An Enzymatically Active β-1,3-Glucanase from Ash Pollen with Allergenic Properties: A Particular Member in the Oleaceae Family

Endo-β-1,3-glucanases are widespread enzymes with glycosyl hydrolitic activity involved in carbohydrate remodelling during the germination and pollen tube growth. Although members of this protein family with allergenic activity have been reported, their effective contribution to allergy is little known. In this work, we identified Fra e 9 as a novel allergenic β-1,3-glucanase from ash pollen. We produced the catalytic and carbohydrate-binding domains as two independent recombinant proteins and characterized them from structural, biochemical and immunological point of view in comparison to their counterparts from olive pollen. We showed that despite having significant differences in biochemical activity Fra e 9 and Ole e 9 display similar IgE-binding capacity, suggesting that β-1,3-glucanases represent an heterogeneous family that could display intrinsic allergenic capacity. Specific cDNA encoding Fra e 9 was cloned and sequenced. The full-length cDNA encoded a polypeptide chain of 461 amino acids containing a signal peptide of 29 residues, leading to a mature protein of 47760.2 Da and a pI of 8.66. An N-terminal catalytic domain and a C-terminal carbohydrate-binding module are the components of this enzyme. Despite the phylogenetic proximity to the olive pollen β-1,3-glucanase, Ole e 9, there is only a 39% identity between both sequences. The N- and C-terminal domains have been produced as independent recombinant proteins in Escherichia coli and Pichia pastoris, respectively. Although a low or null enzymatic activity has been associated to long β-1,3-glucanases, the recombinant N-terminal domain has 200-fold higher hydrolytic activity on laminarin than reported for Ole e 9. The C-terminal domain of Fra e 9, a cysteine-rich compact structure, is able to bind laminarin. Both molecules retain comparable IgE-binding capacity when assayed with allergic sera. In summary, the structural and functional comparison between these two closely phylogenetic related enzymes provides novel insights into the complexity of β-1,3-glucanases, representing a heterogeneous protein family with intrinsic allergenic capacity.

Prunasin hydrolases during fruit development in sweet and bitter almonds

Amygdalin is a cyanogenic diglucoside and constitutes the bitter component in bitter almond (Prunus dulcis). Amygdalin concentration increases in the course of fruit formation. The monoglucoside prunasin is the precursor of amygdalin. Prunasin may be degraded to hydrogen cyanide, glucose, and benzaldehyde by the action of the β-glucosidase prunasin hydrolase (PH) and mandelonitirile lyase or be glucosylated to form amygdalin. The tissue and cellular localization of PHs was determined during fruit development in two sweet and two bitter almond cultivars using a specific antibody toward PHs. Confocal studies on sections of tegument, nucellus, endosperm, and embryo showed that the localization of the PH proteins is dependent on the stage of fruit development, shifting between apoplast and symplast in opposite patterns in sweet and bitter cultivars. Two different PH genes, Ph691 and Ph692, have been identified in a sweet and a bitter almond cultivar. Both cDNAs are 86% identical on the nucleotide level, and their encoded proteins are 79% identical to each other. In addition, Ph691 and Ph692 display 92% and 86% nucleotide identity to Ph1 from black cherry (Prunus serotina). Both proteins were predicted to contain an amino-terminal signal peptide, with the size of 26 amino acid residues for PH691 and 22 residues for PH692. The PH activity and the localization of the respective proteins in vivo differ between cultivars. This implies that there might be different concentrations of prunasin available in the seed for amygdalin synthesis and that these differences may determine whether the mature almond develops into bitter or sweet.

Allergenic contribution of the IgE-reactive domains of the 1,3-beta-glucanase Ole e 9: diagnostic value in olive pollen allergy

BACKGROUND

Designing of methods for an accurate diagnosis is a main goal of allergy research. Olive pollen allergy is currently diagnosed using commercially available pollen extracts that do not allow identification of the molecules that elicit the disease.

OBJECTIVE

To analyze the suitability of using the N- and C-terminal domains (NtD and CtD, respectively) of the 1,3-beta-glucanase Ole e 9, a major allergen from olive pollen, for in vitro diagnosis.

METHODS

Serum samples from 55 olive-allergic patients were assayed using enzyme-linked immunosorbent assay to study hypersensitive patients with IgE reactivity to Ole e 9. The specific IgEs to NtD and CtD, obtained by recombinant technology, were determined by means of immunoblotting, enzyme-linked immunosorbent assay, and inhibition assays.

RESULTS

Thirty-one of 33 serum samples from Ole e 9-allergic patients were IgE reactive to recombinant NtD (rNtD) (n = 26 [79%]), recombinant CtD (rCtD) (n = 22 [67%]), or both (n = 17 [52%]). Nine patients (27%) were exclusively reactive to rNtD and 5 (15%) to rCtD. Inhibition assays of IgE binding to Ole e 9 with a mixture of both domains abolished 90% of the binding, whereas 44% and 45% were abolished when rNtD and rCtD were used, respectively.

