Purification and characterization of alpha-galactosidase from a thermophilic fungus Thermomyces lanuginosus

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.

Characterization of a highly stable α-galactosidase from thermophilic Rasamsonia emersonii heterologously expressed in a modified Pichia pastoris expression system

Background

Structurally stable α-galactosidases are of great interest for various biotechnological applications. More thermophilic α-galactosidases with high activity and structural stability have therefore to be mined and characterized. On the other hand, few studies have been performed to prominently enhance the AOX1 promoter activity in the commonly used Pichia pastoris system, in which production of some heterologous proteins are insufficient for further study.

Results

ReGal2 encoding a thermoactive α-galactosidase was identified from the thermophilic (hemi)cellulolytic fungus Rasamsonia emersonii. Significantly increased production of ReGal2 was achieved when ReGal2 was expressed in an engineered Pastoris pichia expression system with a modified AOX1 promoter and simultaneous fortified expression of Mxr1 that is involved in transcriptionally activating AOX1. Purified ReGal2 exists as an oligomer and has remarkable thermo-activity and thermo-tolerance, exhibiting maximum activity of 935 U/mg towards pNPGal at 80 °C and retaining full activity after incubation at 70 °C for 60 h. ReGal2 is insensitive to treatments by many metal ions and exhibits superior tolerance to protein denaturants. Moreover, ReGal2 efficiently hydrolyzed stachyose and raffinose in soybeans at 70 °C in 3 h and 24 h, respectively.

Conclusion

A modified P. pichia expression system with significantly enhanced AOX1 promoter activity has been established, in which ReGal2 production is markedly elevated to facilitate downstream purification and characterization. Purified ReGal2 exhibited prominent features in thermostability, catalytic activity, and resistance to protein denaturants. ReGal2 thus holds great potential in relevant biotechnological applications.

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.

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.

Enzyme-based processing of soybean carbohydrate: Recent developments and future prospects

Soybean is well known for its high-value oil and protein. Carbohydrate is, however, an underutilized major component, representing almost 26-30% (w/w) of the dried bean. The complex soybean carbohydrate is not easily hydrolyzable and can cause indigestibility when included in food and feed. Enzymes can be used to hydrolyze the carbohydrate for improving soybean processing and value of soybean products. Here the enzyme-based processing developed for the following purposes is reviewed: hydrolysis of different carbohydrate-rich by/products from soybean processing, improvement of soybean oil extraction, and increase of nutritional value of soybean-based food and animal feed. Once hydrolyzed into fermentable sugars, soybean carbohydrate can find more value-added applications and further improve the overall economics of soybean processing.

Response surface methodology-based optimization of production media and purification of α-galactosidase in solid-state fermentation by Fusarium moniliforme NCIM 1099

Response surface methodology was used to enhance the production of α-galactosidase from Fusarium moniliforme NCIM 1099 in solid-state fermentation. Plackett–Burman design was employed for selection of critical media constituents which were optimized by central composite rotatable design. Wheat bran, peptone and FeSO₄·7H₂O were identified as significant medium components using PB design. Further CCRD optimized medium components as wheat bran; 4.62 μg, peptone; 315.42 μg, FeSO₄·7H₂O; 9.04 μg. RSM methodological optimization increased the enzyme production from 13.17 to 207.33 U/g showing 15.74-fold enhancement. The α-galactosidase was purified by 70% fractionation followed by DEAE anion exchange column chromatography which yields 23.33% with 28.68-fold purification. The molecular weight of α-galactosidase was 57 kDa which was determined by SDS-PAGE analysis. Purified enzyme has optimum pH of 4.0 and was found to be stable in wide pH range of 3.0–9.0. Its optimum temperature was 50 °C, whereas its activity remains above 50% up to 2 h at 75 °C. Hg²⁺ was found to be a potent inhibitor and Mg²⁺ acted as an activator of enzyme. No significant change was observed in enzyme activity for galactose concentration, ranging from 1 to 100 mM. The K_m values of enzyme for substrates p-nitrophenyl-α-d-galactopyranoside, melibiose and raffinose were 0.20, 1.36, and 3.66 mM, respectively. Low K_m and stability to various physiological conditions of enzyme represents its potential which can be exploited in various industrial applications.

