Purification, N-terminal amino acid sequence and characterization of pH 2.5 optimum acid phosphatase (E.C. 3.1.3.2) from Aspergillus ficuum

Recombinant HAP Phytase of the Thermophilic Mold Sporotrichum thermophile: Expression of the Codon-Optimized Phytase Gene in Pichia pastoris and Applications

The codon-optimized phytase gene of the thermophilic mold Sporotrichum thermophile (St-Phy) was expressed in Pichia pastoris. The recombinant P. pastoris harboring the phytase gene (rSt-Phy) yielded a high titer of extracellular phytase (480 ± 23 U/mL) on induction with methanol. The recombinant phytase production was ~40-fold higher than that of the native fungal strain. The purified recombinant phytase (rSt-Phy) has the molecular mass of 70 kDa on SDS-PAGE, with K m and V max (calcium phytate), k cat and k cat/K m values of 0.147 mM and 183 nmol/mg s, 1.3 × 10(3)/s and 8.84 × 10(6)/M s, respectively. Mg(2+) and Ba(2+) display a slight stimulatory effect, while other cations tested exert inhibitory action on phytase. The enzyme is inhibited by chaotropic agents (guanidinium hydrochloride, potassium iodide, and urea), Woodward's reagent K and 2,3-bunatedione, but resistant to both pepsin and trypsin. The rSt-Phy is useful in the dephytinization of broiler feeds efficiently in simulated gut conditions of chick leading to the liberation of soluble inorganic phosphate with concomitant mitigation in antinutrient effects of phytates. The addition of vanadate makes it a potential candidate for generating haloperoxidase, which has several applications.

Isolation of a thermostable acid phytase from Aspergillus niger UFV-1 with strong proteolysis resistance

An Aspergillus niger UFV-1 phytase was characterized and made available for industrial application. The enzyme was purified via ultrafiltration followed by acid precipitation, ion exchange and gel filtration chromatography. This protein exhibited a molecular mass of 161 kDa in gel filtration and 81 kDa in sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE), indicating that it may be a dimer. It presented an optimum temperature of 60 °C and optimum pH of 2.0. The K M for sodium phytate hydrolysis was 30.9 mM, while the k cat and k cat / K M were 1.46 ×10 (5) s (-1) and 4.7 × 10 (6) s (-1) .M (-1) , respectively. The purified phytase exhibited broad specificity on a range of phosphorylated compounds, presenting activity on sodium phytate, p-NPP, 2- naphthylphosphate, 1- naphthylphosphate, ATP, phenyl-phosphate, glucose-6-phosphate, calcium phytate and other substrates. Enzymatic activity was slightly inhibited by Mg (2+) , Cd (2+) , K (+) and Ca (2+) , and it was drastically inhibited by F (-) . The enzyme displayed high thermostability, retaining more than 90% activity at 60 °C during 120 h and displayed a t 1/2 of 94.5 h and 6.2 h at 70 °C and 80 °C, respectively. The enzyme demonstrated strong resistance toward pepsin and trypsin, and it retained more than 90% residual activity for both enzymes after 1 h treatment. Additionally, the enzyme efficiently hydrolyzed phytate in livestock feed, liberating 15.3 μmol phosphate/mL after 2.5 h of treatment.

Expression of Aspergillus nidulans phy gene in Nicotiana benthamiana produces active phytase with broad specificities

A full-length phytase gene (phy) of Aspergillus nidulans was amplified from the cDNA library by polymerase chain reaction (PCR), and it was introduced into a bacterial expression vector, pET-28a. The recombinant protein (rPhy-E, 56 kDa) was overexpressed in the insoluble fraction of Escherichia coli culture, purified by Ni-NTA resin under denaturing conditions and injected into rats as an immunogen. To express A. nidulans phytase in a plant, the full-length of phy was cloned into a plant expression binary vector, pPZP212. The resultant construct was tested for its transient expression by Agrobacterium-infiltration into Nicotiana benthamiana leaves. Compared with a control, the agro-infiltrated leaf tissues showed the presence of phy mRNA and its high expression level in N. benthamiana. The recombinant phytase (rPhy-P, 62 kDa) was strongly reacted with the polyclonal antibody against the nonglycosylated rPhy-E. The rPhy-P showed glycosylation, two pH optima (pH 4.5 and pH 5.5), an optimum temperature at 45~55 °C, thermostability and broad substrate specificities. After deglycosylation by peptide-N-glycosidase F (PNGase-F), the rPhy-P significantly lost the phytase activity and retained 1/9 of the original activity after 10 min of incubation at 45 °C. Therefore, the deglycosylation caused a significant reduction in enzyme thermostability. In animal experiments, oral administration of the rPhy-P at 1500 U/kg body weight/day for seven days caused a significant reduction of phosphorus excretion by 16% in rat feces. Besides, the rPhy-P did not result in any toxicological changes and clinical signs.

