alpha-Glucosidase from a strain of deep-sea Geobacillus: a potential enzyme for the biosynthesis of complex carbohydrates

Structural and functional analyses of Pcal_0917, an α-glucosidase from hyperthermophilic archaeon Pyrobaculum calidifontis

Genome analysis of Pyrobaculum calidifontis revealed the presence of α-glucosidase (Pcal_0917) gene. Structural analysis affirmed the presence of signature sequences of Type II α-glucosidases in Pcal_0917. We have heterologously expressed the gene and produced recombinant Pcal_0917 in Escherichia coli. Biochemical characteristics of the recombinant enzyme resembled to that of Type I α-glucosidases, instead of Type II. Recombinant Pcal_0917 existed in a tetrameric form in solution and displayed highest activity at 95 °C and pH 6.0, independent of any metal ions. A short heat-treatment at 90 °C resulted in a 35 % increase in enzyme activity. A slight structural shift was observed by CD spectrometry at this temperature. Half-life of the enzyme was >7 h at 90 °C. Pcal_0917 exhibited apparent V_max values of 1190 ± 5 and 3.9 ± 0.1 U/mg against p-nitrophenyl α-D-glucopyranoside and maltose, respectively. To the best of our knowledge, Pcal_0917 displayed the highest ever reported p-nitrophenyl α-D-glucopyranosidase activity among the characterized counterparts. Moreover, Pcal_0917 displayed transglycosylation activity in addition to α-glucosidase activity. Furthermore, in combination with α-amylase, Pcal_0917 was capable of producing glucose syrup from starch with >40 % glucose content. These properties make Pcal_0917 a potential candidate for starch hydrolyzing industry.

Alteration of Substrate Specificity and Transglucosylation Activity of GH13_31 α-Glucosidase from Bacillus sp. AHU2216 through Site-Directed Mutagenesis of Asn258 on β→α Loop 5

α-Glucosidase catalyzes the hydrolysis of α-d-glucosides and transglucosylation. Bacillus sp. AHU2216 α-glucosidase (BspAG13_31A), belonging to the glycoside hydrolase family 13 subfamily 31, specifically cleaves α-(1→4)-glucosidic linkages and shows high disaccharide specificity. We showed previously that the maltose moiety of maltotriose (G3) and maltotetraose (G4), covering subsites +1 and +2 of BspAG13_31A, adopts a less stable conformation than the global minimum energy conformation. This unstable d-glucosyl conformation likely arises from steric hindrance by Asn258 on β→α loop 5 of the catalytic (β/α)8-barrel. In this study, Asn258 mutants of BspAG13_31A were enzymatically and structurally analyzed. N258G/P mutations significantly enhanced trisaccharide specificity. The N258P mutation also enhanced the activity toward sucrose and produced erlose from sucrose through transglucosylation. N258G showed a higher specificity to transglucosylation with p-nitrophenyl α-d-glucopyranoside and maltose than the wild type. E256Q/N258G and E258Q/N258P structures in complex with G3 revealed that the maltose moiety of G3 bound at subsites +1 and +2 adopted a relaxed conformation, whereas a less stable conformation was taken in E256Q. This structural difference suggests that stabilizing the G3 conformation enhances trisaccharide specificity. The E256Q/N258G-G3 complex formed an additional hydrogen bond between Met229 and the d-glucose residue of G3 in subsite +2, and this interaction may enhance transglucosylation.

Heterologous Expression of Thermotolerant α-Glucosidase in Bacillus subtilis 168 and Improving Its Thermal Stability by Constructing Cyclized Proteins