Improving the Secretory Expression of an -Galactosidase from Aspergillus niger in Pichia pastoris

α-Galactosidases are broadly used in feed, food, chemical, pulp, and pharmaceutical industries. However, there lacks a satisfactory microbial cell factory that is able to produce α-galactosidases efficiently and cost-effectively to date, which prevents these important enzymes from greater application. In this study, the secretory expression of an Aspergillus niger α-galactosidase (AGA) in Pichia pastoris was systematically investigated. Through codon optimization, signal peptide replacement, comparative selection of host strain, and saturation mutagenesis of the P1’ residue of Kex2 protease cleavage site for efficient signal peptide removal, a mutant P. pastoris KM71H (Mut^s) strain of AGA-I with the specific P1’ site substitution (Glu to Ile) demonstrated remarkable extracellular α-galactosidase activity of 1299 U/ml upon a 72 h methanol induction in 2.0 L fermenter. The engineered yeast strain AGA-I demonstrated approximately 12-fold higher extracellular activity compared to the initial P. pastoris strain. To the best of our knowledge, this represents the highest yield and productivity of a secreted α-galactosidase in P. pastoris, thus holding great potential for industrial application.

Purification and characterisation of intracellular alpha-galactosidases from Acinetobacter sp

Two alpha-galactosidases (Ag-I & Ag-II) were purified from Acinetobacter sp. Both the enzymes were monomeric with pH optima of 7.0 and molecular weight of 65 kDa for Ag-I and 37 kDa for Ag-II. The temperature optima for Ag-I was between 50 and 60 °C and that of Ag-II was 40 °C. Both the enzymes were strongly inhibited by metal ions Ag²⁺ and Hg⁺, pCMB and SDS (1 %). The enzymes were found to be active on both natural and synthetic substrates. Artificial substrate, pNPGal, has shown more affinity to enzyme than natural substrate raffinose. The half-life (t_1/2) of Ag-I varied from 1.85 h at 90 °C to 7.6 h at 70 °C.

Hooked on α-d-galactosidases: from biomedicine to enzymatic synthesis

α-d-Galactosidases (EC 3.2.1.22) are enzymes employed in a number of useful bio-based applications. We have depicted a comprehensive general survey of α-d-galactosidases from different origin with special emphasis on marine example(s). The structures of natural α-galactosyl containing compounds are described. In addition to 3D structures and mechanisms of action of α-d-galactosidases, different sources, natural function and genetic regulation are also covered. Finally, hydrolytic and synthetic exploitations as free or immobilized biocatalysts are reviewed. Interest in the synthetic aspects during the next years is anticipated for access to important small molecules by green technology with an emphasis on alternative selectivity of this class of enzymes from different sources.

Biochemical characterization of a novel thermophilic α-galactosidase from Talaromyces leycettanus JCM12802 with significant transglycosylation activity

Thermophilic α-galactosidases have great potentials in biotechnological and medicinal applications due to their high-temperature activity and specific stability. In this study, a novel α-galactosidase gene of glycoside hydrolase family 27 (aga27A) was cloned from Talaromyces leycettanus JCM12802 and successfully expressed in Pichia pastoris GS115. Purified recombinant Aga27A (rAga27A) was thermophilic and thermotolerant, exhibiting the maximum activity at 70°C and retaining stability at 65°C. Like most fungal α-galactosidases, rAga27A had an acidic pH optimum (pH 4.0) but retained stability over a boarder pH range (pH 3.0-11.0) at 70°C. Moreover, the enzyme exhibited strong resistance to most metal ions and chemicals tested (except for Ag(+) and SDS) and great tolerance to galactose (19 mM). The preferable transglycosylation capacity of rAga27A with various substrates further widens its application spectrum. Thus rAga27A with excellent enzymatic properties will be ideal for applications in various industries, especially for the synthesis of galactooligosaccharides.

Stereochemical course of hydrolytic reaction catalyzed by alpha-galactosidase from cold adaptable marine bacterium of genus Pseudoalteromonas

The recombinant α-galactosidase of the marine bacterium (α-PsGal) was synthesized with the use of the plasmid 40Gal, consisting of plasmid pET-40b (+) (Novagen) and the gene corresponding to the open reading frame of the mature α-galactosidase of marine bacterium Pseudoalteromonas sp. KMM 701, transformed into the Escherichia coli Rosetta(DE3) cells. In order to understand the mechanism of action, the stereochemistry of hydrolysis of 4-nitrophenyl α-D-galactopyranoside (4-NPGP) by α-PsGal was measured by ¹H NMR spectroscopy. The kinetics of formation of α- and β-anomer of galactose showed that α-anomer initially formed and accumulated, and then an appreciable amount of β-anomer appeared as a result of mutarotation. The data clearly show that the enzymatic hydrolysis of 4-NPGP proceeds with the retention of anomeric configuration, probably, due to a double displacement mechanism of reaction.

