Separation and characterization of six (1 leads to 3)-beta-glucanases from Saccharomyces cerevisiae

Advances in molecular enzymology of β-1,3-glucanases: A comprehensive review

β-1,3-Glucanases are essential enzymes involved in the hydrolysis of β-1,3-glucans, with significant biological and industrial relevance. These enzymes are derived from diverse sources, including bacteria, fungi, plants, and animals, each exhibiting unique substrate specificities and biochemical properties. This review provides an in-depth analysis of the natural sources and ecological roles of β-1,3-glucanases, exploring their enzymatic properties such as optimal pH, temperature, molecular weight, isoelectric points, and kinetic parameters, which are crucial for understanding their functionality and stability. Advances in molecular enzymology are discussed, focusing on gene cloning, expression in systems like Escherichia coli and Pichia pastoris, and structural-functional relationships. The reaction mechanisms and the role of non-catalytic carbohydrate-binding modules in enhancing substrate hydrolysis are examined. Industrial applications of β-1,3-glucanases are highlighted, including the production of β-1,3-glucooligosaccharides, uses in the food industry, biological control of plant pathogens, and nutritional roles. This review aims to provide a foundation for future research, improving the efficiency and robustness of β-1,3-glucanases for various industrial applications.

Microbial life in preferential flow paths in subsurface clayey till revealed by metataxonomy and metagenomics

BACKGROUND

Subsurface microorganisms contribute to important ecosystem services, yet little is known about how the composition of these communities is affected by small scale heterogeneity such as in preferential flow paths including biopores and fractures. This study aimed to provide a more complete characterization of microbial communities from preferential flow paths and matrix sediments of a clayey till to a depth of 400 cm by using 16S rRNA gene and fungal ITS2 amplicon sequencing of environmental DNA. Moreover, shotgun metagenomics was applied to samples from fractures located 150 cm below ground surface (bgs) to investigate the bacterial genomic adaptations resulting from fluctuating exposure to nutrients, oxygen and water.

RESULTS

The microbial communities changed significantly with depth. In addition, the bacterial/archaeal communities in preferential flow paths were significantly different from those in the adjacent matrix sediments, which was not the case for fungal communities. Preferential flow paths contained higher abundances of 16S rRNA and ITS gene copies than the corresponding matrix sediments and more aerobic bacterial taxa than adjacent matrix sediments at 75 and 150 cm bgs. These findings were linked to higher organic carbon and the connectivity of the flow paths to the topsoil as demonstrated by previous dye tracer experiments. Moreover, bacteria, which were differentially more abundant in the fractures than in the matrix sediment at 150 cm bgs, had higher abundances of carbohydrate active enzymes, and a greater potential for mixotrophic growth.

CONCLUSIONS

Our results demonstrate that the preferential flow paths in the subsurface are unique niches that are closely connected to water flow and the fluctuating ground water table. Although no difference in fungal communities were observed between these two niches, hydraulically active flow paths contained a significantly higher abundance in fungal, archaeal and bacterial taxa. Metagenomic analysis suggests that bacteria in tectonic fractures have the genetic potential to respond to fluctuating oxygen levels and can degrade organic carbon, which should result in their increased participation in subsurface carbon cycling. This increased microbial abundance and activity needs to be considered in future research and modelling efforts of the soil subsurface.

From Cancer Therapy to Winemaking: The Molecular Structure and Applications of β-Glucans and β-1, 3-Glucanases

β-glucans are a diverse group of polysaccharides composed of β-1,3 or β-(1,3-1,4) linked glucose monomers. They are mainly synthesized by fungi, plants, seaweed and bacteria, where they carry out structural, protective and energy storage roles. Because of their unique physicochemical properties, they have important applications in several industrial, biomedical and biotechnological processes. β-glucans are also major bioactive molecules with marked immunomodulatory and metabolic properties. As such, they have been the focus of many studies attesting to their ability to, among other roles, fight cancer, reduce the risk of cardiovascular diseases and control diabetes. The physicochemical and functional profiles of β-glucans are deeply influenced by their molecular structure. This structure governs β-glucan interaction with multiple β-glucan binding proteins, triggering myriad biological responses. It is then imperative to understand the structural properties of β-glucans to fully reveal their biological roles and potential applications. The deconstruction of β-glucans is a result of β-glucanase activity. In addition to being invaluable tools for the study of β-glucans, these enzymes have applications in numerous biotechnological and industrial processes, both alone and in conjunction with their natural substrates. Here, we review potential applications for β-glucans and β-glucanases, and explore how their functionalities are dictated by their structure.

Laminarans and 1,3-β-D-glucanases

The laminarans are biologically active water-soluble polysaccharide (1,3;1,6-β-D-glucans) of brown algae. These polysaccharides are an attractive object for research due to its relatively simple structure, low toxicity, and various biological effects. 1,3-β-D-glucanases are an effective tool for studying the structure of laminarans, and can also be used to obtain new biologically active derivatives. This review is to outline what is currently known about laminarans and enzymes that catalyze of their transformation. We focused on information about sources, structure and properties of laminarans and 1,3-β-D-glucanases, methods of obtaining and structural elucidation of laminarans, and biological activity of laminarans and products of their enzymatic transformation. It has an increased focus on the immunomodulating and anticancer activity of laminarans and their derivatives.

