Monoclonal antibodies against different domains of cellobiohydrolase I and II from Trichoderma reesei

Extracellular protease production regulated by nitrogen and carbon sources in Trichoderma reesei

The filamentous fungus Trichoderma reesei is an important producer of industrial enzymes, and possesses abundant extracellular protease genes based on the genome sequence data. However, the production of extracellular proteases remains poorly understood. Here, protease production was extensively investigated on different carbon (glucose and lactose) and nitrogen sources ((NH₄ )₂ SO₄ , NaNO₃ , peptone, and corn steep liquor). It was found that protease production was dominantly regulated by nitrogen sources. Organic nitrogen sources were beneficial for protease production, while the preferred nitrogen source (NH₄ )₂ SO₄ inhibited the expression of proteases. As for carbon sources, lactose was a more effective inducer than glucose for protease production. The protease activity was further examined by protease inhibitors, which suggested that protease activity was predominantly inhibited by phenylmethanesulfonyl fluoride (PMSF) and slightly suppressed by ethylenediaminetetraacetic acid (EDTA). Moreover, proteomic analysis revealed a total of 29 extracellular proteases, including 13 serine proteases, 6 aspartic proteases, and 10 metalloproteases. In addition, seven proteases were found to be present among all conditions. These results showed the regulatory profile of extracellular protease production in Trichoderma reesei grown on various carbon and nitrogen sources, which will facilitate the development of T. reesei to be an effective workhorse for enzyme or high-value protein production in industry.

Abundance of Secreted Proteins of Trichoderma reesei Is Regulated by Light of Different Intensities

In Trichoderma reesei light is an important factor in the regulation of glycoside hydrolase gene expression. We therefore investigated the influence of different light intensities on cellulase activity and protein secretion. Differentially secreted proteins in light and darkness as identified by mass spectrometry included members of different glycoside hydrolase families, such as CBH1, Cel3A, Cel61B, XYN2, and XYN4. Several of the associated genes showed light-dependent regulation on the transcript level. Deletion of the photoreceptor genes blr1 and blr2 resulted in a diminished difference of protein abundance between light and darkness. The amount of secreted proteins including that of the major exo-acting beta-1,4-glucanases CBH1 and CBH2 was generally lower in light-grown cultures than in darkness. In contrast, cbh1 transcript levels increased with increasing light intensity from 700 to 2,000 lux but dopped at high light intensity (5,000 lux). In the photoreceptor mutants Δblr1 and Δblr2 cellulase activity in light was reduced compared to activity in darkness, showing a discrepancy between transcript levels and secreted cellulase activity. Furthermore, evaluation of different light sensitivities revealed an increased light tolerance with respect to cellulase expression of QM9414 compared to its parental strain QM6a. Investigation of one of the differentially expressed proteins between light and darkness, CLF1, revealed its function as a factor involved in regulation of secreted protease activity. T. reesei secretes a different set of proteins in light compared to darkness, this difference being mainly due to the function of the major known photoreceptors. Moreover, cellulase regulation is adjusted to light intensity and improved light tolerance was correlated with increased cellulase production. Our findings further support the hypothesis of a light intensity dependent post-transcriptional regulation of cellulase gene expression in T. reesei.

Dehydrogenase GRD1 represents a novel component of the cellulase regulon in Trichoderma reesei (Hypocrea jecorina)

Trichoderma reesei (Hypocrea jecorina) is nowadays the most important industrial producer of cellulase and hemicellulase enzymes, which are used for pretreatment of cellulosic biomass for biofuel production. In this study, we introduce a novel component, GRD1 (glucose-ribitol dehydrogenase 1), which shows enzymatic activity on cellobiose and positively influences cellulase gene transcription, expression, and extracellular endo-1,4-β-D-glucanase activity. grd1 is differentially transcribed upon growth on cellulose and the induction of cellulase gene expression by sophorose. The transcription of grd1 is coregulated with that of cel7a (cbh1) under inducing conditions. GRD1 is further involved in carbon source utilization on several carbon sources, such as those involved in lactose and D-galactose catabolism, in several cases in a light-dependent manner. We conclude that GRD1 represents a novel enhancer of cellulase gene expression, which by coregulation with the major cellulase may act via optimization of inducing mechanisms.

Identification of a gene coding for a deglycosylating enzyme in Hypocrea jecorina

An enzyme with mannosyl glycoprotein endo-N-acetyl-beta-D-glucosaminidase (ENGase)-type activity was partially purified from the extracellular medium of the mould Hypocrea jecorina (Trichoderma reesei). Internal peptides were generated and used to identify the gene in the T. reesei genome. The active enzyme is processed both at the N- and at the C-terminus. High-mannose-type glycoproteins are good substrates, whereas complex-type glycans are not hydrolysed. The enzyme represents the first fungal member of glycoside hydrolase family 18 with ENGase-type activity. Bacterial ENGases and the fungal chitinases belonging to the same family show very low homology with Endo T. Database searches identify several highly homologous genes in fungi and the activity is also found within other Trichoderma species. This ENGase activity, not coregulated with cellulase production, could be responsible for the extensive N-deglycosylation observed for several T. reesei cellulases.