CONCLUSIONS

Because sensitization to NtD or CtD of Ole e 9 could be correlated to vegetable food-latex-pollen cross-reactivity processes or to the exacerbation and persistence of asthma, respectively, these molecules could be used in vitro as markers of disease to classify patients and to design a patient-tailored immunotherapy approach.

The role of major olive pollen allergens Ole e 1, Ole e 9, and Ole e 10 on mice sensitization

BACKGROUND

Olive pollen is an important cause of allergy in Mediterranean countries. To date, 10 allergens (Ole e 1 to Ole e 10) have been isolated and characterized. Animal models of olive pollen allergy are suitable tools for testing the efficacy and safety of new forms of immunotherapy.

OBJECTIVES

To characterize the immune response in mice sensitized with olive pollen extract and to compare it with that of allergic patients.

METHODS

BALB/c mice were sensitized by 4 intraperitoneal injections of olive pollen extract in aluminum hydroxide. The allergic state was proved by measuring serum specific IgG1 and total IgE antibody levels. The IgG1 responses to olive pollen allergens were assayed by immunoblotting and enzyme-linked immunosorbent assay. Competition experiments between human IgE and mouse IgG1 binding to olive pollen allergens were performed.

RESULTS

Sensitization with olive pollen extract induced high levels of specific IgG1 and total IgE in all tested animals. Immunoblotting experiments showed that the mouse IgG1 binding pattern to pollen extract was complex and heterogeneous, as occurs with human IgE. High IgG1 antibody levels to the major olive pollen allergens described for humans were detected in serum samples from sensitized mice, whereas minor olive pollen allergens induced no significant IgG1 response. Coincubation of mouse serum samples with a cocktail of Ole e 1, Ole e 9, and Ole e 10 resulted in a significant decrease (60%) in IgG1 binding to olive pollen extract. Specific mouse IgG1 strongly inhibited human IgE binding to olive pollen allergens.

CONCLUSIONS

This mouse model of olive pollen sensitization mimics immunologic features of human pollinosis and could be a useful tool for designing novel forms of immunotherapy for olive pollen allergy based on allergen cocktails.

Variability of Ole e 9 allergen in olive pollen extracts: relevance of minor allergens in immunotherapy treatments

BACKGROUND

Clustered severe adverse reactions to immunotherapy with olive pollen extracts have been occasionally reported in areas where olive trees are extensively grown. Allergic patients from these areas, in addition to the major olive pollen allergen Ole e 1, frequently recognize a recently described allergen, Ole e 9.

OBJECTIVE

We aimed to develop an immunoassay to measure Ole e 9 concentration and to study the variability of this allergen in olive pollen extracts.

METHODS

Monoclonal antibodies (mAb) to Ole e 9 were produced from mice immunized with the pure allergen. One of these mAbs was used to develop a sandwich ELISA with an anti-olive pollen extract rabbit serum as the tracer. Olive pollen batches from several suppliers were analyzed using this method. These batches were also analyzed for Ole e 1 content and biological activity.

RESULTS

A 10-fold variation between the extreme values was found for the biological activity of the batches analyzed. Ole e 1 concentration showed a 25-fold variation. Variability of Ole e 9 concentration was extremely high, up to 161 times. The ratio Ole e 1/Ole e 9 varied in a range from 0.6 to 390.4.

CONCLUSION

The availability of a mAb-based ELISA for Ole e 9 made it possible for us to detect an important source of variability in olive pollen batches. This variability may be the cause of outbreaks of adverse reactions in the course of immunotherapy treatments, which have sometimes been observed among olive-allergic patients living in areas with very high levels of airborne olive pollen.

Prophylactic Intranasal Treatment with Fragments of 1,3-β-Glucanase Olive Pollen Allergen Prevents Airway Inflammation in a Murine Model of Type I Allergy

BACKGROUND

Olive pollen is an important cause of allergy in Mediterranean countries. More than 50% of olive-pollen-allergic patients are sensitized against the 1,3-beta-glucanase Ole e 9. To date, prophylactic and therapeutic treatments using purified recombinant allergens have not been studied in animal models of olive pollen allergy.

METHODS

BALB/c mice were immunized against Ole e 9 combining intraperitoneal injections of the allergen in Al(OH)3 with airway allergen challenges. A prophylactic treatment was performed by intranasal administration of a mixture of the recombinant fragments of the allergen prior to Ole e 9 sensitization. Serum levels of specific IgE, IgG1, IgG2a and IgG2b were measured by ELISA, and total IgE levels by sandwich ELISA. Bronchoalveolar lavage and lungs from mice were collected to study airway inflammation by light microscopy.

RESULTS

BALB/c mice immunized against Ole e 9 developed a predominantly Th2-like immune response with allergen-specific immunoglobulin induction and airway inflammation accompanied by the infiltration of eosinophils, lymphocytes, and neutrophils in the lung. Prophylactic treatment by intranasal application of the recombinant fragments of Ole e 9 avoids airway inflammation induced by sensitization with this allergen although the levels of Ole e 9-specific antibodies remain unchanged.