Yeast engineered translucent cell wall to provide its endosymbiont cyanobacteria with light

In this study, relationship between translucent property of yeast cell wall and occurrence of cyanobacteria inside the yeast vacuole was examined. Microscopic observations on fruit yeast Candida tropicalis showed occurrence of bacterium-like bodies inside the yeast vacuole. Appearance of vacuoles as distinct cavities indicated the perfect harvesting of light by the yeast's cell wall. Transmission electron microscopy observation showed electron-dense outer and electron-lucent inner layers in yeast cell wall. Cyanobacteria-specific 16S rRNA gene was amplified from total DNA of yeast. Cultivation of yeast in distilled water led to excision of intracellular bacteria which grew on cyanobacteria-specific medium. Examination of wet mount and Gram-stained preparations of excised bacteria showed typical bead-like trichomes. Amplification of cyanobacteria-specific genes, 16S rRNA, cnfR and dxcf, confirmed bacterial identity as Leptolyngbya boryana. These results showed that translucent cell wall of yeast has been engineered through evolution for receiving light for vital activities of cyanobacteria.

Excision of endosymbiotic bacteria from yeast under aging and starvation stresses

Although infrequent in our laboratory, growth of bacterial colonies has been observed on top of the purified cultures of yeasts. In this study, the likelihood of bacterial excision from yeast under aging and starvation stresses was assessed using 10 gastric and 10 food-borne yeasts. Yeasts were identified as members of Candida or Saccharomyces genus by amplification and sequencing of D1/D2 region of 26S rDNA. For aging stress, yeasts were cultured on brain heart infusion agar supplemented with sheep blood and incubated at 30 °C for 3-4 weeks. For starvation stress, yeasts were inoculated into distilled water and incubated similarly. After seven days, starved yeasts were cultured on yeast extract glucose agar, incubated similarly and examined daily for appearance of bacterial colonies on top of the yeast's growth. Outgrowth of excised bacteria was observed on top of the cultures of 4 yeasts (Y1, Y3, Y13 and Y18) after 3-7 days. The excised bacteria (B1, B3, B13 and B18) were isolated and identified at the genus level according to their biochemical characteristics as well as amplification and sequencing of 16S rDNA. B1 (Arthrobacter) were excised from Y1 (Candida albicans) upon aging and B3 (Staphylococcus), B13 (Cellulomonas) and B18 (Staphylococcus) were excised from their respective yeasts; Y3 (Candida tropicalis), Y13 (Saccharomyces cerevisiae) and Y18 (Candida glabrata) upon starvation. DNA from yeasts was used for detection of 16S rDNA of their intracellular bacteria and sequencing. Amplified products from yeasts showed sequence similarity to those of excised bacteria. Under normal conditions, yeast exerts tight control on multiplication of its intracellular bacteria. However, upon aging and starvation the control is no longer effective and bacterial outgrowth occurs. Unlimited multiplication of excised bacteria might provide yeast with plenty of food in close vicinity. This could be an evolutionary dialogue between yeast and bacteria that ensures the survival of both partners.

Enhancement of bifidobacteria survival by Williopsis saturnus var. saturnus in milk

The viability of three strains of probiotic Bifidobacterium lactis that were inoculated into UHT milk was examined with and without the presence of the yeast, Williopsis saturnus var. saturnus NCYC 22, in polypropylene tubes at 30 °C. The B. lactis viable cell count for strains HN019 and BB-12 remained above 6.0 Log cfu/ml, while strain B94 had 5.7 Log cfu/ml after six weeks of incubation in the presence of the co-inoculated yeast. Incubating the bifidus milk without added yeast under anaerobic condition did not improve the survival of B. lactis HN019, indicating that oxygen removal may not be responsible for W. saturnus NCYC 22’s viability enhancing property. The addition of yeast supernatant or non-viable yeast also did not show any stabilising effects, suggesting that physical contact and/or interaction between viable W. saturnus and B. lactis plays an important role in sustaining the viability of the probiotic. W. saturnus NCYC 22 could increase the survival of B. lactis in bifidus milk under ambient temperature regardless of the initial concentration of yeast cells inoculated due to yeast growth. This study demonstrated the viability enhancing effect of viable W. saturnus NCYC 22 on B. lactis HN019, which could help towards extending the shelf-life of dairy beverages containing probiotic bifidobacteria.

Effect of production phase on bottle-fermented sparkling wine quality

This review analyzes bottle-fermented sparkling wine research at each stage of production by evaluating existing knowledge to identify areas that require future investigation. With the growing importance of enological investigation being focused on the needs of the wine production industry, this review examines current research at each stage of bottle-fermented sparkling wine production. Production phases analyzed in this review include pressing, juice adjustments, malolactic fermentation (MLF), stabilization, clarification, tirage, lees aging, disgorging, and dosage. The aim of this review is to identify enological factors that affect bottle-fermented sparkling wine quality, predominantly aroma, flavor, and foaming quality. Future research topics identified include regional specific varieties, plant-based products from vines, grapes, and yeast that can be used in sparkling wine production, gushing at disgorging, and methods to increase the rate of yeast autolysis. An internationally accepted sensory analysis method specifically designed for sparkling wine is required.

Characterization of the endo-beta-1,3-glucanase activity of S. cerevisiae Eng2 and other members of the GH81 family

The GH81 family includes proteins with endo-beta-1,3-glucanase widely distributed in yeast and fungi, which are also present in plants and bacteria. We have studied the activity of the Saccharomyces cerevisiae ScEng2 and the Schizosaccharomyces pombe SpEng1 and SpEng2 proteins. All three proteins exclusively hydrolyzed linear beta-1,3-glucan chains. Laminari-oligosaccharide degradation revealed that the minimum substrate length that the three endoglucanases were able to efficiently degrade was a molecule with at least 5 glucose residues, suggesting that the active site of the enzymes recognized five glucose units. Prediction of the secondary structure of ScEng2 and comparison with proteins of known structure allowed the identification of a 404-amino acid region with a structure similar to the Clostridium thermocellum endoglucanase CelA. This fragment showed similar enzymatic characteristics to those of the complete protein, suggesting that it contains the catalytic domain of this family of proteins. Within this domain, four conserved Asp and Glu residues (D518, D588, E609, and E613) are necessary for enzymatic activity.