Atomistic details of effect of disulfide bond reduction on active site of Phytase B from Aspergillus niger: A MD Study

The molecular integrity of the active site of phytases from fungi is critical for maintaining phytase function as efficient catalytic machines. In this study, the molecular dynamics (MD) of two monomers of phytase B from Aspergillus niger, the disulfide intact monomer (NAP) and a monomer with broken disulfide bonds (RAP), were simulated to explore the conformational basis of the loss of catalytic activity when disulfide bonds are broken. The simulations indicated that the overall secondary and tertiary structures of the two monomers were nearly identical but differed in some crucial secondary-structural elements in the vicinity of the disulfide bonds and catalytic site. Disulfide bonds stabilize the β-sheet that contains residue Arg66 of the active site and destabilize the α-helix that contains the catalytic residue Asp319. This stabilization and destabilization lead to changes in the shape of the active-site pocket. Functionally important hydrogen bonds and atomic fluctuations in the catalytic pocket change during the RAP simulation. None of the disulfide bonds are in or near the catalytic pocket but are most likely essential for maintaining the native conformation of the catalytic site.

ABBREVIATIONS

PhyB - 2.5 pH acid phophatese from Aspergillus niger, NAP - disulphide intact monomer of Phytase B, RAP - disulphide reduced monomer of Phytase B, Rg - radius of gyration, RMSD - root mean square deviation, MD - molecular dynamics.

Phytase, a New Life for an “Old” Enzyme

Phytases are phosphohydrolytic enzymes that initiate stepwise removal of phosphate from phytate. Simple-stomached species such as swine, poultry, and fish require extrinsic phytase to digest phytate, the major form of phosphorus in plant-based feeds. Consequently, this enzyme is supplemented in these species’ diets to decrease their phosphorus excretion, and it has emerged as one of the most effective and lucrative feed additives. This chapter provides a comprehensive review of the evolving course of phytase science and technology. It gives realistic estimates of the versatile roles of phytase in animal feeding, environmental protection, rock phosphorus preservation, human nutrition and health, and industrial applications. It elaborates on new biotechnology and existing issues related to developing novel microbial phytases as well as phytase-transgenic plants and animals. And it targets critical and integrated analyses on the global impact, novel application, and future demand of phytase in promoting animal agriculture, human health, and societal sustainability.

Single-step purification and immobilization of MBP-phytase fusion on starch agar beads: application in dephytination of soy milk

Periplasmic phytase, appA from E. coli has been noticed as a superior feed and food additive owing to its high specific activity, acidic pH optimum and resistance to gastric proteases. E. coli phytase was expressed as a fusion protein with maltose-binding protein, affinity-purified to homogeneity and, subsequently, immobilized in one step using a cost-effective matrix prepared from starch agar bead. Immobilized enzyme revealed an activity optimum at pH 6, while that of free enzyme was observed at pH 4. Both the immobilized and free enzyme showed a temperature optimum at 60 °C. Cleavage of 87 kDa fusion protein using factor Xa released 45 kDa appA. Hydrolysis of soy milk using immobilized enzyme led to 10% increase in release of inorganic phosphate at 50 °C relative to free fusion protein. This study suggests the usability of MBP as an immobilizing linker to other food enzymes for economical use in industry.

Purification and characterization of two distinct acidic phytases with broad pH stability from Aspergillus niger NCIM 563

Aspergillus niger NCIM 563 produced two different extracellular phytases (Phy I and Phy II) under submerged fermentation conditions at 30°C in medium containing dextrin-glucose-sodium nitrate-salts. Both the enzymes were purified to homogeneity using Rotavapor concentration, Phenyl-Sepharose column chromatography and Sephacryl S-200 gel filtration. The molecular mass of Phy I and II as determined by SDS–PAGE and gel filtration were 66, 264, 150 and 148 kDa respectively, indicating that Phy I consists of four identical subunits and Phy II is a monomer. The pI values of Phy I and II were 3.55 and 3.91, respectively. Phy I was highly acidic with optimum pH of 2.5 and was stable over a broad pH range (1.5–9.0) while Phy II showed a pH optimum of 5.0 with stability in the range of pH 3.5–9.0. Phy I exhibited very broad substrate specificity while Phy II was more specific for sodium phytate. Similarly Phy II was strongly inhibited by Ag⁺, Hg²⁺ (1 mM) metal ions and Phy I was partially inhibited. Peptide analysis by Mass Spectrometry (MS) MALDI-TOF also indicated that both the proteins were totally different. The K_m for Phy I and II for sodium phytate was 2.01 and 0.145 mM while V_max was 5,018 and 1,671 μmol min⁻¹ mg⁻¹, respectively. The N-terminal amino acid sequences of Phy I and Phy II were FSYGAAIPQQ and GVDERFPYTG, respectively. Phy II showed no homology with Phy I and any other known phytases from the literature suggesting its unique nature. This, according to us, is the first report of two distinct novel phytases from Aspergillus niger.

