A ribonuclease III involved in virulence of Mucorales fungi has evolved to cut exclusively single-stranded RNA

Members of the ribonuclease III (RNase III) family regulate gene expression by processing double-stranded RNA (dsRNA). This family includes eukaryotic Dicer and Drosha enzymes that generate small dsRNAs in the RNA interference (RNAi) pathway. The fungus Mucor lusitanicus, which causes the deadly infection mucormycosis, has a complex RNAi system encompassing a non-canonical RNAi pathway (NCRIP) that regulates virulence by degrading specific mRNAs. In this pathway, Dicer function is replaced by R3B2, an atypical class I RNase III, and small single-stranded RNAs (ssRNAs) are produced instead of small dsRNA as Dicer-dependent RNAi pathways. Here, we show that R3B2 forms a homodimer that binds to ssRNA and dsRNA molecules, but exclusively cuts ssRNA, in contrast to all known RNase III. The dsRNA cleavage inability stems from its unusual RNase III domain (RIIID) because its replacement by a canonical RIIID allows dsRNA processing. A crystal structure of R3B2 RIIID resembles canonical RIIIDs, despite the low sequence conservation. However, the groove that accommodates dsRNA in canonical RNases III is narrower in the R3B2 homodimer, suggesting that this feature could be responsible for the cleavage specificity for ssRNA. Conservation of this activity in R3B2 proteins from other mucormycosis-causing Mucorales fungi indicates an early evolutionary acquisition.

A Collagenolytic Aspartic Protease from Thermomucor indicae-seudaticae Expressed in Escherichia coli and Pichia pastoris

Proteases are produced by the most diverse microorganisms and have a wide spectrum of applications. However, the use of wild microorganisms, mainly fungi, for enzyme production has some drawbacks. They are subject to physiological instability due to metabolic adaptations, causing complications and impairments in the production process. Thus, the objective of this work was to promote the heterologous expression of a collagenolytic aspartic protease (ProTiN31) from Thermomucor indicae seudaticae in Escherichia coli and Pichia pastoris. The pET_28a (+) and pPICZαA vectors were synthesized containing the gene of the enzyme and transformed into E. coli and P. pastoris, respectively. The recombinant enzymes produced by E. coli and P. pastoris showed maximum activity at pH 5.0 and 50 °C, and pH 5.0 and 60 °C, respectively. The enzyme produced by P. pastoris showed better thermostability when compared to that produced by E. coli. Both enzymes were stable at pH 6.0 and 6.5 for 24 h at 4 °C, and sensitive to pepstatin A, β-mercaptoethanol, and Hg²⁺. Comparing the commercial collagen hydrolysate (Artrogen duo/Brazil) and gelatin degradation using protease from P. pastoris, they showed similar peptide profiles. There are its potential applications in a wide array of industrial sectors that use collagenolytic enzymes.

An integrated genomic and transcriptomic survey of mucormycosis-causing fungi

Mucormycosis is a life-threatening infection caused by Mucorales fungi. Here we sequence 30 fungal genomes, and perform transcriptomics with three representative Rhizopus and Mucor strains and with human airway epithelial cells during fungal invasion, to reveal key host and fungal determinants contributing to pathogenesis. Analysis of the host transcriptional response to Mucorales reveals platelet-derived growth factor receptor B (PDGFRB) signaling as part of a core response to divergent pathogenic fungi; inhibition of PDGFRB reduces Mucorales-induced damage to host cells. The unique presence of CotH invasins in all invasive Mucorales, and the correlation between CotH gene copy number and clinical prevalence, are consistent with an important role for these proteins in mucormycosis pathogenesis. Our work provides insight into the evolution of this medically and economically important group of fungi, and identifies several molecular pathways that might be exploited as potential therapeutic targets.

Production and Catalytic Properties of Amylases from Lichtheimia ramosa and Thermoascus aurantiacus by Solid-State Fermentation

The present study compared the production and the catalytic properties of amylolytic enzymes obtained from the fungi Lichtheimia ramosa (mesophilic) and Thermoascus aurantiacus (thermophilic). The highest amylase production in both fungi was observed in wheat bran supplemented with nutrient solution (pH 4.0) after 96 hours of cultivation, reaching 417.2 U/g of dry substrate (or 41.72 U/mL) and 144.5 U/g of dry substrate (or 14.45 U/mL) for L. ramosa and T. aurantiacus, respectively. The enzymes showed higher catalytic activity at pH 6.0 at 60°C. The amylases produced by L. ramosa and T. aurantiacus were stable between pH 3.5-10.5 and pH 4.5-9.5, respectively. The amylase of L. ramosa was stable at 55°C after 1 hour of incubation, whereas that of T. aurantiacus maintained 60% of its original activity under the same conditions. Both enzymes were active in the presence of ethanol. The enzymes hydrolyzed starch from different sources, with the best results obtained with corn starch. The enzymatic complex produced by L. ramosa showed dextrinizing and saccharifying potential. The enzymatic extract produced by the fungus T. aurantiacus presented only saccharifying potential, releasing glucose monomers as the main hydrolysis product.

Enhanced production of industrial enzymes in Mucoromycotina fungi during solid-state fermentation of agricultural wastes/by-products

Cellulolytic, lipolytic and proteolytic enzyme production of zygomycetes Mucor corticolus, Rhizomucor miehei, Gilbertella persicaria and Rhizopus niveus were investigated using agro-industrial wastes as substrates. Solid-state cultures were carried out on untreated corn residues (stalk and leaf) as single substrate (SSF1) or corn residues and wheat bran in mixed fermentation (SSF2). Rapid production of endoglucanase (CMCase) was observed with maximal activity reaching after about 48-h fermentation, while cellobiohydrolase (CBH) and β-glucosidase enzymes generally had their peak after 72-h incubation. Highest filter paper degrading (FPase), CMCase, CBH and β-glucosidase activities obtained were (U g⁻¹ dss) 17.3, 74.1, 12.2 and 158.3, for R. miehei, G. persicaria, M. corticolus and Rh. niveus, respectively. M. corticolus proved to be the best lipolytic enzyme producer in SSF1 presenting 447.6 U g⁻¹ dss yield, while R. miehei showed 517.7 U g⁻¹ dss activity in SSF2. Rh. niveus exhibited significantly greater protease production than the other strains. Suc-AAPF-pNA hydrolyzing activities of this strain were 1.1 and 1.96 U g⁻¹ dss in SSF1 and SSF2, respectively. We conclude that the used corn stalk and leaf residues could potentially be applicable as strong inducers for cellulase and lipase production by Mucoromycotina fungi.

Production and characterization of β-glucosidase obtained by the solid-state cultivation of the thermophilic fungus Thermomucor indicae-seudaticae N31

In this paper, several agro-industrial wastes (soybean meal and wheat straw, rice and peanut husks, corn cob and corn stover, and sugarcane bagasse) were tested for the production of β-glucosidase by the cultivation of thermophilic fungus Thermomucor indicae-seudaticae N31 in solid-state fermentation (SSF). Among the tested substrates, the highest yields were obtained in soybean meal. Other fermentation parameters were also evaluated, such as initial pH, merge substrates, and fermentation time, as well as the physicochemical characterization of the enzyme. The best results were obtained after 192 h of fermentation with the initial pH adjusted to 6.0. The substrate mixture did not improve the enzyme production by microorganism. The β-glucosidase showed best catalytic activity at pH 4.5 and at 75 °C and remained stable in the pH range from 4.5 to 9.5 and the temperature range 40-75 °C. The enzyme showed 80 % of its activity at a concentration of 15 mM glucose and remained stable up to 20 % ethanol.