Release of macromolecules by Saccharomyces cerevisiae during ageing of French flor sherry wine “Vin jaune”

The French flor sherry wine "Vin jaune" spends 6 years and 3 months in the same barrel under a yeast velum. Because of temperature variations in the cellars, this velum sinks partially into the wine and a deposit of dead yeasts cells accumulates in the bottom of the barrels, favouring the formation of new velum. Growth and autolysis occur simultaneously. This study investigated the evolution of macromolecules released by yeasts during the ageing of "Vin jaune" in a model system closely simulating winemaking. It was observed that the release of macromolecules during the formation of the velums by living yeasts was low but greatly increased when the velums fell and yeast viability decreased. The release of macromolecules was then due to the autolysis of dead cells. Analysis of macromolecules during ageing revealed that they contained 73.3-78.5% neutral sugars and 6-7% proteins according to the ageing stage. Their amino acid composition did not change during ageing. A high content of serine and threonine commonly involved in O-glycosidic linkages present in yeast mannoproteins was observed. Throughout ageing, the mannose and glucose contents of macromolecules increased but the ratio of polymeric mannose to glucose decreased. Size exclusion chromatography showed that mannoproteins released in wine were partially hydrolysed by yeast beta-1,3-glucanases freed in wine.

Endophytic fungal beta-1,6-glucanase expression in the infected host grass

Mutualistic fungal endophytes infect many grass species and often confer benefits to the hosts such as reduced herbivory by insects and animals. The physiological interactions between the endophytes and their hosts have not been well characterized. Fungal-secreted proteins are likely to be important components of the interaction. In the interaction between Poa ampla and the endophyte Neotyphodium sp., a fungal beta-1,6-glucanase is secreted into the apoplast, and activity of the enzyme is detectable in endophyte-infected plants. Sequence analysis indicates the beta-1,6-glucanase is homologous to enzymes secreted by the mycoparasitic fungi Trichoderma harzianum and Trichoderma virens. DNA gel-blot analysis indicated the beta-1,6-glucanase was encoded by a single gene. As a secreted protein, the beta-1,6-glucanase may have a nutritional role for the fungus. In culture, beta-1,6-glucanase activity was induced in the presence of beta-1,6-glucans. From RNA gel blots, similar beta-1,6-glucanases were expressed in tall fescue (Festuca arundinacea Schreb.) and Chewings fescue (Festuca rubra L. subsp. fallax [Thuill] Nyman) infected with the endophyte species Neotyphodium coenophialum and Epichloë festucae, respectively.

Isolation, enzymatic properties, and mode of action of an exo-1,3-beta-glucanase from Trichoderma viride

An exo-1,3-beta-glucanase has been isolated from cultural filtrate of T. viride AZ36. The N-terminal sequence of the purified enzyme (m = 61 +/- 1 kDa) showed no significant homology to other known glucanases. The 1,3-beta-glucanase displayed high activity against laminarins, curdlan, and 1,3-beta-oligoglucosides, but acted slowly on 1,3-1,4-beta-oligoglucosides. No significant activity was detected against high molecular mass 1,3-1,4-beta-glucans. The enzyme carried out hydrolysis with inversion of the anomeric configuration. Whereas only glucose was released from the nonreducing terminus during hydrolysis of 1,3-beta-oligoglucosides, transient accumulation of gentiobiose was observed during hydrolysis of laminarins. The gentiobiose was subsequently degraded to glucose. The Michaelis constants Km and Vmax have been determined for the hydrolysis of 1,3-beta-oligoglucosides with degrees of polymerization ranging from 2 to 6. Based on these data, binding affinities for subsites were calculated. Substrate binding site contained at least five binding sites for sugar residues.

Characterization of recombinant yeast exo-beta-1,3-glucanase (Exg 1p) expressed in Escherichia coli cells

Yeast exo-beta-1,3-glucanase gene (EXG1) was expressed in Escherichia coli and the recombinant enzyme (Exg1p) was characterized. The recombinant Exglp had an apparent molecular mass of 45 kDa by SDS-PAGE and the enzyme has a broad specificity for beta-1,3-linkages as well as beta-1,6-linkages, and also for other beta-glucosidic linked substrates, such as cellobiose and pNPG. Kinetic analyses indicate that the enzyme prefers small substrates such as laminaribiose, gentiobiose, and pNPG rather than polysaccharide substrates, such as laminaran or pustulan. With a high concentration of laminaribiose, the enzyme catalyzed transglucosidation forming laminarioligosaccharides. The enzyme was strongly inhibited with high concentrations of laminaran.

Cloning and characterization of the EXG1 gene from the yeast Yarrowia lipolytica

The YlEXG1 gene of Yarrowia lipolytica, encoding an exo-1, 3-beta-glucanase, was isolated by screening a genomic library with a DNA probe obtained by PCR amplification, using oligonucleotides designed according to conserved regions in the EXG1, EXG2 and SSG1 genes from Saccharomyces cerevisiae. YlEXG1 consists of a 1263 bp open reading frame encoding a protein of 421 amino acids with a calculated molecular weight of 48 209 Da. Northern blot analysis revealed a unique YlEXG1-specific transcript, 1.4 kb long. A putative pre(signal)-peptide of 15 amino acids is proposed at the N-terminal domain of the primary translation product. The deduced amino acid sequence shares a high degree of homology with exo-1, 3-beta-glucanases from other yeast species, including S. cerevisiae, Kluyveromyces lactis, Pichia angusta and Debaryomyces occidentalis. YlExg1p contains the invariant amino acid positions which have been shown to be important in the catalytic function of family 5 glycosyl hydrolases. Chromoblot analysis indicated that YlEXG1 is located on chromosome VI. Disruption of YlEXG1 did not result in a phenotype under laboratory conditions and did not prevent the yeast-hypha transition. The sequence data reported in this paper have been assigned EMBL Accession No. Z46872.