α-glucosidase is an essential enzyme for the production of isomaltooligosaccharides (IMOs). Allowing α-glucosidase to operate at higher temperatures (above 60 °C) has many advantages, including reducing the viscosity of the reaction solution, enhancing the catalytic reaction rate, and achieving continuous production of IMOs. In the present study, the thermal stability of α-glucosidase was significantly improved by constructing cyclized proteins. We screened a thermotolerant α-glucosidase (AGL) with high transglycosylation activity from Thermoanaerobacter ethanolicus JW200 and heterologously expressed it in Bacillus subtilis 168. After forming the cyclized α-glucosidase by different isopeptide bonds (SpyTag/SpyCatcher, SnoopTag/SnoopCatcher, SdyTag/SdyCatcher, RIAD/RIDD), we determined the enzymatic properties of cyclized AGL. The optimal temperature of all cyclized AGL was increased by 5 °C, and their thermal stability was generally improved, with SpyTag-AGL-SpyCatcher having a 1.74-fold increase compared to the wild-type. The results of molecular dynamics simulations showed that the RMSF values of cyclized AGL decreased, indicating that the rigidity of the cyclized protein increased. This study provides an efficient method for improving the thermal stability of α-glucosidase.

Current status and applications of genus Geobacillus in the production of industrially important products-a review

The genus Geobacillus is one of the most important genera which mainly comprises gram-positive thermophilic bacterial strains including obligate aerobes, denitrifiers and facultative anaerobes having capability of endospore formation as well. The genus Geobacillus is widely distributed in nature and mostly abundant in extreme locations such as cool soils, hot springs, hydrothermal vents, marine trenches, hay composts and dairy plants. Due to plasticity towards environmental adaptation, the Geobacillus sp. shows remarkable genome diversification and acquired many beneficial properties, which facilitates their exploitation for many biotechnological applications. Many thermophiles are of biotechnological importance and having considerable interest in commercial applications for the production of industrially important products. Recently, due to catabolic versatility especially in the degradation of hemicellulose and starch containing agricultural waste and rapid growth rates, these microorganisms show potential for the production of biofuels, thermostable enzymes and bioremediation. This review mainly summarizes the status of Geobacillus sp. including its notable properties, biotechnological studies and its potential application in the production of industrially important products.

Crystal structure of α-glucosyl transfer enzyme XgtA from Xanthomonas campestris WU-9701

The α-glucosyl transfer enzyme XgtA is a novel type α-Glucosidase (EC 3.2.1.20) produced by Xanthomonas campestris WU-9701. One of the unique properties of XgtA is that it shows extremely high α-glucosylation activity toward alcoholic and phenolic -OH groups in compounds using maltose as an α-glucosyl donor and allows for the synthesis of various useful α-glucosides with high yields. XgtA shows no hydrolytic activity toward sucrose and no α-glucosylation activity toward saccharides to produce oligosaccharides. In this report, the crystal structure of XgtA was solved at 1.72 Å resolution. The crystal belonged to space group P22₁2₁, with unit-cell parameters a = 73.07, b = 83.48, and c = 180.79 Å. The β→α loop 4 of XgtA, which is proximal to the catalytic center, formed a unique structure that is not observed in XgtA homologs. Furthermore, XgtA was found to contain unique amino acid residues around its catalytic center. The unique structure of XgtA provides an insight into the mechanism for the regulation of substrate specificity in this enzyme.

Engineering a Highly Active Sucrose Isomerase for Enhanced Product Specificity by Using a "Battleship" Strategy

The sucrose isomerase SmuA from Serratia plymuthica efficiently catalyses the isomerisation of sucrose into isomaltulose, an artificial sweetener used in the food industry. However, the formation of a hygroscopic by‐product, trehalulose, necessitates additional separation to obtain a crystalline product. Therefore, we have improved the product specificity of SmuA by first introducing a few exploratory amino acid exchanges around the active site and investigating their influence. Then, we devised a second set of mutations, either at promising positions from the preceding cycle, but with a different side chain, or at alternative positions in the vicinity. After seven iterative cycles involving just 55 point mutations, we obtained the triple mutant Y219L/D398G/V465E which showed 2.3 times less trehalulose production but still had high catalytic efficiency (k_cat/K_M=11.8 mM⁻¹ s⁻¹). Not only does this mutant SmuA appear attractive as an industrial biocatalyst, but our semirational protein‐engineering strategy, which resembles the battleship board game, should be of interest for other challenging enzyme optimization endeavours.

