A full length cDNA clone for the alkaline protease from Aspergillus oryzae: structural analysis and expression in Saccharomyces cerevisiae

Advances in recombinant protease production: current state and perspectives

Proteases, enzymes that catalyze the hydrolysis of peptide bonds in proteins, are important in the food industry, biotechnology, and medical fields. With increasing demand for proteases, there is a growing emphasis on enhancing their expression and production through microbial systems. However, proteases' native hosts often fall short in high-level expression and compatibility with downstream applications. As a result, the recombinant production of proteases has become a significant focus, offering a solution to these challenges. This review presents an overview of the current state of protease production in prokaryotic and eukaryotic expression systems, highlighting key findings and trends. In prokaryotic systems, the Bacillus spp. is the predominant host for proteinase expression. Yeasts are commonly used in eukaryotic systems. Recent advancements in protease engineering over the past five years, including rational design and directed evolution, are also highlighted. By exploring the progress in both expression systems and engineering techniques, this review provides a detailed understanding of the current landscape of recombinant protease research and its prospects for future advancements.

Gene Analysis, Cloning, and Heterologous Expression of Protease from a Micromycete Aspergillus ochraceus Capable of Activating Protein C of Blood Plasma

Micromycetes are known to secrete numerous enzymes of biotechnological and medical potential. Fibrinolytic protease-activator of protein C (PAPC) of blood plasma from micromycete Aspergillus ochraceus VKM-F4104D was obtained in recombinant form utilising the bacterial expression system. This enzyme, which belongs to the proteinase-K-like proteases, is similar to the proteases encoded in the genomes of Aspergillus fumigatus ATCC MYA-4609, A. oryzae ATCC 42149 and A. flavus 28. Mature PAPC-4104 is 282 amino acids long, preceded by the 101-amino acid propeptide necessary for proper folding and maturation. The recombinant protease was identical to the native enzyme from micromycete in terms of its biological properties, including an ability to hydrolyse substrates of activated protein C (pGlu-Pro-Arg-pNA) and factor Xa (Z-D-Arg-Gly-Arg-pNA) in conjugant reactions with human blood plasma. Therefore, recombinant PAPC-4104 can potentially be used in medicine, veterinary science, diagnostics, and other applications.

Koji Molds for Japanese Soy Sauce Brewing: Characteristics and Key Enzymes

Soy sauce is a traditional Japanese condiment produced from the fermentation of soybeans, wheat, and salt by three types of microorganisms, namely koji molds, halophilic lactic acid bacteria, and salt-tolerant yeast. The delicate balance between taste, aroma, and color contributes to the characteristic delicious flavor imparted by soy sauce. In soy sauce brewing, protein and starch of the raw materials are hydrolyzed into amino acids and sugars by enzymes derived from koji molds. These enzymatically hydrolyzed products not only directly contribute to the taste but are further metabolized by lactic acid bacteria and yeasts to most of organic acids and aromatic compounds, resulting in its distinctive flavor and aroma. The color of the soy sauce is also due to the chemical reactions between amino acids and sugars during fermentation. Therefore, koji mold, which produces various enzymes for the breakdown of raw materials, is an essential microorganism in soy sauce production and plays an essential role in fermenting the ingredients. In this review, we describe the manufacturing process of Japanese soy sauce, the characteristics of koji molds that are suitable for soy sauce brewing, and the key enzymes produced by koji molds and their roles in the degradation of materials during soy sauce fermentation, focusing on the production of umami taste in soy sauce brewing.

Separation, biochemical characterization and salt-tolerant mechanisms of alkaline protease from Aspergillus oryzae

BACKGROUND

The salt tolerance of proteases secreted by Aspergillus oryzae 3.042 closely relates to the utilization of raw materials and the quality of soy sauce. However, little is known about the salt-tolerant proteases and their salt-tolerant mechanisms.

RESULTS

In this study, we isolated and identified a salt-tolerant alkaline protease (AP, approximately 29 kDa) produced by A. oryzae 3.042. It was considered as a metal-ion-independent serine protease. The optimum and stable pH values were both pH 9.0 and the optimum temperature was 40 °C. Over 20% relative activity of AP remained in the presence of 3.0 mol L^-1 NaCl after 7 days, but its K_m and V_max were only mildly influenced by the presence of 3.0 mol L^-1 NaCl, indicating its outstanding salt tolerance. Furthermore, AP was more stable than non-salt-tolerant protease at high salinity. The salt-tolerant mechanisms of AP could be due to more salt bridges, higher proportion of ordered secondary structures and stronger hydrophobic amino acid residues in the interior.

CONCLUSIONS

The above results are vital for maintaining, activating and/or modulating the activity of AP in high-salt environments. They would also provide theoretical guidance for the modification of AP and the engineering of A. oryzae 3.042 so as to secrete more AP. © 2018 Society of Chemical Industry.

A novel alkaline protease from alkaliphilic Idiomarina sp. C9-1 with potential application for eco-friendly enzymatic dehairing in the leather industry

Alkaline proteases have a myriad of potential applications in many industrial processes such as detergent, food and feed production, waste management and the leather industry. In this study, we isolated several alkaline protease producing bacteria from soda lake soil samples. A novel serine alkaline protease (AprA) gene from alkaliphilic Idiomarina sp. C9-1 was cloned and expressed in Escherichia coli. The purified AprA and its pre-peptidase C-terminal (PPC) domain-truncated enzyme (AprA-PPC) showed maximum activity at pH 10.5 and 60 °C, and were active and stable in a wide range of pH and temperature. Ca²⁺ significantly improved the thermostability and increased the optimal temperature to 70 °C. Furthermore, both AprA and AprA-PPC showed good tolerance to surfactants and oxidizing and reducing agents. We found that the PPC domain contributed to AprA activity, thermostability and surfactant tolerance. With casein as substrate, AprA and AprA-PPC showed the highest specific activity of 42567.1 U mg⁻¹ and 99511.9 U mg⁻¹, the K_m values of 3.76 mg ml⁻¹ and 3.98 mg ml⁻¹, and the V_max values of 57538.5 U mg⁻¹ and 108722.1 U mg⁻¹, respectively. Secreted expression of AprA-PPC in Bacillus subtilis after 48 h cultivation resulted in yield of 4935.5 U ml⁻¹ with productivity of 102.8 U ml⁻¹ h⁻¹, which is the highest reported in literature to date. Without adding any lime or sodium sulfide, both of which are harmful pollutants, AprA-PPC was effective in dehairing cattle hide and skins of goat, pig and rabbit in 8–12 h without causing significant damage to hairs and grain surface. Our results suggest that AprA-PPC may have great potentials for ecofriendly dehairing of animal skins in the leather industry.

