Purification and characterization of two thermostable proteases from the thermophilic fungus Chaetomium thermophilum

Thermostable protease is very effective to improve the industrial processes in many fields. Two thermostable extracellular proteases from the culture supernatant of the thermophilic fungus Chaetomium thermophilum were purified to homogeneity by fractional ammonium sulfate precipitation, ion-exchange chromatography on DEAE-Sepharose, and PhenylSepharose hydrophobic interaction chromatography. By SDS-PAGE, the molecular mass of the two purified enzymes was estimated to be 33 kDa and 63 kDa, respectively. The two proteases were found to be inhibited by PMSF, but not by iodoacetamide and EDTA. The 33 kDa protease (PRO33) exhibited maximal activity at pH 10.0 and the 63 kDa protease (PRO63) at pH 5.0. The optimum temperature for the two proteases was 65 degrees C. The PRO33 had a K(m) value of 6.6 mM and a V(max) value of 10.31 micromol/l/min, and PRO63 17.6 mM and 9.08 micromol/l/min, with casein as substrate. They were thermostable at 60 degrees C. The protease activity of PRO33 and PRO63 remained at 67.2% and 17.31%, respectively, after incubation at 70 degrees C for 1 h. The thermal stability of the two enzymes was significantly enhanced by Ca2+. The residual activity of PRO33 and PRO63 at 70 degrees C after 60 min was approximately 88.59% and 39.2%, respectively, when kept in the buffer containing Ca2+. These properties make them applicable for many biotechnological purposes.     

嗜热毛壳菌外切葡聚糖纤维二糖水解酶的纯化和部分性质研究

研究液体发酵嗜热毛壳菌(Chaetomium thermophilum)产生的一种外切葡聚糖纤维二糖水解酶的分离纯化及特性。粗酶液经硫酸铵沉淀、DEAE-Sepharose Fast Flow阴离子层析、Sephacryl S-100分子筛层析、Q Sepharose Fast Flow强阴离子层析等步骤后获得凝胶电泳均一的外切葡聚糖纤维二糖水解酶。经12.5%SDS-PAGE和凝胶过滤层析方法测得该酶的分子量大小约为66.3kDa和67.1kDa。该酶反应的最适温度和pH值分别为65℃和5.0。在60℃以下酶比较稳定,在70℃酶的半衰期为1h,在80℃下保温20min仍具有20%的活性,该酶的热稳定性较中温真菌的同类酶高,与国外报道的嗜热真菌的同类酶热稳定性接近。以pNPC为底物的Km值为0.956mmol/L。     

Purification and characterization of a thermostable glucoamylase from Chaetomium thermophilum

Thermostable amylolytic enzymes are currently being investigated to improve industrial processes of starch degradation. A thermostable extracellular glucoamylase (exo-1, 4-alpha-D-glucanohydrolase, E.C.3.2.1.3) from the culture supernatant of a thermophilic fungus Chaetomium thermophilum was purified to sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) homogeneity by using ammonium sulfate fraction, DEAE-Sepharose Fast Flow chromatography, and Phenyl-Sepharose Fast Flow chromatography. SDS-PAGE of the purified enzyme showed a single protein band of molecular weight 64 kDa. The glucoamylase exhibited optimum catalytic activity at pH 4.0 and 65 degrees C. It was thermostable at 50 degrees C and 60 degrees C, and retained 50% activity after 60 min at 65 degrees C. The half-life of the enzyme at 70 degrees C was 20 min. N-terminal amino acid sequencing (15 residues) was AVDSYIERETPIAWN. Different metal ions showed different effects on the glucoamylase activity. Ca2+, Mg2+, Na+, and K+ enhanced the enzyme activity, whereas Fe2+, Ag+, and Hg2+ cause obvious inhibition. These properties make it applicable to other biotechnological purposes.     