Heterologous Expression of a Thermostable α-Glucosidase from Geobacillus sp. Strain HTA-462 by Escherichia coli and Its Potential Application for Isomaltose⁻Oligosaccharide Synthesis

Isomaltose-oligosaccharides (IMOs), as food ingredients with prebiotic functionality, can be prepared via enzymatic synthesis using α-glucosidase. In the present study, the α-glucosidase (GSJ) from Geobacillus sp. strain HTA-462 was cloned and expressed in Escherichia coli BL21 (DE3). Recombinant GSJ was purified and biochemically characterized. The optimum temperature condition of the recombinant enzyme was 65 °C, and the half-life was 84 h at 60 °C, whereas the enzyme was active over the range of pH 6.0-10.0 with maximal activity at pH 7.0. The α-glucosidase activity in shake flasks reached 107.9 U/mL and using 4-Nitrophenyl β-D-glucopyranoside (pNPG) as substrate, the K_m and Vmax values were 2.321 mM and 306.3 U/mg, respectively. The divalent ions Mn²⁺ and Ca²⁺ could improve GSJ activity by 32.1% and 13.8%. Moreover, the hydrolysis ability of recombinant α-glucosidase was almost the same as that of the commercial α-glucosidase (Bacillus stearothermophilus). In terms of the transglycosylation reaction, with 30% maltose syrup under the condition of 60 °C and pH 7.0, IMOs were synthesized with a conversion rate of 37%. These studies lay the basis for the industrial application of recombinant α-glucosidase.

Starch biotransformation into isomaltooligosaccharides using thermostable alpha-glucosidase from Geobacillus stearothermophilus

The present study first identified the biotransformation of starch as a novel preparation method was investigated using the alpha-transglucosidase-producing Geobacillus stearothermophilus U2. Subsequently, 5 L- and 20 L-scale fermentations were performed. After isolation and purification, liquid alpha-glucosidase preparations were obtained. Through covalent cross-linking and adsorption cross-linking using chitosan as the carrier and glutaraldehyde as the crosslinking agent, the conditions for immobilization of alpha-glucosidase on chitosan were determined. Moreover, Isomaltooligosaccharides (IMOs) were then prepared using chitosan membrane-immobilized alpha-glucosidase, beta-amylase, pullulanase, fungal alpha-amylase and starch as substrate. The mixed syrup that contained IMOs was evaluated and analyzed by thin-layer chromatography (TLC) and high-performance liquid chromatography (HPLC). In addition, small-scale preparation of IMOs was performed. These results are a strong indication that the alpha-transglucosidase-producing G. stearothermophilus as a potential application technique can be successfully used to prepare industrial IMOs.

Function and structure of GH13_31 α-glucosidase with high α-(1→4)-glucosidic linkage specificity and transglucosylation activity

α-Glucosidase hydrolyzes α-glucosides and transfers α-glucosyl residues to an acceptor through transglucosylation. In this study, GH13_31 α-glucosidase BspAG13_31A with high transglucosylation activity is reported in Bacillus sp. AHU2216 and biochemically and structurally characterized. This enzyme is specific to α-(1→4)-glucosidic linkage as substrates and transglucosylation products. Maltose is the most preferred substrate. Crystal structures of BspAG13_31A wild-type for the substrate-free form and inactive acid/base mutant E256Q in complexes with maltooligosaccharides were solved at 1.6-2.5 Å resolution. BspAG13_31A has a catalytic domain folded by an (β/α)₈ -barrel. In subsite +1, Ala200 and His203 on β→α loop 4 and Asn258 on β→α loop 5 are involved in the recognition of maltooligosaccharides. Structural basis for specificity of GH13_31 enzymes to α-(1→4)-glucosidic linkage is first described.