Aspergillus niger pH 2.1 optimum acid phosphatase with high affinity for phytate

An extracellular acid phosphatase isolated from the culture of a wild strain Aspergillus niger, producing the dephosphorylating 3-phytase, was obtained in a homogeneous form by sequential application of ultrafiltration through PS 50 membrane, gel filtration on Sephadex G-100 and ion exchange chromatography on DEAE-Sepharose CL 6B and CM-Sepharose CL 6B. The enzyme showed a maximum catalytic value in a strongly acidic range (pH 2.0-2.4) with pHopt 2.1 and topt 66 degrees C. The acid phosphatase showed a wide substrate specificity and a high affinity for sodium phytate, 2.5x higher than with 4-nitrophenyl phosphate. This property of the acid phosphatase demonstrated that it is a potent 3-phytase at pH 2.1 and is of great significance for a practical application of the dephosphorylating complex--its addition to the diets of monogastric animals in view of the low pH values in the digestive tract.

Properties of beta-propeller phytase expressed in transgenic tobacco

Phytases are enzymes that liberate inorganic phosphates from phytate. In a previous study, a beta-propeller phytase (168phyA) from Bacillus subtilis was introduced into transgenic tobacco, which resulted in certain phenotypic changes. In the study described herein, the recombinant phytase (t168phyA) was purified from transgenic tobacco to near homogeneity by a three-step purification scheme. The biochemical properties and kinetic parameters of t168phyA were compared with those of its counterpart from B. subtilis. t168phyA was glycosylated, and it showed a 4 kDa increase in molecular size in SDS-PAGE (44 kDa vs. 40 kDa). Although its thermostability remained unchanged, its temperature optimum shifted from 60 degrees C to 45-50 degrees C and its pH optimum shifted from pH 5.5 to 6.0. Kinetic data showed that the t168phyA had a lower Kcat, but a higher Km than the native enzyme. Despite these changes, t168phyA remained catalytically active and has a specific activity of 2.3 U/mg protein. These results verify the activity of recombinant Bacillus phytase that is expressed in plants.

Expression and characterization of extracellular fungal phytase in transformed sesame hairy root cultures

A recombinant fungal phytase was produced by cultures of sesame hairy roots transformed with Agrobacterium rhizogenes, purified and its molecular properties were characterized. Its transcription level and the phytase production were rapidly increased after 4 weeks of the cultures, suggesting that its transcription and protein synthesis might concur. Western blot analysis provided evidence that the recombinant fungal phytase was secreted into the liquid culture medium of the hairy roots. The phytase enzyme secreted was purified by three steps of ultrafiltration, DEAE-Sepharose ion exchange chromatography, and Sephadex G-100 size-exclusion chromatography. As a result, one single band signal was observed with SDS-PAGE, indicating that the purification step was reasonable. The positive signs of both the zymogram and the PAS staining on SDS-PAGE suggested that the activity of the final product phytase was active and glycosylated. The optimal reaction temperature of the phytase was between 50 and 60 degrees C and at over 60 degrees C its activity was reduced by 30-90%, depending on the temperatures applied. Pre-incubation at temperatures of 20-50 degrees C showed stable catalytic activity, while at over 50 degrees C the phytase activity was gradually decreased by 90%. The optimal pH was between 4 and 5 pH values for the recombinant fungal phytase, while for native phytase it was at pH 5.0. Addition of iron ion inhibited the phytase activity but treatments of some cations, EDTA, and PMSF showed no effect on the activity or slightly stimulated it positively.