Cloning of a gene encoding thermostable cellobiohydrolase from the thermophilic fungus Chaetomium thermophilum and its expression in Pichia pastoris

Aims:  A new cellobiohydrolase (CBH) gene ( cbh3 ) from Chaetomium thermophilum was cloned, sequenced and expressed in Pichia pastoris .
Methods and Results:  Using RACE-PCR, a new thermostable CBH gene ( cbh3 ) was cloned from C. thermophilum . The cDNA of the CBH was 1607 bp and contained a 1356 bp open reading frame encoding a protein CBH precursor of 451 amino acid residues. The mature protein structure of C. thermophilum CBH3 only comprises a catalytic domain and lacks cellulose-binding domain and a hinge region. The gene was expressed in P. pastoris . The recombinant CBH purified was a glycoprotein with a size of about 48·0 kDa, and exhibited optimum catalytic activity at pH 5·0 and 60 °C. The enzyme was more resistant to high temperature. The CBH could hydrolyse microcrystalline cellulose and filter paper.
Conclusions:  A new thermostable CBH gene of C. thermophilum was cloned, sequenced and overexpressed in P. pastoris .
Significance and Impact of the Study:  This CBH offers an interesting potential in saccharification steps in both cellulose enzymatic conversion and alcohol production.     

Studies on a thermostable alpha-amylase from the thermophilic fungus Scytalidium thermophilum

An alpha-amylase produced by Scytalidium thermophilum was purified using DEAE-cellulose and CM-cellulose ion exchange chromatography and Sepharose 6B gel filtration. The purified protein migrated as a single band in 6% PAGE and 7% SDS-PAGE. The estimated molecular mass was 36 kDa (SDS-PAGE) and 49 kDa (Sepharose 6B). Optima of pH and temperature were 6.0 and 60 degrees C, respectively. In the absence of substrate the purified alpha-amylase was stable for 1 h at 50 degrees C and had a half-life of 12 min at 60 degrees C, but was fully stable in the presence of starch. The enzyme was not activated by several metal ions tested, including Ca(2+) (up to 10 mM), but HgCl(2 )and CuCl(2) inhibited its activity. The alpha-amylase produced by S. thermophilum preferentially hydrolyzed starch, and to a lesser extent amylopectin, maltose, amylose and glycogen in that order. The products of starch hydrolysis (up to 6 h of reaction) analyzed by thin layer chromatography, showed oligosaccharides such as maltotrioses, maltotetraoses and maltopentaoses. Maltose and traces of glucose were formed only after 3 h of reaction. These results confirm the character of the enzyme studied to be an alpha-amylase (1,4-alpha-glucan glucanohydrolase).     

Purification and characterization of a thermostable glucoamylase from the thermophilic fungus Thermomyces lanuginosus.

Glucoamylase (1,4-alpha-D-glucan glucohydrolase, EC 3.2.1.3) was purified from the culture filtrates of the thermophilic fungus Thermomyces lanuginosus and was established to be homogeneous by a number of criteria. The enzyme was a glycoprotein with an average molecular weight of about 57 000 and a carbohydrate content of 10-12%. The enzyme hydrolysed successive glucose residues from the non-reducing ends of the starch molecule. It did not exhibit any glucosyltransferase activity. The enzyme appeared to hydrolyse maltotriose by the multi-chain mechanism. The enzyme was unable to hydrolyse 1,6-alpha-D-glucosidic linkages of isomaltose and dextran. It was optimally active at 70 degrees C. The enzyme exhibited increase in the Vmax. and decreased in Km values with increasing chain length of the substrate molecule. The enzyme was inhibited by the substrate analogue D-glucono-delta-lactone in a non-competitive manner. The enzyme inhibited remarkable resistance towards chemical and thermal denaturation.     