CONCLUSIONS

Prophylactic intranasal treatment with recombinant fragments of Ole e 9 prevents airway inflammation triggered by immunization to this allergen in a murine model of type I allergy.

1,3-beta-glucanases as candidates in latex-pollen-vegetable food cross-reactivity

BACKGROUND

1,3-beta-glucanases (group 2 of pathogenesis-related proteins) are enzymes widely distributed among higher plants and have been recently proven to be significant allergens.

OBJECTIVE

The aim of this work was to study the potential implication of 1,3-beta-glucanases in cross-reactivities among latex, pollen and vegetable foods.

METHODS

The cDNA encoding the N-terminal domain (NtD) of Ole e 9, a major allergenic 1,3-beta-glucanase from olive pollen, was amplified by polymerase chain reaction and produced as a recombinant protein in Pichia pastoris (recombinant N-terminal domain, rNtD). Circular dichroism, ELISA, immunoblotting and immunoblotting inhibition experiments were carried out. Sera from olive pollen allergic patients and a rNtD-specific polyclonal antiserum were used.

RESULTS

The NtD of Ole e 9 has been produced at high yield in the yeast P. pastoris and possesses 1,3-beta-glucanase activity. The expressed polypeptide conserves IgE and IgG immunodominant epitopes of the whole Ole e 9. A rNtD-specific polyclonal antiserum and sera from olive pollen allergic patients allowed detection of IgG and IgE reactive peptidic epitopes common to 1,3-beta-glucanase Ole e 9 in extracts from ash and birch pollen, tomato, potato, bell-pepper, banana and latex.

CONCLUSION

rNtD and homologous glucanases are new molecules to be used in diagnostic protocols as they could help to identify allergic pollen patients who are at risk for developing allergic symptoms to fruits, vegetables and latex.

Beta-glucosidase enzymatic activity of crystal polypeptide of the Bacillus thuringiensis strain 1.1

The crystals of Bacillus thuringiensis strain 1.1 consist of the 140 kDa delta-endotoxin, which exhibits beta-glucosidase enzymatic activity, based on the following data. (i) Purified crystals exhibit beta-glucosidase enzymatic activity. When the crystals are reacted with specific antibodies directed either against the commercial (almond purified) beta-glucosidase or against the 140 kDa polypeptide, then considerable reduction of enzymatic activity is observed almost at the same level with both antibodies. (ii) Commercial beta-glucosidase and the 140 kDa crystal polypeptide share antigenic similarities; in Western immunoblots, the 140 kDa crystal polypeptide is recognized by anti-beta-glucosidase antibodies, and commercial beta-glucosidase is recognized by anti-140-kDa antibodies. (iii) The enzymatic properties of commercial beta-glucosidase and that resident in the crystals of B. thuringiensis strain 1.1 are very similar. Thus, both enzymes hydrolyze a wide range of substrates (aryl-beta-glucosides, disaccharides with alpha- or beta-linkage polysaccharides) and have an optimum activity at 40 degrees C and pH 5. Both enzymes are relatively thermostable and are resistant to end-product inhibition by glucose. Additionally, they show the same pattern of inhibition or activation by several chemical compounds. (iv) The crystals and commercial beta-glucosidase show almost equivalent levels of insecticidal activity against Drosophila melanogaster larvae and, furthermore, cause reduction in adult flies that emerge from larvae surviving treatment.

Significance of carbohydrate epitopes in a latex allergen with beta-1,3-glucanase activity

BACKGROUND

One of the latex allergens, Hev b 2, has beta-1,3-glucanase activity. The entire sequence of this allergen is already known. There is one potential N-glycosylation site in this molecule ((27)Asn). Heterogeneous glycosylation of this Asn residue could be a source of the multiplicity of natural Hev b 2. Possible participation of the carbohydrate epitopes of latex beta-1,3-glucanase isoenzymes in their IgE-binding capacity and cross-reactivity was investigated in this study.

METHODS

beta-1,3-Glucanase isoenzymes were separated based on their affinities for concanavalin A. IgE-binding capacity and cross-reactivity were examined by immunoblotting and enzyme-linked immunosorbent assay (ELISA). Sequence heterogeneity among the isoenzymes was probed by peptide mass mapping after lysyl endopeptidase digestion. To clarify the relation to Hev b 2, N-terminal sequencing was performed on a fragmented peptide common to the separated isoenzymes.

RESULTS

Basic beta-1,3-glucanase was subdivided into two glycosylated isoenzymes (GI and GII) and one non-glycosylated isoenzyme (GIII). IgE antibodies in latex-positive sera chiefly recognized the glycosylated isoenzymes. Inhibition ELISA supported the significance of the carbohydrate epitopes for the IgE recognition and cross-reactivity. However, non-glycosylated GIII, as well as GI and GII, produced positive results in a skin prick test. The three beta-1,3-glucanase isoenzymes shared a partial sequence in common with Hev b 2.

