Lysis of intact yeast cells and isolated cell walls by an inducible enzyme system of Arthrobacter GJM-1.

Bacterium Arthrobacter GJM-1 known in the literature as a good producer of alpha-mannanase was found to accumulate in the culture fluid lytic activities against viable yeast cells during growth on isolated cell walls or beta-glucan fractions of yeast. The accumulation of the lytic activities showed an inducible character. The lytic system produced in the medium containing baker's yeast cell walls was capable of complete solubiliaztion of cell wals in vitro. The system lysed viable cells of a number of yeast species and induced their conversion to protoplasts in an osmotically stabilized medium. The lytic system showed different pH and temperature optima when viable cells or isolated cell walls were used as substrates. The pH optimum of the lysis of isolated cell walls was identical with pH optimum of beta-glucanase activities in the crude system. The results pointed out that in the lysis of intact cells, in addition to beta-glucanases, some other factor is involved. Substantial differences in the nature of the outer and the inner surface of cell walls of Saccharomuces cerevisiae were confirmed in this paper based on the different susceptibility to lysis of the cell walls in vivo and in vitro.     

The separation of β-glucanases produced by Cytophaga johnsonii and their role in the lysis of yeast cell walls

1. When Cytophaga johnsonii was grown in the presence of suitable inducers the culture fluid was capable of lysing thiol-treated yeast cell walls in vitro. 2. Autoclaved or alkali-extracted cells, isolated cell walls and glucan preparations made from them were effective inducers, but living yeast cells or cells killed by minimal heat treatment were not. 3. Chromatographic fractionation of lytic culture fluids showed the presence of two types of endo-beta-(1-->3)-glucanase and several beta-(1-->6)-glucanases; the latter may be induced separately by growing the myxo-bacterium in the presence of lutean. 4. Extensive solubilization of yeast cell walls was obtained only with preparations of one of these glucanases, an endo-beta-(1-->3)-glucanase producing as end products mainly oligosaccharides having five or more residues. Lysis by the other endo-beta-(1-->3)-glucanase was incomplete. 5. The beta-(1-->6)-glucanases produced a uniform thinning of the cell walls, and mannan-peptide was found in the solution. 6. These results, and the actions of the enzyme preparations on a variety of wall-derived preparations made from baker's yeast, are discussed in the light of present conceptions of yeast cell-wall structure.     

Lysis of yeast cell walls. Lytic beta-(1 leads to 6)-glucanase from Bacillus circulans WL-12.

When grown in a mineral medium with yeast cell walls or yeast glucan as the sole carbon source, Bacillus circulans WL-12 produces wall-lytic enzymes in addition to non-lytic beta-(1 leads to 3) and beta-(1 leads to 6)-glucananases. The lytic enzymes were isolated from the culture liquid by adsorption on insoluble yeast glucan in batch operation. After digestion of the glucan, the mixture of enzymes was chromatographed on hydroxylapatite on which the lytic activity could be resolved into one lytic beta-(1 leads to 6)glucanase and two lytic beta-(1 leads to 3)-glucanase was further purified by chromatography over diethylamino-ehtyl-agarose and carboxymethyl cellulose. Its specific activity on pustulan was 6.2 units per mg of protein. The enzyme moved as a single protein with a molecular weight of 54000 during sodium dodecylsulphate electrophoresis in slab gels. Hydrolysis of pustulan went thorugh a series of oligosaccharides, leading to a mixture of gentiotriose, gentiobiose and glucose. The enzyme also produced small amounts of gentiobiose from laminarin and pachyman and on this basis its lytic activity on yeast cell walls,was attribut beta-(1 leads to 3)-linked oligosaccharides were not detected. The lytic beta-(1 leads to 6)-glucanase has an optimum pH of 6.0. Pustulan hydrolysis followed Michaelis-Menten kinetics. A Km of 0.29 mg pustulan per ml and a V of 9.1 micro-equivalents of glucose released/min per mg of enzyme were calculated. The enzyme has no metal ion requirement. The lytic beta-(1 leads to 6)-glucanase differs in essence from the non-lytic beta-(1 leads to 6)-glucanase of the same organism by its positive action on yeast cell walls and yeast glucan and its much lower specific activity on soluble pustulan.     