Characterization of an Exo-beta-1,3-Glucanase Produced by Pichia anomala Strain K, Antagonist of Botrytis cinerea on Apples

ABSTRACT The exo-beta-1,3-glucanase (EC 3.2.1.58) activity of Pichia anomala strain K, an antagonistic yeast of Botrytis cinerea on postharvest apples, was studied in a synthetic medium supplemented with laminarin, a cell wall preparation (CWP) of B. cinerea, or glucose. The highest enzyme activity was detected in culture media containing a CWP of B. cinerea as the sole carbon source, whereas the lowest activity was observed in culture media supplemented with glucose. Exoglc1, an exo-beta-1,3-glucanase, was purified to homogeneity from culture filtrates of strain K containing a CWP. The molecular mass of exoglc1 was estimated to be under 15 kDa. Optimum activity of exoglc1 was recorded at 50 degrees C and pH 5.5. The exoglc1 K(m) value was estimated at 22.4 mg/ml. Exoglc1 showed in vitro a stronger inhibitory effect on germ tube growth of B. cinerea than on conidia germination and caused morphological changes such as leakage of cytoplasm and cell swelling. Exo-beta-1,3-glucanase activity was detected on apples treated with strain K and was similar to exoglc1 on the basis of activity on native gel. Moreover, the addition of a CWP to a suspension of P. anomala stimulated both in situ exo-beta-1,3-glucanase activity and protective activity against the pathogen, strengthening the hypothesis that exo-beta-1,3-glucanase activity is one of the mechanisms of action involved in the suppression of B. cinerea by P. anomala strain K.

Differential patterns of activity displayed by two exo-beta-1,3-glucanases associated with the Aspergillus fumigatus cell wall

Two exo-beta-1,3-glucanases (herein designated exoG-I and exoG-II) were isolated from the cell wall autolysate of the filamentous fungus Aspergillus fumigatus and purified by ion-exchange, hydrophobic-interaction, and gel filtration chromatographies. Molecular masses estimated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and gel filtration chromatography were 82 kDa for the monomeric exoG-I and 230 kDa for the dimeric exoG-II. exoG-I and exoG-II were glycosylated, and N glycans accounted, respectively, for 2 and 44 kDa. Their pH optimum is 5.0. Their optimum temperatures are 55 degrees C for exoG-I and 65 degrees C for exoG-II. By a sensitive colorimetric method and high-performance anion-exchange chromatography for product analysis, two patterns of exo-beta-1,3-glucanase activities were found. The 230-kDa exoG-II enzyme acts on p-nitrophenyl-beta-D-glucoside, beta-1,6-glucan, and beta-1,3-glucan. This activity, which retains the anomeric configuration of glucose released, presented a multichain pattern of attack of the glucan chains and a decrease in the maximum initial velocity (Vm) with the increasing size of the substrate. In contrast, the 82-kDa exoG-I, which inverts the anomeric configuration of the glucose released, hydrolyzed exclusively the beta-1,3-glucan chain with a minimal substrate size of 4 glucose residues. This enzyme presented a repetitive-attack pattern, characterized by an increase in Vm with an increase in substrate size and by a degradation of the glucan chain until it reached laminaritetraose, the limit substrate size. The 82-kDa exoG-I and 230-kDa exoG-II enzymes correspond to a beta-1,3-glucan-glucohydrolase (EC 3.2.1.58) and to a beta-D-glucoside-glucohydrolase (EC 3.2.1.21), respectively. The occurrence and functions of these two classes of exo-beta-1,3-glucanases in other fungal species are discussed.

Purification and characterization of an endo-1,3-beta-glucanase from Aspergillus fumigatus

An endo-1,3-beta-glucanase was purified from a cell wall autolysate of Aspergillus fumigatus. This beta-glucanase activity was associated with a glycosylated 74-kDa protein. Using a sensitive colorimetric assay and a high-performance anion-exchange chromatography with a pulsed electrochemical detector for product analysis, it was shown that the endoglucanase hydrolysed exclusively linear 1,3-beta-glucan chains, had an optimum pH of 7.0 and an optimum temperature of 60 degrees C. A substrate kinetic study gave a Km value of 0.3 mg/ml for soluble (laminarin and laminari-oligosaccharides) and 1.18 mg/ml for insoluble (curdlan) 1,3-beta-glucan. Laminari-oligosaccharide degradation, analysed by HPLC, showed that the endoglucanase bind to the subtrate at several positions and suggested that the active site of the enzyme recognized five glucose units linked by a 1,3-beta bond. The association of the present endo-1,3-beta-glucanase with the cell wall of A. fumigatus suggests a putative role for this enzyme during cell-wall morphogenesis.