Secretome analysis of the thermophilic xylanase hyper-producer Thermomyces lanuginosus SSBP cultivated on corn cobs

Thermomyces lanuginosus is a thermophilic fungus known for its ability to produce industrially important enzymes including large amounts of xylanase, the key enzyme in hemicellulose hydrolysis. The secretome of T. lanuginosus SSBP was profiled by shotgun proteomics to elucidate important enzymes involved in hemicellulose saccharification and to characterise the presence of other industrially interesting enzymes. This study reproducibly identified a total of 74 proteins in the supernatant following growth on corn cobs. An analysis of proteins revealed nine glycoside hydrolase (GH) enzymes including xylanase GH11, β-xylosidase GH43, β-glucosidase GH3, α-galactosidase GH36 and trehalose hydrolase GH65. Two commercially produced Thermomyces enzymes, lipase and amylase, were also identified. In addition, other industrially relevant enzymes not currently explored in Thermomyces were identified including glutaminase, fructose-bisphosphate aldolase and cyanate hydratase. Overall, these data provide insight into the novel ability of a cellulase-free fungus to utilise lignocellulosic material, ultimately producing a number of enzymes important to various industrial processes.

A novel promising strain of Trichoderma evansii (WF-3) for extracellular α-galactosidase production by utilizing different carbon sources under optimized culture conditions

A potential fungal strain of Trichoderma sp. (WF-3) was isolated and selected for the production of α-galactosidase. Optimum conditions for mycelial growth and enzyme induction were determined. Basal media selected for the growth of fungal isolate containing different carbon sources like guar gum (GG), soya bean meal (SM), and wheat straw (WS) and combinations of these carbon substrates with basic sugars like galactose and sucrose were used to monitor their effects on α-galactosidase production. The results of this study indicated that galactose and sucrose enhanced the enzyme activity in guar gum (GG) and wheat straw (WS). Maximum α-galactosidase production (213.63 UmL⁻¹) was obtained when the basic medium containing GG is supplemented with galactose (5 mg/mL). However, the presence of galactose and sucrose alone in the growth media shows no effect. Soya meal alone was able to support T. evansii to produce maximum enzyme activity (170.36 UmL⁻¹). The incubation time, temperature, and pH for the maximum enzyme synthesis were found to be 120 h (5 days), 28°C, and 4.5–5.5, respectively. All the carbon sources tested exhibited maximum enzyme production at 10 mg/mL concentration. Among the metal ions tested, Hg was found to be the strongest inhibitor of the enzyme. Among the chelators, EDTA acted as stronger inhibitor than succinic acid.

A thermophilic α-galactosidase from Neosartorya fischeri P1 with high specific activity, broad substrate specificity and significant hydrolysis ability of soymilk

An extracellular α-galactosidase (Gal27A) with high specific activity of 423Umg(-1) was identified in thermophilic Neosartorya fischeri P1. Its coding gene (1680bp) was cloned and functionally expressed in Pichia pastoris. Sequence analysis indicated that deduced Gal27A contains a catalytic domain of glycoside hydrolase family 27. The native and recombinant enzymes shared some similar properties, such as pH optima at 4.5, temperature optima at 60-70°C, resistance to most chemicals and saccharides, and great abilities to degrade raffinose and stachyose in soymilk. Considering the high yield (3.1gL(-1)) in P. pastoris, recombinant rGal27A is more favorable for industrial applications. This is the first report on purification and gene cloning of Neosartorya α-galactosidase.

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.