Cloning and Sequence Analysis of cDNA encodingRhizopus niveusLipase

Complementary DNA encoding Rhizopus niveus lipase (RNL) was isolated from the R. niveus IF04759 cDNA library using a synthetic oligonucleotide corresponding to the amino acid sequence of the enzyme. A clone, which had an insert of 1.0 kilobase pairs, was found to contain the coding region of the enzyme. The lipase gene was expressed in Escherichia coli as a lacZ fusion protein. The mature RNL consisted of 297 amino acid residues with a molecular mass of 32 kDa. The RNL sequence showed significant overall homology to Rhizomucor miehei lipase and the putative active site residues were strictly conserved.

Specific Characteristics of Family 45 Endoglucanases from Mucorales in the Use of Textiles and Laundry

We examined the characteristics of family 45 endoglucanases (glycoside hydrolases family 45; GH45) from Mucorales belonging to Zygomycota in the use of textiles and laundry. The defibrillation activities on lyocell fabric of family 45 endoglucanases from Mucorales, such as RCE1 and RCE2 from Rhizopus oryzae, MCE1 and MCE2 from Mucor circinelloides, and PCE1 from Phycomyces nitens, were much higher than those of the other family 45 endoglucanases. By contrast, family 45 endoglucanases from Mucorales were less resistant to anionic surfactant and oxidizing agent, main components in detergents, than the other family 45 endoglucanases. RCE1 consists of two distinct modules, a catalytic module and a carbohydrate-binding module family 1 (CBM1), and these common specific characteristics were considered to due to the catalytic module, but not to the CBM1.

Carotenoid synthesis and phytoene synthase activity during mating of Blakeslea trispora

Carotenoid formation was investigated in wild type and carotenogenic mutants of Blakeslea trispora after mating (-) and (+) strains. The highest yields of carotenoids, especially β-carotene was observed following mating. In vitro incorporation of geranylgeranyl pyrophosphate into phytoene and β-carotene corresponded to increased carotenogenesis in the mated strains. Immuno determination of phytoene synthase protein levels revealed that the amounts of this enzyme is concurrent with the increases in carotenoid content. In fungi, phytoene synthase together with lycopene cyclase are encoded by a fusion gene crtYB or carRA with two individual domains. These domains were both heterologously expressed in an independent manner and antisera raised against both. These antisera were used, to assess protein levels in mated and non-mated B. trispora. The phytoene synthase domain was detected as an individual soluble protein with a molecular weight of 40 kDa and the lycopene cyclase an individual protein of mass about 30 kDa present in the membrane fraction following sub-cellular fractionation. This result demonstrates a post-translational cleavage of the protein transcribed from a single mRNA into independent functional phytoene synthase and lycopene cyclase.

Specificity of carboxypeptidases from Actinomucor elegans and their debittering effect on soybean protein hydrolysates

The specificities of carboxypeptidases from Actinomucor elegans were investigated by determining enzymatic activities at pH 7.0 and pH 4.0 with 16 Z-dipeptides and three Z-tripeptides as substrates. The debittering effect was evaluated and the free amino acid compositions of the soybean protein hydrolysates were analyzed before and after treatment with A. elegans extract at pH 7.0 and pH 4.0, with carboxypeptidases from Aspergillus oryzae as control. The results of the enzyme activity determinations indicated that carboxypeptidases from A. elegans prefer hydrophobic substrates, such as Z-Phe-Leu, Z-Phe-Tyr-Leu, and Z-Phe-Tyr. The sensory evaluation and free amino acid composition analysis showed that these carboxypeptidases are efficient tools for decreasing the bitterness of peptides because they liberated the fewest free amino acids, which consisted of 73% hydrophobic amino acids, under acidic conditions. Carboxypeptidases from A. elegans display promising prospects for future applications in the protein hydrolysate industry.

Application of standard addition for the determination of carboxypeptidase activity in Actinomucor elegans bran koji

Leucine carboxypeptidase (EC 3.4.16) activity in Actinomucor elegans bran koji was investigated via absorbance at 507 nm after stained by Cd-nihydrin solution, with calibration curve A, which was made by a set of known concentration standard leucine, calibration B, which was made by three sets of known concentration standard leucine solutions with the addition of three concentrations inactive crude enzyme extract, and calibration C, which was made by three sets of known concentration standard leucine solutions with the addition of three concentrations crude enzyme extract. The results indicated that application of pure amino acid standard curve was not a suitable way to determine carboxypeptidase in complicate mixture, and it probably led to overestimated carboxypeptidase activity. It was found that addition of crude exact into pure amino acid standard curve had a significant difference from pure amino acid standard curve method (p < 0.05). There was no significant enzyme activity difference (p > 0.05) between addition of active crude exact and addition of inactive crude kind, when the proper dilute multiple was used. It was concluded that the addition of crude enzyme extract to the calibration was needed to eliminate the interference of free amino acids and related compounds presented in crude enzyme extract.

[Cloning of Blakeslea trispora carRA gene by PCR-driven overlap extension and construction of an activity detection system]

Blakeslea trispora CarRA has both lycopene cyclase and phytoene synthase activity. In order to analyze the double functional activity of CarRA proteins and to detect the active sites of lycopene cyclase, we constructed two detection systems in Escherichia coli by color complementary. Through PCR-driven overlap extension we got carRA gene cDNA, then constructed prokaryotes expression vector pET28a-carRA. pET28a-carRA with plasmid pAC-LYC carrying crtl/crtB/crtE gene clusters were co-transformed to BL21(DE3) to validate lycopene cyclase activity. We constructed the plasmid pAC-LYC delta (crtB) carrying crtl/crtE gene clusters, then co-transtormed them with pET28a-carRA to BL21(DE3) to validate phytoene synthase activity. Based on color complementary, and HPLC analysis of metabolites, we confirmed that the CarRA protein activity detection system was reliable. Our study provides a screening model for specific mutation of lycopene cyclase without affecting phytoene synthase activity.

Pectinase production by a Brazilian thermophilic fungus Thermomucor indicae-seudaticae N31 in solid-state and submerged fermentation

Thermophilic organisms produce thermostable enzymes, which have a number of applications, justifying the interest in the isolation of new thermophilic strains and study of their enzymes. Thirty-four thermophilic and thermotolerant fungal strains were isolated from soil, organic compost, and an industrial waste pile based on their ability to grow at 45 degrees C and in a liquid medium containing pectin as the only carbon source. Among these fungi, 50% were identified at the genus level as Thermomyces, Aspergillus, Monascus, Chaetomium, Neosartoria, Scopulariopsis, and Thermomucor. All isolated strains produced pectinase during solid-state fermentation (SSF). The highest polygalacturonase (PG) activity was obtained in the culture medium of thermophilic strain N31 identified as Thermomucor indicae-seudaticae. Under SSF conditions on media containing a mixture of wheat bran and orange bagasse (1:1) at 70% of initial moisture, this fungus produced the maximum of 120 U/ml of exo-PG, while in submerged fermentation (SmF) it produced 13.6 U/ml. The crude PG from SmF was more thermostable than that from SSF and exhibited higher stability in acidic pH.