CONCLUSIONS

Our results suggest that the carbohydrate epitopes in Hev b 2 homologues are relevant to an in vitro diagnosis of latex allergy and the accompanying cross-reactivity. Carbohydrate epitopes do not necessarily provoke allergic symptoms. Therefore, the actual allergenicity of Hev b 2 and its homologues should be carefully evaluated not only by in vitro IgE tests but also by in vivo tests.

Allergens and natural rubber proteins

BACKGROUND

Allergy to natural rubber latex (NRL) results from exposure to proteins derived from Hevea brasiliensis. Type I latex hypersensitivity is observed in certain occupational and other high-risk groups with frequent exposure to NRL products. This includes health care workers (HCWs), workers in the latex industry, children with spina bifida, and atopic individuals.

OBJECTIVES

Early reliable diagnosis and avoidance are required for better patient care. Standardized reagents are not presently available for in vitro and in vivo testing and treatment of patients with latex allergy. However, a number of allergens have been isolated and characterized from Hevea latex and NRL products. Currently, a total of 11 major and minor allergens are designated by the International Allergen Nomenclature Committee. This article reviews the structural and functional characteristics of these latex allergenic proteins.

RESULTS

NRL-allergenic proteins include those involved in the biosynthesis of polyisoprene and coagulation of latex rubber elongation factor, small rubber particle protein, prohevein, and patatin. Pathogenesis-related proteins include beta-1,3-glucanases, chitinases, and hevamine; and the structural proteins include microhelix protein complex, proline-rich protein, profilins, enolases, and manganese superoxide dismutase. Recombinant allergens demonstrated skin test reactivity in patients with latex allergy. The minimal level of skin test reactivity was about 70 pg/mL for NRL and 1 ng/mL for recombinant allergens. The use of selected recombinant latex allergens (Hev b 5, Hev b 6, and Hev b 7) in skin prick tests identified 93% of allergic individuals, mainly health care workers.

CONCLUSIONS

Recombinant latex allergens are clinically reactive and can be produced in a standardized manner, which could potentially provide safe and sensitive reagents for the diagnosis and treatment of type I latex allergy.

Atopic allergens of plant foods

The exact knowledge of what structural characteristics of an antigen are responsible for its allergenicity may not be available for several years. However, it is striking that the majority of the plant food allergens are clustered within a few protein families, and these are reviewed in this article. In most cases, plant food allergens are proteins that ensure the survival of the species as either seed storage proteins or proteins that are actively involved in the defence of the organism.

Cloning and expression of the gene which encodes a tube precipitin antigen and wall-associated beta-glucosidase of Coccidioides immitis

We report the structure and expression of the Coccidioides immitis BGL2 gene which encodes a previously characterized 120-kDa glycoprotein of this fungal respiratory pathogen. The glycoprotein is recognized by immunoglobulin M tube precipitin (TP) antibody present in sera of patients with coccidioidomycosis, a reaction which has been used for serodiagnosis of early coccidioidal infection. The deduced amino acid sequence of BGL2 shows 12 potential N glycosylation sites and numerous serine-threonine-rich regions which could function as sites for O glycosylation. In addition, the protein sequence includes a domain which is characteristic of family 3 glycosyl hydrolases. Earlier biochemical studies of the purified 120-kDa TP antigen revealed that it functions as a beta-glucosidase (EC 3.2.1.21). Its amino acid sequence shows high homology to several other reported fungal beta-glucosidases which are members of the family 3 glycosyl hydrolases. Results of previous studies have also suggested that the 120-kDa beta-glucosidase participates in wall modification during differentiation of the parasitic cells (spherules) of C. immitis. In this study we showed that expression of the BGL2 gene is elevated during isotropic growth of spherules and the peak of wall-associated BGL2 enzyme activity correlates with this same phase of parasitic cell differentiation. These data support our hypothesis that the 120-kDa beta-glucosidase plays a morphogenetic role in the parasitic cycle of C. immitis.

Plant allergens and pathogenesis-related proteins. What do they have in common?

In the recent past a great number of proteins causing type 1 allergic reactions in humans have been isolated and characterised. The main sources containing allergens are plants, mites, fungal spores and insects. Plant-derived allergens may either be taken in from the upper respiratory tract or they are present in a vast range of plant food causing food allergic reactions. Compared to the enormous amount of different plant proteins only a small number out of them are identified as a an allergen at present. Looking at the allergen encoding sequences, relationships by sequence similarity can be found quite frequently to a restricted number of plant protein families. Predominantly, these protein families are seed storage proteins, structural proteins and proteins involved in the defence-related system - pathogenesis-related proteins. In the following, a short overview of a number of pathogenesis-related protein families is presented in relation to the already known homologous plant allergens.