Quantitative transcriptional analysis of the genes encoding glycoside hydrolase family 7 cellulase isozymes in the basidiomycete Phanerochaete chrysosporium

Cellulolytic fungi generally secrete a cellulase mixture consisting mainly of glycoside hydrolase family 7 cellulases (Cel7s) during degradation of crystalline cellulose. Although several Cel7s have been investigated so far, the marked similarity in their amino acid and nucleotide sequences makes independent quantitative analysis difficult. Here, we present a real-time PCR method for the detection and quantification of Cel7 genes (cel7A-F/G) in the basidiomycete Phanerochaete chrysosporium using PCR primer sets designed based on the 3' untranslated region sequences. It was confirmed by agarose gel electrophoresis, sequencing, and dissociation curve analysis of the PCR products that each cel7 transcript was specifically amplified by the corresponding primers. We applied this real-time reverse-transcription PCR method using the presented primer sets to evaluate quantitatively the expression changes of cel7 genes in P. chrysosporium under conditions of carbon catabolite derepression.

Statistical coupling analysis of aspartic proteinases based on crystal structures of the Trichoderma reesei enzyme and its complex with pepstatin A

The crystal structures of an aspartic proteinase from Trichoderma reesei (TrAsP) and of its complex with a competitive inhibitor, pepstatin A, were solved and refined to crystallographic R-factors of 17.9% (R(free)=21.2%) at 1.70 A resolution and 15.8% (R(free)=19.2%) at 1.85 A resolution, respectively. The three-dimensional structure of TrAsP is similar to structures of other members of the pepsin-like family of aspartic proteinases. Each molecule is folded in a predominantly beta-sheet bilobal structure with the N-terminal and C-terminal domains of about the same size. Structural comparison of the native structure and the TrAsP-pepstatin complex reveals that the enzyme undergoes an induced-fit, rigid-body movement upon inhibitor binding, with the N-terminal and C-terminal lobes tightly enclosing the inhibitor. Upon recognition and binding of pepstatin A, amino acid residues of the enzyme active site form a number of short hydrogen bonds to the inhibitor that may play an important role in the mechanism of catalysis and inhibition. The structures of TrAsP were used as a template for performing statistical coupling analysis of the aspartic protease family. This approach permitted, for the first time, the identification of a network of structurally linked residues putatively mediating conformational changes relevant to the function of this family of enzymes. Statistical coupling analysis reveals coevolved continuous clusters of amino acid residues that extend from the active site into the hydrophobic cores of each of the two domains and include amino acid residues from the flap regions, highlighting the importance of these parts of the protein for its enzymatic activity.

Application of DNA bar codes for screening of industrially important fungi: the haplotype of Trichoderma harzianum sensu stricto indicates superior chitinase formation

Selection of suitable strains for biotechnological purposes is frequently a random process supported by high-throughput methods. Using chitinase production by Hypocrea lixii/Trichoderma harzianum as a model, we tested whether fungal strains with superior enzyme formation may be diagnosed by DNA bar codes. We analyzed sequences of two phylogenetic marker loci, internal transcribed spacer 1 (ITS1) and ITS2 of the rRNA-encoding gene cluster and the large intron of the elongation factor 1-alpha gene, tef1, from 50 isolates of H. lixii/T. harzianum, which were also tested to determine their ability to produce chitinases in solid-state fermentation (SSF). Statistically supported superior chitinase production was obtained for strains carrying one of the observed ITS1 and ITS2 and tef1 alleles corresponding to an allele of T. harzianum type strain CBS 226.95. A tef1-based DNA bar code tool, TrichoCHIT, for rapid identification of these strains was developed. The geographic origin of the strains was irrelevant for chitinase production. The improved chitinase production by strains containing this haplotype was not due to better growth on N-acetyl-beta-D-glucosamine or glucosamine. Isoenzyme electrophoresis showed that neither the isoenzyme profile of N-acetyl-beta-glucosaminidases or the endochitinases nor the intensity of staining of individual chitinase bands correlated with total chitinase in the culture filtrate. The superior chitinase producers did not exhibit similarly increased cellulase formation. Biolog Phenotype MicroArray analysis identified lack of N-acetyl-beta-D-mannosamine utilization as a specific trait of strains with the chitinase-overproducing haplotype. This observation was used to develop a plate screening assay for rapid microbiological identification of the strains. The data illustrate that desired industrial properties may be an attribute of certain populations within a species, and screening procedures should thus include a balanced mixture of all genotypes of a given species.

Identification of genes encoding microbial glucuronoyl esterases

One type of covalent linkages connecting lignin and hemicellulose in plant cell walls is the ester linkage between 4-O-methyl-D-glucuronic acid of glucuronoxylan and lignin alcohols. An enzyme that could hydrolyze such linkages, named glucuronoyl esterase, occurs in the cellulolytic system of the wood-rotting fungus Schizophyllum commune. Here we report partial amino acid sequences of the enzyme and the results of subsequent search for homologous genes in sequenced genomes. The homologous genes of unknown functions were found in genomes of several filamentous fungi and one bacterium. The gene corresponding to the cip2 gene of Hypocrea jecorina (Trichoderma reesei), known to be up-regulated under conditions of induction of cellulolytic and hemicellulolytic enzymes, was over-expressed in H. jecorina. The product of the cip2 gene was purified to homogeneity and shown to exhibit glucuronoyl esterase activity.

d-Galactose induces cellulase gene expression in Hypocrea jecorina at low growth rates