Characteristics of the Copper,Zinc Superoxide Dismutase of a Hadal Sea Cucumber (Paelopatides sp.) from the Mariana Trench

Superoxide dismutases (SODs) are among the most important antioxidant enzymes and show great potential in preventing adverse effects during therapeutic trials. In the present study, cloning, expression, and characterization of a novel Cu,Zn superoxide dismutase (Ps-Cu,Zn-SOD) from a hadal sea cucumber (Paelopatides sp.) were reported. Phylogenetic analysis showed that Ps-Cu,Zn-SOD belonged to a class of intracellular SOD. Its Km and Vmax were 0.0258 ± 0.0048 mM and 925.1816 ± 28.0430 units/mg, respectively. The low Km value of this enzyme represents a high substrate affinity and can adapt to the low metabolic rate of deep sea organisms. The enzyme functioned from 0 °C to 80 °C with an optimal temperature of 40 °C. Moreover, the enzyme activity was maintained up to 87.12% at 5 °C. The enzyme was active at pH 4 to 12 with an optimal pH of 8.5. Furthermore, Ps-Cu,Zn-SOD tolerated high concentration of urea and GuHCl, resisted hydrolysis by proteases, and maintained stability at high pressure. All these features demonstrated that the deep sea Ps-Cu,Zn-SOD is a potential candidate for application to the biopharmaceutical field.

A new GH13 α-glucosidase from alkaliphilic Bacillus pseudofirmus 703 with both exo-α-l, 4-glucosidase and oligo-l, 6-glucosidase activities toward amylopectin

Debranching of (1, 6)-α-linkages in starch is of great significance as it is widely used in different industries. In recent years, identifying a single potential enzyme that could debranch (1, 6)-α-linkages and cleave (1, 4)-α-linkages brought great interest as amylopectin possessed both (1, 4)-α- and (1, 6)-α-linkages. In the present study, a 64\,kDa exo-α-l, 4-glucosidase from Bacillus pseudofirmus 703, annotated as Amy112, was cloned and characterized. Biochemical analysis indicated that heterologous Amy112 expressed in Escherichia coli exhibited a high activity against amylopectin, with the optimal temperature and pH of 40°C and pH 7.0, respectively. Addition of K⁺ ions improved the amy112 activity by 12%, but Li⁺, Ca²⁺ and Mg²⁺ ions showed no significant effect. Amy112 sequence homology revealed that it belonged to glycoside hydrolase family 13, showing 65% identity with α-glucosidase GSJ from Geobacillus sp. HTA-462. This is the first report indicating that Amy112 from B. pseudofirmus 703 belongs to GH13 enzyme family, having both exo-α-1, 4-glucosidase and oligo-l, 6-glucosidase activities. However, no transglycosylation activity was detected in LC-MS analysis. Amy112 would be of great significance of being utilized to debranch starch in different industries in a cost effective manner.

Evaluation and directed evolution for thermostability improvement of a GH 13 thermostable α-glucosidase from Thermus thermophilus TC11

Background

Thermal stable α-glucosidases with transglycosylation activity could be applied to the industrial production of oligosaccharides as well as conjugation of sugars to biologically useful materials. Therefore, α-glucosidases isolated from thermophiles have gained attention over the past decade. In this study, the characterization of a highly thermostable α-glucosidase and its thermostability improved mutant from newly isolated strain Thermus thermophilus TC11 were investigated.

Results

The recombinant α-glucosidase (TtAG) from Thermus thermophilus TC11 was expressed in Escherichia coli BL21 (DE3) and purified. The purified enzyme had a molecular mass of 184 kDa and consisted of 59-kDa subunits; it showed hydrolytic activity for pNP-α-d-glucopyranoside (pNPG), sucrose, trehalose, panose, and isomaltooligosaccharides and very low activity for maltose. The highest specific activity of 288.96 U/mg was observed for pNPG at 90 °C and pH 5.0; Pb²⁺ provided a 20 % activity increase. TtAG was stable at 70 °C for more than 7 h and had a half-life of 195 min at 80 °C and 130 min at 90 °C. Transglycosylation activity was also observed with sucrose and trehalose as substrates. TtAG showed differences on substrate specificity, transglycosylation, multimerization, effects of metal ions and optimal pH from other reported Thermus α-glucosidases. One single-substitution TtAG mutant Q10Y with improved thermostability was also obtained from random mutagenesis library. The site-saturation mutagenesis and structural modelling analysis indicated that Q10Y substitution stabilized TtAG structure via additional hydrogen bonding and hydrophobic interactions.