Flocculation of dimorphic yeast Benjaminiella poitrasii is altered by modulation of NAD-glutamate dehydrogenase

A strategy to control flocculation is investigated using dimorphic yeast, Benjaminiella poitrasii as a model. Parent form of this yeast (Y) exhibited faster flocculation (11.1 min) than the monomorphic yeast form mutant Y-5 (12.6 min). Atomic force microscopy revealed higher surface roughness of Y (439.34 rms) than Y-5 (52 rms). Also, the former had a zeta potential of -65.97+/-3.45 as against -50.21+/-2.49 for the latter. Flocculation of both Y and Y-5 could be altered by supplementing either substrates or inhibitor of NAD-glutamate dehydrogenase (NAD-GDH) in the growth media. The rate of flocculation was promoted by alpha-ketoglutarate or isophthalic acid and decelerated by glutamate with a statistically significant inverse correlation to corresponding NAD-GDH levels. These interesting findings open up new possibilities of using NAD-GDH modulating agents to control flocculation in fermentations for easier downstream processing.

[7alpha-hydroxylation of steroid 5-olefins by mold fungi]

Hydroxylation activity of the mold fungi belonging to the orders Dothideales, Hypocreales, and Mucorales towards delta(5)-3beta-hydroxysteroids was studied. The fungi Bipolaris sorokiniana, Fusarium sp., and Rhizopus nigricans were able to introduce hydroxy group at position 7alpha; however, this ability was detected only at a low substrate load and with a low yield. A 7alpha-hydroxylase activity of the Curvularia lunata VKPM F-981 culture was shown for the first time. It was demonstrated that the studied strain was capable of stereo- and regioselective transformations of androstane 5-olefins at a load not less than 2 g/l. Conversion of pregnane steroids by this culture yielded both 7alpha and 11beta-hydroxy derivatives. The introduction of 7alpha-hydroxy group by this strain occurred concurrently with enzymatic hydrolysis of ester groups, which proceeded under mild conditions to give the corresponding alcohols in the cases of both 3-acetate of delta(5)-androstenes and mono- and triacetates of delta(5)-pregnenes.

Identification and functional characterization of the delta 6-fatty acid desaturase gene from Thamnidium elegans

A cDNA sequence was cloned from the filamentous fungus Thamnidium elegans As3.2806 using reverse transcription polymerase chain reaction (RT-PCR) and rapid amplification of cDNA ends method (RACE). Sequence analysis indicated that this cDNA sequence has an open reading frame of 1,380 bp, which encodes a 52.4 kDa peptide of 459 amino acids. The designated amino acid sequence has high similarity with that found in fungal delta 6-fatty acid desaturases: it shows three conserved histidine-rich motifs and two hydrophobic domains. A cytochrome b5-like domain was observed at the N-terminus. To elucidate the function of this novel putative desaturase, the open reading frame was cloned into the intracellular expression vector pPIC3.5K and the gene was expressed heterologously in Pichia pastoris. Accumulation of gamma-linolenic acid to the level of 6.83% in total fatty acid demonstrated that the deduced amino acid sequence possesses of delta 6-fatty acid desaturase activity.

Role of hydrolytic enzymes and oxidative stress in autolysis and morphology of Blakeslea trispora during β-carotene production in submerged fermentation

The role of hydrolytic enzymes (proteases and chitinase) and oxidative stress in the autolysis and morphology of Blakeslea trispora during beta-carotene production from a chemically defined medium in shake flask culture was investigated. The process of cellular autolysis was studied by measuring the changes in biomass dry weight, pH, concentration of beta-carotene, specific activity of the hydrolytic enzymes and micromorphology of the fungus using a computerized image analysis system. In addition, the phenomenon of autolysis was associated with high concentrations of reactive oxygen species (ROS). The accumulation of ROS produced during fermentation causes oxidative stress in B. trispora. Oxidative stress was examined in terms of the activities of two key defensive enzymes: catalase (CAT) and superoxide dismutase (SOD). The profile of the specific activities of the above enzymes appeared to correlate with the oxidative stress of the fungus. The high activities of CAT and SOD showed that B. trispora is found under oxidative stress during beta-carotene production. The culture began to show signs of autolysis nearly in the growth phase and autolysis increased significantly during the production phase. The morphological differentiation of the fungus was a result of the degradation of the cell membrane by hydrolytic enzymes and oxidative stress. Increased beta-carotene production is correlated with intense autolysis of clumps, which has as a consequence the increase of the freely dispersed mycelia.

A remodeling system for the oligosaccharide chains on glycoproteins with microbial endo-β-N-acetylglucosaminidases

Endo-M, endo-beta-N-acetylglucosaminidase from Mucor hiemalis, transferred the complex type oligosaccharide of sialoglycopeptide to partially deglycosylated proteins (N-acetylglucosamine-attached proteins), which were prepared by excluding high-mannose type oligosaccharides from glycoproteins with Endo-H, endo-beta-N-acetylglucosaminidase from Streptomyces plicatus. This finding indicated that the high-mannose type oligosaccharides on glycoproteins can be changed to complex type ones by the transglycosylation activity of Endo-M. This is the first report of the establishment of a remodeling system for the different types of oligosaccharides on glycoproteins with microbial endo-beta-N-acetylglucosaminidases having different substrate specificities. Endo-M is a powerful tool for the in vitro synthesis of glycoproteins containing complex type oligosaccharides from glycoproteins produced by yeast.

Fluorescein Thiocarbamoyl-Kappa-Casein Assay for the Specific Testing of Milk-Clotting Proteases

Milk-clotting proteases, which are widely used in the cheese-making industry, are enzymes that use soluble caseins as their preferential substrates. Here, we propose a modification to a method previously described for the specific determination of milk-clotting proteases by using kappa-casein labeled with fluorescein isothiocyanate as substrate. Validation of the modified method was confirmed using natural bacterial, fungal, plant, and animal milk-clotting proteases, as well as a milk-clotting enzyme of recombinant origin. The new modified method described here allowed specific quantification of the activity of milk-clotting proteases in a very sensitive way and permitted determination of the appropriate kinetic parameters of all the enzymes tested, consistent with their origin and degree of purity.

[A method using long primers for cloning the upstream sequence of delta-6 fatty acid desaturases gene of Thamnidium elegans by nested inverse PCR]