Directed evolution and structural prediction of cellobiohydrolase II from the thermophilic fungus Chaetomium thermophilum

Cellulases can be engineered with enhanced properties for broad use in scientific and industrial applications. In this study, the wild-type cbh2 gene of the thermophilic fungus Chaetomium thermophilum encoding cellobiohydrolase II (CBHII) was mutagenized through in vitro directed evolution. The resulting Pichia pastoris yeast library was screened, and two transformants were selected for enhanced CBHII activities that were not attributed to increased gene copy numbers. The optimum fermentation times of the two mutant transformants were shortened to 4-5?days after methanol induction compared to 6?days for the wild-type. The optimum reaction temperature (60?°C) and pH level (5 or 6) of the mutant CBHII proteins, designated CBHIIX16 and CBHIIX305, were higher than those of wild-type CBHII (50?°C and pH 4). Kept at 80?°C for 1?h, CBHIIX16 and CBHIIX305 retained >50% of their activities, while the wild-type CBHII lost all activity. Sequence analysis of CBHIIX16 and CBHIIX305 revealed that they contained five and six mutated amino acids, respectively. Structural modeling confirmed the presence of carbohydrate binding type-1 and catalytic domains, where the hydrogen bond numbers between the 227th and 203rd amino acids were increased, which perhaps contributed to the elevated enzyme stability. Therefore, the two CBHII mutants selected for increased enzymatic activities also demonstrated elevated optimum reaction temperature and pH levels and enhanced thermal stability. These properties may be beneficial in practical applications for CBHII.     

疏绵状嗜热丝孢菌热稳定几丁质酶的纯化及其性质研究

采用硫酸铵沉淀、DEAE SepharoseFastFlow阴离子层析、Phenyl Sepharose疏水层析等步骤获得了凝胶电泳均一的疏绵状嗜热丝孢菌 (Thermomyceslanuginosus)几丁质酶。经SDS PAGE和凝胶过滤层析测得纯酶蛋白的分子量在 4 8～ 4 9 .8kD之间。该酶反应的最适温度和最适pH分别为 5 5℃和 4 5 ,在pH4 5条件下 ,该酶在 5 0℃以下稳定 ;6 5℃的半衰期为 2 5min ;70℃保温 2 0min后 ,仍保留 2 4 %的酶活性。其N 端氨基酸序列为AQGYLSVQYFVNWAI。金属离子对几丁质酶的活性影响较大 ,Ca2 、Na 、K 、Ba2 对酶有激活作用 ;Ag 、Fe2 、Cu2 、Hg2 对酶有显著的抑制作用 ;以胶体几丁质为底物的Km 和Vmax值分别为 9 .5 6mg mL和 2 2 . 12 μmol min。抗菌活性显示 ,该酶对供试病原菌有不同程度的抑制作用。     

Purification and characterization of alpha-galactosidase from a thermophilic fungus Thermomyces lanuginosus

An extracellular alpha-galactosidase was purified to electrophoretic homogeneity from a locust bean gum-spent culture fluid of a mannanolytic strain of the thermophilic fungus Thermomyces lanuginosus. Molecular mass of the enzyme is 57 kDa. The pure enzyme which has a glycoprotein nature, afforded several forms on IEF, indicating its microheterogeneity. Isoelectric point of the major form was 5.2. Enzyme is the most active against aryl alpha-D-galactosides but efficiently hydrolyzed alpha-glycosidically linked non-reducing terminal galactopyranosyl residues occurring in natural substrates such as melibiose, raffinose, stachyose, and fragments of galactomannan. In addition, the enzyme is able to catalyze efficient degalactosylation of polymeric galactomannans leading to precipitation of the polymers. Stereochemical course of hydrolysis of two substrates, 4-nitrophenyl alpha-galactopyranoside and galactosyl(1)mannotriose, followed by (1)H NMR spectroscopy, pointed out the alpha-anomer of D-galactose was the primary product of hydrolysis from which the beta-anomer was formed by mutarotation. Hence the enzyme is a retaining glycosyl hydrolase. In accord with its retaining character the enzyme catalyzed transgalactosylation from 4-nitrophenyl alpha-galactopyranoside as a glycosyl donor. Amino acid sequence alignment of N-terminal and two internal sequences suggested that the enzyme is a member of family 27 of glycosyl hydrolases.     