TGF-β/SMAD4 mediated UCP2 downregulation contributes to Aspergillus protease-induced inflammation in primary bronchial epithelial cells

Elevated levels of mitochondrial reactive oxygen species (ROS) can lead to the development of airway inflammation. In this study, we investigated the role of Aspergillus proteases—which contribute to the pathogenesis of Aspergillus-induced diseases such as allergic bronchopulmonary aspergillosis, hypersensitivity pneumonitis, and atopic asthma—and their mechanisms of action in airway inflammation using primary human bronchial epithelial cells, and evaluated the inflammatory responses mediated by mitochondrial ROS. We found that Aspergillus proteases regulated the expression of multifunctional inflammatory cytokines such as interleukin (IL)− 1β, − 6, and − 8, and transforming growth factor (TGF)-β, which stimulated cytokine production and chemokines involved in leukocyte migration and activated an inflammatory cascade. Expression of these factors and activator protein (AP)− 1 were decreased by treatment with the mitochondrial ROS scavenger Mito-TEMPO, suggesting that mitochondria are important sources of ROS in the context of inflammatory response by Aspergillus protease. The regulation of mitochondrial ROS influenced the production of proinflammatory mediators by preventing mitochondrial ROS-induced AP-1 activation in airway epithelial cells. In addition, Aspergillus protease-mediated mitochondrial ROS production was associated with downregulation of uncoupling protein (UCP)− 2 expression by TGF-β-SMAD4 signaling, which may play a regulatory role in mitochondrial ROS formation during fungal protease-mediated epithelial inflammation. This improved understanding of the allergenic fungal protease-induced inflammatory mechanism in the bronchial epithelium will help in developing intervention strategies for the regulation of inflammatory response in allergic airway diseases.

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Fungal protease induce inflammatory cytokines, ROS, and mitochondrial ROS production.

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Fungal protease-induced mitochondrial ROS regulate AP-1 activation and neutrophil migration.

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Fungal protease-induced mitochondrial ROS modulate airway epithelial inflammation.

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Downregulation of UCP-2 expression by TGF-β-SMAD4 signaling induce mitochondrial ROS production.

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TGF-β/SMAD4 mediated UCP2 downregulation contributes to fungal protease-induced inflammation.

In silico characterization of alkaline proteases from different species of Aspergillus

A total of 49 protein sequences of alkaline proteases retrieved from GenBank representing different species of Aspergillus have been characterized for various physiochemical properties, homology search, multiple sequence alignment, motif, and super family search and phylogenetic tree construction. The sequence level homology was obtained among different groups of alkaline protease enzymes, viz alkaline serine protease, oryzin, calpain-like protease, serine protease, subtilisin-like alkaline proteases. Multiple sequence alignment of alkaline protease protein sequence of different Aspergillus species revealed a stretch of conserved region for amino acid residues from 69 to 110 and 130-204. The phylogenetic tree constructed indicated several Aspergillus species-specific clusters for alkaline proteases namely Aspergillus fumigatus, Aspergillus niger, Aspergillus oryzae, Aspergillus clavatus. The distributions of ten commonly observed motifs were analyzed among these proteases. Motif 1 with a signature amino acid sequence of 50 amino acids, i.e., ASFSNYGKVVDIFAPGQDILSCWIGSTTATNTISGTSMATPHIVGLSCYL, was uniformly observed in proteases protein sequences indicating its involvement with the structure and enzymatic function. Motif analysis of acidic proteases of Aspergillus and bacterial alkaline proteases has revealed different signature amino acid sequences. The superfamily search for these proteases revealed the presence of subtilases, serine-carboxyl proteinase, calpain large subunit, and thermolysin-like superfamilies with 45 representing the subtilases superfamily.

Purification and characterization of a novel serine protease from the mushroom Pholiota nameko

A novel serine protease, with a molecular mass of 19 kDa and the N-terminal sequence of ARTPEAPAEV, was isolated from dried fruiting bodies of the mushroom Pholiota nameko. The purification protocol comprised ion exchange chromatography on DEAE-cellulose, Q-Sepharose and SP-Sepharose, and gel filtration on Superdex 75. It was unadsorbed on DEAE-cellulose and Q-Sepharose but adsorbed on SP-Sepharose. It exhibited an optimum temperature at 50°C, an optimum pH at pH 8.8, a Km of 5.64 mg/mL and a Vmax of 0.98 μmol/min/mL against substrate casein. A number of metal ions inhibited the enzyme including Pb(2+), Mn(2+), Ca(2+), Hg(2+), Zn(2+), Cu(2+), Co(2+), Fe(3+) and Al(3+), with the inhibition of the last two cations being the most potent. K(+) and Mg(2+) slightly enhanced, while Li(+) moderately potentiated the activity of the protease. The protease was strongly inhibited by phenylmethylsulfonyl fluoride (PMSF), suggesting that it is a serine protease.

Heterotrimeric G protein mediated regulation of proteinase production in Aspergillus nidulans

Extracellular proteinase production induced by carbon starvation was studied in a series of heterotrimeric G protein signaling pathway mutants of Aspergillus nidulans. All the mutants tested--including deltafadA (Galpha), deltasfaD (Gbeta), deltagpgA (Ggamma) and deltasfgA (regulator of FadA signaling)--showed an elevated proteinase production after glucose depletion. Our results strongly support the view that during growth, FadA/SfaD/GpgA G protein signaling inhibits proteinase production via both Galpha and Gbetagamma subunits, and all conditions, which are not sufficient to support vegetative growth and, hence, inhibit this type of G protein signaling, elevate extracellular proteinase activities.

The spectrum of fungal allergy

Fungi can be found throughout the world. They may live as saprophytes, parasites or symbionts of animals and plants in indoor as well as outdoor environment. For decades, fungi belonging to the ascomycota as well as to the basidiomycota have been known to cause a broad panel of human disorders. In contrast to pollen, fungal spores and/or mycelial cells may not only cause type I allergy, the most prevalent disease caused by molds, but also a large number of other illnesses, including allergic bronchopulmonary mycoses, allergic sinusitis, hypersensitivity pneumonitis and atopic dermatitis; and, again in contrast to pollen-derived allergies, fungal allergies are frequently linked with allergic asthma. Sensitization to molds has been reported in up to 80% of asthmatic patients. Although research on fungal allergies dates back to the 19th century, major improvements in the diagnosis and therapy of mold allergy have been hampered by the fact that fungal extracts are highly variable in their protein composition due to strain variabilities, batch-to-batch variations, and by the fact that extracts may be prepared from spores and/or mycelial cells. Nonetheless, about 150 individual fungal allergens from approximately 80 mold genera have been identified in the last 20 years. First clinical studies with recombinant mold allergens have demonstrated their potency in clinical diagnosis. This review aims to give an overview of the biology of molds and diseases caused by molds in humans, as well as a detailed summary of the latest results on recombinant fungal allergens.