Thamnidium elegans is a kind of phycomycete that produces essential unsaturated fatty acids, particularly y-linolenic acid. In this process, delta6-Fatty acid desaturase (D6D) plays a key role due to its enzymatic properties that catalyze the delta6 site dehydrogenation of precursor linoleic acid (18:2delta(9, 12) n-6) and a-linolenic acid (18:3delta(9, 12, 15) n-3). This reaction is the first and rate-limiting step of highly unsaturated fatty acids (HUFA) synthesis pathways. After we have isolated and cloned the gene coding delta6-fatty acid desaturase from Thamnidium elegans As3.2806 (GenBank accession number DQ099380), our interest focuses on the promotion and regulation of the gene transcription. To achieve this aim, we designed long primers and used nested inverse PCR to amplify DNA flanking sequences. First, genome of Thamnidium elegans was extracted and digested with restriction enzymes EcoR I and Kpn I , respectively. Then we ligated the digested DNA with T4 ligase at low concentration which is propitious for linear DNA to joint intromolecule. According to the sequence of delta6-fatty acid desaturase gene of Thamnidium elegans, we designed a couple of 35nt long inverse primers and two couples of shorter inverse primers for inverse PCR. Three rounds of PCR reactions were performed. In the primary reaction, the ligated DNA was used as a template, and the product was used as the template of the secondary reaction, the tertiary reaction was achieved in the same way. After all the three rounds of reactions, we got a nice product about 4 kb from the EcoR I digested sample, in which a 1.3kb 5' upstream sequence (GenBank accession number DQ309425) of delta6-fatty acid desaturase gene containing several putative regulatory elements including TATA. box, FSE-2, AP-1 sites, CCAAT cis-element site and STRE-binding site was derived after sequencing. All of these implied intensely that this 1.3kb fragment is a condition-regulated promoter. It is the first report about Thamnidium elegans detla6-fatty acid desaturase gene promoter. The procedure described here is a rapid and simple method and particularly useful to isolate flanking sequences from fungal genome. box, FSE-2, AP-1 sites, CCAAT cis-element site and STRE-binding site was derived after sequencing. All of these implied intensely that this 1.3 kb fragment is a condition-regulated promoter. It is the first report about Thamnidium elegans delta6-fatty acid desaturase gene promoter. The procedure described here is a rapid and simple method and particularly useful to isolate flanking sequences from fungal genome.

[Cloning and expression of delta6-desaturase gene from Thamnidium elegans in Saccharomyces cerevisiae]

A 459 bp DNA fragment was amplified from Thamnidium elegans As3.2806 with degenerate oligonucleotides primers designed based on the sequences information from the conserved histidine-rich motifs II and near III of fungal delta6-fatty acid desaturases genes by RT-PCR and sequenced. Gene specific primers designed according to this partial sequence were used for the amplification of the 3'- and 5'- end of this cDNA by RACE method, and sequence information coming from these two ends were used to design two GSPs to clone the 1504bp full-length cDNA. Sequence analysis showed this cDNA sequence had an open reading frame (ORF) of 1377bp encoding 458 amino acids of 52.4kD. The deduced amino acid sequence of the ORF showed similarity to those of the above delta6-fatty acid desaturases which comprise the characteristics of membrane-bound desaturases, including three conserved histidine-rich boxes and hydropathy profile. A cytochrome b5-like domain was observed at the N-terminus. To elucidate the function of the protein, two specific primers corresponding to the nucleotide sequences of start and stop codons were used to amplify the coding sequence. The amplified cDNA TED6 was subcloned into the expression vector pYES2.0 to generate a recombinant plasmid pYTED6, which was subsequently transformed into Saccharomyces cerevisiae strain INVScl for heterologous expression by lithium acetate method. Grown to logarithmic phase at 30 degrees C, the transformed cells were supplemented with 0.5 mmol/L Linoleic acid and induced by 2% galactose for a further 48 h of cultivation at 20 degrees C. Total fatty acids were extracted from the induced cell and subjected to methyl-esterification. The resultant fatty acid methyl esters (FAME) were analyzed by gas chromatography (GC). A novel peak corresponding to gamma-linolenic acid (GLA) methyl ester standards was detected with the same retention time, which was absent in the cell transformed with empty vector. The percentage of this new fatty acid to total fatty acids was 7.5%. Gas chromatography-mass spectrometry (GC-MS) analysis of this fatty acid methyl derivative demonstrated that the novel peak was GLA methyl ester. These results showed that the coding product of this sequence exhibited the activity of converting linoleic acid (LA) to gamma-linolenic (GLA), and indicated that amino-acid sequence exhibited delta6-fatty acid desaturase activity.

Microbial transformation of 17alpha-ethynyl- and 17alpha-ethylsteroids, and tyrosinase inhibitory activity of transformed products

The microbial transformation of the 17alpha-ethynyl-17beta-hydroxyandrost-4-en-3-one (1) (ethisterone) and 17alpha-ethyl-17beta-hydroxyandrost-4-en-3-one (2) by the fungi Cephalosporium aphidicola and Cunninghamella elegans were investigated. Incubation of compound 1 with C. aphidicola afforded oxidized derivative, 17alpha-ethynyl-17beta-hydroxyandrosta-1,4-dien-3-one (3), while with C. elegans afforded a new hydroxy derivative, 17alpha-ethynyl-11alpha,17beta-dihydroxyandrost-4-en-3-one (4). On the other hand, the incubation of compound 2 with the fungus C. aphidicola afforded 17alpha-ethyl-17beta-hydroxyandrosta-1,4-dien-3-one (5). Two new hydroxylated derivatives, 17alpha-ethyl-11alpha,17beta-dihydroxyandrost-4-en-3-one (6) and 17alpha-ethyl-6alpha,17beta-dihydroxy-5alpha-androstan-3-one (7) were obtained from the incubation of compound 2 with C. elegans. Compounds 1-6 exhibited tyrosinase inhibitory activity, with compound 6 being the most potent member (IC(50)=1.72 microM).

[Study on the properties of a novel glycine amino peptidase from Actinomucor elegans]

The glycine amino peptidase of Actinomucor elegans was studied in this work. For the enzyme production Actinomucor elegans was cultured with an enzyme producing medium. Then the cells were collected and subjected to enzyme purification. The glycine aminopeptidase was purified 592 times by a DEAE-Toyopearl column, a Toyopearl HW 65-C column and a Superdex 200 column subsequently and the purified enzyme had a specific activity of 14.2 u/mg. The enzyme was estimated to have molecular mass of 320kD by gel filtration and a subunit size of 56.5kD by SDS-PAGE. It hydrolyzes glycine residue containing substrates such as glycine-betanaphthylamine more efficiently than those containing other amino acid residue. Addition to Gly-betaNA, the enzyme could also hydrolyze Ala-betaNA, Met-betaNA, Leu-betaNA, Arg-betaNA and Ser-betaNA but it had no activity on the substrates such as Trp-betaNA, Pyr-betaNA, Pro-betaNA, Asp-betaNA, Lys-betaNA, Val-betaNA. It was also observed when the glycine-betanaphthylamine concentration was higher than 2mmol/L the enzyme showed a substrate inhibition, and at the 20 mmol/L the enzyme only showed about 55% activity as it showed at the 2mmol/L. Whereas no such phenomenon was observed on the other substrate such as alanine-betanaphthylamine. The optimal temperature and pH for the reaction of this enzyme is 30 degrees C and pH 8.0, respectively. The Km and Kcat of the enzyme for glycine-betanaphthylamine is 0.24 mmol/L and 100.8 s(-1), respectively. Zn2+, Cu2+ and Cd2+ suppress almost all activities of the enzyme at the concentration of 1.0 mmol/L. Based on the study of chelating reagents, GAP belongs to the metalloenzyme. When a gelatin solution was hydrolyzed with 0.5% of alkaline proteinase together with glycine aminopeptidase at 50 degrees C for 18 hours, the glycine aminopeptidase could improve the hydrolysis degree of the protease. The total free amino acid was improved about 13% and although the enzyme mainly had the activity to hydrolyze the glycine residue, individual amino acids analysis with an amino acid analyzer showed that the contents of glycine, proline, alanine, arginine and glutamate were considerably increased. The results of this study showed that the glycine aminopeptidase would be useful in the food industry.