Conclusion

Our findings indicate that TtAG is a highly thermostable and more acidic α-glucosidase distinct from other reported Thermus α-glucosidases. And this work also provides new insights into the catalytic and thermal tolerance mechanisms of α-glucosidases, which may guide molecular engineering of α-glucosidase and other thermostable enzymes for industrial application.

Electronic supplementary material

The online version of this article (doi:10.1186/s12896-015-0197-x) contains supplementary material, which is available to authorized users.

A model of extracellular enzymes in free-living microbes: which strategy pays off?

An initial modeling approach was applied to analyze how a single, nonmotile, free-living, heterotrophic bacterial cell may optimize the deployment of its extracellular enzymes. Free-living cells live in a dilute and complex substrate field, and to gain enough substrate, their extracellular enzymes must be utilized efficiently. The model revealed that surface-attached and free enzymes generate unique enzyme and substrate fields, and each deployment strategy has distinctive advantages. For a solitary cell, surface-attached enzymes are suggested to be the most cost-efficient strategy. This strategy entails potential substrates being reduced to very low concentrations. Free enzymes, on the other hand, generate a radically different substrate field, which suggests significant benefits for the strategy if free cells engage in social foraging or experience high substrate concentrations. Swimming has a slight positive effect for the attached-enzyme strategy, while the effect is negative for the free-enzyme strategy. The results of this study suggest that specific dissolved organic compounds in the ocean likely persist below a threshold concentration impervious to biological utilization. This could help explain the persistence and apparent refractory state of oceanic dissolved organic matter (DOM). Microbial extracellular enzyme strategies, therefore, have important implications for larger-scale processes, such as shaping the role of DOM in ocean carbon sequestration.

Structural analysis of the α-glucosidase HaG provides new insights into substrate specificity and catalytic mechanism

α-Glucosidases, which catalyze the hydrolysis of the α-glucosidic linkage at the nonreducing end of the substrate, are important for the metabolism of α-glucosides. Halomonas sp. H11 α-glucosidase (HaG), belonging to glycoside hydrolase family 13 (GH13), only has high hydrolytic activity towards the α-(1→4)-linked disaccharide maltose among naturally occurring substrates. Although several three-dimensional structures of GH13 members have been solved, the disaccharide specificity and α-(1→4) recognition mechanism of α-glucosidase are unclear owing to a lack of corresponding substrate-bound structures. In this study, four crystal structures of HaG were solved: the apo form, the glucosyl-enzyme intermediate complex, the E271Q mutant in complex with its natural substrate maltose and a complex of the D202N mutant with D-glucose and glycerol. These structures explicitly provide insights into the substrate specificity and catalytic mechanism of HaG. A peculiar long β→α loop 4 which exists in α-glucosidase is responsible for the strict recognition of disaccharides owing to steric hindrance. Two residues, Thr203 and Phe297, assisted with Gly228, were found to determine the glycosidic linkage specificity of the substrate at subsite +1. Furthermore, an explanation of the α-glucosidase reaction mechanism is proposed based on the glucosyl-enzyme intermediate structure.

Deep-sea Rhodococcus sp. BS-15, lacking the phytopathogenic fas genes, produces a novel glucotriose lipid biosurfactant

Glycolipid biosurfactant-producing bacteria were isolated from deep-sea sediment collected from the Okinawa Trough. Isolate BS15 produced the largest amount of the glycolipid, generating up to 6.31 ± 1.15 g l(-1) after 4 days at 20 °C. Glucose was identified in the hydrolysate of the purified major component of the biosurfactant glycolipid. According to gas chromatography/mass spectrometry analysis, the hydrophobic moieties in the major component were hexadecanoate, octadecanoate, 3-hydroxyhexadecanoate, 2-hydroxyoctanoate, and succinate. The molecular weight of the purified major glycolipid was calculated to be 1,211, while (1)H and (13)C nuclear magnetic resonance spectra confirmed that the major component consisted of 2 mol of α-glucoside and 1 mol of β-glucoside. The molecular structure was assigned as novel trisaccharide-type glycolipid biosurfactant, glucotriose lipids. The critical micelle concentration of the purified major glycolipid was 2.3 × 10(-6) M, with a surface tension of 29.5 mN m(-1). Phylogenetic analysis showed isolate BS15 was closely related to a Rhodococcus strains isolated from Antarctica, and to Rhodococcus fascians, a phytopathogen. PCR analysis showed that the fasA, fasB, fasC, fasD, fasE, and fasF genes, which are involved in phytohormone-like cytokinin production, were not present in the genome of BS15; however, analysis of a draft genome sequence of BS15 (5.5 Mb) identified regions with 31 %, 53 %, 46 %, 30 %, and 31 % DNA sequence identity to the fasA, fasB, fasC, and fasD genes, respectively.