Molecular basis of cell integrity and morphogenesis in Saccharomyces cerevisiae

In fungi and many other organisms, a thick outer cell wall is responsible for determining the shape of the cell and for maintaining its integrity. The budding yeast Saccharomyces cerevisiae has been a useful model organism for the study of cell wall synthesis, and over the past few decades, many aspects of the composition, structure, and enzymology of the cell wall have been elucidated. The cell wall of budding yeasts is a complex and dynamic structure; its arrangement alters as the cell grows, and its composition changes in response to different environmental conditions and at different times during the yeast life cycle. In the past few years, we have witnessed a profilic genetic and molecular characterization of some key aspects of cell wall polymer synthesis and hydrolysis in the budding yeast. Furthermore, this organism has been the target of numerous recent studies on the topic of morphogenesis, which have had an enormous impact on our understanding of the intracellular events that participate in directed cell wall synthesis. A number of components that direct polarized secretion, including those involved in assembly and organization of the actin cytoskeleton, secretory pathways, and a series of novel signal transduction systems and regulatory components have been identified. Analysis of these different components has suggested pathways by which polarized secretion is directed and controlled. Our aim is to offer an overall view of the current understanding of cell wall dynamics and of the complex network that controls polarized growth at particular stages of the budding yeast cell cycle and life cycle.

Regulation of cell wall beta-glucan assembly: PTC1 negatively affects PBS2 action in a pathway that includes modulation of EXG1 transcription

Analysis of genes involved in yeast cell wall beta-glucan assembly has led to the isolation of EXG1, PBS2 and PTC1. EXG1 and PBS2 were isolated as genes that, when expressed from multicopy plasmids, led to a dominant killer toxin-resistant phenotype. The PTC1 gene was cloned by functional complementation of the calcofluor white-hypersensitive mutant cwh47-1. PTC1/CWH47 is the structural gene for a type 2C serine/threonine phosphatase, EXG1 codes for an exo-beta-glucanase, and PBS2 encodes a MAP kinase kinase in the Pbs2p-Hog1p signal transduction pathway. Overexpression of EXG1 on a 2 mu plasmid led to reduction in a cell wall beta 1,6-glucan and caused killer resistance in wild type cells; while the exg1 delta mutant displayed modest increases in killer sensitivity and beta 1,6-glucan levels. Disruption of PTC1/CWH47 and overexpression of PBS2 gave rise to similar beta-glucan related phenotypes, with higher levels of EXG1 transcription, increased exo-beta-glucanase activity, reduced beta 1,6-glucan levels, and resistance to killer toxin. Genetic analysis revealed that loss of function of the PBS2 gene was epistatic to PTC1/CWH47 disruption, indicating a functional role for the Ptc1p/Cwh47p phosphatase in the Pbs2p-Hog1p signal transduction pathway. These results suggest that Ptc1p/Cwh47p and Pbs2p play opposing regulatory roles in cell wall glucan assembly, and that this is effected in part by modulating Exg1p activity.

Purification and characterization of three extracellular (1-->3)-beta-D-glucan glucohydrolases from the filamentous fungus Acremonium persicinum

Three (1-->3)-beta-D-glucanases (GNs) were isolated from the culture filtrates of the filamentous fungus Acremonium persicinum and purified by (NH4)2SO4 precipitation followed by anion-exchange and gel-filtration chromatography. Homogeneity of the purified proteins was confirmed by SDS/PAGE, isoelectric focusing and N-terminal amino acid sequencing. All three GNs (GN I, II and III) are non-glycosylated, monomeric proteins with apparent molecular masses, estimated by SDS/PAGE, of 81, 85 and 89 kDa respectively. pI values for the three enzymes are 5.3, 5.1, and 4.4 respectively. The pH optimum for GN I is 6.5, and 5.0 for GN II and III. All three purified enzymes displayed stability over the pH range 4.5-10.0. Optimum activities for GN I, II and III were recorded at 65, 55 and 60 degrees C respectively, with both GN II and III having short-term stability up to 50 degrees C and GN I up to 55 degrees C. The purified GNs have high specificity for (1-->3)-beta-linkages and hydrolysed a range of (1-->3)-beta- and (1-->3)(1-->6)-beta-D-glucans, with laminarin from Laminaria digitata being the most rapidly hydrolysed substrate of those tested. K(m) values for GN I, II, and III against L. digitata laminarin were 0.1, 0.23 and 0.22 mg/ml respectively. D-Glucono-1,5-lactone does not inhibit any of the three GNs, some metals ions are mild inhibitors, and N-bromosuccinimide and KMnO4 are strong inhibitors. All three GNs acted in an exo-hydrolytic manner, determined by the release of alpha-glucose as the initial and major product of hydrolysis of (1-->3)-beta-D-glucans, and confirmed by viscometric analysis and the inability to cleave periodate-oxidized laminarin, and may be classified as (1-->3)-beta-D-glucan glucohydrolases (EC 3.2.1.58).

Detection of exo-beta-1,3-glucanase activity in polyacrylamide gels after electrophoresis under denaturing or nondenaturing conditions

A method for the visualization of exo-beta-1,3-glucanase activity in polyacrylamide gels is presented. The procedure consists of the enzyme reaction in the gel with the substrate alpha-naphthylglucopyranoside, and a subsequent staining of the obtained alpha-naphthol with dyes Fast Red B, or Fast Blue BB, respectively. A mixture of exoglucanases produced by the fungus Polyporus squamosus was used for the optimization of the method. The procedure is applicable for the standard Laemmli discontinuous electrophoresis system, even in the presence of sodium dodecyl sulfate, as well as for electrophoresis in linear gradients of the polyacrylamide concentration. The staining method was used for the analysis of exoglucanases secreted by several yeast genera. All yeasts tested produced two types of exoglucanases, a high molecular mass species heterogeneous in size, and one or two smaller homogeneous enzymes.