Purification and characterization of a thermostable α-galactosidase from Thielavia terrestris NRRL 8126 in solid state fermentation

Several seeds and husks of some plants belonging to leguminosae, Graminae, Compositae and Palmae were evaluated as carbon substrates to produce α-galactosidase (α-Gal) by the thermophilic fungus, Thielavia terrestris NRRL 8126 in solid substrate fermentation. The results showed that Cicer arietinum (chick pea seed) was the best substrate for α-Gal production. The crude enzyme was precipitated by ammonium sulphate (60%) and purified by gel filtration on sephadex G-100 followed by ion exchange chromatography on DEAE-Cellulose. The final purification fold of the enzyme was 30.42. The temperature and pH optima of purified α-Gal from Thielavia terrestris were 70 °C and 6.5, respectively. The enzyme showed high thermal stability at 70 °C and 75 °C and the half-life of the α-Gal at 90 °C was 45 min. Km of the purified enzyme was 1.31 mM. The purified enzyme was inhibited by Ag2+, Hg2+, Zn2+, Ba2+, Mg2+, Mn2+ and Fe2+ at 5 mM and 10 mM. Also, EDTA, sodium arsenate, L-cysteine and iodoacetate inhibited the enzyme activity. On the other hand, Ca2+, Cu2+, K+ and Na+ slightly enhanced the enzyme activity at 5 mM while at 10 mM they caused inhibition. The molecular weight of the α-Gal was estimated to be 82 kDa by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. This enzyme displays a number of biochemical properties that make it a potentially strong candidate for biotechnological and medicinal applications.

Purification and characterization of Aspergillus terreus α-galactosidases and their use for hydrolysis of soymilk oligosaccharides

α-Galactosidases has the potential to hydrolyze α-1-6 linkages in raffinose family oligosaccharides (RFO). Aspergillus terreus cells cultivated on wheat bran produced three extracellular forms of α-galactosidases (E1, E2, and E3). E1 and E2 α-galactosidases presented maximal activities at pH 5, while E3 α-galactosidase was more active at pH 5.5. The E1 and E2 enzymes showed stability for 6 h at pH 4-7. Maximal activities were determined at 60, 55, and 50 °C, for E1, E2, and E3 α-galactosidase, respectively. E2 α-galactosidase retained 90% of its initial activity after 70 h at 50 °C. The enzymes hydrolyzed ρNPGal, melibiose, raffinose and stachyose, and E1 and E2 enzymes were able to hydrolyze guar gum and locust bean gum substrates. E1 and E3 α-galactosidases were completely inhibited by Hg²⁺, Ag⁺, and Cu²⁺. The treatment of RFO present in soy milk with the enzymes showed that E1 α-galactosidase reduced the stachyose content to zero after 12 h of reaction, while E2 promoted total hydrolysis of raffinose. The complete removal of the oligosaccharides in soy milk could be reached by synergistic action of both enzymes.

Ability of selected lactic acid bacteria to ferment a pearl millet-soybean slurry to produce gruels for complementary foods for young children

To assess the ability of lactic acid bacteria to improve some nutritional characteristics of the pearl millet-soybean slurry to prepare complementary foods for young children in African countries, inoculation was performed using strains previously selected for their ability to hydrolyse starch, phytate, or alpha-galactooligosaccharides (alpha-GOS). For the sake of comparison with the action of a natural microflora, fermentation was also performed by back slopping inoculation, that is, with a sample obtained from spontaneously fermented traditional pearl millet slurry obtained from a small scale processing unit in Burkina Faso (Ouagadougou). Starter cultures thrived on the slurry as shown by counts on MRS agar, TTGE fingerprints, and fermentation patterns. The fermentation of precooked slurries inoculated by back slopping or with mixed cultures containing the amylolytic strain Lb. plantarum A6 enabled partial starch hydrolysis. Corresponding gruels had a suitable consistency for young child feeding at high dry matter content, and a high energy density: 88.7 +/- 4.2 and 75.8 +/- 5.1 kcal/100 g of sweetened gruel, for the gruels inoculated by back slopping or with Lb. plantarum A6, respectively. Unexpectedly, no decrease in phytates was observed in any of the experiments, suggesting the presence of one or more inhibitory compounds in soybean. Furthermore, preprocessing conditions before fermentation affect the carbohydrate composition of slurry and have a more profound effect than fermentation on the reduction of the alpha-GOS content.