Synthesis of hexyl α-glucoside and α-polyglucosides by a novel Microbacterium isolate

Alkyl-glucosides and alkyl-polyglucosides are the new-generation biodegradable surfactants with good emulsifying and wetting properties. The α-forms of these glucosides occur in antibiotics and also stimulate nasal absorption of many drugs. In this paper, we report the synthesis of hexyl α-glucoside and α-polyglucosides using cell-bound α-glucosidase activity of a novel strain of Microbacterium paraoxydans. A number of cell-bound glycosyl hydrolase activities were detected in the isolate with the maximum hydrolytic activity of 180 IU g(-1) dry wt cells on p-nitrophenyl-α-D-glucopyranoside. In a micro-aqueous system, at a water activity of 0.69, 1.8 g l(-1) of hexyl α-glucoside (corresponding to about 25 % yield) was synthesized by whole cells with maltose and hexanol as substrates. The concentration was enhanced to 11 g l(-1) (~60 % yield) in a biphasic system at a water content of 60 %. (1)H and (13)C NMR spectra of the purified compound confirmed the synthesized product to be hexyl-α-D-glucopyranoside, while the presence of hexyl di- and tri-glucosides was confirmed by electrospray ionization mass spectrometry. The cell-driven synthesis makes this an extremely attractive alternative for synthesis of such compounds.

Unique substrate specificity of a thermostable glycosyl hydrolase from an uncultured Anaerolinea, derived from bacterial mat on a subsurface geothermal water stream

To investigate novel extremozymes encoded by sequenced metagenes from a microbial community in an extreme environment, we have characterized a recombinant glycosyl hydrolase (rGH) from an uncultured bacterium within the order Chloroflexi. rGH formed insoluble bodies in an Escherichia coli protein expression system. The protein was partially dissolved by a surfactant and was enzymatically characterized. The MW of the monomeric peptide was ~62 kDa, and it formed a homodimers in buffer. It was optimally active at 65 °C and from pH 4 to 8. rGH showed hydrolytic activity for α-1,1, α-1,2 and α-1,6 linkages, including isomaltose, but not α-1,4 and β-linkages.

Characterization of Halomonas sp. strain H11 α-glucosidase activated by monovalent cations and its application for efficient synthesis of α-D-glucosylglycerol

An α-glucosidase (HaG) with the following unique properties was isolated from Halomonas sp. strain H11: (i) high transglucosylation activity, (ii) activation by monovalent cations, and (iii) very narrow substrate specificity. The molecular mass of the purified HaG was estimated to be 58 kDa by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). HaG showed high hydrolytic activities toward maltose, sucrose, and p-nitrophenyl α-D-glucoside (pNPG) but to almost no other disaccharides or malto-oligosaccharides higher than trisaccharides. HaG showed optimum activity to maltose at 30°C and pH 6.5. Monovalent cations such as K(+), Rb(+), Cs(+), and NH(4)(+) increased the enzymatic activity to 2- to 9-fold of the original activity. These ions shifted the activity-pH profile to the alkaline side. The optimum temperature rose to 40°C in the presence of 10 mM NH(4)(+), although temperature stability was not affected. The apparent K(m) and k(cat) values for maltose and pNPG were significantly improved by monovalent cations. Surprisingly, k(cat)/K(m) for pNPG increased 372- to 969-fold in their presence. HaG used some alcohols as acceptor substrates in transglucosylation and was useful for efficient synthesis of α-d-glucosylglycerol. The efficiency of the production level was superior to that of the previously reported enzyme Aspergillus niger α-glucosidase in terms of small amounts of by-products. Sequence analysis of HaG revealed that it was classified in glycoside hydrolase family 13. Its amino acid sequence showed high identities, 60%, 58%, 57%, and 56%, to Xanthomonas campestris WU-9701 α-glucosidase, Xanthomonas campestris pv. raphani 756C oligo-1,6-glucosidase, Pseudomonas stutzeri DSM 4166 oligo-1,6-glucosidase, and Agrobacterium tumefaciens F2 α-glucosidase, respectively.