Production and ecological significance of yeast cell wall-degrading enzymes from oerskovia

Motile actinomycetes capable of degrading walls of viable yeast cells were isolated from soil and identified as Oerskovia xanthineolytica. A lytic assay based on susceptibility of enzyme-treated cells to osmotic shock was developed, and 10 of 15 strains of O. xanthineolytica, Oerskovia turbata, and nonmotile Oerskovia- like organisms from other collections were found to possess yeast lytic activities. All lytic strains produced laminaranase and alpha-mannanase, but the amounts, determined by reducing group assays, were not proportional to the observed lytic activities. The Oerskovia isolates demonstrated chemotactic, predatory activity against various yeast strains and killed yeasts in mixed cultures. Of 15 carbon sources tested for production of lytic enzyme, purified yeast cell walls elicited the highest activity. Glucose repressed enzyme production and caused cells to remain in the microfilamentous and motile rod stages of the Oerskovia cell cycle. Crude lytic activity was optimal at pH 5.6 to 7.0 and inactivated by heating for 6 min at 50 degrees C. Partial purification by isoelectric focusing showed that all lytic activity was associated with four beta-(1-->3)-glucanases. The absence of protein disulfide reductase, N-acetyl-beta-d-hexosaminidase, and phosphomannanase in crude preparations indicated that the principal enzyme responsible for yeast wall lysis was a beta-(1-->3)-glucanase that produced relatively little reducing sugar from yeast glucan.     

A refined method for the determination of Saccharomyces cerevisiae cell wall composition and beta-1,6-glucan fine structure.

In yeast and other fungi, cell division, cell shape, and growth depend on the coordinated synthesis and degradation of cell wall polymers. We have developed a reliable and efficient micro method to determine Saccharomyces cerevisiae cell wall composition that distinguishes between beta1,3- and beta1,6-glucan. The method is based on the sequential treatment of cell walls with specific hydrolytic enzymes followed by dialysis. The low molecular weight (MW) products thus separated account for each particular cell wall polymer. The method can be applied to as little as 50-100 mg (wet wt) of radioactively labeled cells. A combination of chitinase and recombinant beta-1,3-glucanase is initially used, releasing all of the chitin and 60-65% of the beta1,3-glucan from the cell walls. Next, recombinant endo-beta-1,6-glucanase from Trichoderma harzianum is utilized to release all the beta-1,6-glucan present in the wall. The chromatographic pattern of endoglucanase digested beta-1,6-glucan provides a characteristic "fingerprint" of beta-1,6-glucan and the fine structure of the oligosaccharides in this pattern was determined by 1H NMR and electrospray ionization mass spectroscopy. The final enzymatic step uses laminarinase and beta-glucosidase to release the remaining beta-1,3-glucan. The cell wall mannan remains as a high MW fraction at the end of the fractionation procedure. Good sensitivity and correlation with cell wall composition determined by traditional methods were observed for wild-type and several cell wall mutants.     

Some thaumatin-like proteins hydrolyse polymeric β-1,3-glucans

Thaumatin and 12 purified thaumatin-like (TL) proteins were surveyed for their capacity to hydrolyse beta-1,3-glucans by using an in-gel glucanase assay. Six TL proteins identified by N-terminal amino acid microsequencing were found to be active on carboxymethyl(CM)-pachyman: a barley leaf stress-related permatin, two tomato fruit osmotins, a cherry fruit and two tobacco stigma proteins. TL enzymes ranged in specific activity from 0.07 to 89 nkat mg-1 with CM-pachyman as substrate. Hydrolytic activities were not restricted to TL proteins strongly binding to water-insoluble beta-1,3-glucans since the two osmotins were active without tight binding to pachyman. Some TL proteins hydrolysed crude fungal walls and one barley TL enzyme even lysed fungal spores. No activity was observed on laminarin in the in-gel hydrolase assay. Thin-layer chromatography revealed that the six enzymes acted as endo-beta-1, 3-glucanases leading to the formation of various oligoglucosides. Thus far, the TL enzymes (EC 3.2.1.x) appeared different from the well-known beta-1,3-glucanases (EC 3.2.1.39). No activity was found with thaumatin, zeamatin, tobacco leaf PR-R protein and four stress-related TL proteins from barley and pea. This is the first demonstration that diverse TL proteins are enzymatically active. The functions of some TL proteins must be reassessed because they display endo-beta-1,3-glucanase activity on polymeric beta-1, 3-glucans.     