The hypo-osmolarity-sensitive phenotype of the Saccharomyces cerevisiae hpo2 mutant is due to a mutation in PKC1, which regulates expression of beta-glucanase

To obtain more information about the cell wall organization of Saccharomyces cerevisiae, we have developed a novel screening system to obtain cell wall-defective mutants, using a density gradient centrifugation method. Nine hypo-osmolarity-sensitive mutants were classified into two complementation groups, hpo1 and hpo2. Phase contrast microscopic observation showed that mutant cells bearing lesions at either locus became abnormally large. A gene that complemented the mutant phenotype of hpo2 was cloned and sequenced. This gene turned out to be identical to PKC1, which encodes the yeast homologue of mammalian protein kinase C. Complementation tests with pkc1 delta showed that hpo2 is allelic to pkc1. To study the reason for the fragility of hpo2 cells, cell wall was isolated and the glucan was analyzed. The amount of alkali, acid-insoluble glucan, which is responsible for the rigidity of the cell wall, was reduced to about 30% that of the wild-type cell and this may be the major cause of the fragility of the hpo2 mutant cell. Analysis of total wall proteins in hpo2 mutant cells on SDS-polyacrylamide gels revealed that a 33 kDa protein was overproduced two- to threefold relative to the wild-type level. This 33 kDa protein was identified as a beta-glucanase, encoded by BGL2. Disruption of BGL2 in the hpo2 mutant partially rescued the growth rate defect. This suggests that the PKC1 kinase cascade regulates BGL2 expression negatively and overproduction of the beta-glucanase is partially responsible for the growth defect.(ABSTRACT TRUNCATED AT 250 WORDS)

SSG1, a gene encoding a sporulation-specific 1,3-beta-glucanase in Saccharomyces cerevisiae

In Saccharomyces cerevisiae, the meiotic process is accompanied by a large increase in 1,3-beta-glucan-degradative activity. The molecular cloning of the gene (SSG1) encoding a sporulation-specific exo-1,3-beta-glucanase was achieved by screening a genomic library with a DNA probe obtained by polymerase chain reaction amplification using synthetic oligonucleotides designed according to the nucleotide sequence predicted from the amino-terminal region of the purified protein. DNA sequencing indicates that the SSG1 gene specifies a 445-amino-acid polypeptide (calculated molecular mass, 51.8 kDa) showing extensive similarity to the extracellular exo-1,3-beta-glucanases encoded by the EXG1 gene (C. R. Vazquez de Aldana, J. Correa, P. San Segundo, A. Bueno, A. R. Nebreda, E. Mendez, and F. del Rey, Gene 97:173-182, 1991). The N-terminal domain of the putative precursor is a very hydrophobic segment with structural features resembling those of signal peptides of secreted proteins. Northern (RNA) analysis reveals a unique SSG1-specific transcript, 1.7 kb long, which can be detected only in sporulating diploids (MATa/MAT alpha) but does not appear in vegetatively growing cells or in nonsporulating diploids (MAT alpha/MAT alpha) when incubated under nitrogen starvation conditions. The meiotic time course of SSG1 induction indicates that the gene is transcribed only in the late stages of the process, beginning at the time of meiosis I and reaching a maximum during spore formation. Homozygous ssg1/ssg1 mutant diploids are able to complete sporulation, although with a significant delay in the appearance of mature asci.

Noncellulolytic fungal beta-glucanases: their physiology and regulation

The occurrence, regulation, and action of fungal enzymes capable of degrading noncellulosic beta-glucans, especially 1,3-beta- and 1,6-beta-glucans, are reviewed. Special consideration is given to their roles in both metabolic and morphogenetic events in the fungal cell, including cell wall extension, hyphal branching, sporulation, budding, and autolysis. Also examined are the protocols currently available for their purification, with some of the properties of purified beta-glucanases discussed in terms of their potential applications in industrial, agricultural, and medical fields.

Formation, separation and characterization of three beta-1,3-glucanases from Sclerotium glucanicum

The appearance of beta-1,3-glucanases in supernatants of Sclerotium glucanicum cultures was followed by SDS-PAGE and shown to be dependent on cultivation time. Three beta-1,3-glucanases were isolated and purified. Glucanase I and III appeared homogeneous on SDS-PAGE with molecular masses of 85 and 33.5 kDa, respectively. Enzyme I was an endo-splitting beta-1,3-glucanase. In hydrolyzing laminarin it released glucose, laminaritriose and laminaribiose as major endproducts and smaller amounts of higher oligosaccharides. Enzyme III was an exo-beta-1,3-glucanase removing glucose from laminarin and gentiobiose and glucose from scleroglucan. For laminarin as substrate the Km of enzyme I and III was 2.5 and 3.33 mg/ml, respectively. Enzyme II was only partially purified and found to be also an exo-beta-1,3-glucanase, releasing glucose as the only hydrolysis product from laminarin. It did not attack scleroglucan. Its molecular weight was determined to be 78 kDa. Optimum pH and temperature of the three enzymes were determined. The three activities were significantly inhibited by 1 mM Hg2+.

Microbial beta-glucanases different from cellulases

The beta-glucans different from cellulose are the most abundant class of polysaccharides. They are found in microorganisms and higher plants as structural entities of cell wall, as cytoplasmic and vacuolar reserve materials, and as extracellular substances. Enzyme systems capable to hydrolyze beta-glucans are produced by different microorganisms. The occurrence and nature of beta-glucanases and their substrates are reviewed. The regulation of biosynthesis of these enzymes, their properties, substrate and product specificities, mode of action and molecular cloning are described. The participation of beta-glucanases in the morphogenetic events of yeast cell is presented. The role and synergism of different types of 1,3-beta-glucanases in microbial cell wall lysis and the potential application for isolation of intracellular materials like proteins, carbohydrates, enzymes and as an analytical tool are discussed in the light of current knowledge.