Purification and characterization of thermostable aspartate aminotransferase from a thermophilic Bacillus species.

Aspartate aminotransferase (EC 2.6.1.1) was purified to homogeneity from cell extracts of a newly isolated thermophilic bacterium, Bacillus sp. strain YM-2. The enzyme consisted of two subunits identical in molecular weight (Mr, 42,000) and showed microheterogeneity, giving two bands with pIs of 4.1 and 4.5 upon isoelectric focusing. The enzyme contained 1 mol of pyridoxal 5'-phosphate per mol of subunit and exhibited maxima at about 360 and 415 nm in absorption and circular dichroism spectra. The intensities of the two bands were dependent on the buffer pH; at neutral or slightly alkaline pH, where the enzyme showed its maximum activity, the absorption peak at 360 nm was prominent. The enzyme was specific for L-aspartate and L-cysteine sulfinate as amino donors and alpha-ketoglutarate as an amino acceptor; the KmS were determined to be 3.0 mM for L-aspartate and 2.6 mM for alpha-ketoglutarate. The enzyme was most active at 70 degrees C and had a higher thermostability than the enzyme from Escherichia coli. The N-terminal amino acid sequence (24 residues) did not show any similarity with the sequences of mammalian and E. coli enzymes, but several residues were identical with those of the thermoacidophilic archaebacterial enzyme recently reported.     

Purification and characterization of a thermostable intracellular β-xylosidase from the thermophilic fungus Sporotrichum thermophile

An intracellular β-xylosidase from the thermophilic fungus Sporotricum thermophile strain ATCC 34628 was purified to homogeneity by Q-Sepharose and Mono-Q column chromatographies. The protein properties correspond to molecular mass and pI values of 45 kDa and 4.2, respectively. The enzyme is optimally active at pH 7.0 and 50 °C. The purified β-xylosidase is fully stable at pH 6.0–8.0 and temperatures up to 50 °C and retained over 58% of its activity after 1 h at 60 °C. The enzyme hydrolyzes β-1,4-linked xylo-oligosaccharides with chain lengths from 2 to 6, releasing xylose from the non-reducing end, but is inactive against xylan substrates. The apparent K_m and V_max values from p-nitrophenyl β-d-xylopyranoside are 1.1 mM and 114 μmol p-nitrophenol min⁻¹ mg⁻¹, respectively. Alcohols inactivate the enzyme, ethanol at 10% (v/v) yields a 30% decrease of its activity. The enzyme is irreversibly inhibited by 2,3-epoxypropyl β-d-xylobioside while alkyl epoxides derived from d-xylose were not inhibitors of the enzyme. The enzyme catalyses the condensation reaction using high donor concentration, up to 60% (w/v) xylose.     

Cloning of a gene encoding thermostable glucoamylase from Chaetomium thermophilum and its expression in Pichia pastoris