Lactose (1,4-O-β-d-galactopyranosyl-d-glucose) is a soluble and economic carbon source for the industrial production of cellulases or recombinant proteins by Hypocrea jecorina (anamorph Trichoderma reesei). The mechanism by which lactose induces cellulase formation is not understood. Recent data showed that the galactokinase step is essential for cellulase induction by lactose, but growth on d-galactose alone does not induce cellulases. Consequently, the hypothesis was tested that d-galactose may be an inducer only at a low growth rate, which is typically observed when growing on lactose. Carbon-limited chemostat cultivations of H. jecorina were therefore performed at different dilution rates with d-galactose, lactose, galactitol and d-glucose. Cellulase gene expression was monitored by using a strain carrying a fusion between the cbh2 (encoding cellobiohydrolase 2, Cel6A) promoter region and the Aspergillus niger glucose oxidase gene and by identification of the two major cellobiohydrolases Cel7A and Cel6A. The results show that d-galactose indeed induces cbh2 gene transcription and leads to Cel7A and Cel6A accumulation at a low (D=0·015 h−1) but not at higher dilution rates. At the same dilution rate, growth on d-glucose did not lead to cbh2 promoter activation or Cel6A formation but a basal level, lower than that observed on d-galactose, was detected for the carbon-catabolite-derepressible Cel7A. Lactose induced significantly higher cellulase levels at 0·015 h−1 than d-galactose and induced cellulases even at growth rates up to 0·042 h−1. Results of chemostats with an equimolar mixture of d-galactose and d-glucose essentially mimicked the behaviour on d-galactose alone, whereas an equimolar mixture of d-galactose and galactitol, the first intermediate of a recently described second pathway of d-galactose catabolism, led to cellulase induction at D=0·030 h−1. It is concluded that d-galactose indeed induces cellulases at low growth rate and that the operation of the alternative pathway further increases this induction. However, under those conditions lactose is still a superior inducer for which the mechanism remains to be clarified.

Use of monoclonal antibodies to quantify the dynamics of alpha-galactosidase and endo-1,4-beta-glucanase production by Trichoderma hamatum during saprotrophic growth and sporulation in peat

Trichoderma species are ubiquitous soil and peat-borne saprotrophs that have received enormous scientific interest as biocontrol agents of plant diseases caused by destructive root pathogens. Mechanisms of biocontrol such as antibiosis and hyperparasitism are well documented and the biochemistry and molecular genetics of these processes defined. An aspect of biocontrol that has received little attention is the ability of Trichoderma species to compete for nutrients in their natural environments. Trichoderma species are efficient producers of polysaccharide-degrading enzymes that enable them to colonize organic matter thereby preventing the saprotrophic spread of plant pathogens. This study details the use of monoclonal antibodies (mAbs) to quantify the production of two enzymes implicated in the saprotrophic growth of Trichoderma species in peat. Using mAbs specific to the hemicellulase enzyme alpha-galactosidase (AGL) and the cellulase enzyme endo-1,4-beta-glucanase (EG), the relationship between the saprotrophic growth dynamics of a biocontrol strain of Trichoderma hamatum and the concomitant production of these enzymes in peat-based microcosms was studied. Enzyme activity assays and enzyme protein concentrations derived by enzyme-linked immunosorbent assay (ELISA) established the precision and sensitivity of mAb-based assays in quantifying enzyme production during active growth of the fungus. Trends in enzyme activities and protein concentrations were similar for both enzymes, during a 21-day sampling period in which active growth and sporulation of the fungus in peat was quantified using an independent mAb-based assay. There was a sharp increase in active biomass of T. hamatum 3 days after inoculation of microcosms with phialoconidia. After 3 days there was a rapid decline in active biomass which coincided with sporulation of the fungus. A similar trend was witnessed with EG activities and concentrations. This showed that EG production related directly to active growth of the fungus. The trend was not found, however, with AGL. There was a rapid increase in enzyme activities and protein concentrations on day 3, after which they remained static. The reason for the maintenance of elevated AGL probably resulted from secretion of the enzyme from conidia and chlamydospores. ELISA, immunofluoresence and immunogold electron microscopy studies of these cells showed that the enzyme is localized within the cytoplasm and is secreted extracellularly into the surrounding environment. It is postulated that release of oligosaccharides from polymeric hemicellulose by the constitutive spore-bound enzyme leads to AGL induction and could act as an environmental cue for spore germination.

Role of the bga1-encoded extracellular {beta}-galactosidase of Hypocrea jecorina in cellulase induction by lactose

Lactose is the only soluble and economically feasible carbon source for the production of cellulases or heterologous proteins regulated by cellulase expression signals by Hypocrea jecorina (Trichoderma reesei). We investigated the role of the major beta-galactosidase of H. jecorina in lactose metabolism and cellulase induction. A genomic copy of the bga1 gene was cloned, and this copy encodes a 1,023-amino-acid protein with a 20-amino-acid signal sequence. This protein has a molecular mass of 109.3 kDa, belongs to glycosyl hydrolase family 35, and is the major extracellular beta-galactosidase during growth on lactose. Its transcript was abundant during growth on l-arabinose and l-arabinitol but was much less common when the organism was grown on lactose, d-galactose, galactitol, d-xylose, and xylitol. Deltabga1 strains grow more slowly and accumulate less biomass on lactose, but the cellobiohydrolase I and II gene expression and the final cellulase yields were comparable to those of the parental strain. Overexpression of bga1 under the control of the pyruvate kinase promoter reduced the lag phase, increased growth on lactose, and limited transcription of cellobiohydrolases. We detected an additional extracellular beta-galactosidase activity that was not encoded by bga1 but no intracellular beta-galactosidase activity. In conclusion, cellulase production on lactose occurs when beta-galactosidase activity levels are low but decreases as the beta-galactosidase activities increase. The data indicate that bga1-encoded beta-galactosidase activity is a critical factor for cellulase production on lactose.