Inhibition of yeast exoglucanases by glucosidase inhibitors

Castanospermine, 1-deoxynojirimycin, and N-methyl-1-deoxynojirimycin, three well-characterized inhibitors of the glucosidases involved in the processing of N-linked oligosaccharides, did not affect the biosynthesis or the secretion of exoglucanases (EC 3.2.1.58) from Saccharomyces cerevisiae and Candida albicans but inhibited the activity itself. Regardless of the substrate used, laminarin or p-nitrophenyl beta-D-glucoside (pNPG), all three inhibitors proved to act in a competitive manner. Castanospermine was the most potent inhibitor, with Ki values ranging from 0.16 to 0.5 microM for three different purified yeast exoglucanases. The inhibition caused by 1-deoxynojirimycin and N-methyl-1-deoxynojirimycin was poorer, but still significant. By contrast, the glucosidase inhibitors did not show any action on a partially purified endoglucanase (EC 3.2.1.39) Candida albicans. A purified exoglucanase from Basidiomycete QM 806, which was specific for laminarin, was unaffected by castanospermine but it was still inhibited in an uncompetitive manner by 1-deoxynojirimycin and N-methyl-1-deoxynojirimycin. The presence of castanospermine in the culture medium of growing yeasts did not have any effect on yeast growth in spite of the fact that, under the conditions used, the external exoglucanase was fully inhibited. None of the yeast exoglucanases hydrolyzed the glucan synthesized in vitro by membrane preparations derived from either yeast. These results support the concept that yeast exoglucanases are glucosidases that also attack laminarin, rather than glucanases capable of attacking pNPG.

Molecular cloning of a cell wall exo-beta-1,3-glucanase from Saccharomyces cerevisiae

A major protein of Saccharomyces cerevisiae cell walls is a 29-kilodalton glycoprotein which shows lectinlike binding to beta-1,3-glucan and chitin. It was solubilized by heating isolated cell walls at 90 degrees C and purified to homogeneity by running two high-pressure liquid chromatography columns. With the sequence information of the N terminus and seven peptides, two oligonucleotides were synthesized and the gene was cloned. Its sequence is similar to those of two plant beta-glucanases, and the protein was shown to possess beta-1,3-exoglucanase activity with laminarin as substrate. Haploid yeast cells contained one copy of the gene (BGL2). Gene disruption did not result in a phenotype.

Direct detection of beta-1,3-glucanase isozymes on polyacrylamide electrophoresis and isoelectrofocusing gels

A procedure to assay isozymes of beta-1,3-glucanase directly on polyacrylamide gel electrophoresis (PAGE) and isoelectrofocusing (IEF) gels by using 2,3,5-triphenyltetrazolium chloride is described. The reagent reacts with reducing sugars released by beta-1,3-glucanases from the substrate laminarin. Acidic and neutral isozymes of beta-1,3-glucanase were detected and quantified on 17.5% native PAGE gels run with an anodic buffer system. A significant linear relationship (alpha = less than 0.01, R = 0.991) was observed between amounts of beta-1,3-glucanase loaded and intensity of bands stained with the reagent on native PAGE gels. A full isozyme pattern was obtained on 7.5% IEF gels with a pH range of 3.5-9.5. The IEF gels were heated in a microwave oven during the staining process to minimize diffusion.

A similar protein portion for two exoglucanases secreted by Saccharomyces cerevisiae

Exoglucanase (exo-1,3-beta-D-glucan glycohydrolase, EC 3.2.1.56) activity secreted by Saccharomyces cerevisiae into the culture medium was separated by ion exchange chromatography into two glycoprotein isoenzymes which contributed 10% (exoglucanase I) and 90% (exoglucanase II) towards the total activity. Analysis of the "in vitro" deglycosylated products by polyacrylamide gel electrophoresis under native or denaturing conditions indicated that the protein portions of both exoglucanases exhibited identical mobility, each one consisting of two polypeptides with Mr of 47,000 and 48,000. The same profile was shown by the exoglucanase secreted in the presence of tunicamycin. Antibodies raised against the protein portion of exoglucanase II did react with both native exoglucanases and their deglycosylated products with a pattern indicative of immunological identity. Digestion of the "in vitro" deglycosylated products of both exoglucanases with Staphylococcus aureus V-8 protease or trypsin generated the same proteolytic fragments in each case. Only exoglucanase II was secreted by protoplasts. These and previously reported results indicate that the protein portions of both isoenzymes may be the product of the same gene (or a family of related genes), and that exoglucanase I is a product of enzyme II, modified by a process occurring beyond the permeability barrier of the cell.

Chitinases and beta-1,3-Glucanases in the Apoplastic Compartment of Oat Leaves (Avena sativa L.)

To isolate chitinases and beta-1,3-glucanases from the intercellular space of oats (Avena sativa L.), primary leaves were infiltrated with buffer and subjected to gentle centrifugation to obtain intercellular washing fluid (IWF). Approximately 5% of the chitinase and 10% of the beta-1,3-glucanase activity of the whole leaf were released. Only small amounts (0.01-0.03%) of the intracellular marker malate-dehydrogenase were released into the IWF during infiltration. Activities of chitinase and beta-1,3-glucanase in the IWF and in the leaf extract were compared by different chromatographic methods. On Sephadex G-75, chitinase appeared as a single peak (M(r) 29.8 kD) both in IWF and homogenate. beta-1,3-Glucanase, however, showed two peaks in the IWF (M(r) 52 and 31.3 kD), whereas the elution pattern of the homogenate showed only one major peak at 22 kD. Chromatofocusing indicated that the IWF contained four chitinases and five beta-1,3-glucanases. The elution pattern of the homogenate and IWF were similar with regard to the elution pH, but the peak intensities were distinctly different. Our results demonstrate that extracellular beta-1,3-glucanases are different from those located intracellularly. Extracellular and intracellular chitinases do not differ in molecular properties, except for one isozyme which seems to be confined to the extracellular space. We suggest that both enzymes might play a special role in pathogenesis during fungal infection.