AIMS: Chaetomium thermophilum is a soil-borne thermophilic fungus whose molecular biology is poorly understood. Only a few genes have been cloned from the Chaetomium genus. This study attempted to clone, to sequence and to express a thermostable glucoamylase gene of C. thermophilum. METHODS AND RESULTS: First strand cDNA was prepared from total RNA isolated from C. thermophilum and the glucoamylase gene amplified by using PCR. Degenerate primers based on the N-terminal sequences of the purified glucoamylase according to our previous works and a cDNA fragment encoding the glucoamylase gene was obtained through RT-PCR. Using RACE-PCR, full-length cDNA of glucoamylase gene was cloned from C. thermophilum. The full-length cDNA of the glucoamylase was 2016 bp and contained a 1797-bp open reading frame encoding a protein glucoamylase precursor of 599 amino acid residues. The amino-acid sequence from 31 to 45 corresponded to the N-terminal sequence of the purified protein. The first 30 amino acids were presumed to be a signal peptide. The alignment results of the putative amino acid sequence showed the catalytic domain of the glucoamylase was high homology with the catalytic domains of the other glucoamylases. The C. thermophilum glucoamylase gene was expressed in Pichia pastoris, and the glucoamylase was secreted into the culture medium by the yeast in a functionally active form. The recombinant glucoamylase purified was a glycoprotein with a size of about 66 kDa, and exhibited optimum catalytic activity at pH 4.5-5.0 and 65 degrees C. The enzyme was stable at 60 degrees C, the enzyme activity kept 80% after 60 min incubation at 70 degrees C. The half-life was 40 and 10 min under incubation at 80 and 90 degrees C respectively. CONCLUSIONS: A new thermostable glucoamylase gene of C. thermophilum was cloned, sequenced, overexpressed successfully in P. pastoris. SIGNIFICANCE AND IMPACT OF THE STUDY: Because of its thermostability and overexpression, this glucoamylase enzyme offers an interesting potential in saccharification steps in both starch enzymatic conversion and in alcohol production.     

Purification and characterization of a thermostable carboxypeptidase from the extreme thermophilic archaebacterium Sulfolobus solfataricus.

A carboxypeptidase was purified to electrophoretic homogeneity from the thermoacidophilic archaebacterium Sulfolobus solfataricus. Molecular masses assessed by SDS/PAGE and gel filtration were 42 kDa and 170 kDa, respectively, which points to a tetrameric structure for the molecule. An isoelectric point of 5.9 was also determined. The enzyme was proven to be a metalloprotease, as shown by the inhibitory effects exerted by EDTA and o-phenanthroline; furthermore, dialysis against EDTA led to a complete loss of activity, which could be restored by addition of Zn2+ in the micromolar range, and, to a lesser extent, by Co2+. The enzyme was endowed with a broad substrate specificity, as shown by its ability to release basic, acidic and aromatic amino acids from the respective benzoylglycylated and benzyloxycarbonylated amino acids. An esterase activity of the carboxypeptidase was also demonstrated on different esterified amino acids and dipeptides blocked at the N-terminus. The enzyme displayed broad pH optima ranging over 5.5-7.0, or 5.5-9.0, when using an acidic or a basic benzyloxycarbonylated amino acid, respectively. With regard to thermostability, it was proven to be completely stable on incubation for 15 min at 85 degrees C. Furthermore, thanks to its relatively low activation energy, i.e. 31.0 kJ/mol, it was still significantly active at room temperature. At 40 degrees C, the enzyme could withstand 0.1% SDS and different organic solvents: particularly ethanol up to 99%. Amino acid and N-terminal sequence analyses did not evidence any similarity to carboxypeptidases A nor thermolysin. A weak similarity was only found with bovine carboxypeptidase B.     

Purification and characterization of two beta-glucosidases from the thermophilic fungus Thermoascus aurantiacus

β-Glucosidase from the fungusThermoascus aurantiacus grown on semi-solid fermentation medium (using ground corncob as substrate) was partially purified in 5 steps—ultrafiltration, ethanol precipitation, gel filtration and 2 anion exchange chromatography runs, and characterized. After the first anion exchange chromatography, β-glucosidase activity was eluted in 3 peaks (Gl-1, Gl-2, Gl-3). Only the Gl-2 and Gl-3 fractions were adsorbed on the gel matrix. Gl-2 and Gl-3 exhibited optimum pH at 4.5 and 4.0, respectively. The temperature optimum of both glucosidases was at 75–80°C. The pH stability of Gl-2 (4.0–9.0) was higher than Gl-3 (5.5–8.5); both enzyme activities showed similar patterns of thermostability. Under conditions of denaturing gel chromatography the molar mass of Gl-2 and Gl-3 was 175 and 157 kDa, respectively. Using 4-nitrophenyl β-d-glucopyranoside as substrate,K _m values of 1.17±0.35 and 1.38±0.86 mmol/L were determined for Gl-2 and Gl-3, respectively. Both enzymes were inhibited by Ag⁺ and stimulated by Ca²⁺.     