Morphology-associated expression of NADP-dependent glutamate dehydrogenases during yeast-mycelium transition of a dimorphic fungus Benjaminiella poitrasii

Benjaminiella poitrasii, a dimorphic zygomycetous fungus possesses three glutamate dehydrogenases, one requiring NAD while the other two use NADP as a coenzyme. In the activity staining after electrophoresis on native polyacrylamide gel NAD- dependent glutamate dehydrogenase revealed the presence of one enzyme that was expressed in both, yeast- and mycelium-form cells. While in case of NADP- dependent glutamate dehydrogenase two distinct activity bands that were differentially expressed in yeast- and mycelium-form cells were seen. Interestingly, during yeast-mycelium transition and reverse, quantitative changes in form-specific native NADP-dependent glutamate dehydrogenase activities were seen. The biochemical data on temperature and pH optima, thermostability, and kinetic properties confirmed the presence of two NADP-dependent proteins in B. poitrasii, parent strain. The monomorphic mutant (Y-5, yeast form) showed NADP- glutamate dehydrogenase similar to parent yeast-form enzyme. For the first time the significance of differential expression of these enzymes during morphological transition in B. poitrasii has been suggested.

Sexual reactions in Mortierellales are mediated by the trisporic acid system

Several species of Mortierella (Mortierellales, Zygomycota) were examined for substances regulating their sexual reactions. Compounds isolated from both mated and single growing Mortierella strains were purified by thin layer chromatography. Some of these compounds showed UV absorbance-characteristics similar to those of trisporoids, a group of compounds involved in sexual regulation in Mucorales. A compound with a 4-dihydromethyltrisporate-like absorbance spectrum was detected. To test for the interspecific sexual responses typically induced by trisporoids, the compounds extracted from Mortierella spp. were tested against the Mucorales Mucor mucedo and Phycomyces blakesleeanus and were found to induce sexual reactions in both tester strains. A gene encoding 4-dihydromethyltrisporate dehydrogenase was identified in several Mortierella species and the activity of the gene product was shown using a histochemical assay. We suggest that the regulation of sexual processes by trisporoids is common to both Mucorales and Mortierellales and may be more widespread within the Zygomycota.

Cloning, characterization and heterologous expression of the Blakeslea trispora gene encoding orotidine-5'-monophosphate decarboxylase

The pyrG gene of the fungus Blakeslea trispora, encoding orotidine-5'-monophosphate decarboxylase (OMPD) enzyme, was cloned by heterologous hybridization of a genomic library with the Mucor circinelloides pyrG gene. The deduced amino acid sequence of the B. trispora pyrG gene is highly similar to the OMPD from other organisms. Hybridization analyses revealed that the only copy of this gene present in the genome of B. trispora is constitutively expressed. Heterologous complementation of a mutant of M. circinelloides deficient in OMPD activity with the B. trispora pyrG gene and promoter sequence confirmed the function of this gene. This functional complementation demonstrates that heterologous expression in M. circinelloides might be used to investigate the function of genes of B. trispora.

Decolorization of synthetic dyes and production of manganese-dependent peroxidase by new fungal isolates

Two yeasts, Debaryomyces polymorphus, Candida tropicalis, and two filamentous fungi, Umbelopsis isabellina, Penicillium geastrivorus, could completely decolorize 100 mg Reactive Black 5 (RB 5) l-1 within 16-48 h. Manganese-dependent peroxidase (MnP) activities between 60 and 424 U l-1 were detected in culture supernatants of three of these organisms indicating the color removal by enzymatic biodegradation but with P. geastrivorus there was no ligninolytic enzyme activity in its culture and the decolorization was mainly due to biosorption to mycelium. Extensive decolorization by D. polymorphus (69-94%) and C. tropicalis (30-97%) was obtained with five other azo dyes and one anthraquinone dye. Except for Reactive Brilliant Blue KNR and Reactive Yellow M-3R, the four azo dyes, Reactive Red M-3BE, Procion Scharlach H-E3G, Procion Marine H-EXL and Reactive Brilliant Red K-2BP, induced D. polymorphus to produce MnP (105-587 U l-1). However, MnP activities of 198-329 U l-1 were only detected in the culture of C. tropicalis containing Reactive Red M-3BE and Reactive Brilliant Red K-2BP, respectively.

Purification and kinetics of a raw starch-hydrolyzing, thermostable, and neutral glucoamylase of the thermophilic mold Thermomucor indicae-seudaticae

The purified glucoamylase of the thermophilic mold Thermomucor indicae-seudaticaehad a molecular mass of 42 kDa with a pI of 8.2. It is a glycoprotein with 9-10.5% carbohydrate content, which acted optimally at 60 degrees C and pH 7.0, with a t(1/2) of 12 h at 60 degrees C and 7 h at 80 degrees C. Its experimental activation energy was 43 KJ mol(-1) with temperature quotient (Q(10)) of 1.35, while the values predicted by response surface methodology (RSM) were 43 KJ mol(-1) and 1.28, respectively. The enzyme hydrolyzed soluble starch at 50 degrees C (K(m) 0.50 mg mL(-1) and V(max) 109 micromol mg(-1) protein min(-1)) and at 60 degrees C (K(m) 0.40 and V(max) 143 micromol mg(-1) protein min(-1)). The experimental K(m) and V(max) values are in agreement with the predicted values at 50 degrees C (K(m) 0.45 mg mL(-1) and V(max) 111.11 micromol mg(-1) protein min(-1)) and at 60 degrees C (K(m) 0.36 mg mL(-1)and V(max) 142.85 micromol mg(-1) protein min(-1)). An Arrhenius plot indicated thermal activation up to 60 degrees C, and thereafter, inactivation. The enzyme was strongly stimulated by Co(2+), Fe(2+), Ag(2+), and Ca(2+), slightly stimulated by Cu(2+) and Mg(2+), and inhibited by Hg(2+), Zn(2+), Ni(2+), and Mn(2+). Among additives, dextran and trehalose slightly enhanced the activity. Glucoamylase activity was inhibited by EDTA, beta-mercaptoethanol, dithiothreitol, and n-bromosuccinimide, and n-ethylmaleimide inhibited its activity completely. This suggested the involvement of tryptophan and cysteine in catalytic activity and the critical role of disulfide linkages in maintaining the conformation of the enzyme. The enzyme hydrolyzed around 82% of soluble starch and 65% of raw starch (K(m) 2.4 mg mL(-1), V(max) 50 micromol mg(-1) protein min(-1)), and it was remarkably insensitive to glucose, suggesting its applicability in starch saccharification.

[Mechanisms of degradation of the fungal ornithine decarboxylase]

Ornithine decarboxylase (ODC) is the first enzyme in polyamine biosynthesis in numerous living organisms, from bacteria to mammalian cells. Its control is under negative feedback regulation by the end products of the pathway. In dimorphic fungi, ODC activity and therefore polyamine concentrations are related to the morphogenetic process. From the fission yeast Schizosaccharomyces pombe to human, polyamines induce antizyme synthesis which in turn inactivates ODC. This is hydrolyzed by the 26S proteasome without ubiquitination. The regulatory mechanism of antizyme on polyamines is conserved, although to date no antizyme homology has been identified in some fungal species. The components that are responsible for regulating polyamine levels in cells and the current knowledge of ODC regulation in dimorphic fungi are presented in this review. ODC degradation is of particular interest because inhibitors of this pathway may lead to the discovery of novel antifungal drugs.