The galactokinase of Hypocrea jecorina is essential for cellulase induction by lactose but dispensable for growth on d-galactose

Lactose is the only soluble carbon source which can be used economically for the production of cellulases or heterologous proteins under cellulase expression signals by Hypocrea jecorina (=Trichoderma reesei). Towards an understanding of lactose metabolism and its role in cellulase formation, we have cloned and characterized the gal1 (galactokinase) gene of H. jecorina, which catalyses the first step in d-galactose catabolism. It exhibits a calculated Mr of 57 kDa, and shows moderate identity (about 40%) to its putative homologues of Saccharomyces cerevisiae and Kluyveromyces lactis. Gal1 is a member of the GHMP family, shows conservation of a Gly/Ser rich region involved in ATP binding and of amino acids (Arg 51, Glu 57, Asp 60, Asp 214, Tyr 270) responsible for galactose binding. A single transcript was formed constitutively during the rapid growth phase on all carbon sources investigated and accumulated to about twice this level during growth on d-galactose, l-arabinose and their corresponding polyols. Deletion of gal1 reduces growth on d-galactose but does only slightly affect growth on lactose. This is the result of the operation of a second pathway for d-galactose catabolism, which involves galactitol as an intermediate, and whose transient concentration is strongly enhanced in the delta-gal1 strain. In this pathway, galactitol is catabolised by the lad1-encoded l-arabinitol-4-dehydrogenase, because a gal1/lad1 double delta-mutant failed to grow on d-galactose. In the delta-gal1 strain, induction of the Leloir pathway gene gal7 (encoding galactose-1-phosphate uridylyltransferase) by d-galactose, but not by l-arabinose, is impaired. Induction of cellulase gene expression by lactose is also impaired in a gal1 deleted strain, whereas their induction by sophorose (the putative cellulose-derived inducer) was shown to be normal, thus demonstrating that galactokinase is a key enzyme for cellulase induction during growth on lactose, and that induction by lactose and sophorose involves different mechanisms.

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.

Overexpression of the Saccharomyces cerevisiae mannosylphosphodolichol synthase-encoding gene in Trichoderma reesei results in an increased level of protein secretion and abnormal cell ultrastructure

Production of extracellular proteins plays an important role in the physiology of Trichoderma reesei and has potential industrial application. To improve the efficiency of protein secretion, we overexpressed in T. reesei the DPM1 gene of Saccharomyces cerevisiae, encoding mannosylphosphodolichol (MPD) synthase, under homologous, constitutively acting expression signals. Four stable transformants, each with different copy numbers of tandemly integrated DPM1, exhibited roughly double the activity of MPD synthase in the respective endoplasmic reticulum membrane fraction. On a dry-weight basis, they secreted up to sevenfold-higher concentrations of extracellular proteins during growth on lactose, a carbon source promoting formation of cellulases. Northern blot analysis showed that the relative level of the transcript of cbh1, which encodes the major cellulase (cellobiohydrolase I [CBH I]), did not increase in the transformants. On the other hand, the amount of secreted CBH I and, in all but one of the transformants, intracellular CBH I was elevated. Our results suggest that posttranscriptional processes are responsible for the increase in CBH I production. The carbohydrate contents of the extracellular proteins were comparable in the wild type and in the transformants, and no hyperglycosylation was detected. Electron microscopy of the DPM1-amplified strains revealed amorphous structure of the cell wall and over three times as many mitochondria as in the control. Our data indicate that molecular manipulation of glycan biosynthesis in Trichoderma can result in improved protein secretion.

Role of endoproteolytic dibasic proprotein processing in maturation of secretory proteins in Trichoderma reesei

Cell extracts of Trichoderma reesei exhibited dibasic endopeptidase activity toward the carboxylic side of KR, RR, and PR sequences. This activity was stimulated by the presence of Ca2+ ions and localized in vesicles of low bouyant density; it therefore exhibited some similarity to yeast Kex2. Analytical chromatofocusing revealed a single peak of activity. The dibasic endopeptidase activity was strongly and irreversibly inhibited in vitro as well as in vivo by 1 mM p-amidinophenylmethylsulfonyl fluoride (pAPMSF) but not by PMSF at concentrations up to 5 mM. We therefore used pAPMSF to study the role of the dibasic endopeptidase in the secretion of protein by T. reesei. Secretion of xylanase I (proprotein processing sequence -R-R- downward arrow-R- downward arrow-A-) and xylanase II (-K-R- downward arrow-Q-) was strongly inhibited by 1 mM pAPMSF, and a larger, unprocessed enzyme form was detected intracellularly under these conditions. Secretion of cellobiohydrolase II (CBH II; -E-R- downward arrow-Q-) was only slightly inhibited by pAPMSF, and no accumulation of unprocessed precursors was detected. In contrast, secretion of CBH I (-R-A- downward arrow-Q-) was stimulated by pAPMSF addition, and a simultaneous decrease in the concentration of intracellular CBH I was detected. Similar experiments were also carried out with a single heterologous protein, ShBLE, the phleomycin-binding protein from Streptoalloteichus hindustanus, fused to a series of model proprotein-processing sequences downstream of the expression signals of the Aspergillus nidulans gpdA promoter. Consistent with the results obtained with homologous proteins, pAPMSF inhibited the secretion of ShBLE with fusions containing dibasic (RK and KR) target sequences, but it even stimulated secretion in fusions to LR, NHA, and EHA target sequences. Addition of 5 mM PMSF, a nonspecific inhibitor of serine protease, nonspecifically inhibited the secretion of heterologous proteins from fusions bearing the NHA and LR targets. These data point to the existence of different endoproteolytic proprotein processing enzymes in T. reesei and demonstrate that dibasic processing is obligatory for the secretion of the proproteins containing this target.