Cloning and heterologous expression of glycosidase genes from Saccharomyces cerevisiae

Genomic clones were isolated that code for three glycosidases proposed to be involved in the catabolism of cell wall components in Saccharomyces cerevisiae. alpha-Mannosidase (AMS1), exoglucanase (BGL1), and endochitinase (CTS1) genes were isolated with the aid of filter assays based on the hydrolysis of 4-methylumbelliferyl glycosides, which permitted the in situ monitoring of these glycosidase activities in yeast colonies. Uracil prototrophs resulting from transformation with a multicopy YEp24 yeast genomic library were screened, leading to the identification of transformants possessing high levels of glycosidase activity. Restriction maps of plasmids from multiple isolates were used to localize glycosidase-overproduction genes, which were subcloned into a Schizosaccharomyces pombe/S. cerevisiae shuttle vector. Transformation of Sch. pombe with BGL1 and CTS1 subclones resulted in the appearance of these activities in this organism, and an AMS1 plasmid caused a 2-fold increase in endogenous alpha-mannosidase levels. Insertion of the marker gene LEU2 into putative AMS1 sequences disrupted plasmid-encoded alpha-mannosidase overproduction. S. cerevisiae strains that incorporated a restriction fragment containing ams1::LEU2 into their chromosomal DNA by homologous recombination expressed no detectable alpha-mannosidase activity in either the haploid or homozygous recessive diploid states, whereas heterozygous and wild-type cells exhibited levels proportional to AMS1 gene dosage. No readily apparent phenotype was associated with the alpha-mannosidase deficiency; however, labeling experiments utilizing [2-3H]mannose suggest that alpha-mannosidase may function in mannan turnover.

Cloning and nucleotide sequence of the gene coding for enzymatically active fragments of the Bacillus polymyxa beta-amylase

The gene encoding beta-amylase was cloned from Bacillus polymyxa 72 into Escherichia coli HB101 by inserting HindIII-generated DNA fragments into the HindIII site of pBR322. The 4.8-kilobase insert was shown to direct the synthesis of beta-amylase. A 1.8-kilobase AccI-AccI fragment of the donor strain DNA was sufficient for the beta-amylase synthesis. Homologous DNA was found by Southern blot analysis to be present only in B. polymyxa 72 and not in other bacteria such as E. coli or B. subtilis. B. polymyxa, as well as E. coli harboring the cloned DNA, was found to produce enzymatically active fragments of beta-amylases (70,000, 56,000, or 58,000, and 42,000 daltons), which were detected in situ by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Nucleotide sequence analysis of the cloned 3.1-kilobase DNA revealed that it contains one open reading frame of 2,808 nucleotides without a translational stop codon. The deduced amino acid sequence for these 2,808 nucleotides encoding a secretory precursor of the beta-amylase protein is 936 amino acids including a signal peptide of 33 or 35 residues at its amino-terminal end. The existence of a beta-amylase of larger than 100,000 daltons, which was predicted on the basis of the results of nucleotide sequence analysis of the gene, was confirmed by examining culture supernatants after various cultivation periods. It existed only transiently during cultivation, but the multiform beta-amylases described above existed for a long time. The large beta-amylase (approximately 160,000 daltons) existed for longer in the presence of a protease inhibitor such as chymostatin, suggesting that proteolytic cleavage is the cause of the formation of multiform beta-amylases.

Topography of cell wall lytic enzyme in Chlamydomonas reinhardtii: form and location of the stored enzyme in vegetative cell and gamete

Chlamydomonas lytic enzyme of the cell wall (gamete wall-autolysin) is responsible for shedding of cell walls during mating of opposite mating-type gametes. This paper reports some topographic aspects of lytic enzyme in cells. Both vegetative and gametic cells contain the same wall lytic enzyme. The purified enzyme is a glycoprotein with an apparent molecular mass of 67 kD by gel filtration and 62 kD by SDS PAGE, and is sensitive to metal ion chelators and SH-blocking agents. These properties are the same as those of the gamete wall-autolysin released into the medium by mating gametes. However, the storage form of the enzyme proves to be quite different between the two cell types. In vegetative cells, the lytic enzyme is found in an insoluble form in cell homogenates and activity is released into the soluble fraction only by sonicating the homogenates or freeze-thawing the cells, whereas gametes always yield lytic activity in the soluble fractions of cell homogenates. When vegetative cells are starved for nitrogen, the storage form of enzyme shifts from its vegetative state to gametic state in parallel with the acquisition of mating ability. Adding nitrogen to gametes converts it to the vegetative state concurrently with the loss of mating ability. We also show that protoplasts obtained by treatment of vegetative cells or gametes with exogenously added enzyme have little activity of enzyme in the cell homogenates, suggesting that lytic enzyme is stored outside the plasmalemma. When the de-walled gametes or gametes of the wall-deficient mutant, cw-15, of opposite mating types are mixed together, they mate normally but the release of lytic enzyme into the medium is practically negligible. When the de-walled vegetative cells are incubated, the lytic enzyme is again accumulated in the cells after the wall regeneration is almost complete.