Hydrosoluble antioxidants by enzymatic glucosylation of a vitamin E derivative using marine α-D-glucosidase from Aplysia fasciata

Relevant examples of polyglycosylating exo-glycosidases were reported among enzymes of marine origin (Aplysia fasciata, Geobacillus, and Pecten maximus). Herein we describe the enzymatic polyglucosylation of a chromane-methanol (2-hydroxymethyl-2,5,7,8-tetramethylchroman-6-ol) performed by using the α-D-glucosidase from the sea hare Aplysia fasciata. New di-, tri-, and tetrasaccharide derivatives were synthesized and their antioxidant activities were evaluated by DPPH test. High enzymatic substrate conversion was assessed by NMR spectroscopy, and the products were easily purified. These findings suggest that the proposed procedure is an effective process both for the molecular diversity of products and for the peculiar stereochemistry of the enzyme. At the beginning of the enzymatic reaction, only (S)-diastereomer of the monoglucoside was obtained. The isomaltoside was the most abundant disaccharide obtained and showed a radical scavenging activity similar to that of the chromane-methanol. The disaccharide can be considered a new hydrosoluble antioxidant agent useful for various technological applications (cosmetics, food industry, etc.). A relationship between the interglycosidic linkage present in disaccharides and trisaccharides and their scavenging activity was also pointed out.

Glycoside hydrolases in Aplysia fasciata: analysis and applications

Glycosylation is considered to be an important reaction for the chemical modification of compounds with useful biological activities. Glycoside hydrolases are biotechnologically attractive enzymes which can be used in synthetic reactions for assembling glycosidic linkages with absolute stereoselectivity at an anomeric centre. Most of these enzymes are commercially available but there is great interest in the search for new biocatalysts with original catalytic characteristics. The marine environment has shown to be a very interesting source for new glycosyl hydrolases for both hydrolytic and synthetic aspects. In particular, Aplysia fasciata a marine herbivorous mollusc has been shown to be a potent producer of a library of glycoside hydrolases applied to the synthesis of glycosidic bonds. The impressive assortment of glycosidases in marine organisms clearly indicates that the potential biodiversity of these enzymes is still largely unexplored and that potential applications of biocatalysts from the sea will increase in the near future.

Marine biocatalysts: enzymatic features and applications

In several recent reports related to biocatalysis the enormous pool of biodiversity found in marine ecosystems is considered a profitable natural reservoir for acquiring an inventory of useful biocatalysts. These enzymes are characterized by well-known habitat-related features such as salt tolerance, hyperthermostability, barophilicity and cold adaptivity. In addition, their novel chemical and stereochemical characteristics increase the interest of biocatalysis practitioners both in academia and research industry. In this review, starting from the analysis of these featuring habitat-related properties, important examples of marine enzymes in biocatalysis will be reported. Completion of this report is devoted to the analysis of novel chemical and stereochemical biodiversity offered by marine biocatalysts with particular emphasis on current or potential applications of these enzymes in chemical and pharmaceutical fields. The analysis of literature cited here and the many published patent applications concerning the use of marine enzymes supports the view that these biocatalysts are just waiting to be discovered, reflecting the importance of the marine environment. The potential of this habitat should be thoroughly explored and possibly the way to access useful biocatalysts should avoid destructive large-scale collections of marine biomass for enzyme production. These two aspects are day by day increasing in interest and a future increase in the use of marine enzymes in biocatalysis should be expected.