Use of rifampicin in T7 RNA polymerase-driven expression of a plant enzyme: rifampicin improves yield and assembly

Expression systems based on high selectivity and activity of T7 RNA polymerase and presence of a strong T7 promoter have been commonly used for cloning and expression of various recombinant proteins in Escherichia coli. When the expression system is designed in such a way that the produced protein is not being transferred into periplasm, bacterial cells must be lysed in order to isolate and purify the protein. The final yield and quality of the synthesized protein then depend on various factors, protein size, amino acid sequence, solubility in cytoplasm, and folding requirements among them. The yield in the T7 RNA polymerase/promoter system can be positively influenced by use of rifampicin. In this report we demonstrate usefulness of the antibiotic in detail. We describe rifampicin-enhanced expression of a plant cytokinin-specific beta-glucosidase. Two bacterial cultures are compared, one expressing the enzyme without and one in the presence of rifampicin. The antibiotic not only increased the yield of the recombinant protein, which seems to be a general phenomenon, but also favored the final assembly of the protein's subunits into a catalytically active dimer form.

[Plant defense-related proteins as latex allergens]

Immediate-type allergic reactions to latex products made from natural rubber are called latex allergy. One of the notable features of latex-allergic people is their cross-reactivity to various vegetable foods and pollen. The structurally similar proteins which most kinds of plants potentially induce must be responsible for these cross-reactions. However, the taxonomical dissimilarity among the causative plants has kept us from concrete explanations of such cross-reactive allergens. We have speculated that plant defense-related proteins are a possible cause of the latex allergy. The well-known serologic relationships and sequence similarities of these ubiquitous plant proteins can explain the cross-reactivity without difficulty. Rubber trees cultured in plantation farms are repeatedly tapped and treated with phytohormones. These stresses would result in the significant induction of defense-related proteins. Indeed, we were able to detect defense-related enzymes in latex extracts. Moreover, three hydrolytic enzymes (beta-1,3-glucanase, chitinase/lysozyme, and carboxylesterase) that are very likely to take a defensive role were specifically recognized by the IgE antibodies of latex-allergic people and atopic patients. These experimental results strongly support our hypothesis. Because of their conserved structures, defense-related proteins should form a family of plant pan-allergens.

Characterization of linamarase of latex and its localization in petioles in cassava

The distribution of linamarase in latex and its purification, characterization, and immunocytochemical localization in petioles were studied in order to get an insight into the process of cyanogenesis in cassava. Crude latex exudate exhibited low linamarase activity, but on dilution the activity increased about fivefold. Assay using petiole latex collected in isotonic medium showed that the enzyme was distributed in vesicle-like structures. In vitro studies showed that about 50% activity was released from the vesicle into the medium within an hour. Latex linamarase was purified by ammonium sulfate fractionation and DEAE-cellulose chromatography and was characterized with respect to its amino acid composition and kinetic properties. Gel filtration and SDS-PAGE analysis showed that the enzyme was made up of a 70,000-Da peptide. Immunocytochemical studies on the localization of linamarase in cassava petioles showed sporadic positive staining in the phloem and intense staining in the thickened corners of the collenchyma cells of the cortex, suggesting the distribution of linamarase in laticifers as well as in the cell wall.

Purification and characterization of a microsomal bile acid beta-glucosidase from human liver

A human liver microsomal beta-glucosidase has been purified to apparent homogeneity in sodium dodecyl sulfate-polyacrylamide gel electrophoresis where a single protein band of Mr 100,000 was obtained under reducing conditions. The enzyme was enriched about 73, 000-fold over starting microsomal membranes by polyethylene glycol fractionation, anion exchange chromatographies on DEAE-Trisacryl, and Mono Q followed by affinity chromatography on N-(9-carboxynonyl)-1-deoxynojirimycin-AH-Sepharose 4B. The purified enzyme had a pH optimum between 5.0 and 6.4, was activated by divalent metal ions, and required phospholipids for exhibition of activity. The enzyme catalyzed the hydrolysis of 3beta-D-glucosido-lithocholic and 3beta-D-glucosido-chenodeoxycholic acids with high affinity (Km, 1.7 and 6.2 microM, respectively) and of the beta-D-glucoside (Km, 210 microM) and the beta-D-galactoside of 4-methylumbelliferone. The ratio of relative reaction rates for these substrates was about 6:3:11:1. No activity was detectable toward 6beta-D-glucosido-hyodeoxycholic acid, glucocerebroside, and the following glycosides of 4-methylumbelliferone: alpha-D-glucoside, alpha-L-arabinoside, beta-D-fucoside or beta-D-xyloside. Immunoinhibition and immunoprecipitation studies using antibodies prepared against lysosomal glucocerebrosidase showed no cross-reactivity with microsomal beta-glucosidase suggesting that these two enzymes are antigenically unrelated.