Trichoderma reesei cellobiohydrolase I with an endoglucanase cellulose-binding domain: action on bacterial microcrystalline cellulose

Cellulolytic enzymes consist of distinct catalytic and cellulose-binding domains (CBDs). The presence of a CBD improves the binding and activity of cellulases on insoluble substrates but has no influence on their activities on soluble substrates. Structural and biochemical studies of a fungal CBD from Trichoderma reesei cellobiohydrolase I have revealed a wedge shaped structure with a flat cellulose binding surface containing three essential tyrosine residues. The face of the wedge is strictly conserved in all fungal CBDs while many differences occur on the other face of the wedge. Here we have studied the importance of these differences on the function of the T. reesei CBHI by replacing its CBD by a homologous CBD from the endoglucanase, EGI. Our data shows that, apart from slightly improved affinity of the hybrid enzyme, the domain exchange does not significantly influence the function of CBHI.

Proteolytic inactivation of an extracellular (1-->3)-beta-glucanase from the fungus Acremonium persicinum is associated with growth at neutral or alkaline medium pH

The filamentous fungus Acremonium persicinum released high levels of proteolytic enzyme activity into the culture fluid during growth at pH 7 or above. Almost total inhibition of this crude activity by phenylmethylsulfonyl fluoride suggested that it was mainly due to the presence of a serine protease. This protease inactivated one of three extracellular (1-->3)-beta-glucanases produced by this fungus, although the activities of the remaining two (1-->3)-beta-glucanases did not appear to be affected. Growth of A. persicinum in acidic conditions resulted in the presence of much lower extracellular proteolytic activity and no apparent (1-->3)-beta-glucanase inactivation.

Developments in biotechnological research in Austria

Austria is a small European country with a small number of universities and biotechnological industries, but with great efforts in the implementation of environmental consciousness and corresponding legal standards. This review attempts to describe the biotechnological landscape of Austria, thereby focusing on the highlights in research by industry, universities, and research laboratories, as published during 1990 to early 1995. These will include microbial metabolite (organic acids, antibiotics) and biopolymer (polyhydroxibutyrate, S-layers) production; enzyme (cellulases, hemicellulases, ligninases) technology and biocatalysis; environmental biotechnology; plant breeding and plant protection; mammalian cell products; fermenter design; and bioprocess engineering.

Effects of pH and high ionic strength on the adsorption and activity of native and mutated cellobiohydrolase I from Trichoderma reesei

Cellobiohydrolase I (CBHI) is the major cellulase of Trichoderma reesei. The enzyme contains a discrete cellulose-binding domain (CBD), which increases its binding and activity on crystalline cellulose. We studied cellulase-cellulose interactions using site-directed mutagenesis on the basis of the three-dimensional structure of the CBD of CBHI. Three mutant proteins which have earlier been produced in Saccharomyces cerevisiae were expressed in the native host organism. The data presented here support the hypothesis that a conserved tyrosine (Y492) located on the flat and more hydrophilic surface of the CBD is essential for the functionality. The data also suggest that the more hydrophobic surface is not directly involved in the CBD function. The pH dependence of the adsorption revealed that electrostatic repulsion between the bound proteins may also control the adsorption. The binding of CBHI to cellulose was significantly affected by high ionic strength suggesting that the interaction with cellulose includes a hydrophobic effect. High ionic strength increased the activity of the isolated core and of mutant proteins on crystalline cellulose, indicating that once productively bound, the enzymes are capable of solubilizing cellulose even with a mutagenized or with no CBD.

The bgl1 gene of Trichoderma reesei QM 9414 encodes an extracellular, cellulose-inducible beta-glucosidase involved in cellulase induction by sophorose

We have investigated the effect of disruption of the bgl1-(beta-glucosidase l-encoding) gene of Trichoderma reesei on the formation of other beta-glucosidase activities and on the induction of cellulases. To this end the bgl1 locus was disrupted by insertion of the Aspergillus nidulans amdS (acetamidase-encoding) gene. The bgl1-disrupted strain did not produce the 75 kDa extracellular beta-glucosidase on cellulose or lactose, but still formed beta-glucosidase activity on glucose, cellobiose, xylan or beta-1,3-glucan, suggesting that the enzyme(s) exhibiting this beta-glucosidase activity is (are) not encoded by bgl1. The cellulase-inducer sophorose induced the bgl1-encoded beta-glucosidase, whereas the remaining beta-glucosidase activity was induced by methyl-beta-D-glucoside. The bgl1-gene product was mainly secreted into the medium, whereas the other beta-glucosidase activity was mainly associated with the cells. A bgl1-multicopy strain formed higher amounts of cellulases than the parent strain. Nonsaturating concentrations of sophorose efficiently induced cellobiohydrolase l formation in the bgl1-multicopy strain, but less efficiently in the bgl1-disrupted strain. The multicopy strain and the parent strain were comparably efficient at saturating sophorose concentrations. The beta-glucosidase inhibitor nojirimycin strongly inhibited induction in all strains. These data suggest that the bgl1-encoded beta-glucosidase is not identical to the plasma-membrane-bound, constitutive, methyl-beta-glucoside inducible beta-glucosidase, but represents an extracellular cellulose-induced enzyme. Both enzymes contribute to rapid induction of cellulases by modifying the inducer sophorose.