Analysis of the beta-1,3-Glucanolytic System of the Biocontrol Agent Trichoderma harzianum

The biocontrol agent Trichoderma harzianum IMI206040 secretes beta-1,3-glucanases in the presence of different glucose polymers and fungal cell walls. The level of beta-1,3-glucanase activity secreted was found to be proportional to the amount of glucan present in the inducer. The fungus produces at least seven extracellular beta-1,3-glucanases upon induction with laminarin, a soluble beta-1,3-glucan. The molecular weights of five of these enzymes fall in the range from 60,000 to 80,000, and their pIs are 5.0 to 6.8. In addition, a 35-kDa protein with a pI of 5.5 and a 39-kDa protein are also secreted. Glucose appears to inhibit the formation of all of the inducible beta-1,3-glucanases detected. A 77-kDa glucanase was partially purified from the laminarin culture filtrate. This enzyme is glycosylated and belongs to the exo-beta-1,3-glucanase group. The properties of this complex group of enzymes suggest that the enzymes might play different roles in host cell wall lysis during mycoparasitism.     

Wide-range antifungal antagonism of Paenibacillus ehimensis IB-X-b and its dependence on chitinase and beta-1,3-glucanase production

Previously, we isolated a strain of Bacillus that had antifungal activity and produced lytic enzymes with fungicidal potential. In the present study, we identified the bacterium as Paenibacillus ehimensis and further explored its antifungal properties. In liquid co-cultivation assays, P. ehimensis IB-X-b decreased biomass production of several pathogenic fungi by 45%-75%. The inhibition was accompanied by degradation of fungal cell walls and alterations in hyphal morphology. Residual medium from cultures of P. ehimensis IB-X-b inhibited fungal growth, indicating the inhibitors were secreted into the medium. Of the 2 major lytic enzymes, chitinases were only induced by chitin-containing substrates, whereas beta-1,3-glucanase showed steady levels in all carbon sources. Both purified chitinase and beta-1,3-glucanase degraded cell walls of macerated fungal mycelia, whereas only the latter also degraded cell walls of intact mycelia. The results indicate synergism between the antifungal action mechanisms of these enzymes in which beta-1,3-glucanase is the initiator of the cell wall hydrolysis, whereas the degradation process is reinforced by chitinases. Paenibacillus ehimensis IB-X-b has pronounced antifungal activity with a wide range of fungi and has potential as a biological control agent against plant pathogenic fungi.     

Simple method for the isolation of astaxanthin from the basidiomycetous yeast Phaffia rhodozyma.

A method is described for the quantitative and, possibly, large-scale extraction of astaxanthin from the yeast Phaffia rhodozyma. The method utilizes extracellular enzymes produced by the bacterium Bacillus circulans WL-12, which partially digests the yeast cell wall and renders the carotenoid pigments extractable by acetone or ethanol. Complete recovery of astaxanthin from heat-killed P. rhodozyma cells was obtained after growing B. circulans WL-12 on these yeast cells for 26 h and then extracting the yeast-bacterium mixture with acetone. A bacteria-free lytic system, which gave quantitative extraction of astaxanthin from P. rhodozyma, was obtained by concentrating the culture broth from the growth of B. circulans WL-12 on P. rhodozyma cells. Hydrolytic enzyme activities detected in this concentrate included beta-(1 leads to 3)-glucanase, beta-(1 leads to 6)-glucanase, alpha-(1 leads to 3)-glucanase, xylanase, and chitinase. The lytic system was found to work most efficiently at pH 6.5 and with low concentrations of yeast.     

Simple method for the isolation of astaxanthin from the basidiomycetous yeast Phaffia rhodozyma.

A method is described for the quantitative and, possibly, large-scale extraction of astaxanthin from the yeast Phaffia rhodozyma. The method utilizes extracellular enzymes produced by the bacterium Bacillus circulans WL-12, which partially digests the yeast cell wall and renders the carotenoid pigments extractable by acetone or ethanol. Complete recovery of astaxanthin from heat-killed P. rhodozyma cells was obtained after growing B. circulans WL-12 on these yeast cells for 26 h and then extracting the yeast-bacterium mixture with acetone. A bacteria-free lytic system, which gave quantitative extraction of astaxanthin from P. rhodozyma, was obtained by concentrating the culture broth from the growth of B. circulans WL-12 on P. rhodozyma cells. Hydrolytic enzyme activities detected in this concentrate included beta-(1 leads to 3)-glucanase, beta-(1 leads to 6)-glucanase, alpha-(1 leads to 3)-glucanase, xylanase, and chitinase. The lytic system was found to work most efficiently at pH 6.5 and with low concentrations of yeast.     