Predominant allylic hydroxylation at carbons 6 and 7 of 4 and 5-ene functionalized steroids by the thermophilic fungus Rhizomucor tauricus IMI23312

This paper demonstrates for the first time transformation of a series of steroids (progesterone, androst-4-en-3,17-dione, testosterone, pregnenolone and dehydroepiandrosterone) by the thermophilic fungus Rhizomucor tauricus. All transformations were found to be oxidative (monohydroxylation and dihydroxylation) with allylic hydroxylation the predominant route of attack functionalizing the steroidal skeleta. Timed experiments demonstrated that dihydroxylation of progesterone, androst-4-en-3,17-dione and pregnenolone all initiated with hydroxylation on ring-B followed by attack on ring-C. Similar patterns of steroidal transformation to those observed with R. tauricus have been observed with some species of thermophilic Bacilli and mesophilic fungi. All metabolites were isolated by column chromatography and were identified by (1)H, (13)C NMR, DEPT analysis and other spectroscopic data. The application of thermophilic fungi to steroid transformation may represent a potentially rich source for the generation of new steroidal compounds as well as for uncovering inter and intraspecies similarities and differences in steroid metabolism.

Optimization of the fermentation medium for alpha-galactosidase production from Aspergillus foetidus ZU-G1 using response surface methodology

The optimization of fermentation medium for alpha-galactosidase production by Aspergillus foetidus ZU-G1 was investigated in shaker flask fermentation. A one-factor-at-a-time experiment was used to screen the preferable nutriment (carbon sources, nitrogen sources, and essential elements) for alpha-galactosidase production. A fractional factorial design was used to screen the main 5 factors, soybean meal, wheat bran, KH2PO4, FeSO4 x 7 H2O, and the medium initial pH, that affected the production of alpha-galactosidase. The central composite experimental design was further adopted to derive a statistical model for optimizing the composition of the fermentation medium. The experimental results showed that the optimum fermentation medium for alpha-galactosidase production by Aspergillus foetidus ZU-G1 was composed of 3.2% soybean meal (w/v), 2% wheat bran (w/v), 0.1% KH2PO4 (w/v), and 0.05% FeSO4 x 7 H2O (w/v); initial medium pH was 6.31. The results further predicted that alpha-galactosidase activity reached 64.75 U/mL after 96-h incubation in this medium, which was approximately 7 times higher than that incubated in the nonoptimized medium. The time course of alpha-galactosidase production in the optimized medium composition was also carried out to validate the model.

A novel thermostable α-galactosidase from the thermophilic fungus Thermomyces lanuginosus CBS 395.62/b: Purification and characterization

High levels of an extracellular alpha-galactosidase are produced by the thermophilic fungus Thermomyces lanuginosus CBS 395.62/b when grown in submerse culture and induced by sucrose. The enzyme was purified 114-fold from the culture supernatant by (NH(4))(2)SO(4) fractionation, and by chromatographical steps including Sepharose CL-6B gel filtration, DEAE-Sepharose FF anion-exchange, Q-Sepharose FF anion-exchange and Superose 12 gel filtration. The purified enzyme exhibits apparent homogeneity as judged by sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) and iso-electric focusing (IEF). The native molecular weight of the monomeric alpha-galactosidase is 93 kDa with an isoelectric point of 3.9. The enzyme displays a pH and temperature optimum of 5-5.5 and 65 degrees C, respectively. The purified enzyme retains more than 90% of its activity at 45 degrees C in a pH range from 5.5 to 9.0. The enzyme proves to be a glycoprotein and its carbohydrate content is 5.3%. Kinetic parameters were determined for the substrates p-nitrophenyl-alpha-galactopyranoside, raffinose and stachyose and very similar K(m) values of 1.13 mM, 1.61 mM and 1.17 mM were found. Mn(++) ions activates enzyme activity, whereas inhibitory effects can be observed with Ca(++), Zn(++) and Hg(++). Five min incubation at 65 degrees with 10 mM Ag(+) results in complete inactivation of the purified alpha-galactosidase. Amino acid sequence alignment of N-terminal sequence data allows the alpha-galactosidase from Thermomyces lanuginosus to be classified in glycosyl hydrolase family 36.