CEL1: a novel cellulose binding protein secreted by Agaricus bisporus during growth on crystalline cellulose

The cel1 gene of Agaricus bisporus encodes a protein (CEL1) that has an architecture resembling the multi-domain fungal cellulases, although the sequence of its putative catalytic core is not matched by any other in the protein and nucleic acid data bases. The N-terminal half of the putative catalytic domain of CEL1 was expressed in Escherichia coli as a fusion protein with glutathione-S-transferase. The fusion protein was used to raise a CEL1-specific antibody. CEL1 was detected as an extracellular 49.8 kDa protein in A. bisporus cellulose-grown cultures, where it bound strongly to cellulose. CEL1 was neither an endoglucanase, a cellobiohydrolase able to hydrolyze fluorogenic cellobiosides, a beta-glucosidase, a xylanase, nor a cellobiose: quinone oxidoreductase. CEL1 was present in some fractions of culture fluid separated by electrophoresis which released soluble sugars from crystalline cellulose.

Mode of action of endoglucanase III from Trichoderma reesei

Endoglucanase III (EG III) was purified to homogeneity from the culture medium of Trichoderma reesei QM 9414. It has a molecular mass of 48 kDa, and an isoelectric point of 5.1. Maximal activity was observed between pH4 and 5. Celloligosaccharides and their chromophoric derivatives were used as substrates, and the reaction products were analysed by quantitative h.p.l.c. Nucleophilic competition experiments (between methanol and water) allowed unequivocal assessment of cleavage sites. EG III preferentially released cellobiose (or the corresponding glycoside) from the reducing end of the higher cellodextrins. A putative binding model containing five subsites is proposed. The pH-dependence of 4'-methylumbelliferyl beta-cellotrioside hydrolysis indicates the presence of a protonated group with a pK 5.5 in the reaction mechanism, and the possible involvement of a carboxy group is corroborated by a temperature study (delta Hion = -15.9 J/mol). This, together with independent evidence from affinity-labelling experiments [Tomme, Macarrón and Claeyssens (1991) Cellulose '91, New Orleans, Abstr. 32] and n.m.r. studies [Gebbler, Gilkes, Claeyssens, Wilson, Béguin, Wakarchuk, Kilburn, Miller, Warren and Withers (1992) J. Biol. Chem. 267, 12559-12561], favours the assumption of a lysozyme-type (retention of configuration, two essential carboxy groups) mechanism for this family A cellulase.

The Trichoderma cellulase regulatory puzzle: from the interior life of a secretory fungus

Novel applications for cellulases have reinitiated interest in the regulation of production of these enzymes by the soft rot fungus Trichoderma reesei and related species. This paper reviews the current state of knowledge concerning the question "How can insoluble molecules like cellulose initiate their own breakdown by a microorganism?" The evidence available--based on biochemical as well as molecular biological approaches--favors a model in which conidial bound cellobiohydrolases carry out a first exo-exo-wise attack on the cellulose molecule. The disaccharides so formed (cellobiose, alpha-cellobiono-1,5-lactone) are then taken up by the mycelia and promote further cellulase biosynthesis. Evidence available suggests that they are further metabolized to, rather than being, the "true" inducer. Speculations on the nature of the inducer are presented. The roles of the beta-glucosidases of Trichoderma in this process are discussed. The pathway of cellulase secretion is discussed on the basis of electron microscopical as well as gene sequence information.

Investigation of the function of mutated cellulose-binding domains of Trichoderma reesei cellobiohydrolase I

The function of the cellulose-binding domain (CBD) of the cellobiohydrolase I of Trichoderma reesei was studied by site-directed mutagenesis of two amino acid residues identified by analyzing the 3D structure of this domain. The mutant enzymes were produced in yeast and tested for binding and activity on crystalline cellulose. Mutagenesis of the tyrosine residue (Y492) located at the tip of the wedge-shaped domain to alanine or aspartate reduced the binding and activity on crystalline cellulose to the level of the core protein lacking the CBD. However, there was no effect on the activity toward small oligosaccharide (4-methylumbelliferyl beta-D-lactoside). The mutation tyrosine to histidine (Y492H) lowered but did not destroy the cellulose binding, suggesting that the interaction of the pyranose ring of the substrate with an aromatic side chain is important. However, the catalytic activity of this mutant on crystalline cellulose was identical to the other two mutants. The mutation P477R on the edge of the other face of the domain reduces both binding and activity of CBHI. These results support the hypothesis that both surfaces of the CBD are involved in the interaction of the binding domain with crystalline cellulose.

Structure, organization, and transcription of a cellobiohydrolase gene cluster from Phanerochaete chrysosporium

Restriction mapping and sequence analysis of cosmid clones revealed a cluster of three cellobiohydrolase genes in Phanerochaete chrysosporium. P. chrysosporium cbh1-1 and cbh1-2 are separated by only 750 bp and are located approximately 14 kb upstream from a cellulase gene previously cloned from P. chrysosporium (P. Sims, C. James, and P. Broda, Gene 74:411-422, 1988). Within a well-conserved region, the deduced amino acid sequences of P. chrysosporium cbh1-1 and cbh1-2 are, respectively, 80 and 69% homologous to that of the Trichoderma reesei cellobiohydrolase I gene. The conserved cellulose-binding domain typical of microbial cellulases is absent from cbh1-1. Transcript levels of the three P. chrysosporium genes varied substantially, depending on culture conditions. cbh1-1 and cbh1-2 were not induced in the presence of cellulose, nor did they appear to be subject to glucose repression. Therefore, aspects of the chromosomal organization, structure, and transcription of these genes are unlike those of any previously described cellulase genes.