Avenacosidase from oat: purification, sequence analysis and biochemical characterization of a new member of the BGA family of beta-glucosidases

A protein consisting of 60 kDa subunits (As-P60) was isolated from etiolated oat seedlings (Avena sativa L.) and characterized as avenacosidase, a beta-glucosidase that belongs to a preformed defence system of oat against fungal infection. The enzyme is highly aggregated; it consists of 300-350 kDa aggregates and multimers thereof. Dissociation by freezing/thawing leads to complete loss of enzyme activity. The specificity of the enzyme was investigated with para-nitrophenyl derivatives which serve as substrates, in decreasing order beta-fucoside, beta-glucoside, beta-galactoside, beta-xyloside. The corresponding orthonitrophenyl glycosides are less well accepted. No hydrolysis was found with alpha-glycosides and beta-thioglucoside. An anti-As-P60 antiserum was prepared and used for isolation of a cDNA clone coding for As-P60. A presequence of 55 amino acid residues was deduced from comparison of the cDNA sequence with the N-terminal sequence determined by Edman degradation of the mature protein. The presequence has the characteristics of a stroma-directing signal peptide; localization of As-P60 in plastids of oat seedlings was confirmed by western blotting. The amino acid sequence revealed significant homology (> 39% sequence identity) to beta-glucosidases that are constituents of a defence mechanism in dicotyledonous plants. 34% sequence identity was even found with mammalian and bacterial beta-glucosidases of the BGA family. Avenacosidase extends the occurrence of this family of beta-glucosidases to monocotyledonous plants.

An exo-beta-(1,3)-glucanase of Candida albicans: purification of the enzyme and molecular cloning of the gene

A nucleotide sequence encoding an exo-beta-(1,3)-glucanase was cloned from a library of genomic DNA of Candida albicans ATCC 10261. The sequenced gene encodes a protein of 438 amino acid residues. The amino terminal and an internal peptide sequence of the enzyme matched with deduced sequences within the cloned gene. Analysis of the sequence indicated that the nascent protein is processed during secretion by the signal peptidase and a Kex2-like proteinase, yielding a predicted mature enzyme of 400 residues. There is 58% identity and 85% similarity between the amino acid sequences of this exoglucanase and the homologous enzyme of Saccharomyces cerevisiae. An antiserum to the purified exoglucanase cross-reacted with the S. cerevisiae exoglucanase and a similar protein secreted by other C. albicans strains and Candida species. There are no sites for N-linked glycosylation in the sequence and this is consistent with the carbohydrate content of the secreted enzyme. Putative upstream promoter elements are associated with the gene. Southern analysis of the gene indicated that it was present at one copy per genome and that the diploid genome of C. albicans ATCC 10261 is heterozygous at this locus for a BglII RFLP. A 2.5 kb mRNA transcript was detected by Northern analysis and gene expression, as monitored by Northern and Western blots, reflected the growth rates of the cultures.

A seroreactive 120-kilodalton beta-1,3-glucanase of Coccidioides immitis which may participate in spherule morphogenesis

A beta-glucosidase of Coccidioides immitis was identified in electrophoresis gel separations of the concanavalin A-bound mycelial culture-filtrate-plus-lysate preparation. p-Nitrophenol-beta-D-glucopyranoside was used as the substrate to visualize the enzymatically active fraction in nonreducing gels. The gel-isolated, chromatographically purified enzyme has an optimal pH of 8.0 and cleaves beta-1,3-glycosyl linkages. The alkaline beta-glucosidase was further characterized by a pI of 3.8 to 4.0, optimal activity at 37 to 40 degrees C, and molecular size of 120 kDa as identified by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The purified beta-glucosidase is identical to a previously reported 120-kDa antigen (Ag) which reacts with immunoglobulin M (IgM) tube precipitin (TP) antibody in sera from patients with coccidioidomycosis. The TP-Ag was described as a valuable serodiagnostic reagent for detection of specific IgM in patients with early coccidioidal infections. The beta-glucosidase, like the TP-Ag, was localized in the cell wall and cytoplasmic vesicles of parasitic cells (spherules) by immunofluorescence and immunoelectron microscopy with specific antiserum raised against the purified enzyme. The boiled cell wall fraction isolated from these same young (presegmented) spherules was partially digested by the beta-glucosidase. Addition of a potent beta-glucosidase inhibitor, 1-deoxynojirimycin, to the parasitic-phase culture medium at a concentration of 200 microM blocked or retarded conversion of arthroconidia to spherules. Antibody was raised in guinea pigs against chromatographically purified 1-deoxynojirimycin which was conjugated with bovine serum albumin. The inhibitor was localized by immunofluorescence in the wall of the 1-deoxynojirimycin-treated cells. We suggest that the spherule wall-associated, alkaline hydrolase functions as a beta-1,3-glucanase to provide for wall plasticity as well as intussusception of newly synthesized wall polymers during the period of rapid diametric growth of parasitic cells of C. immitis.