The role of the Aspergillus niger furin-type protease gene in processing of fungal proproteins and fusion proteins

We have characterized growth and protein processing characteristics of Aspergillus niger strains carrying a disrupted allele of the previously cloned and characterized kexB gene [Appl. Environ. Microbiol. 66 (2000) 363] encoding a furin-type endoprotease. Deletion of the single-copy gene confirms it to be non-essential but disruptant strains exhibit a morphologically distinct phenotype characterized by hyperbranching. Processing of homologous pro-proteins and fusion proteins comprised of a heterologous protein fused down-stream of glucoamylase and separated at the fusion junction by an endoproteolytic cleavage site was compared in wildtype and mutant strains of A. niger. We show that maturation of the native glucoamylase requires KexB, whereas maturation of aspergillopepsin does not. The processing of fusion proteins carrying Lys-Arg requires KexB, although alternative endoproteases are capable of cleaving protein fusions at sites adjacent to Lys-Arg.

Molecular and immunological characterization of Pen ch 18, the vacuolar serine protease major allergen of Penicillium chrysogenum

BACKGROUND

We have suggested previously that the 32 and 34 kDa major allergens of Penicillium chrysogenum (also known as P. notatum) are the vacuolar (Pen ch 18) and the alkaline (Pen ch 13) serine proteases, respectively, of P. chrysogenum. The purpose of this study is to characterize the 32 kDa allergen of P. chrysogenum and its immunoglobulin E (IgE)cross-reactivity with Pen ch 13 allergen.

METHODS

The full-length cDNA of Pen ch 18 was isolated by reverse transcriptase-polymerase chain reaction and the 5'-rapid amplification cDNA end reaction. Recombinant Pen ch 18 was expressed as his-tagged proteins in Escherichia coli. Its reactivity with IgE and monoclonal antibodies against fungal serine protease allergens was analyzed by immunoblotting. The IgE cross-reactivity between Pen ch 18 and Pen ch 13 was analyzed by immunoblot inhibition. Overlapping recombinant fragments and synthetic peptides were used to map the B cell epitopes on Pen ch 18.

RESULTS

In this study, we isolated a 1857 bp cDNA fragment containing an open reading frame of 494 amino acids that encodes the preproenzyme of Pen ch 18. Similar to other vacuolar serine proteases, this precursor appears to undergo N- and possibly C-terminal cleavage upon maturation. The his-tagged recombinant Pen ch 18 containing the putative sequence of the mature protein reacted with IgE antibodies in serum samples from asthmatic patients. In addition, IgE-binding to the 32 kDa major allergen of P. chrysogenum was inhibited when a positive serum sample was absorbed with recombinant Pen ch 18 before immunoblotting. Both inhibition and almost no inhibition of IgE-binding to the 32 kDa major allergen of Pen ch 18 were detected when eight positive serum samples were preabsorbed individually with purified Pen ch 13 before immunoblotting. The major IgE binding region was located in a fragment (PN1) encompassing the N-terminal 102 amino acid residues of the recombinant Pen ch 18. A dominant linear IgE epitope was further mapped within residues 73-95 (peptide PN1-e) of the N-terminally processed allergen. Monoclonal antibody FUM20 that reacts with Pen ch 18 but not with Pen ch 13 binds a synthetic peptide with sequence encompassing the N-terminal 23 residues of the recombinant Pen ch 18. Monoclonal antibody PCM39 that reacts with both Pen ch 13 and Pen ch 18 recognizes a peptide containing residues 132-154 of the allergen.

CONCLUSIONS

Our results confirm that the Pen ch 18 allergen is a vacuolar serine protease of P. chrysogenum that matures through N- and possibly C-terminal processing. The finding that there are cross-reactive and allergen-specific IgE epitopes for Pen ch 18 and Pen ch 13 suggests that both major allergens should be included in clinically diagnostic P. chrysogenum extracts.

Kinetic analysis of enhanced thermal stability of an alkaline protease with engineered twin disulfide bridges and calcium-dependent stability

The thermal stability of a cysteine-free alkaline protease (Alp) secreted by the eukaryote Aspergillus oryzae was improved both by the introduction of engineered twin disulfide bridges (Cys-69/Cys-101 and Cys-169/Cys-200), newly constructed as part of this study, and by the addition of calcium ions. We performed an extensive kinetic analysis of the increased thermal stability of the mutants as well as the role of calcium dependence. The thermodynamic activation parameters for irreversible thermal inactivation, the activation free energy (deltaG), the activation enthalpy (deltaH), and the activation entropy (deltaS) were determined from absolute reaction rate theory. The values of deltaH and deltaS were significantly and concomitantly increased as a result of introducing the twin disulfide bridges, for which the increase in the value of deltaH outweighed that of deltaS, resulting in significant increases in the value of deltaG. The enhancement of the thermal stability obtained by introducing the twin disulfide bridges is an example of the so-called low-temperature stabilization of enzymes. The stabilizing effect of calcium ions on wild-type Alp is similar to the results we obtained by introducing the engineered twin disulfide bridges.

Secreted proteases from pathogenic fungi

Many species of human pathogenic fungi secrete proteases in vitro or during the infection process. Secreted endoproteases belong to the aspartic proteases of the pepsin family, serine proteases of the subtilisin family, and metalloproteases of two different families. To these proteases has to be added the non-pepsin-type aspartic protease from Aspergillus niger and a unique chymotrypsin-like protease from Coccidioides immitis. Pathogenic fungi also secrete aminopeptidases, carboxypeptidases and dipeptidyl-peptidases. The function of fungal secreted proteases and their importance in infections vary. It is evident that secreted proteases are important for the virulence of dermatophytes since these fungi grow exclusively in the stratum corneum, nails or hair, which constitutes their sole nitrogen and carbon sources. The aspartic proteases secreted by Candida albicans are involved in the adherence process and penetration of tissues, and in interactions with the immune system of the infected host. For Aspergillus fumigatus, the role of proteolytic activity has not yet been proved. Although the secreted proteases have been intensively investigated as potential virulence factors, knowledge on protease substrate specificities is rather poor and few studies have focused on the research of inhibitors. Knowledge of substrate specificities will increase our understanding about the action of each protease secreted by pathogenic fungi and will help to determine their contribution to virulence.