Cloning and expression in Escherichia coli of the gene for an Arthrobacter beta-(1----3)-glucanase.

When inserted in the correct orientation at the BamHI site of plasmid YRp7, an 8.6-kilobase BamHI fragment of Arthrobacter sp. strain YCWD3 DNA gave Escherichia coli HB101 cells harboring the recombinant plasmid pBX20 the ability to lyse bakers' yeast cell walls or bakers' yeast glucan in agar medium. An extract of the transformed E. coli cells contained an endo-beta-(1----3)-glucanase with the same activity pattern as that of glucanase I produced by Arthrobacter sp. strain YCWD3. Although part of the glucanase activity was contributed by apparently defective molecules, two protein species were found which had high lytic activity on yeast cell walls and adsorbed to microcrystalline cellulose, and both had a single constituent polypeptide with a molecular weight of about 55,000, as determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. In these properties the protein species were indistinguishable from those glucanase I protein species of Arthrobacter sp. strain YCWD3 which we believe are nearly the intact molecule. We conclude that the cloned fragment of Arthrobacter sp. strain YCWD3 DNA contains the structural gene for glucanase I. A recombinant plasmid obtained by subcloning a PstI fragment of pBX20 into pBR322 caused the transformed E. coli cells to produce apparently defective glucanase molecules only. This observation serves as additional supporting evidence for our conclusion.     

Co-operative action by endo- and exo-β-(1→3)-glucanases from parasitic fungi in the degradation of cell-wall glucans of Sclerotinia sclerotiorum (Lib.) de Bary

1. Two fungi, Coniothyrium minitans Campbell and Trichoderma viride Pers. ex Fr., were grown on autoclaved crushed sclerotia of the species Sclerotinia sclerotiorum, which they parasitize. 2. In vitro the crude culture filtrates would lyse walls isolated from hyphal cells or the inner pseudoparenchymatous cells of the sclerotia, in which a branched beta-(1-->3)-beta-(1-->6)-glucan, sclerotan, is a major constituent. 3. Chromatographic fractionation of the enzymes in each culture filtrate revealed the presence of several laminarinases, the most active being an exo-beta-(1-->3)-glucanase, known from previous studies to attack sclerotan. Acting alone this brought about a limited degradation of the glucan, but the addition of fractions containing an endo-beta-(1-->3)-glucanase led to almost complete breakdown. A similar synergism between the two enzymes was found in their lytic action on cell walls. 4. When acting alone the endo-beta-(1-->3)-glucanase had a restricted action, the products including a trisaccharide, tentatively identified as 6(2)-beta-glucosyl-laminaribiose. 5. These results are discussed in relation to the structure of the cell walls and of their glucan constituents.     

Lysis of yeast cell walls. Lytic beta-(1 leads to 3)-glucanases from Bacillus circulans WL-12.

Bacillus circulans WL-12 when grown in a mineral medium with yeast cell walls or yeast glucan as the soli carbon source, produced five beta-glucanases. Two beta-(1 leads to 3)-glucanases (I and II), which are lytic to yeast cell walls, were isolated from the culture liquid by batch adsorption on yeast glucan, and separated by chromatography on hydroxylapatite. Lytic beta-(1 leads to 3)-glucanase I was further purified by carboxymethylcellulose chromatography. The specific activity of lytic beta-(1 leads to 3)-glucanase I on laminarin was 4.1 U per mg of protein. The enzyme moved as a single protein with a molecular weight of 40000 during sodium dodecylsulfate electrophoresis in slab gels. It was specific for the beta-(1 leads to 3)-glucosidic bond but the enzyme did not hydrolyze laminaribiose. Hydrolysis of laminarin went through a series of oligosaccharides, and laminaribiose and glucose accumulated till the end of the reaction. A small amount of gentibiose was also produced from laminarin. Products from yeast cell walls and yeast glucan included laminaripentaose, laminaritriose, laminaribiose, glucose and gentiobiose, but no laminaritetraose was detected. This glucanase has an optimum pH of 5.5.     