The major exoglucanase from Candida albicans: a non-glycosylated secretory monomer related to its counterpart from Saccharomyces cerevisiae

Exoglucanases secreted by two different strains from Candida albicans have been purified to homogeneity. The purified enzyme from each strain behaved as a non-glycosylated monomer (molecular weight 38,000) that was identical in terms of sodium dodecyl sulphate/polyacrylamide gel electrophoresis comigration, amino acid analysis and amino terminal sequence. The amino acid composition was similar to that of the major exoglucanase from Saccharomyces cerevisiae. In addition, these two enzymes displayed a 50% homology in the first 35 amino acids of the amino terminus. Antibodies against the deglycosylated exoglucanase (treated with Endo H) from S. cerevisiae were reactive with the exoglucanase from C. albicans and vice versa. Immunoblotting proved to be a semiquantitative method to detect C. albicans antigen in culture fluids. The exoglucanase from C. albicans appears to enter the secretory pathway without undergoing N-glycosylation.

Kinetic study of a cellobiase purified from Neocallimastix frontalis EB188

A cellobiase was purified from the culture supernatant of Neocallimastix frontalis EB188. This enzyme possessed a molecular weight of 85,000 and an isoelectric point of 6.95. The enzyme rapidly hydrolyzed cellobiose, p-nitrophenyl (pNP) beta-D-glucopyranoside (pNPG) and cellotriose and slowly hydrolyzed cellopentaose and salicin. The enzyme did not hydrolyze pNP alpha-D-glucopyranoside or pNP beta-D-cellobioside. Substrate inhibition was observed when cellobiose or pNPG were used as the substrates and glucose production was measured. The kinetic parameters were: K = 0.053 mM, V = 5.88 U/mg of protein and Ki = 0.95 mM for cellobiose; K = 0.36 mM, V = 1.05 U/mg and Ki = 8.86 mM for pNPG. Substrate inhibition was not detected during the hydrolysis of pNPG when pNP production was measured. The kinetic parameters for pNPG were: K = 0.67 mM and V = 1.49 U/mg of protein. The presence of an enzyme.glucose.substrate complex and transglucosylation was evident during the catalysis. Glucose, cellobiose, glucono-delta-lactone, galactose, lactose, maltose and salicin acted as competitive inhibitors during the hydrolysis of pNPG with the apparent inhibition constants (Kis) of 4.8 mM, 0.035 mM, 0.062 mM, 28.5 mM, 0.38 mM, 15.0 mm and 31.0 mM, respectively.

Human acid beta-glucosidase. Use of inhibitory and activating monoclonal antibodies to investigate the enzyme's catalytic mechanism and saposin A and C binding sites

Of 14 identified epitopes on human GCase (acid beta-glucosidase), monoclonal antibodies (MCABs) recognizing 3 produced inhibition and 1 resulted in activation of GCase. MCABs F1 and F2 completely, and MCAB 61 partially (approximately 70%), inhibited GCase activity. Substrates and active site-directed inhibitors (specific sphingolipid and 5-amino-5-deoxyglucose derivatives) protected the enzyme from inhibition by MCAB F1 and F2, but not that by MCAB 61. Conduritol B epoxide did not protect GCase from the inhibition by these MCABs when covalently bound to the active site. These results indicated highly specific binding requirements of MCABs F1 and F2 for residues in a complex active site. In comparison, kinetic analyses using GCase transition state analogues, N-alkyl-glucosylamines, and MCAB 61 demonstrated that this MCAB "freezes" the conformation of the enzyme and inhibits GCase by preventing formation of a conformer needed for maximal catalytic rates. The activating MCAB 122 mimicked the effects of saposin C and competed with this natural activator for residues on the enzyme. Interaction of saposin A and saposin C or MCAB 122 with GCase produced a synergistic effect leading to a marked sensitization of the enzyme to these activators. No such synergism or additivity was found for the maximal catalytic rate since it could be achieved by saturating amounts of any one or combinations of these activators. In the presence of MCAB 61, only 15 to 25% of the maximal activation of GCase was obtained by saposin C or MCAB 122, indicating that the major activation effects of these effectors derived from an induction of a GCase conformational change. These results demonstrate that saposins A and C mediate their activating effects by binding to distinct sites on GCase. Furthermore, major components of the mechanisms for catalysis and saposin C activation are due to conformational changes during the transition state. These findings have implications for understanding the perturbations of GCase function due to the missense mutations which cause Gaucher disease.

Maize genotypes classified as null at the glu locus have beta-glucosidase activity and immunoreactive protein

Maize beta-glucosidase (beta-D-glucoside glucohydrolase; EC 3.2.1.21) was extracted from coleoptiles of 15 maize genotypes (3 normals, 10 nulls, and 2 hybrids) in two fractions, the soluble and the insoluble. The enzyme activity was measured spectrophotometrically in the soluble fraction and also studied on zymograms after native gel electrophoresis and isoelectric focusing. The enzyme was purified from a normal genotype by anion-exchange chromatography and preparative electrophoresis. Antisera were raised in four rabbits, and the soluble and the insoluble extracts of each genotype were analyzed for a cross-reacting material by ELISA and immunoblotting. The results showed that extracts from both the normal and the null genotypes had beta-glucosidase activity, and the activity measured spectrophotometrically was 2- to 10-fold higher in normals than in nulls. Zymograms of the null genotypes were devoid of distinct bands that were present in those of normals and hybrids from crosses between normals and nulls. Zymograms of both the normal and the null genotypes had a diffuse, smeared zone of activity at the cathodic end of native gels. A cross-reacting antigen was present in extracts of both genotypes when assayed by ELISA and a 60-kD polypeptide (beta-glucosidase monomer) was detected by four different monospecific beta-glucosidase antisera on Western blots by immunostaining. Moreover, six of seven null genotypes had a larger amount of their 60-kD polypeptide in the insoluble fraction than in the soluble fraction. These data show that both the null and the normal genotypes have similar amounts of the enzyme protein, but the enzyme occurs mostly as insoluble or poorly soluble polymers in nulls, and the monogenic inheritance reported for the null alleles of the glu locus is likely to be for a factor encoded by another locus which affects directly or indirectly the solubility of the enzyme by increasing its polymerization into large quaternary structures.