Purification and properties of an alkaline proteinase of Fusarium culmorum

The disease Fusarium head blight (scab) causes severe problems for farmers and for the industries that use cereals. It is likely that the fungi that cause scab (Fusarium spp.) use various enzymes when they invade grains. We are studying enzymes that the fungi may use to hydrolyze grain proteins. To do this, Fusarium culmorum was grown in a gluten-containing medium from which an alkaline serine proteinase with a molecular mass of 28.7 kDa was purified by size-exclusion and cation exchange chromatographies. The enzyme was maximally active at pH 8.3-9.6 and 50 degrees C, but was unstable under these conditions. It hydrolyzed the synthetic substrates N-succinyl-Ala-Ala-Pro-Phe p-nitroanilide and, to a lesser extent, N-succinyl-Ala-Ala-Pro-Leu p-nitroanilide. It was inhibited by phenylmethanesulfonyl fluoride and chymostatin, but not by soybean trypsin or Bowman-Birk inhibitors. Parts of the amino-acid sequence were up to 82% homologous with those of several fungal subtilisins. One of the active site amino acids was detected and it occupied the same relative position as in the other subtilisins. Therefore, on the basis of these characteristics, the proteinase is subtilisin-like. Purification of the enzyme was complicated by the fact that, when purified, it apparently underwent autolysis. The presence of extraneous protein stabilized the activity.

Molecular characterization of a subtilase from the vascular wilt fungus Fusarium oxysporum

The gene prt1 was isolated from the tomato vascular wilt fungus Fusarium oxysporum f. sp. lycopersici, whose predicted amino acid sequence shows significant homology with subtilisin-like fungal proteinases. Prt1 is a single-copy gene, and its structure is highly conserved among different formae speciales of F. oxysporum. Prt1 is expressed constitutively at low levels during growth on different carbon and nitrogen sources and strongly induced in medium containing collagen and glucose. As shown by reverse transcription-polymerase chain reaction and fluorescence microscopy of F. oxysporum strains carrying a prt1-promoter-green fluorescent protein fusion, prt1 is expressed at low levels during the entire cycle of infection on tomato plants. F. oxysporum strains transformed with an expression vector containing the prt1 coding region fused to the inducible endopolygalacturonase pg1 gene promoter and grown under promoter-inducing conditions secreted high levels of extracellular subtilase activity that resolved into a single peak of pI 4.0 upon isoelectric focusing. The active fraction produced two clearing bands of 29 and 32 kDa in sodium dodecyl sulfate gels containing gelatin. Targeted inactivation of prt1 in F. oxysporum f. sp. lycopersici had no detectable effect on mycelial growth, sporulation, and pathogenicity on tomato plants.

The Aspergillus nidulans xprF gene encodes a hexokinase-like protein involved in the regulation of extracellular proteases

The extracellular proteases of Aspergillus nidulans are produced in response to limitation of carbon, nitrogen, or sulfur, even in the absence of exogenous protein. Mutations in the A. nidulans xprF and xprG genes have been shown to result in elevated levels of extracellular protease in response to carbon limitation. The xprF gene was isolated and sequence analysis indicates that it encodes a 615-amino-acid protein, which represents a new type of fungal hexokinase or hexokinase-like protein. In addition to their catalytic role, hexokinases are thought to be involved in triggering carbon catabolite repression. Sequence analysis of the xprF1 and xprF2 alleles showed that both alleles contain nonsense mutations. No loss of glucose or fructose phosphorylating activity was detected in xprF1 or xprF2 mutants. There are two possible explanations for this observation: (1) the xprF gene may encode a minor hexokinase or (2) the xprF gene may encode a protein with no hexose phosphorylating activity. Genetic evidence suggests that the xprF and xprG genes are involved in the same regulatory pathway. Support for this hypothesis was provided by the identification of a new class of xprG(-) mutation that suppresses the xprF1 mutation and results in a protease-deficient phenotype.

Evidence for tryptophan in proximity to histidine and cysteine as essential to the active site of an alkaline protease

The presence, microenvironment, and proximity of an essential Trp with the essential His and Cys residues in the active site of an alkaline protease have been demonstrated for the first time using chemical modification, chemo-affinity labeling, and fluorescence spectroscopy. Kinetic analysis of the N-bromosuccinimide- (NBS) or p-hydroxymercuribenzoate- (PHMB) modified enzyme from Conidiobolus sp. revealed that a single Trp and Cys are essential for activity in addition to the Asp, His, and Ser residues of the catalytic triad. Full protection by casein against inactivation of the enzyme by NBS and quenching of Trp fluorescence upon binding of the enzyme with NBS, substrate (sAAPF-pNA), or inhibitor (SSI) confirmed participation of the Trp residue at the substrate/inhibitor binding site of the alkaline protease. Comparison of the K(sv) values for the charged quenchers CsCI (1.66) and KI (7.0) suggested that the overall Trp microenvironment in the protease is electropositive. The proximity of Trp with His was demonstrated by the sigmoidal shape of the pH-dependent fluorometric titration curve with a pK(F) of 6.1. The vicinity of Trp with Cys was indicated by resonance energy transfer between the intrinsic fluorophore (Trp) and 5-iodoacetamide-fluorescein labeled Cys (extrinsic fluorophore). Our results on the proximity of Trp with essential His and Cys thus confirm the presence of Trp in the active site of the alkaline protease.

Characterization of a novel allergen, a major IgE-binding protein from Aspergillus flavus, as an alkaline serine protease

Aspergillus species of fungi have been known to be one of the most prevalent aeroallergens. One important A. flavus allergen (Asp fl 1) was identified by means of immunoblotting with a serum pool of allergic patients on a two-dimensional electrophoretic gel. The cDNA coding for Asp fl 1 was cloned and sequenced. The clone encodes a full-length protein of 403 amino acid precursors of 42 kDa. After cleavage of a putative signal peptide of 21 amino acids and a prepeptide of 100 amino acids, a mature protein of 282 amino acids was obtained with a molecular mass of 33 kDa and a pI of 6.3. A degree of identity was found in a range of 27 to 84% among related allergens derived from bacteria allergen subtilisin, mold allergen Pen c 1, and virulence factor of A. fumigatus. Recombinant Asp fl 1 (rAsp fl 1) was cloned into vector pQE-30 and expressed in E. coli M15 as a histidine-tag fusion protein and purified to homogeneity. The IgE binding capacity of rAsp fl 1 was tested by immunoblotting using a serum pool of Aspergillus-allergic patients. Recombinant allergen cross-reacted strongly with IgE specific for natural Asp fl 1 and Pen c 1, indicating that common IgE epitopes may exist between allergens of A. flavus and P. citrinum.