Crystal structure of GH13 alpha-glucosidase GSJ from one of the deepest sea bacteria

The crystal structure of the GH13 alpha-glucosidase (GSJ) from deep-sea bacterium Geobacillus sp. strain HTA-462 was determined to a 2.0 A resolution. Comparisons of the GSJ structure with that of other GH13 enzymes with different catalytic activities revealed that the catalytic cleft of GSJ was widely opened when compared with the homologues. The wide opening of the catalytic cleft originated from conformational changes of active site residues and disorder of the regions close to the catalytic center. This structural feature of GSJ would explain the ability of this enzyme to accept a wide variety of nonsugar molecules as acceptors in the transglycosylation reaction.

Deep-sea natural products

This review covers the 390 novel marine natural products described to date from deep-water (>50 m) marine fauna, with details on the source organism, its depth and country of origin, along with any reported biological activity of the metabolites. Relevant synthetic studies on the deep-sea natural products have also been included.

Marine glycosyl hydrolases in the hydrolysis and synthesis of oligosaccharides

The marine ecosystem can be considered a rather unexplored source of biological material (e.g. natural substances with therapeutic activity) and can also be a surprising source of enzymes carrying new and interesting catalytic activities to be applied in biocatalysis. The use of glycosyl hydrolases from marine environments dates back to the end of the 1960s and was mainly focused on the development of sensitive and reliable hydrolytic methods for the analysis of sugar chains. As a result not all the benefits of a particular enzymatic activity have been investigated, especially regarding the transglycosylation potential of these enzymes for the synthesis of glycosidic bonds. In this review, the potential of marine sources will be demonstrated reporting on the few examples found in literature for the synthesis and hydrolysis of biologically relevant oligosaccharides catalyzed by glycosyl hydrolases of marine origin. Particular emphasis is given to the synthesis of glycosidic bonds, which is easy by the use of glycosyl hydrolases. Further aspects considered in this review are applications of these biocatalysts for vegetal waste treatment in recovering useful materials, for structural identification and for preparation of target materials from new purified polysaccharides, for the synthesis or modification of food-related compounds and for glycobiology related studies.

Purification, characterization, and synergistic action of phytate-resistant alpha-amylase and alpha-glucosidase from Geobacillus thermodenitrificans HRO10

The alpha-amylase (1, 4-alpha-d-glucanohydrolase; EC 3.2.1.1) and alpha-glucosidase (alpha-d-glucoside glucohydrolase; EC 3.2.1.20) secreted by Geobacillus thermodenitrificans HRO10 were purified to homogeneity (13.6-fold; 11.5% yield and 25.4-fold; 32.0% yield, respectively) through a series of steps. The molecular weight of alpha-amylase was 58kDa, as estimated by sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE). The alpha-amylase activity on potato starch was optimal at pH 5.5 and 80 degrees Celsius. In the presence of Ca(2+), the alpha-amylase had residual activity of more than 92% after 1h of incubation at 70 degrees Celsius. The alpha-amylase did not lose any activity in the presence of phytate (a selective alpha-amylase inhibitor) at concentrations as high as 10mM, rather it retained 90% maximal activity after 1h of incubation at 70 degrees Celsius. EGTA and EDTA were strong inhibitory substances of the enzyme. The alpha-amylase hydrolyzed soluble starch at 80 degrees Celsius, with a K(m) of 3.05mgml(-1) and a V(max) of 7.35Uml(-1). The molecular weight of alpha-glucosidase was approximately 45kDa, as determined by SDS-PAGE. The enzyme activity was optimal at pH 6.5-7.5 and 55 degrees Celsius. Phytate did not inhibit G. thermodenitrificans HRO10 alpha-glucosidase activity, whereas pCMB was a potent inhibitor of the enzyme. The alpha-glucosidase exhibited Michaelis-Menten kinetics with maltose at 55 degrees Celsius (K(m): 17mM; V(max): 23micromolmin(-1)mg(-1)). Thin-layer chromatography studies with G. thermodenitrificans HRO10 alpha-amylase and alpha-glucosidase showed an excellent synergistic action and did not reveal any transglycosylation catalyzed reaction by the alpha-glucosidase.