Characterization and comparison of Clostridium cellulovorans endoglucanases-xylanases EngB and EngD hyperexpressed in Escherichia coli

By the use of a T7 expression system, endoglucanases-xylanases EngB and EngD from Clostridium cellulovorans were hyperexpressed and purified from Escherichia coli. The two enzymes demonstrated both endoglucanase and xylanase activities. The substrate specificities of both endoglucanases were similar except that EngD had four-times-greater p-nitrophenyl beta-1,4-cellobiosidase activity. The two proteins were very homologous (80%) up to the Pro-Thr-Thr region which divided the protein into -NH2- and -COOH-terminals. The -COOH- region of EngB has high homology to the endoglucanases and a xylanase from Clostridium thermocellum and to an endoglucanase from Clostridium cellulolyticum and did not show strong binding to cellulose (Avicel). However, the -COOH- region of EngD, which had homology to the cellulose-binding domains of Cellulomonas fimi exo- and endoglucanases and to Pseudomonas fluorescens endoglucanase, demonstrated binding ability to cellulose even when the domain was fused to the N-terminal domain of EngB. By probing the Avicel-purified cellulase complex (F8) with anti-EngB and anti-EngD antibodies, both EngB and EngD were shown to be present on the cellulase complex of C. cellulovorans. Many proteins homologous to EngB and EngD were also present on the complex.

Double-antibody sandwich enzyme-linked immunosorbent assay for quantitation of endoglucanase I of Trichoderma reesei

A sensitive and specific enzyme-liked immunosorbent assay for endoglucanase I (EG-I) has been developed. The monoclonal antibody a-EG-I 2, directed against an epitope on the core part of the enzyme, was used to capture the antigen in microtiter plate wells. A second, polyclonal antibody against the enzyme was then used to detect and quantitate the bound antigen. The test was specific for EG-I; neither endoglucanase II nor cellobiohydrolase I or II interfered. As little as 20 pg of EG-I protein could be detected. The coefficients of variation were 3.8% within plates and 6% between plates for a diluted Trichoderma reesei culture supernatant that contained 31 ng of EG-I per ml. Binding of the antigen to the monoclonal antibody was pH dependent and restricted to values between pH 6.5 and 10.5 with a maximum around pH 9. Standard solutions of EG-I were very stable at concentrations as low as 5 ng/ml when prepared in buffer that contained 1% bovine serum albumin and that was stored at -20 degrees C. After 37 weeks the antigenicity was still 97%. With this test it was possible to monitor the production of EG-I in a cellulase-producing strain of T. reesei and to demonstrate the apparent absence of the enzyme in a strain with the eglI gene deleted.

Monoclonal antibodies against core and cellulose-binding domains of Trichoderma reesei cellobiohydrolases I and II and endoglucanase I

Cellulases from Trichoderma reesei form an enzyme group with a common structural organization. Each cellulase enzyme is composed of two functional domains, the core region containing the active site and the cellulose-binding domain (CBD). To facilitate the specific detection of each domain, monoclonal antibodies (mAb) against cellobiohydrolase I (CBHI), cellobiohydrolase II (CBHII) and endoglucanase I (EGI) were produced. Five mAb were obtained against CBHI, ten against CBHII and eight against EGI. The location of the antigenic epitope for each antibody was mapped by allowing the antibodies to react with truncated cellulases, synthesized from deleted cDNA in Saccharomyces cerevisiae. Proteolytic fragments of Trichoderma cellulases, obtained by papain digestion, were used to confirm the results. Specific antibodies were detected against the core and the CBD epitopes for all three cellulases. Using the truncated enzymes, it was possible to locate the epitopes to a reasonably short region within the protein. To obtain a quantitative assay for each enzyme, a specific mAb against each antigen was chosen, based on the affinity to the corresponding antigen on Western-blot staining and on filter blots of the cellulolytic yeasts. The mAb were used to quantitative the corresponding enzymes in T. reesei culture medium. Specific quantitation of each cellulase enzyme has not been possible by biochemical assays or using polyclonal antibodies, due to their cross-reactions. Now, these mAb can be specifically used to recognize and quantitate different domains of these three important cellulolytic enzymes.

Cellobiohydrolase II is the main conidial-bound cellulase in Trichoderma reesei and other Trichoderma strains

Monoclonal antibodies have been used to determine the presence of cellobiohydrolases I and II (CBH I and II), and endoglucanase I (EG I) on the surface of conidia from Trichoderma reesei QM 9414 and RUT C-30, and 8 other Trichoderma species. For this purpose, proteins were released from the conidial surface by treatment with a non-ionic detergent (Triton X-100 and beta-octylglucoside), followed by SDS-PAGE/Western blotting and immunostaining. Both CBH I and II were clearly present, but - unlike in extracellular culture fluids from Trichoderma - CBH II was the predominant cellulase. In T. reesei EG I could not be detected. The higher producer strain T. reesei RUT C-30 exhibited a higher conidial level of CBH II than T. reesei QM 9414. In order to assess the importance of the conidial CBH II level for cellulase induction by cellulose, multiple copies of the chb2 gene were introduced into the T. reesei genome by cotransformation using PyrG as a marker. Stable multicopy transformants secreted the 2- to 4-fold level of CBH II into the culture medium when grown on lactose as a carbon source, but their CBH I secretion was unaltered. Upon growth on cellulose, both CBH I and CBH II secretion was enhanced. Those strain showing highest cellulase activity on cellulose also appeared to contain the highest level of conidial bound CBH II. CBH II was also the predominant conidial cellulase in various other Trichoderma sp. However, roughly the same amount of conidial bound CBH II was detected in all strains, although their cellulase production differed considerably.

