of the major anti-nutritional factors for poultry and livestocks. α-Galactosidase is commonly supplemented into the animal feed to hydrolyze α-1,6-galactosidic bonds on the RFOs. To simplify the feed processing, a protease-resistant α-galactosidase encoding gene from Gibberella sp. strain F75, aga-F75, was modified by codon optimization and heterologously expressed in the embryos of transgentic maize driven by the embryo-specific promoter ZM-leg1A. The progenies were produced by backcrossing with the commercial inbred variety Zheng58. PCR, southern blot and western blot analysis confirmed the stable integration and tissue specific expression of the modified gene, aga-F75m, in seeds over four generations. The expression level of Aga-F75M reached up to 10,000 units per kilogram of maize seeds. In comparison with its counterpart produced in Pichia pastoris strain GS115, maize seed-derived Aga-F75M showed a lower temperature optimum (50 °C) and lower stability over alkaline pH range, but better thermal stability at 60 °C to 70 °C and resistance to feed pelleting inactivation (80 °C). This is the first report of producing α-galactosidase in transgenic plant. The study offers an effective and economic approach for direct utilization of α-galactosidase-producing maize without any purification or supplementation procedures in the feed processing.

Characterization of Sphingomonas sp. JB13 exo-inulinase: a novel detergent-, salt-, and protease-tolerant exo-inulinase

A glycoside hydrolase family 32 exo-inulinase gene was cloned from Sphingomonas sp. JB13 and expressed in Escherichia coli BL21 (DE3). The purified recombinant enzyme (rInuAJB13) showed an apparently optimal activity at pH 5.5 and 55 °C and remained activity at 10-70 °C. The addition of most metal ions and chemical reagents showed little or no effect (retaining more than 76.5 % activity) on the enzyme activity, notably the addition of surfactants SDS, CTAB, Tween 80, and Triton X-100. Most local liquid detergents, including Balin, Walch, Ariel, Tide, Tupperware, and Bluemoon, also showed little or no effect (retaining more than 77.8 % activity) on the enzyme activity. rInuAJB13 exhibited 135.3-163.6 % activity at the NaCl concentration of 1.0-4.5 M. After incubation with up to 57.0 mg mL(-1) trypsin and 90.0 mg mL(-1) proteinase K at 37 °C for 60 min (pH 7.2), rInuAJB13 retained more than 80 % of its initial activity. The enzyme presents a high proportion (28.0 %) of amino acid residues G, A, and V. This paper is the first to report a detergent-, salt-, and protease-tolerant exo-inulinase.

Enzymatic hydrolysis preparation of mono-O-lauroylsucrose via a mono-O-lauroylraffinose intermediate

1'-O-Lauroylsucrose and 6'-O-lauroylsucrose were formed through hydrolysis of the C-6″ galactose group of 1'-O-lauroylraffinose and 6'-O-lauroylraffinose, respectively, in the presence of α-galactosidase. The enzymatic hydrolysis of 1'-O-lauroylraffinose and 6'-O-lauroylraffinose is discussed in detail. Acetic acid-sodium acetate was chosen as the buffer solution of the enzymatic hydrolysis reaction. The optimum conditions for the enzymatic hydrolysis reaction were as follows: buffer solution, pH 3.8; enzymatic time, 48 h; and enzymatic temperature, 37 °C. Under the optimal process conditions, the efficiency of α-galactosidase was ca. 82.6%. The isomers were fully compared in solubility, hydrophile-lipophile balance (HLB) values, critical micelle concentration (CMC), and thermal stability. The results showed that all lauroylsucrose isomers have similar solubilities in polar solvent, HLB values, CMC values, and thermal stabilities.

Characterization of a protease-resistant α-galactosidase from the thermophilic fungus Rhizomucor miehei and its application in removal of raffinose family oligosaccharides

The α-galactosidase gene, RmGal36, from Rhizomucor miehei was cloned and expressed in Escherichia coli. The gene has an open reading frame of 2256bp encoding 751 amino acid residues. RmGal36 was optimally active at pH 4.5 and 60°C, but is stable between pH 4.5 and 10.0 and at a temperature of up to 55°C for 30min retaining more than 80% of its relative activity. It displayed remarkable resistance to proteases and its activity was not inhibited by galactose concentrations of 100mM. The relative specificity of RmGal36 towards various substrates is in the order of p-nitrophenyl α-galactopyranoside>melibiose>stachyose>raffinose, with a K(m) of 0.36, 16.9, 27.6, and 47.9mM, respectively. The enzyme completely hydrolyzed raffinose and stachyose present in soybeans and kidney beans at 50°C within 60min. These features make RmGal36 useful in the food and feed industries and in processing of beet-sugar.

Crystal structure of α-galactosidase from Lactobacillus acidophilus NCFM: insight into tetramer formation and substrate binding

Lactobacillus acidophilus NCFM is a probiotic bacterium known for its beneficial effects on human health. The importance of α-galactosidases (α-Gals) for growth of probiotic organisms on oligosaccharides of the raffinose family present in many foods is increasingly recognized. Here, the crystal structure of α-Gal from L. acidophilus NCFM (LaMel36A) of glycoside hydrolase (GH) family 36 (GH36) is determined by single-wavelength anomalous dispersion. In addition, a 1.58-Å-resolution crystallographic complex with α-d-galactose at substrate binding subsite -1 was determined. LaMel36A has a large N-terminal twisted β-sandwich domain, connected by a long α-helix to the catalytic (β/α)(8)-barrel domain, and a C-terminal β-sheet domain. Four identical monomers form a tightly packed tetramer where three monomers contribute to the structural integrity of the active site in each monomer. Structural comparison of LaMel36A with the monomeric Thermotoga maritima α-Gal (TmGal36A) reveals that O2 of α-d-galactose in LaMel36A interacts with a backbone nitrogen in a glycine-rich loop of the catalytic domain, whereas the corresponding atom in TmGal36A is from a tryptophan side chain belonging to the N-terminal domain. Thus, two distinctly different structural motifs participate in substrate recognition. The tetrameric LaMel36A furthermore has a much deeper active site than the monomeric TmGal36A, which possibly modulates substrate specificity. Sequence analysis of GH36, inspired by the observed structural differences, results in four distinct subgroups having clearly different active-site sequence motifs. This novel subdivision incorporates functional and architectural features and may aid further biochemical and structural analyses within GH36.

An acidophilic and acid-stable beta-mannanase from phialophora sp. p13 with high mannan hydrolysis activity under simulated gastric conditions

A beta-mannanase gene, man5AP13, was cloned from Phialophora sp. P13 and expressed in Pichia pastoris. The deduced amino acid sequence of the mature enzyme, MAN5AP13, had highest identity (53%) with the glycoside hydrolase family 5 beta-mannanase from Bispora sp. MEY-1. The purified recombinant beta-mannanase was acidophilic and acid stable, exhibiting maximal activity at pH 1.5 and retaining >60% of the initial activity over the pH range 1.5-7.0. The optimum temperature was 60 degrees C. The specific activity, K(m) and V(max) for locust bean gum substrate were 851 U/mg, 2.5 mg/mL, and 1667.7 U/min.mg, respectively. The enzyme had excellent activity and stability under simulated gastric conditions, and the released reducing sugar of locust bean gum was significantly enhanced by one-fold in simulated gastric fluid containing pepsin in contrast to that without pepsin. All these properties make MAN5AP13 a potential additive for use in the food and feed industries.