Induction and characterization of an unusual alpha-D-galactosidase from Talaromyces flavus

An extracellular alpha-d-galactosidase from Talaromyces flavus CCF 2686 with extremely broad and unusual acceptor specificity is produced exclusively in the presence of the specific inducer--6-deoxy-D-glucose (quinovose). The procedure for the preparation of this very expensive substance has been modified and optimized. Surprisingly, any of other common alpha-D-galactosidase inducers or substrates, e.g., D-galactose, melibiose and raffinose, did not stimulate its production. The crude alpha-D-galactosidase preparation was purified by anion-exchange chromatography and three isoenzymes with different substrate specificities were identified. The main isoenzyme (alphaGal1) was further purified by cation-exchange chromatography and fully characterized. When compared with other alpha-galactosidases and also with other isoenzymes produced by T. flavus, it showed a markedly different regioselectivity and also negligible hydrolytic activity towards melibiose. Moreover, it was active on polymeric substrates (locust bean gum, guar gum) and significantly inhibited by alpha-D-galactopyranosyl azide, D-galactose, D-xylose, melibiose, methyl alpha- and beta-D-galactopyranoside and lactose.

Extracellular alpha-galactosidase from Debaryomyces hansenii UFV-1 and its use in the hydrolysis of raffinose oligosaccharides

Raffinose oligosaccharides (RO) are the factors primarily responsible for flatulence upon ingestion of soybean-derived products. ROs are hydrolyzed by alpha-galactosidases that cleave alpha-1,6-linkages of alpha-galactoside residues. The objectives of this study were the purification and characterization of extracellular alpha-galactosidase from Debaryomyces hansenii UFV-1. The enzyme purified by gel filtration and anion exchange chromatographies presented an Mr value of 60 kDa and the N-terminal amino acid sequence YENGLNLVPQMGWN. The Km values for hydrolysis of pNP alphaGal, melibiose, stachyose, and raffinose were 0.30, 2.01, 9.66, and 16 mM, respectively. The alpha-galactosidase presented absolute specificity for galactose in the alpha-position, hydrolyzing pNPGal, stachyose, raffinose, melibiose, and polymers. The enzyme was noncompetitively inhibited by galactose (Ki = 2.7 mM) and melibiose (Ki = 1.2 mM). Enzyme treatments of soy milk for 4 h at 60 degrees C reduced the amounts of stachyose and raffinose by 100%.

Thermomyces lanuginosus: properties of strains and their hemicellulases

The non-cellulolytic Thermomyces lanuginosus is a widespread and frequently isolated thermophilic fungus. Several strains of this fungus have been reported to produce high levels of cellulase-free beta-xylanase both in shake-flask and bioreactor cultivations but intraspecies variability in terms of beta-xylanase production is apparent. Furthermore all strains produce low extracellular levels of other hemicellulases involved in hemicellulose hydrolysis. Crude and purified hemicellulases from this fungus are stable at high temperatures in the range of 50-80 degrees C and over a broad pH range (3-12). Various strains are reported to produce a single xylanase with molecular masses varying between 23 and 29 kDa and pI values between 3.7 and 4.1. The gene encoding the T. lanuginosus xylanase has been cloned and sequenced and is shown to be a member of family 11 glycosyl hydrolases. The crystal structure of the xylanase indicates that the enzyme consists of two beta-sheets and one alpha-helix and forms a rigid complex with the three central sugars of xyloheptaose whereas the peripheral sugars might assume different configurations thereby allowing branched xylan chains to be accepted. The presence of an extra disulfide bridge between the beta-strand and the alpha-helix, as well as to an increase in the density of charged residues throughout the xylanase might contribute to the thermostability. The ability of T. lanuginosus to produce high levels of cellulase-free thermostable xylanase has made the fungus an attractive source of thermostable xylanase with potential as a bleach-boosting agent in the pulp and paper industry and as an additive in the baking industry.

alpha-Galactosidase from cultured rice (Oryza sativa L. var. Nipponbare) cells

The alpha-galactosidase from rice cell suspension cultures was purified to homogeneity by different techniques including affinity chromatography using N-epsilon-aminocaproyl-alpha-D-galactopyranosylamine as the ligand. From 11 l of culture filtrate, 28.7 mg of purified enzyme was obtained with an overall yield of 51.9%. The cDNA coding for the alpha-galactosidase was cloned and sequenced. The enzyme was found to contain 417 amino acid residues composed of a 55 amino acid signal sequence and 362 amino acid mature alpha-galactosidase; the molecular weight of the mature enzyme was thus calculated to be 39,950. Seven cysteine residues were also found but no putative N-glycosylation sites were present. The observed homology between the deduced amino acid sequences of the mature enzyme and alpha-galactosidases from coffee (Coffea arabica), guar (Cyamopsis tetragonolooba), and Mortierella vinacea alpha-galactosidase II were over 73, 72, and 45%, respectively. The enzyme displayed maximum activity at 45 degrees C when p-nitrophenyl-alpha-D-galactopyranoside was used as substrate. The rice alpha-galactosidase and Mortierella vinacea alpha-galactosidase II acted on both the terminal alpha-galactosyl residue and the side-chain alpha-galactosyl residue of the galactomanno-oligosaccharides.