A thermostable lipolytic enzyme from a thermophilic Bacillus sp.: Purification and characterization

A thermophilic Bacillus sp. was isolated that secreted an extracellular, thermostable lipolytic enzyme. The enzyme was purified to 58 folds with a specific activity of 9730 units/mg of protein and yield of 10% activity by ammonium sulphate precipitation, Phenyl Sepharose chromatography, gel-permeation followed by Q Sepharose chromatography. The relative molecular mass of the protein was determined to be 61 kDa by SDS-PAGE and approximately 60 kDa by gel permeation chromatography. The enzyme showed optimal activity at 60–65 ^∘C and retained 100% activity after incubation at 60 ^∘C and pH 8.0 for 1 h. The optimum pH was determined to be 8.5. It exhibited 50% of its original activity after 65 min incubation at 70 ^∘C and 23 min incubation at 80 ^∘C. Catalytic function of lipase was activated by Mg⁺⁺ (10 mM), while mercury (10 mM) inactivated the enzyme completely. No effect on enzyme activity was observed with trypsin and chymotrypsin treatment, while 50% inhibition was observed with thermolysin. It was demonstrated that PMSF, SDS, DTT, EDTA, DEPC, βME (100 mM each) and eserine (10 mM) inhibited the activity of the lipolytic enzyme. With p-nitrophenyl laurate as a substrate, the enzyme exhibited a K _m and V _max of 0.5 mM and 0.139 μM/min/ml. The enzyme showed preference for short chain triacylglycerol and hydrolyzes triolein at all positions. In contrast to other thermostable Bacillus lipases, this enzyme has very low content of hydrophobic amino acids (22.58 %). Immunological studies showed that the active site and antigen-binding site of enzyme do not overlap.     

Thermostable conidial and mycelial alkaline phosphatases from the thermophilic fungus Scytalidium thermophilum

An extracellular (conidial) and an intracellular (mycelial) alkaline phosphatase from the thermophilic fungus Scytalidium thermophilum were purified by DEAE-cellulose and Concanavalin A-Sepharose chromatography. These enzymes showed allosteric behavior either in the presence or absence of MgCl₂, BaCl₂, CuCl₂, and ZnCl₂. All of these ions increased the maximal velocity of both enzymes. The molecular masses of the conidial and mycelial enzymes, estimated by gel filtration, were 162 and 132 kDa, respectively. Both proteins migrated on SDS-PAGE as a single polypeptide of 63 and 58.5 kDa, respectively, suggesting that these enzymes were dimers of identical subunits. The best substrate for the conidial and mycelial phosphatases was p-nitrophenylphosphate, but β-glycerophosphate and other phosphorylated compounds also served as substrates. The optimum pH for the conidial and mycelial alkaline phosphatases was 10.0 and 9.5 in the presence of AMPOL buffer, and their carbohydrate contents were about 54% and 63%, respectively. The optimum temperature was 70–75°C for both activities. The enzymes were fully stable up to 1 h at 60°C. These and other properties suggested that the alkaline phosphatases of S. thermophilum might be suitable for biotechnological applications. Journal of Industrial Microbiology & Biotechnology (2001) 27, 265–270. Received 10 January 2001/ Accepted in revised form 10 July 2001     

Purification and characterization of a thermostable glutamate dehydrogenase from a thermophilic bacterium isolated from a sterilization drying oven

Glutamate dehydrogenase from axenic bacterial cultures of a new microorganism, called GWE1, isolated from the interior of a sterilization drying oven, was purified by anion-exchange and molecular-exclusion liquid chromatography. The apparent molecular mass of the native enzyme was 250.5 kDa and was shown to be an hexamer with similar subunits of molecular mass 40.5 kDa. For glutamate oxidation, the enzyme showed an optimal pH and temperature of 8.0 and 70 degrees C, respectively. In contrast to other glutamate dehydrogenases isolated from bacteria, the enzyme isolated in this study can use both NAD(+) and NADP(+) as electron acceptors, displaying more affinity for NADP(+) than for NAD(+). No activity was detected with NADH or NADPH, 2-oxoglutarate and ammonia. The enzyme was exceptionally thermostable, maintaining more than 70% of activity after incubating at 100(o)C for more than five hours suggesting being one of the most thermoestable enzymes reported in the family of dehydrogenases.     