Immunogold localization of beta-1,3-glucanases in two plants infected by vascular wilt fungi

An antiserum raised against a purified tobacco beta-1,3-glucanase (PR-N) was used to study the subcellular localization of enzyme in fungus-infected plant tissues by means of post-embedding immunogold labeling. In susceptible tomato plants, the enzyme accumulation was found to occur as a result of successful tissue colonization, whereas it appeared to be an early event associated with limited spread of the fungus in resistant tissues. Although marked differences between susceptible and resistant tomato cultivars were observed in the rate of production of beta-1,3-glucanase, the pattern of enzyme distribution was similar. The enzyme was found to accumulate predominantly in host cell walls and secondary thickenings of xylem vessels. By contrast, a very low amount of enzyme was associated with compound middle lamellae. The occurrence of beta-1,3-glucanase at the cell surface of invading fungi was an indication of their possible antifungal activity. A low enzyme concentration was detected in vacuoles of both healthy and infected tissues. In infected eggplant tissue, the pattern of beta-1,3-glucanase distribution was similar to that observed with tomato. Whether these hydrolases accumulate first in vacuoles and are subsequently conveyed toward the outside to participate in fungal wall lysis remains to be determined.

The use of tolerization in the production of monoclonal antibodies against minor antigenic determinants

An initial attempt to prepare monoclonal antibodies specific for the Dictyostelium discoideum lysosomal enzyme beta-glucosidase was unsuccessful. All of the antibodies resulting from this fusion recognized an extremely immunogenic epitope that is present on all of the lysosomal enzymes of Dictyostelium. In two succeeding fusions, changes in the immunization schedule intended to increase the immune response to enzyme-specific epitopes were not entirely successful. Although nine hybridomas producing antibodies specific for beta-glucosidase resulted from these two fusions, most (70%) of the cell lines isolated secrete antibodies that recognize the shared, immunodominant epitope. Moreover, the nine beta-glucosidase-specific antibodies proved to be of limited utility since none recognize the native enzyme. Therefore, we attempted to tolerize a BALB/c mouse to the common epitope by injecting the lysosomal enzyme, N-acetylglucosaminidase, within 40 h after birth. As an adult, this animal was immunized with beta-glucosidase. Fusion of the spleen cells from this mouse with myeloma cells resulted in the isolation of nine hybridoma lines that produce antibodies specific for beta-glucosidase. No antibodies reactive with the common epitope were detected. These results suggest that tolerization may provide a means whereby an undesired class of antibody-producing cell lines can be selectively eliminated from the products of a fusion.

Enzyme therapy: II. Effect of covalent attachment of polyethylene glycol on biochemical parameters and immunological determinants of beta-glucosidase and alpha-galactosidase

The covalent attachment of polyethylene glycol (PEG) to beta-glucosidase from sweet almonds and alpha-galactosidase from green coffee beans results in alterations of their catalytic properties and masking of specific determinant sites on the enzymes. Both enzymes have increased Km and decreased Vmax values against their respective p-nitrophenyl substrate analogs after PEG attachment. When PEG is attached to 30% of alpha-galactosidase epsilon-amino groups, 12% activity remains against ceramide trihexoside, while its ability to convert type B erythrocytes to type H specificity is lost. However, it still is able to cleave terminal galactose residues from human saliva blood group substance B. PEG-beta-glucosidase (38%) did not elicit the production of complement-fixing antibodies, nor did it react with antibodies produced against the native enzyme. Antibody and lectin-specific binding were lost from both modified enzymes (PEG-beta-glucosidase and PEG-alpha-galactosidase). After conjugation with PEG, beta-glucosidase lost its ability to bind to concanavalin A-Sepharose. Antibodies directed against native alpha-galactosidase blocked its enzyme activity, but lost their ability to inhibit activity in progressively higher modified preparations of the enzyme. Antisera against PEG-alpha-galactosidase (53%) did not inhibit enzyme activity in any alpha-galactosidase or PEG-alpha-galactosidase preparation. These results indicate that PEG tends to cover lectin-specific carbohydrate moieties and antigenic determinants and that these sites probably remain cryptic during in vivo processing of PEG-enzymes.