Fungal proteinase expression in the interaction of the plant pathogen Magnaporthe poae with its host

Infection by pathogenic fungi involves breaching the outer layer of the host by either mechanical or enzymatic means. Subtilisin-like proteinases are considered to be important in the infection process of entomopathogenic, nematophagous, and mycoparasitic fungi. Little is known regarding the expression of such proteinases by plant pathogenic fungi. Magnaporthe poae, a fungal pathogen of Kentucky bluegrass, expressed a subtilisin-like proteinase, proteinase Mp1, in the infected roots. Antibody was produced against the purified enzyme. From immunoblot analysis, expression of the proteinase in infected roots correlated with increasing severity of disease symptoms. Sequence analysis of a genomic clone indicated proteinase Mp1 was homologous to other fungal subtilisin-like proteinases. DNA gel blot analysis indicated proteinase Mp1 was encoded by a small gene family.

Characterization of allergens from Penicillium oxalicum and P. notatum by immunoblotting and N-terminal amino acid sequence analysis

BACKGROUND

Penicillium species are important causative agents of extrinsic bronchial asthma. However, little is known about the allergens of these ubiquitous fungal species. Objective The object was to analyse the composition, the allergenic cross-reactivity and the N-terminal sequences of allergens from two prevalent airborne Penicillium species, P. oxalicum and P. notatum.

METHODS

The allergenic composition and the immunoglobulin (Ig)E cross-reactivity were analysed by immunoblot and immunoblot inhibition, respectively, using sera from asthmatic patients. The N-terminal amino acid sequences of major allergens were determined by Edman degradation. Allergens identified were also characterized by immunoblotting using monoclonal antibody (MoAb) PCM39 against the alkaline serine proteinase major allergen of P. citrinum.

RESULTS

Among the 70 asthmatic sera tested, 18 (26%) and 17 (24%) had IgE immunoblot reactivity towards components of P. oxalicum and P. notatum, respectively. Major allergens (> 80% frequency of IgE-binding) from both species are the 34 and 30 kDa proteins of P. oxalicum and the 34 and 32 kDa proteins of P. notatum. IgE cross-reactivity among these major allergens and the 33 kDa major allergen of P. citrinum can be detected by immunoblot inhibition studies. The N-terminal amino acid sequences of the 34 kDa allergen of P. oxalicum and of the 32 and the 28 kDa allergens of P. notatum share homology with sequences of the vacuolar serine proteinase from Aspergillus fumigatus. The N-terminal amino acid sequence of the 34 kDa allergen of P. notatum shows sequence homology with that of alkaline serine proteinase from P. citrinum. Results obtained from immunoblotting showed that MoAb PCM39 reacted with the 34, 30 and 16 kDa IgE-binding components of P. oxalicum, and with the 34, 32 and 28 kDa IgE-binding components of P. notatum.

CONCLUSIONS

Results obtained suggest that the 34 kDa major allergen of P. oxalicum may be a vacuolar serine proteinase. The 34 and the 32 kDa major allergens of P. notatum may be the alkaline and the vacuolar serine proteinases of P. notatum, respectively. The 30 and 16 kDa IgE-binding components of P. oxalicum and the 28 kDa IgE-binding component of P. notatum may be breakdown products of the 34 and the 32 kDa major vacuolar serine proteinase allergens of P. oxalicum and P. notatum, respectively.

Characterization of the prolyl dipeptidyl peptidase gene (dppIV) from the koji mold Aspergillus oryzae

The koji mold Aspergillus oryzae secretes a prolyl dipeptidyl peptidase (DPPIV) when the fungus is cultivated in a medium containing wheat gluten as the sole nitrogen and carbon source (MMWG). We cloned and sequenced the DPPIV gene from an A. oryzae library by using the A. fumigatus dppIV gene as a probe. Reverse transcriptase PCR experiments showed that the A. oryzae dppIV gene consists of two exons, the first of which is only 6 bp long. The gene encodes an 87.2-kDa polypeptide chain which is secreted into the medium as a 95-kDa glycoprotein. Introduction of this gene into A. oryzae leads to overexpression of prolyl dipeptidyl peptidase activity, while disruption of the gene abolishes all prolyl dipeptidyl peptidase activity in MMWG. The dppIV null mutants did not exhibit any change in phenotype other than the absence of prolyl dipeptidyl peptidase activity, suggesting that this activity is not essential. This loss of activity diminished the number of dipeptides and increased the number of larger peptides present in the MMWG culture broth. These effects were reversed by the addition of purified, recombinant DPPIV from the methylotrophic yeast expression vector Pichia pastoris. Our results suggest that the DPPIV enzyme may be of importance in industrial hydrolysis of what gluten-based substrates, which are rich in Pro residues.

Molecular and biotechnological aspects of microbial proteases

Proteases represent the class of enzymes which occupy a pivotal position with respect to their physiological roles as well as their commercial applications. They perform both degradative and synthetic functions. Since they are physiologically necessary for living organisms, proteases occur ubiquitously in a wide diversity of sources such as plants, animals, and microorganisms. Microbes are an attractive source of proteases owing to the limited space required for their cultivation and their ready susceptibility to genetic manipulation. Proteases are divided into exo- and endopeptidases based on their action at or away from the termini, respectively. They are also classified as serine proteases, aspartic proteases, cysteine proteases, and metalloproteases depending on the nature of the functional group at the active site. Proteases play a critical role in many physiological and pathophysiological processes. Based on their classification, four different types of catalytic mechanisms are operative. Proteases find extensive applications in the food and dairy industries. Alkaline proteases hold a great potential for application in the detergent and leather industries due to the increasing trend to develop environmentally friendly technologies. There is a renaissance of interest in using proteolytic enzymes as targets for developing therapeutic agents. Protease genes from several bacteria, fungi, and viruses have been cloned and sequenced with the prime aims of (i) overproduction of the enzyme by gene amplification, (ii) delineation of the role of the enzyme in pathogenecity, and (iii) alteration in enzyme properties to suit its commercial application. Protein engineering techniques have been exploited to obtain proteases which show unique specificity and/or enhanced stability at high temperature or pH or in the presence of detergents and to understand the structure-function relationships of the enzyme. Protein sequences of acidic, alkaline, and neutral proteases from diverse origins have been analyzed with the aim of studying their evolutionary relationships. Despite the extensive research on several aspects of proteases, there is a paucity of knowledge about the roles that govern the diverse specificity of these enzymes. Deciphering these secrets would enable us to exploit proteases for their applications in biotechnology.