Trimeric crystal structure of the glycoside hydrolase family 42 beta-galactosidase from Thermus thermophilus A4 and the structure of its complex with galactose

The beta-galactosidase from an extreme thermophile, Thermus thermophilus A4 (A4-beta-Gal), is thermostable and belongs to the glycoside hydrolase family 42 (GH-42). As the first known structures of a GH-42 enzyme, we determined the crystal structures of free and galactose-bound A4-beta-Gal at 1.6A and 2.2A resolution, respectively. A4-beta-Gal forms a homotrimeric structure resembling a flowerpot. Each monomer has an active site located inside a large central tunnel. The N-terminal domain of A4-beta-Gal has a TIM barrel fold, as predicted from hydrophobic cluster analysis. The putative catalytic residues of A4-beta-Gal (Glu141 and Glu312) superimpose well with the catalytic residues of Escherichia coli beta-galactosidase. The environment around the catalytic nucleophile (Glu312) is similar to that in the case of E.coli beta-galactosidase, but the recognition mechanism for a substrate is different. Trp182 of the next subunit of the trimer constitutes a part of the active-site pocket, indicating that the trimeric structure is essential for the enzyme activity. Structural comparison with other glycoside hydrolases revealed that many features of the 4/7 superfamily are conserved in the A4-beta-Gal structure. On the basis of the results of 1H NMR spectroscopy, A4-beta-Gal was determined to be a "retaining" enzyme. Interestingly, the active site was similar with those of retaining enzymes, but the overall fold of the TIM barrel domain was very similar to that of an inverting enzyme, beta-amylase.

Chain Elongation of raffinose in pea seeds. Isolation, characterization, and molecular cloning of mutifunctional enzyme catalyzing the synthesis of stachyose and verbascose

Raffinose oligosaccharides are major soluble carbohydrates in seeds and other tissues of plants. Their biosynthesis proceeds by stepwise addition of galactose units to sucrose, which are provided by the unusual donor galactinol (O-alpha-d-galactopyranosyl-(1-->1)-l-myo-inositol). Chain elongation may also proceed by transfer of galactose units between raffinose oligosaccharides. We here report on the purification, characterization, and heterologous expression of a multifunctional stachyose synthase (EC ) from developing pea (Pisum sativum L.) seeds. The protein, a member of family 36 of glycoside hydrolases, catalyzes the synthesis of stachyose, the tetrasaccharide of the raffinose series, by galactosyl transfer from galactinol to raffinose. It also mediates the synthesis of the pentasaccharide verbascose by galactosyl transfer from galactinol to stachyose as well as by self-transfer of the terminal galactose residue from one stachyose molecule to another. These activities show optima at pH 7.0. The enzyme also catalyzes hydrolysis of the terminal galactose residue of its substrates, but is unable to initiate the synthesis of raffinose oligosaccharides by galactosyl transfer from galactinol to sucrose. A minimum reaction mechanism which accounts for the broad substrate specificity and the steady-state kinetic properties of the protein is presented.

Enzymic α-galactosylation of a cyclic glucotetrasaccharide derived from alternan

Alternanase catalyzes the hydrolysis of alternan, an alpha-(1-->3)-alpha-(1-->6)-D-glucan produced by Leuconostoc mesenteroides, resulting in the formation of a cyclic tetramer cyclo -->3)-alpha-D-Glcp-(1-->6)-alpha-D-Glcp-(1-->(2) (cGlc(4)). Two alpha-galactosidases, one from coffee bean and the other produced by a fungus, currently described as Thermomyces lanuginosus, were found to catalyze an efficient 6-O-alpha-D-galactopyranosylation of cGlc(4). The attachment of a nonreducing alpha-D-galactopyranosyl residue to the cGlc(4) molecule opens new possibilities for future applications of the cyclic tetramer, since the D-galactopyranosyl residue can be easily modified by D-galactose oxidase to introduce a reactive aldehyde group. The results also extend our knowledge about the synthetic potential of T. lanuginosus alpha-galactosidase.