[Initial stages of trisporic acid synthesis in Blakeslea trispora]

Biotransformation of beta-carotene with enzyme preparations isolated from the mycelium of Blakeslea trispora resulted in the formation of its hydroxylated metabolite and apocarotenals, products of oxidative degradation of this compound. By spectral, chromatographic, and chemical properties, the beta-carotene derivative was identified as 4-hydroxy-beta-carotene (isocryptoxanthine). One of the products of oxidative degradation of beta-carotene, beta-apo-13-carotenone, underwent modification in the presence of enzyme preparations from Blakeslea trispora with the formation of trisporic acid precursors. It should be emphasized that beta-apo-13-carotenone transformation proceeded more rapidly than beta-carotene oxidation by carbon in the 4-position. Our findings suggest that under conditions of oxidative stress, oxidative degradation of beta-carotene into beta-apo-13-carotenone leads to the formation of considerable amounts of trisporic acids.

Selection of Gongronella butleri strains for enhanced chitosan yield with UV mutagenesis

This paper describes the selection of Gongronella butleri strains producing higher chitosan yield using UV mutagenesis. We have devised an enzyme-linked immunosorbent assay for the selection of high chitin deacetylase (CDA) yielding strains. Mutant strains M+1, M+2 and M+7 could produce twice the extractable chitosan yield and double the CDA activity, as compared to the wild type strain.

Decolourisation of textile and dye amended soils by fungi

Four fungi viz. Aspergillus niger, Curvularia lunata, Fusarium oxysporum, Mucor mucedo isolated from textile and dye contaminated soils were tried for their efficiency in colour removal. The physical, chemical and biological characteristics were analysed and related to the process of decolourisation. The role of extracellular enzymes, alpha-amylase, protease, catalase and glucose oxidase was studied during 7, 14, and 21 days of incubation period. A. niger and M. mucedo were resistant in the soils and also efficient (92 percent) in decolourisation and in the enzyme production. C. lunata and F. oxysporum though occurred abundantly were not so successful in the process of colour removal or in enzyme secretions.

Genetic variability of the postharvest pathogen Gilbertella persicaria: identification of randomly amplified polymorphic DNA (RAPD) markers correlating with (+) and (-) mating types

Random amplified polymorphic DNA (RAPD) and isoenzyme polymorphisms among 16 isolates of the postharvest pathogen Gilbertella persicaria were examined. Six different 10-bp primers were used to determine the extent of intraspecific genetic variability. Nine composite amplification types were identified. RAPD markers were obtained which correlated with the mating types of the G. persicaria isolates. The variability of the isoenzyme patterns was very low and no correlation was found between the isoenzyme markers and the mating abilities. When 80 single carbon substrates were tested in utilization assays, most of them were utilized uniformly by the 16 G. persicaria strains. However, some compounds elicited differences between the isolates representing the two mating types. Beta-alanine (0.2%) has little effect on the germination of the sporangiospores of the (+) isolates, but inhibited the germination of (-) sporangiospores. Glycerol-1-monoacetate supported the growth of both mating types, but at concentrations higher than 4% this was accompanied with a compact (colonial) growth for plus mating type isolates only.

Sesamin inhibits lysophosphatidylcholine acyltransferase in Mortierella alpina

The filamentous fungus, Mortierella alpina, accumulates complex lipids relatively rich in arachidonic acid (C(20:4) Delta(5,8,11,14)). The lignan, sesamin, has been used to reduce arachidonic acid production by specifically inhibiting Delta(5)-desaturation [Shimizu, Akimoto, Shinmen, Kawashima, Sugano and Yamada (1991) Lipids 26, 512-516]. Microsomal membrane preparations from M. alpina exhibit acyl-CoA:1-acyl lysophosphatidylcholine acyltransferase (LPCAT) activity. LPCAT is an enzyme involved in channelling fatty acid substrates to phosphatidylcholine for subsequent desaturation. Sesamin was found to inhibit this enzyme as measured in both spectrophotometric and radioactive assays. The inhibitory effect of sesamin on LPCAT was only evident in species of Mortierella and could not be demonstrated in other organisms.

Polyunsaturated fatty acid-specific elongation enzymes

We have isolated a novel gene (GLELO) from Mortierella alpina and its homologue (CEELO1) from Caenorhabditis elegans and demonstrate the involvement of their encoded proteins in the elongation of C(18) polyunsaturated fatty acids.

Protein structure and gene cloning of Syncephalastrum racemosum nuclease

The complete amino acid sequence of the fungus Syncephalastrum racemosum (Sr-) nuclease has been delineated on the basis of protein sequencing of the intact protein and its protease-digested peptides. The resulting 250-residue sequence shows a carbohydrate side chain attached at Asn134 and two half-cystine residues (Cys242 and Cys247) cross-linked to form a small disulphide loop. On the basis of the sequence of Sr-nuclease, a computer search in the sequence database yielded 60% and 48% positional identities with the sequences of Cunninghamella echinulata nuclease C1 and yeast mitochondria nuclease respectively, and very little similarity to those of several known mammalian DNases I. Sequence alignment of the three similar nucleases reveals that the single small disulphide loop is unchanged but the carbohydrate attachment in Sr-nuclease is absent from the other two nucleases. Alignment also shows a highly conserved region harbouring Sr-nuclease His85, which is assigned as one of the essential residues in the active site. The cDNA encoding Sr-nuclease was amplified by using reverse transcriptase-mediated PCR with degenerate primers based on its amino acid sequence. Subsequently, specific primers were synthesized for use in the 3' and 5' rapid amplification of cDNA ends (RACE). Direct sequencing of the RACE products led to the deduction of a 1.1 kb cDNA sequence for Sr-nuclease. The cDNA contains an open reading frame of 320 amino acid residues including a 70-residue putative signal peptide and the 250-residue mature protein. Finally, the recombinant Sr-nuclease was expressed in Escherichia coli strain BL21(DE3) in which the recombinant protein, after solubilization with detergent and renaturation, showed both DNase and RNase activities. The assignment of His85 to the active site was further supported by evidence that the mutant protein Sr-nuclease (H85A), in which His85 was replaced by Ala, was not able to degrade DNA or RNA.

Stereoselectivity of Mucorales lipases toward triradylglycerols--a simple solution to a complex problem

The lipases from Rhizopus and Rhizomucor are members of the family of Mucorales lipases. Although they display high sequence homology, their stereoselectivity toward triradylglycerols (sn-2 substituted triacylglycerols) varies. Four different triradylglycerols were investigated, which were classified into two groups: flexible substrates with rotatable O'-C1' ether or ester bonds adjacent to C2 of glycerol and rigid substrates with a rigid N'-C1' amide bond or a phenyl ring in sn-2. Although Rhizopus lipase shows opposite stereopreference for flexible and rigid substrates (hydrolysis in sn-1 and sn-3, respectively), Rhizomucor lipase hydrolyzes both groups of triradylglycerols preferably in sn-1. To explain these experimental observations, computer-aided molecular modeling was applied to study the molecular basis of stereoselectivity. A generalized model for both lipases of the Mucorales family highlights the residues mediating stereoselectivity: (1) L258, the C-terminal neighbor of the catalytic histidine, and (2) G266, which is located in a loop contacting the glycerol backbone of a bound substrate. Interactions with triradylglycerol substrates are dominated by van der Waals contacts. Stereoselectivity can be predicted by analyzing the value of a single substrate torsion angle that discriminates between sn-1 and sn-3 stereopreference for all substrates and lipases investigated here. This simple model can be easily applied in enzyme and substrate engineering to predict Mucorales lipase variants and synthetic substrates with desired stereoselectivity.