Characterization of the Aspergillus nidulans aspnd1 gene demonstrates that the ASPND1 antigen, which it encodes, and several Aspergillus fumigatus immunodominant antigens belong to the same family

For the first time, an immunodominant Aspergillus nidulans antigen (ASPND1) consistently reactive with serum samples from aspergilloma patients has been purified and characterized, and its coding gene (aspnd1) has been cloned and sequenced. ASPND1 is a glycoprotein with four N-glycosidically-bound sugar chains (around 2.1 kDa each) which are not necessary for reactivity with immune human sera. The polypeptide part is synthesized as a 277-amino-acid precursor of 30.6 kDa that after cleavage of a putative signal peptide of 16 amino acids, affords a mature protein of 261 amino acids with a molecular mass of 29 kDa and a pI of 4.24 (as deduced from the sequence). The ASPND1 protein is 53.1% identical to the AspfII allergen from Aspergillus fumigatus and 48% identical to an unpublished Candida albicans antigen. All of the cysteine residues and most of the glycosylation sites are perfectly conserved in the three proteins, suggesting a similar but yet unknown function. Analysis of the primary structure of the ASPND1 coding gene (aspnd1) has allowed the establishment of a clear relationship between several previously reported A. fumigatus and A. nidulans immunodominant antigens.

Heterologous expression, isolation, and characterization of versicolorin B synthase from Aspergillus parasiticus. A key enzyme in the aflatoxin B1 biosynthetic pathway

Aflatoxin B1 is a potent environmental carcinogen produced by certain strains of Aspergillus. Central to the biosynthesis of this mycotoxin is the reaction catalyzed by versicolorin B synthase (VBS) in which a racemic substrate, versiconal hemiacetal, is cyclized to an optically active product whose absolute configuration is crucial to the interaction of aflatoxin B1 with DNA. Attempted over-production of VBS in Escherichia coli led principally to protein aggregated into inclusion bodies but also small amounts of soluble but catalytically inactive enzyme. Comparisons to wild-type VBS by SDS-polyacrylamide gel electrophoresis and after N-glycosidase F treatment revealed that extensive glycosylation accounted for the mass discrepancy (7,000+/-1,500 Da) between the native and bacterially expressed proteins. Several over-expression systems in Saccharomyces cerevisiae were surveyed in which one that incorporated a secretion signal was found most successful. VBS of indistinguishable mass on SDS-polyacrylamide gel electrophoresis and kinetic properties from the wild-type enzyme could be obtained in 50-100-fold greater amounts and whose catalytic behavior has been examined. The translated protein sequence of VBS showed three potential N-glycosylation sites (Asn-Xaa-Ser/Thr) consistent with the modifications observed above and unexpectedly revealed extensive homology to the ADP-binding region prominently conserved in the glucose-methanol-choline (GMC) family of flavoenzymes. Over-production of VBS in yeast marks the first aflatoxin biosynthetic enzyme to be so obtained and opens the way to direct study of the enzymology of this complex biosynthetic pathway.

Cloning and sequencing of the gene encoding tannase and a structural study of the tannase subunit from Aspergillus oryzae

We cloned the Aspergillus oryzae tannase gene using three oligodeoxyribonucleotide (oligo) probes synthesized according to the tannase N-terminal and an internal amino acid (aa) sequence. The nucleotide (nt) sequence of the tannase gene was determined and compared with that of a tannase DNA complementary to RNA (cDNA) by means of reverse transcriptase PCR. The results indicated that there was no intron in the tannase gene and that it coded for 588 aa with a molecular weight of about 64,000. The tannase low-producing strain A. oryzae AO1 was transformed with the plasmid pT1 which contained the tannase gene, and tannase activities of the transformants increased in proportion to the number of copies. Tannase consisted of two kinds of subunits, linked by a disulfide bond(s) with molecular weights of about 30,000 and 33,000, respectively. We purified these subunits and determined their N-terminal aa sequences. The large and small subunits of tannase were encoded by the first and second halves, respectively. Judging from the above results, the tannase gene product is translated as a single polypeptide that is cleaved by post-translational modification into two tannase subunits linked by a disulfide bond(s). We concluded that native tannase consisted of four pairs of the two subunits, forming a hetero-octamer with a molecular weight of about 300,000.

Acid proteinase secreted by Candida tropicalis: functional analysis of preproregion cleavages in C. tropicalis and Saccharomyces cerevisiae

The 40 kDa secreted aspartyl proteinase (Sapt1) of Candida tropicalis is a pepsin-like enzyme encoded by the SAPT1 gene. According to the deduced amino acid sequence. Sapt1 has a putative preproregion of 60 amino acids preceding the mature enzyme. Maturation and processing of Sapt1 was analysed in C. tropicalis and Saccharomyces cerevisiae strains expressing wild-type or mutated forms of SAPT1. In S. cerevisiae, the glycosylated 46 kDa proenzyme was converted to the mature 40 kDa form of Sapt1 by KEX2-dependent proteolytic cleavage following the Lys59-Arg60 sequence. The replacement of Lys59-Arg60 by Lys59-Gly60 revealed that the precursor can be processed by an autocatalytic cleavage. This alternative processing pathway to produce mature Sapt1 is less efficient than the Kex2-mediated pathway. Finally, it was shown that in C. tropicalis and S. cerevisiae the removal of the proregion was a prerequisite for the secretion of Sapt1.