Characterization of a thermostable extracellular beta-galactosidase from a thermophilic fungus Rhizomucor sp

An extracellular beta-galactosidase from a thermophilic fungus Rhizomucor sp. has been purified to homogeneity by successive DEAE cellulose chromatography followed by gel filtration on Sephacryl S-300. The native molecular mass of the enzyme is 250,000 and it is composed of two identical subunits with molecular mass of 120,000. It is an acidic protein with a pI of 4.2. Purified beta-galactosidase is a glycoprotein and contains 8% neutral sugar. The optimum pH and temperature for enzyme activity are 4.5 and 60 degrees C, respectively. The enzyme is stable at 60 degrees C for 4 h, and has a t(1/2) of 150 min(-1) at 70 degrees C which is one of the highest reported for fungal beta-galactosidases. Substrate specificity studies indicated that the enzyme is specific for beta-linked galactose residues with a preference for p-nitrophenyl-beta-D-galactopyranoside (pNPG). The Km and Vmax values for the synthetic substrates pNPG and o-nitrophenyl-beta-D-galactopyranoside (oNPG) were 0.66 mM and 1.32 mM; and 22.4 mmol min(-1) mg(-1) and 4.45 mmol min(-1) mg(-1), respectively, while that for the natural substrate, lactose, was 50.0 mM and 12 mmol min(-1) mg(-1). The end product galactose and the substrate analogue isopropyl thiogalactopyranoside (ITPG) inhibited the enzyme with Ki of 2.6 mM and 12.0 mM, respectively. The energy of activation for the enzyme using pNPG and oNPG were 27.04 kCal and 9.04 kCal, respectively. The active site characterization studies using group-specific reagents revealed that a tryptophan and lysine residue play an important role in the catalytic activity of the enzyme.     

Production, purification and characterization of thermostable phytase from thermophilic fungus Thermomyces lanuginosus TL-7

Ten different strains of Thermomyces lanuginosus, isolated from composting soils were found to produce phytase when grown on PSM medium. The wild type strain CM was found to produce maximum amount ofphytase (4.33 units/g DW substrate). Culturing T. lanuginosus strain CM on medium containing wheat bran and optimizing other culture conditions (carbon source, media type, nitrogen source, level of nitrogen, temperature, pH, inoculum age, inoculum level and moisture), increased the phytase yield to 13.26 units/g substrate. This culture was further subjected to UV mutagenesis for developing phytase hyperproducing mutants. The mutant (TL-7) showed 2.29-fold increase in phytase activity as compared to the parental strain. Employing Box-Behnken factor factorial design of response surface methodology resulted in optimized phytase production (32.19 units/g of substrate) by mutant TL-7. A simple two-step purification (40.75-folds) ofphytase from mutant TL-7 was achieved by anion exchange and gel filtration chromatography. The purified phytase (approximately 54 kDa) was characterized to be optimally active at pH 5.0 and temperature 70 degrees C, though the enzyme showed approximately 70% activity over a wide pH and temperature range (2.0-10.0 and 30-90 degrees C, respectively). The phytase showed broad substrate specificity with activity against sodium phytate, ADP and riboflavin phosphate. The phytase from T. lanuginosus was thermoacidstable as it showed up to 70% residual activity after exposure to 70 degrees C at pH 3.0 for 120 min. The enzyme showed Km 4.55 microM and Vmax 0.833 microM/min/mg against sodium phytate as substrate.