1H-NMR on line monitoring of water activity during lipase catalysed esterification

1H-NMR spectroscopy is used to determine simultaneously the water activity (aw) and the time course of an esterification reaction catalysed by a lipase. Chemical shifts signals of hydroxylic hydrogens in fast exchange (i.e the average hydroxylic signal of acid, alcohol and water) varies with water activity and ester content. Calibration curves have been established from model media composed of the substrates and various ester contents, at different water activities, in order to mimic a reaction medium. One relationship is established between water activity, hydroxylic hydrogen signal chemical shift and ester content. In order to estimate the water activity evolution as a function of time, this last relationship is applied to the hydroxylic hydrogen chemical shift measured in a reaction medium where the Rhizomucor miehei lipase in a powder form is suspended in the liquid substrates. This alternative way of determining the water activity based on hydroxylic hydrogen chemical shift presents some advantages over more classical means, i.e. time saved and inaccuracies avoided by monitoring without handling the sample.

Purification, characterization and complete amino acid sequence of nuclease C1 from Cunninghamella echinulata var. echinulata

It is known, from the zymogram method of nuclease activity assay, that the crude extracts of Cunninghamella echinulata var. echinulata contained at least three distinct extracellular nucleases. Among them, the major form was 30 kDa in molecular mass and termed nuclease C1. In this report, nuclease C1 was purified to apparent homogeneity by chromatography on Cibacron blue-3GA, phenyl-Sepharose 4B and HiTrap Heparin. Nuclease C1 acquired enzymatic activity in the presence of Mn2+ or Mg2+ and was inhibited by EDTA. The activity was maximal at pH 7-8.5. The primary structure of nuclease C1 was completely determined using enzymatic digestion and gene cloning. The N-terminal 49 residues of nuclease C1 were first elucidated from a tryptic digest. Two degenerate upstream primers were subsequently designed to amplify the cDNA encoding nuclease C1. The resulting protein sequence of nuclease C1 was shown to be composed of 252 residues. It was intriguing to find that the protein sequence of nuclease C1 showed significant similarities with the sequences of the mitochondrial nucleases of Saccharomyces cerevisiae (44% identity) and Schizosaccharomyces pombe (42% identity). Residue His87 of nuclease C1 was postulated to be located at the active site from sequence similarity with secreted nuclease from Serratia marcescens.

Isolation of a Delta5-fatty acid desaturase gene from Mortierella alpina

Arachidonic acid (C20:4 Delta5,8,11,14) is a polyunsaturated fatty acid synthesized by the Delta5-fatty acid desaturation of di-homo-gamma-linolenic acid (C20:3 Delta8,11,14). In mammals, it is known to be a precursor of the prostaglandins and the leukotrienes but it is also accumulated by the filamentous fungus Mortierella alpina. We have isolated a cDNA encoding the Delta5-fatty acid desaturase from M. alpina via a polymerase chain reaction-based strategy using primers designed to the conserved histidine box regions of microsomal desaturases, and confirmed its function by expression in the yeast Saccharomyces cerevisiae. Analysis of the lipids from the transformed yeast demonstrated the accumulation of arachidonic acid. The M. alpina Delta5-desaturase is the first example of a cloned Delta5-desaturase, and differs from other fungal desaturases previously characterized by the presence of an N-terminal domain related to cytochrome b5.

Conformational change in the activation of lipase: an analysis in terms of low-frequency normal modes

The interfacial activation of Rhizomucor miehei lipase (RmL) involves the motion of an alpha-helical region (residues 82-96) which acts as a "lid" over the active site of the enzyme, undergoing a displacement from a "closed" to an "open" conformation upon binding of substrate. Normal mode analyses performed in both low and high dielectric media reveal that low-frequency vibrational modes contribute significantly to the conformational transition between the closed and open conformations. In these modes, the lid displacement is coupled to local motions of active site loops as well as global breathing motions. Atomic fluctuations of the first hinge of the lid (residues 83-84) are substantially larger in the low dielectric medium than in the high dielectric medium. Our results also suggest that electrostatic interactions of Arg86 play an important role in terms of both the intrinsic stability of the lid and its displacement, through enhancement of hinge mobility in a high dielectric medium. Additional calculations demonstrate that the observed patterns of atomic fluctuations are an intrinsic feature of the protein structure and not dependent on the nature of specific energy minima.

Single-column purification of syncephapepsin--an aspartic proteinase from Syncephalastrum racemosum

Syncephapepsin is a fungal aspartic proteinase from Syncephalastrum racemosum. By using the property of syncephapepsin after having increased activity at higher temperature, two rapid purification protocols were developed. In the former case, a crude extract was initially diluted fivefold with an activity assay buffer and heated at 50 degrees C overnight. In this situation, syncephapepsin would digest most of the proteins that the crude extract contained. Subsequently, syncephapepsin of the crude extract was precipitated from 50 to 70% of ammonium sulfate and the preparation was then directly applied to the Superdex 200 HR FPLC column. In this manner, syncephapepsin was rapidly purified to apparent homogeneity within 24 h. In this report, an alternative method of purification is also provided. Compared with the procedure mentioned above, the heating step was proceeded after FPLC chromatography through which the same result was obtained. Using cytochrome c and RNase A as substrates, the cleavage sites of both substrates were identified by HPLC peptide mapping. The results showed that syncephapepsin had a broad specificity. Residues recognized to be cleaved were primarily those of trypsin and chymotrypsin and Lys was the most susceptible.

Activity and stability of a Rhizomucor miehei lipase in hydrophobic media

The effects of detergents and organic solvents on a commercial lipase (Lipozyme) from Rhizomucor miehei were investigated. It was shown that the detergent sodium cholate is possibly an activator of the enzyme, increasing lipase activity 2.5 times (250% of the control) when the enzyme was preincubated with 7 mM cholate. Lipozyme activity was over twice as high (230% of the control) in the presence of 80 mM Tween 80 or 90 mM Tween 20 (polyoxyethylenesorbitan monolaurate), apparently through an additional emulsifying action on the substrate. Preincubation with Tween 80 (polyoxyethylenesorbitan mono-oleate) did not affect enzyme activity. In contrast, lipase activity was completely inhibited in the presence of an 8.9 mM concentration of another non-ionic detergent, Brij 58, whereas with a 16.4 mM concentration of the cationic detergent cetyltrimethylammonium bromide (CTAB), enzyme activity was reduced by 80%. Preincubation of Lipozyme with the same concentrations of Brij 58 [poly(oxyethylene)20 cetyl ether] and CTAB promoted total inactivation of the enzyme. Organic solvents had different effects on lipase activity and stability. Of the tested solvents, hexane was least deleterious to lipase activity and did not alter enzyme stability on preincubation. These results suggest that Lipozyme can be used in esterification reactions with hexane as solvent or in hydrolysis reactions with Tween 20 or Tween 80 as emulsifying agents, after pretreatment with sodium cholate.