Digestion of Yeasts and Beta-1,3-Glucanases in Mosquito Larvae: Physiological and Biochemical Considerations

Aedes aegypti larvae ingest several kinds of microorganisms. In spite of studies regarding mosquito digestion, little is known about the nutritional utilization of ingested cells by larvae. We investigated the effects of using yeasts as the sole nutrient source for A. aegypti larvae. We also assessed the role of beta-1,3-glucanases in digestion of live yeast cells. Beta-1,3-glucanases are enzymes which hydrolyze the cell wall beta-1,3-glucan polyssacharide. Larvae were fed with cat food (controls), live or autoclaved Saccharomyces cerevisiae cells and larval weight, time for pupation and adult emergence, larval and pupal mortality were measured. The presence of S. cerevisiae cells inside the larval gut was demonstrated by light microscopy. Beta-1,3-glucanase was measured in dissected larval samples. Viability assays were performed with live yeast cells and larval gut homogenates, with or without addition of competing beta-1,3-glucan. A. aegypti larvae fed with yeast cells were heavier at the 4^th instar and showed complete development with normal mortality rates. Yeast cells were efficiently ingested by larvae and quickly killed (10% death in 2h, 100% in 48h). Larvae showed beta-1,3-glucanase in head, gut and rest of body. Gut beta-1,3-glucanase was not derived from ingested yeast cells. Gut and rest of body activity was not affected by the yeast diet, but head homogenates showed a lower activity in animals fed with autoclaved S. cerevisiae cells. The enzymatic lysis of live S. cerevisiae cells was demonstrated using gut homogenates, and this activity was abolished when excess beta-1,3-glucan was added to assays. These results show that live yeast cells are efficiently ingested and hydrolyzed by A. aegypti larvae, which are able to fully-develop on a diet based exclusively on these organisms. Beta-1,3-glucanase seems to be essential for yeast lytic activity of A. aegypti larvae, which possess significant amounts of these enzyme in all parts investigated.     

Purification and properties of a β-1,6-glucanase from Streptomyces sp. EF-14, an actinomycete antagonistic to Phytophthora spp.

Extracellular enzymes with glucanase activities are an important component of actinomycete-fungus antagonism. Streptomyces sp. EF-14 has been previously identified as one of the most potent antagonists of Phytophthora spp. A beta-1,6-glucanase (EC 3.2.1.75; glucan endo-1,6-beta-glucosidase) was purified by four chromatographic steps from the culture supernatant of strain EF-14 grown on a medium with lyophilized cells of Candida utilis as main nutrient source. The glucanase level in this medium followed a characteristic pattern in which the rise of beta-1,6-glucanase activity always preceded that of beta-1,3-glucanase. The molecular mass of the enzyme was estimated to be 65 kDa and the pI approximately 5.5. It hydrolyzed pustulan by an endo-mechanism generating gentiobiose and glucose as final products. Laminarin was not hydrolyzed indicating that the enzyme does not recognize beta-1,6-links flanked by beta-1,3-links. No significant clearing of yeast cell walls in liquid suspensions or in agar plates was observed indicating that this beta-1,6-glucanase is a non-lytic enzyme. This is the first beta-1,6-glucanase characterized from an actinomycete.     

Lysis of Yeast Cell Wall by Enzymes from Streptomycetes

This paper deals with yeast cell-wall lytic enzymes formed by Streptomyces with regard to the connection with the cell-wall structure.

In the first place, 29 organisms of β-glucanase-producing Streptomycetes were selected among 777 strains belonging to genus Streptomyces by means of a cylinder-plate method employing the yeast glucan as a substrate. As for these organisms, the depolymerizing activity against the yeast glucan was considered to be mainly due to β-1,3-glucanase activity. Against the heat-treated cell of bakers’ yeast, the crude enzymes merely showed poor lytic activities, however, in the combined employment with some protease preparations, especially with an alkaline protease from St. satsumaensis nov. sp., a remarkable increase of the lytic activities was demonstrated. On the other hand, the intact cell wall of bakers’ yeast, or both the heat-treated and the intact cells of Sacch. cerevisiae 18.29 strain were dissolved very easily by a sole action of β-glucanase or of protease, respectively. In consequence, it seemed that the lysis occurred with different mechanisms in response to differences of substrates. On this subject, the results of investigations and discussions were described in special measure. In addition, the possibility, that some other enzymes than β-glucanase or protease might concern to the lysis of the cell wall, was also investigated and discussed.     

Production and catabolite repression of Penicillium italicum beta-glucanases.