Aspergillusproteinases and their interactions with host tissues

Invasive aspergillosis is a life-threatening infection that is caused primarily by the species Aspergillus fumigatus and A. flavus, both of which are highly angioinvasive. From this observation, interest has focused on proteinases produced by these organisms and their possible roles in the pathogenesis of infection. Both species produce alkaline serine proteinases (ALP) and metalloproteinases during the course of infection based on immunohistochemistry of experimental lesions and serologic response of patients. These enzymes can be shown to degrade numerous biologically relevant targets, including elastin, collagen, laminin, fibrinogen, and iC3b. Physicochemical properties, immunoreactivities, and amino acid sequences of the ALP of A. fumigatus and A. flavus show that these two enzymes are closely related. The metalloproteinases, however, appear to represent members of a small family of similar enzymes. Finally, although studies using conventionally produced mutants support roles for these hydrolases as virulence factors in aspergillosis, similar studies using strains of A. fumigatus in which the enzymatic activity has been ablated through gene disruption do not reveal differences in virulence between the wild-type strains and the mutants. Key words: aspergillosis, proteinase, pathogenesis.

Efficient expression and secretion of Aspergillus niger RH5344 polygalacturonase in Saccharomyces cerevisiae

An Aspergillus niger endopolygalacturonase (EC 3.2.1.15) cDNA was expressed in the yeast Saccharomyces cerevisiae. Secretion of the protein into the growth medium was efficiently directed by the fungal leader sequence, and processing occurred at the same site as in Aspergillus. The expression level was significantly enhanced by using a "short" version of the yeast ADHI promoter. An additional increase in the yield of heterologous protein was due to a higher plasmid stability and a rise in plasmid copy number. This was achieved by deleting most of the bacterial sequences from the expression vector. The yeast-derived enzyme showed the same enzymatic and biochemical properties as the fungal polygalacturonase, such as substrate specificity, pH and temperature optima and pI value. The yeast-derived enzyme, however, showed a higher degree of glycosylation and exhibited a more pronounced temperature stability than the fungal enzyme.

Cloning and disruption of the gene encoding an extracellular metalloprotease of Aspergillus fumigatus

Aspergillus fumigatus secretes a serine alkaline protease (ALP) and a metalloprotease (MEP) when the fungus is cultivated in the presence of collagen as sole nitrogen and carbon source. The gene encoding ALP was isolated and characterized previously. We report here the cloning and the sequencing of the gene encoding MEP. Genomic and cDNA clones were isolated from A. fumigatus libraries using synthetic oligonucleotides as probes. Stretches of the deduced amino acid sequence were found to be in agreement with the N-terminal amino acid sequence of MEP and with internal peptide sequences. The amino acid sequence of the enzyme contains a putative active-site sequence HEYTH homologous to the active site of other bacterial and eukaryotic zinc metalloproteases. Sequence analysis reveals that MEP has a pre-proregion consisting of 245 amino acid residues preceding the 388 amino acid residues of the mature region (molecular mass of 42 kDa). An alp mep mutant, deficient in proteolytic activity at neutral pH in vitro, was constructed and tested for pathogenicity in a murine model. No difference in pathogenicity was observed between the wild-type strain and the alp mep double mutant, suggesting that ALP and MEP are not essential for the invasion of the lung tissues by A. fumigatus.

Cloning and characterization of the pepE gene of Aspergillus niger encoding a new aspartic protease and regulation of pepE and pepC

We have cloned the pepE gene of Aspergillus niger, encoding an aspartic protease (PEPE), by screening a lambda genomic DNA library with a heterologous probe, the Neurospora crassa gene coding for a vacuolar proteinase. Sequencing of pepE genomic and cDNA clones revealed that the gene contains three introns, which are 91, 56 and 58-bp long. The deduced protein consists of 398 amino acids, has a putative signal sequence to allow transport into the endoplasmic reticulum and probably undergoes a second proteolytic processing step at its N terminus to yield the mature enzyme. The putative mature part of PEPE has extensive homology with other aspartic proteinases such as pepsins, cathepsins and, in particular, with proteinase A of Saccharomyces cerevisiae and pepsin 1 of Candida albicans. Northern blot analyses revealed that cells contain an abundant pepE transcript whose amount does not change upon carbon or nitrogen limitation, the presence of proteins in the medium or changes in the pH of the medium. We also show that pepC, the A. niger homologue of yeast protease B, is also expressed constitutively under these conditions.

Identification and characterization of genes induced during sexual differentiation in Schizosaccharomyces pombe

Five cDNA clones, harboring genetic messages preferentially expressed during the sexual differentiation process, were isolated from a cDNA library of Schizosaccharomyces pombe by subtractive screening. Transcription of the corresponding genes, termed isp3, 4, 5, 6, and 7, was dependent on nitrogen starvation and their induction occurred at several stages of spore formation. Analysis of the cDNA primary structures revealed a capacity for the coding of polypeptides of 19.2 kDa, 88.3 kDa, 60.1 kDa, 49.7 kDa, and 43.8 kDa, respectively. The translated amino-acid sequences of isp5 and isp6 were found to show significant similarities to those of amino-acid permeases and proteinase B of Saccharomyces cerevisiae, respectively. Disruption of isp6 arrested the cell cycle prior to conjugation and caused a drastic blocking effect on spore formation.

Cloning and characterization of the pepD gene of Aspergillus niger which codes for a subtilisin-like protease

Serine proteases constitute an important group of extra- and intracellular proteases in fungi. These enzymes are characterized by conserved regions around the active site residues, Asp, His and Ser. Based on this amino acid (aa) sequence conservation, we have used degenerate primer PCR to isolate subtilisin-specific genomic probes from Aspergillus niger, and cloned a gene, pepD, by screening a lambda genomic library using a PCR probe. The pepD gene contains three putative introns, which are 51-, 47- and 55-bp long and has an open reading frame coding for a protein which consists of 416 aa. The deduced aa sequence shows similarity to subtilisin-like proteases, in particular to fungal alkaline proteases. Signal sequence cleavage prediction indicates that the first 20 aa are probably removed upon transfer to the endoplasmic reticulum. The conservation of the pro-enzyme cleavage site in fungal alkaline proteases suggests that the mature protein is derived from this polypeptide via the removal of an additional 101 aa, resulting in a mature 30,294-Da enzyme consisting of 295 aa.

Isolation, characterization, and cloning of cDNA and the gene for an elastinolytic serine proteinase from Aspergillus flavus

An elastinolytic serine proteinase produced by Aspergillus flavus 28 that was isolated from a patient who died of aspergillosis has been purified and characterized. The enzyme was inhibited by the serine proteinase inhibitors phenylmethylsulfonyl fluoride and diisopropyl fluorophosphate. The metal-chelating agents EDTA and EGTA [ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid] did not severely inhibit the enzyme. A cDNA and a 2.95-kb segment of genomic DNA containing the proteinase gene were sequenced. The open reading frame that would code for a protein containing 403 amino acids was interrupted by three introns. The mature protein lacks 121 N-terminal amino acids including a putative 21-amino-acid signal peptide. The purified mature protein showed a molecular mass of 36 kDa by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, whereas that calculated from the deduced protein sequence was 30 kDa. This elastinolytic serine proteinase of A. flavus has 83 and 82% sequence homology to the similar proteinases from A. fumigatus and A. oryzae. The catalytic properties and the sequence homology around the putative catalytic amino acids suggest that this enzyme belongs to the serine proteinases of the subtilisin family.