Carbon Source Control of Cellobiohydrolase I and II Formation by Trichoderma reesei

Regulation of the formation and secretion of two cellulase components from Trichoderma reesei QM 9414, cellobiohydrolases I and II (CBH I and CBH II, respectively), by the carbon source was investigated. With monoclonal antibodies against CBH I and CBH II it was found that during cultivation on carbon sources which enable fast growth (glucose, glycerol, and fructose), no formation of CBH I occurred, whereas low levels of CBH II were formed. Lactose and cellulose, which allow comparably slower growth, promoted the formation of both CBH I and CBH II. However, noncarbohydrate carbon sources as citrate or acetate, which also enable only slow growth, did not promote the formation of CBH I or CBH II. The addition of glucose or glycerol to lactose- or cellulose-pregrown mycelia, on the other hand, only partially reduced the formation of CBH I. This reduction was also achieved by several other metabolizable and nonmetabolizable carbon compounds, e.g., fructose, galactose, β-methylglucoside, 2-deoxyglucose, and rhamnose, as well as by transfer to no carbon source at all. This result indicates that the control of CBH I synthesis by the carbon source is due to induction and not to repression. The use of cycloheximide and 5-fluorouracil as inhibitors at and before translation, respectively, revealed a half-life for CBH I mRNA of at least several hours, which may, at least in part, account for the prolonged synthesis of some CBH I under these conditions. Northern (RNA) hybridization with full copies of cbh1 and cbh2 genes indicated that the control of CBH I and CBH II biosyntheses by the carbon source operates mainly at the pretranslational level. We conclude that the low rate of cellulase synthesis on glucose and some other carbon sources is due to the lack of an inducer and not to carbon source repression.

A re-appraisal of multiplicity of endoglucanase I from Trichoderma reesei using monoclonal antibodies and plasma desorption mass spectrometry

An endo beta-1,4-glucanase (EC 3.2.1.4, 1.4-(1,3;1,4)-beta-D-glucan 4 glucanhydrolase) was purified to apparent homogeneity from culture filtrates of Trichoderma reesei QM 9414. Identity of the protein with endoglucanase I (EG I) was examined by subjecting CNBr fragments of the protein to analysis by plasma desorption mass spectrometry. Seven non-glycosylated fragments, mapped on the eg1 gene sequence, could be identified, hence proving at least 39.4% identity of the amino acid sequence. No sign for microheterogeneity was observed. Purified EG I was used to prepare monoclonal antibodies. 17 stable clones were obtained, of which one--Mab EG 3--was used to analyze several commercial T. reesei cellulase preparations as well as culture filtrates from T. pseudokoningii and T. longibrachiatum for the presence of EG I. Most of them contained immunoreactive material migrating as a prominent 50-55 kDa band on SDS-PAGE, resembling EG I, but in some instances additional lower molecular weight bands were also observed. Cultivation of T. reesei at low pH led to an increase of these lower molecular weight bands. EG I was rather stable against proteolysis by papain in vitro, but after prolonged treatment, immunopositive products of 50 and 45 kDa were produced at the expense of the 55 kDa band. Our monoclonal antibodies failed to react with a low-molecular-weight endoglucanase, which was previously shown to be detectable with polyclonal antiserum against EG I. However, all monoclonals reacted with a 118 kDa protein which is most probably a dimer of EG I. These results are discussed with respect to the occurrence of multiple forms of EG I in T. reesei cellulase preparations.

Double-Antibody Sandwich Enzyme-Linked Immunosorbent Assay for Cellobiohydrolase I

A double-antibody sandwich enzyme-linked immunosorbent assay was developed for quantifying cellobiohydrolase I (CBH I) in crude preparations of the cellulase complex from Trichoderma reesei. The other enzymes (endoglucanase and β-glucosidase) in this complex and other ingredients in culture broth did not interfere with this assay. The antibody configuration that resulted in the highest specificity for the assay of CBH I employed a monoclonal antibody to coat wells in polystyrene plates and peroxidase-labeled polyclonal antibody to detect cellobiohydrolase bound to the immobilized monoclonal antibody. Previously, procedures have not been available for the direct assay of CBH I activity in the presence of the other enzymes in the complex, and current indirect procedures are cumbersome and inaccurate. The direct procedure described here is highly specific for CBH I and useful for quantifying this enzyme in the range of 0.1 to 0.8 μg/ml.

Cross-reactive and specific monoclonal antibodies against cellobiohydrolases I and II and endoglucanases I and II of Trichoderma reesei

Splenocytes derived from mice inoculated with a commercial cellulase preparation or purified cellulases were fused with a stable myeloma cell line (SP2/0). Specific monoclonal antibodies to cellobiohydrolases I and II and endoglucanases I and II were established. In addition to specific monoclonal antibodies, we were also able to establish stable hybridoma cell lines which produced monoclonal antibodies that recognized similar epitopes possessed by two or more of the above cellulases. By obtaining monospecific antibodies for all four individual cellulases, the role and function of the individual cellulases can thus be studied in greater detail.