Regulation of chitin synthase activity in the dimorphic fungus Benjaminiella poitrasii by external osmotic pressure

The effects of changes in external osmotic pressure on chitin synthase activity of a dimorphic fungus, Benjaminiella poitrasii, have been investigated. Mycelial and yeast cells incubated in medium of low osmolality (distilled water, 0 mOsm) for 10 min had 2-3-fold higher specific activities of native chitin synthase in mixed membrane preparations than cells that had been subjected to a high osmolality medium (1.2 M sorbitol in distilled water, 1612 mOsm). Cells suspended in media of different osmolalities for 10 min were also affected in the extent of germ tube formation. Germ tube formation was highest in cells incubated in low osmolality medium. The addition of protein phosphatase inhibitors (cyclosporin A, 1.2 micrograms/ml; cantharidin, 20 microM) abolished the effect of hypo-osmotic stress on chitin synthase activation of yeast mixed membrane preparations. The presence of protein kinase inhibitors (genistein, 40 micrograms/ml; H-7, 100 microM) and a Ca2+ channel blocker (verapamil, 50 microM) reduced chitin synthase activity to 50-60% of that observed in cells under hypo-osmotic shock. These inhibitors also inhibited germ tube formation. This suggests that chitin synthase activity and yeast hyphal morphogenesis are both subject to regulation by osmotic pressure, phosphorylation and calcium.

A kinesin-like mechanoenzyme from the zygomycete Syncephalastrum racemosum shares biochemical similarities with conventional kinesin from Neurospora crassa

The kinesin superfamily consists of mechanoenzymes that convert chemical energy, stored in nucleoside triphosphates, into movement along microtubules. The founding member of this protein superfamily, the so-called conventional kinesin, was only known from animal sources until the recent description of kinesin from the filamentous fungus Neurospora crassa (G. Steinberg, M. Schliwa, Mol. Biol. Cell 6, 1605-1618 (1995)). To determine whether similar motors with comparable features are common in other filamentous fungi, a kinesin from a zygomycete, Syncephalastrum racemosum, was purified. Here, the isolation and characterization of this motorenzyme is described. The purified protein consisted of a doublet at 112 kDa and 115 kDa with no additional polypeptides. This was consistent with a calculated molecular mass of approximately 240 kDa and suggests that the motor is a dimer with a more globular shape than conventional kinesin from animal sources. In gliding assays the enzyme moved microtubules at 2.5 to 3.4 microns/s and had a nucleotide specificity similar to the Neurospora kinesin motor. Peptide antibodies against conserved regions in the head and the tall domain of conventional kinesins cross-reacted with the Syncephalastrum motor. In vitro, the enzyme was able to drive the microtubule-dependent movement of vesicles isolated from Syncephalastrum racemosum, as well as Neurospora crassa, and Aspergillus nidulans. In summary, the Syncephalastrum motor has many of the unique features in common with the conventional kinesin from the ascomycete Neurospora crassa and probably shares a similar function in living hyphae.

Purification and characterization of diacylglycerol acyltransferase from the lipid body fraction of an oleaginous fungus

Diacylglycerol acyltransferase (DGAT) [EC 2.3.1.20] was purified to apparent homogeneity from the lipid body fraction of an oleaginous fungus, Mortierella ramanniana var. angulispora. The enzyme was solubilized from the lipid body fraction with 0.1% Triton X-100, and purified by subsequent column chromatography on Yellow 86 agarose, Superdex-200, Heparin-Sepharose, second Superdex-200, and second Yellow 86 agarose. The enzyme activity was finally enriched 4,802-fold over that of the starting 1,500X g supernatant. The apparent molecular mass of the enzyme was 53 kDa on SDS polyacrylamide gel electrophoresis. The purified enzyme did not exhibit glycerol-3-phosphate acyltransferase, lysophosphatidic acid acyltransferase, lipase, transacylase, or acyl-CoA hydrolase activities, although 2-monoolein was acylated with about a half of the enzyme activity toward 1,2-diolein. The purified DGAT depended on exogenous sn-1,2-diolein and oleoyl-CoA, with the highest activity at about 200 and 20 microM, respectively. Purified DGAT utilized a broad range of molecular species of both diacylglycerol and acyl-CoA as substrates. The highest activity was observed with sn-1,2-diolein and lauroyl-CoA. Anionic phospholipids such as phosphatidic acid (PA) activated the purified enzyme, as found for the Triton X-100 extract. Sphingosine dose-dependently inhibited DGAT activity activated by PA and basal activity without PA. These results provide a basis for further studies on the molecular mechanism of triacylglycerol biosynthesis and lipid body formation, in which DGAT plays an important role.

Crystal structure of the aspartic proteinase from Rhizomucor miehei at 2.15 A resolution

The crystal structure of the aspartic proteinase from Rhizomucor miehei (RMP, EC 3. 4. 23. 23) has been refined to 2.15 A resolution to a crystallographic R-value of 0.215 and an Rfree of 0.281. The root-mean-square (r.m.s.) error for the atomic coordinates estimated from a Luzzati plot is 0.2 A. The r.m.s. deviations for the bond distances and bond angles from ideality are 0.01 A and 1.7 degrees, respectively. RMP contains two domains that consist predominantly of beta-sheets. A large substrate-binding cleft is clearly visible between the two domains, and the two catalytic residues Asp38 and Asp237 are located in the middle of the cleft with a water molecule bridging the carboxyl groups of Asp38 and Asp237. Due to crystal packing, the C-terminal domain is more mobile than the N-terminal domain. Most of the aspartic proteinases (except renin) reach their maximum activity at acidic pH. We propose that the optimum pH of each aspartic proteinase is determined by the electrostatic potential at the active site, which, in turn, is determined by the positions and orientations of all the residues near the active site. RMP is the most glycosylated among the aspartic proteinases. The carbohydrate moieties are linked to Asn79 and Asn188. Asn79 is in the middle of a beta-strand and Asn188 is on a surface loop in contrast to the previous hypothesis proposed by Brown and Yada that they are both on surface beta-turns. RMP has a very high thermal stability. The high thermal stability is probably due to the high level of glycosylation. We propose that the highly flexible carbohydrates act as heat reservoirs to stabilize the conformation of RMP and therefore give the enzyme a high level of thermal stability. Three-dimensional structural and sequence alignments of RMP with other aspartic proteinases show that RMP is most structurally homologous to that of Mucor pusillus (MPP), and differs from other fungal enzymes as much as it does from the mammalian enzymes. This suggests that RMP and MPP diverged from the main stream of aspartic proteinases at an early stage of evolution. The present study adds a second member to this subfamily of aspartic proteinases.

Molecular modelling studies of substrate binding to the lipase from Rhizomucor miehei

Lipase enzymes have found increasingly widespread use, especially in biotransformation reactions in organic synthesis. Due to their efficiency and high enantioselectivity, they can be employed in a variety of reactions to carry out asymmetric hydrolyses, esterifications and transesterifications. However, the reasons for their stereospecificity have not been fully correlated with the enzyme structure. Employing molecular modelling techniques and existing experimental data, a transesterification reaction using Rhizomucor miehei lipase was studied. The results indicate that the major controlling factor for this reaction is hydrophobic in nature, providing support for previous literature hypotheses. In addition, computational experiments suggest that the origin of enantioselectivity is the formation of essential hydrogen bonds in and around the catalytic triad of active site residues. Only one enantiomer of the substrate is able to form these hydrogen bonds during the formation of the first tetrahedral transition state.