The filamentous fungus Penicillium italicum, grown in a defined liquid medium, produced beta-1,3-glucanase, which remained essentially bound to the cells, and beta-1,6-glucanase, an essentially extracellular enzyme. When glucose was depleted from the medium, when a limited concentration of glucose (0.2%) was maintained, or when the carbon source was galactose (3%) or lactose (3%), a significant increase in the specific activity of beta-1,3-glucanase, in cell extracts, took place. This was paralleled by a very slow rate of growth, and under glucose limitation, the appearance of beta-1,3-glucanase in the medium was also observed. On the other hand, when an excess of glucose, fructose, or sucrose was present, the specific activity remained constant and active growth was promoted. Laminarin, cellobiose, gentiobiose, and isolated Penicillium italicum walls were not capable of significantly inducing beta-1,3-glucanase synthesis to a level beyond that attained by glucose limitation. A similar behavior was observed for beta-1,6-glucanase. beta-1,3-Glucanase and beta-1,6-glucanase are therefore constitutive enzymes subjected to catabolite repression. The results are discussed in the context of the possible functions that have been suggested for glucanases and related enzymes.     

Purification and properties of a beta-1,6-glucanase from Penicillium brefeldianum.

An inducible endo-beta-1,6-glucanase was purified from Penicillium brefeldianum by DEAE-cellulose, Bio-Gel P-150 and high-pressure liquid chromatography. The final preparation was essentially free from beta-1,3-glucanase and beta-glucosidase activities. Sodium dodecyl sulphate/polyacrylamide-gel electrophoresis revealed one protein band with an Mr of 44000. The Vmax. and Km values were calculated to be 624 units (mumol/min)/mg and 2.78 mg/ml respectively. The glucanase had lytic activity against mycelial cells of the yeast Candida albicans. The yield of purified beta-1,6-glucanase from 100 mg dry weight of freeze-dried culture filtrate varied from 60 to 180 units.     

Kinetics of enzymatic lysis and disruption of yeast cells: I. Evaluation of two lytic systems with different properties

Many microorganisms produce enzymes which lyse the walls of yeasts, fungi, and bacteria. The proportions of different enzyme activities present in the lytic system, their action patterns, synergism, and dependence on inhibitors, constitute the activity profile of the lytic system. Taken together, the activity profile and process conditions for lysis determine the reaction rate and the distribution of products from lysis of any given type of cells. Kinetics of glucan hydrolysis, proteolysis, and lysis of brewer's yeast were compared for two extracellular yeast-lytic enzyme systems with different properties. The enzyme sources used were filtered culture broths from Cytophaga sp. NCIB 9497 grown in batch culture and from Oerskovia xanthineolytica LL-G109, grown under carbon limitation in continuous culture. Rate and extent of cell hydrolysis, and the accumulation of soluble proteins, peptides, and carbohydrates from the lysed yeast cells, are discussed in terms of the activity profiles and potential applications of the two enzyme systems.     

Crystal structure at 1.45-A resolution of the major allergen endo-beta-1,3-glucanase of banana as a molecular basis for the latex-fruit syndrome

Resolution of the crystal structure of the banana fruit endo-beta-1,3-glucanase by synchrotron X-ray diffraction at 1.45-A resolution revealed that the enzyme possesses the eightfold beta/alpha architecture typical for family 17 glycoside hydrolases. The electronegatively charged catalytic central cleft harbors the two glutamate residues (Glu94 and Glu236) acting as hydrogen donor and nucleophile residue, respectively. Modeling using a beta-1,3 linked glucan trisaccharide as a substrate confirmed that the enzyme readily accommodates a beta-1,3-glycosidic linkage in the slightly curved catalytic groove between the glucose units in positions -2 and -1 because of the particular orientation of residue Tyr33 delimiting subsite -2. The location of Phe177 in the proximity of subsite +1 suggested that the banana glucanase might also cleave beta-1,6-branched glucans. Enzymatic assays using pustulan as a substrate demonstrated that the banana glucanase can also cleave beta-1,6-glucans as was predicted from docking experiments. Similar to many other plant endo-beta-1,3-glucanases, the banana glucanase exhibits allergenic properties because of the occurrence of well-conserved IgE-binding epitopes on the surface of the enzyme. These epitopes might trigger some cross-reactions toward IgE antibodies and thus account for the IgE-binding cross-reactivity frequently reported in patients with the latex-fruit syndrome.