The detection of Aspergillus spp. by the polymerase chain reaction and its evaluation in bronchoalveolar lavage fluid

Invasive pulmonary aspergillosis (IPA) is an important cause of mortality and morbidity in the immunocompromised host. However, the diagnosis of this condition may be difficult, and it is sometimes missed because of the lack of sensitivity of available tests. Therefore, we used polymerase chain reaction (PCR)-based amplification of fragments of genes-encoding alkaline proteases from Aspergillus fumigatus and A. flavus to detect these organisms in bronchoalveolar lavage fluid specimens. The predicted size of the product (747 base pairs) after amplification of A. fumigatus was larger than that for A. flavus (690 base pairs). The reaction was highly sensitive (after amplification of 500 fg of A. fumigatus DNA, product could be detected by Southern analysis), and it was specific for A. fumigatus and A. flavus. Bronchoalveolar lavage fluid from four immunosuppressed patients with proved or probable IPA was positive by this assay (sensitivity, 100%); in addition, the sample from one patient with possible IPA was PCR-positive. Only one specimen from 18 immunosuppressed patients with no evidence of IPA was PCR-positive (specificity, 94.4%). Five of 28 bronchoalveolar lavage samples from nonimmunosuppressed patients were PCR-positive, probably representing colonization of the respiratory tract. PCR-based detection may prove useful in the diagnosis of IPA.

Characterization of an aspartic proteinase of Mucor pusillus expressed in Aspergillus oryzae

The aspartic proteinase (MPP) gene from the zygomycete fungus Mucor pusillus was introduced into an ascomycete fungus, Aspergillus oryzae, by protoplast transformation using the nitrate reductase (niaD) gene as the selective marker. Southern blot analysis indicated that the MPP gene was integrated into the resident niaD locus at a copy number of 1-2. MPP secreted by the recombinant A. oryzae was correctly processed but was more highly glycosylated than that produced in the original M. pusillus strain. Treatment with endo-beta-N-acetylglucosaminidase H and analysis of the carbohydrate composition of the secreted MPP revealed that the extra glycosylation of the MPP secreted by the recombinant A. oryzae was due to altered processing of mannose residues. The extra glycosylation of MPP affected its enzyme properties including its milk-clotting and proteolytic activities.

The alkaline protease of Aspergillus fumigatus is not a virulence determinant in two murine models of invasive pulmonary aspergillosis

Little is known of the pathophysiology of invasive pulmonary aspergillosis (IPA), an opportunistic fungal infection usually caused by Aspergillus fumigatus. It has been suggested that the ability of the fungus to degrade elastin may aid its invasion and growth in lung tissue. We have described previously the construction of a strain of A. fumigatus in which the gene encoding an alkaline protease, AFAlp, had been disrupted (C.M. Tang, J. Cohen, and D.W. Holden, Mol. Microbiol. 6:1663-1671, 1992); this mutant is deficient in extracellular proteolytic and elastinolytic activity over a broad pH range. In this study, we compared the pathogenicity of this and another AFAlp disruptant with their isogenic, elastase-producing parental strains in two murine models of IPA. In both models, animals were inoculated via the respiratory tract. In the first model, the inoculum was delivered as airborne conidia and animals developed signs of respiratory distress within 2 to 4 days. In the second model, conidia were administered intranasally as a suspension and the disease developed over a 2-week period. No difference was observed between the wild-type and AFAlp disruptants in terms of mortality, and elastin breakdown was detected in lung tissue from animals inoculated with all four strains. We conclude that AFAlp is not a virulence determinant in these models of IPA.

Molecular characterization of the proteinase-encoding gene, prb1, related to mycoparasitism by Trichoderma harzianum

The soil fungus Trichoderma harzianum is a mycoparasitic fungus known for its use as a biocontrol agent of phytopathogenic fungi. Among other factors, Trichoderma produces a series of antibiotics and fungal cell wall-degrading enzymes. These enzymes are believed to play an important role in mycoparasitism. Among the hydrolytic enzymes, we have identified a basic proteinase (Prb1) which is induced by either autoclaved mycelia, fungal cell wall preparation or chitin; however, the induction does not occur in the presence of glucose. The proteinase was purified and biochemically characterized as a serine proteinase of 31 kDa and pI 9.2. Based on the sequence of three internal peptides, synthetic oligonucleotide probes were designed. These probes allowed subsequent isolation of a cDNA and its corresponding genomic clone. The deduced amino acid sequence indicates that the proteinase is synthesized as a pre-proenzyme and allows its classification as a serine proteinase. Northern analysis shows that the induction of this enzyme is due to an increase in the corresponding mRNA level.

A heat-labile serine proteinase from Penicillium citrinum

A serine proteinase from Penicillium citrinum was purified. The M(r) and isoelectric point were determined as about 26,000 and 9.5, respectively. Activity was retained up to above 40 degrees at pH 7 for 30 min, but the enzyme was completely inactivated at 50 degrees. The first amino acids in the N-terminal region were ANVVQSNVPSWGLARISSKRPGTTSYTYDSTAGEGVVFYGVDTG. The specificity differs from that of other serine proteinases. Kinetic studies on fluorogenic substrates were determined.

Cloning and characterisation of pepC, a gene encoding a serine protease from Aspergillus niger

We have cloned a gene, pepC, encoding a serine proteinase, PEPC, from Aspergillus niger by screening a phage lambda genomic DNA library with a gene (PRB1) from Saccharomyces cerevisiae which codes for proteinase YscB. The nucleotide (nt) sequence of pepC revealed that the gene is composed of two exons of 369 nt and 1230 nt separated by a single 70-nt intron. The deduced protein of 533 amino acids (aa) has a putative signal sequence for transport into the endoplasmic reticulum. Based on the extensive homology shown with serine proteinases (SerP) of the subtilisin family, which includes the active site triad, we hypothesise that the protein is made as a larger precursor which is matured by the cleavage of 130-140 aa from its N terminus and possibly by the removal of approx. 70 aa from its C terminus.