Biochemical characterisation of extracellular phytase (myo-inositol hexakisphosphate phosphohydrolase) from a hyper-producing strain of Aspergillus niger van Teighem

Aspergillus niger van Teighem, isolated in our laboratory from samples of rotten wood logs, produced extracellular phytase having a high specific activity of 22,592 units (mg protein)-1 . The enzyme was purified to near homogeneity using ion-exchange and gel-filtration chromatography. The molecular properties of the purified enzyme suggested the native phytase to be oligomeric, with a molecular weight of 353 kDa, the monomer being 66 kDa. The purified enzyme exhibited maximum activity at pH 2.5 and 52-55 degrees C. The enzyme retained 97% activity after a 24-h incubation at 55 degrees C in the presence of 10 mM glycine, while 87% activity was retained when no thermoprotectant was added. Phytase activity was not affected by most metal ions, inhibitors and organic solvents. Non-ionic and cationic detergents (0.1-5%) stabilise the enzyme, while the anionic detergent (SDS), even at a 0.1% level, severely inhibited enzyme activity. The chaotropic agents guanidinium hydrochloride, urea, and potassium iodide (0.5-8 M), significantly affected phytase activity. The maximum hydrolysis rate (Vmax) and apparent Michaelis-Menten constant (Km) were 1,074 IU/mL and 606 microM, respectively, with a catalytic turnover number of 3x10(5) s-1 and catalytic efficiency of 3.69x10(8) M-1 s-1.

Advances in phytase research

Since its discovery in 1907, a complex of technological developments has created a potential $500 million market for phytase as an animal feed additive. During the last 30 years, research has led to increased use of soybean meal and other plant material as protein sources in animal feed. One problem that had to be overcome was the presence of antinutritional factors, including phytate, in plant meal. Phytate phosphorus is not digested by monogastric animals (e.g., hogs and poultry), and in order to supply enough of this nutrient, additional phosphate was required in the feed ration. Rock phosphate soon proved to be a cost-effective means of supplying this additional phosphorus, and the excess phytin phosphorus could be disposed of easily with the animals' manure. However, this additional phosphorus creates a massive environmental problem when the land's ability to bind it is exceeded. Over the last decade, numerous feed studies have established the efficacy of a fungal phytase, A. niger NRRL 3135, to hydrolyze phytin phosphorus in an animal's digestive tract, which benefits the animal while reducing total phosphorus levels in manure. The gene for phytase has now been cloned and overexpressed to provide a commercial source of phytase. This monomeric enzyme, a type of histidine acid phophatase (HAP), has been characterized and extensively studied. HAPs are also found in other fungi, plants, and animals. Several microbial and plant HAPs are known to have significant phytase activity. A second A. niger phytase (phyB), a tetramer, is known and, like phyA, has had its X-ray crystal structure determined. The model provided by this crystal structure research has provided an enhanced understanding of how these molecules function. In addition to the HAP phytase, several other phytases that lack the unique HAP active site motif RHGXRXP have been studied. The best known group of the non-HAPs is phytase C (phyC) from the genus Bacillus. While a preliminary X-ray crystallographic analysis has been initiated, no enzymatic mechanism has been proposed. Perhaps the pivotal event in the last century that created the need for phytase was the development of modern fertilizers after the Second World War. This fostered a transformation in agriculture and a tremendous increase in feed-grain production. These large quantities of cereals and meal in turn led to the transition of one segment of agriculture into "animal agriculture," with their its animal production capability. The huge volumes of manure spawned by these production units in time exceeded both the capacity of their crops and crop lands to utilize or bind the increased amount of phosphorus. Nutrient runoff from this land has now been linked to a number of blooms of toxin-producing microbes. Fish kills associated with these blooms have attracted public and governmental concern, as well as greater interest in phytase as a means to reduce this phosphorus pollution. Phytase research efforts now are focused on the engineering of an improved enzyme. Improved heat tolerance to allow the enzyme to survive the brief period of elevated temperature during the pelletization process is seen as an essential step to lower its cost in animal feed. Information from the X-ray crystal structure of phytase is also relevant to improving the pH optimum, substrate specificity, and enzyme stability. Several studies on new strategies that involve synergistic interactions between phytase and other hydrolytic enzymes have shown positive results. Further reduction in the production cost of phytase is also being pursued. Several studies have already investigated the use of various yeast expression systems as an alternative to the current production method for phytase using overexpression in filamentous fungi. Expression in plants is underway as a means to commercially produce phytase, as in biofarming in which plants such as alfalfa are used as "bioreactors," and also by developing plant cultivars that would produce enough transgenic phytase so that additional supplementation of their grain or meals is not necessary. Ultimately, transgenic poultry and hogs may produce their own digestive phytase. Another active area of current phytase research is expanding its usage. One area that offers tremendous opportunity is increasing the use of phytase in aquaculture. Research is currently centered on utilizing phytase to allow producers in this industry to switch to lower-cost plant protein in their feed formulations. Development of a phytase for this application could significantly lower production costs. Other areas for expanded use range from the use of phytase as a soil amendment, to its use in a bioreactor to generate specific myo-inositol phosphate species. The transformation of phytase into a peroxidase may lead to another novel use for this enzyme. As attempts are made to widen the use of phytase, it is also important that extended exposure and breathing its dust be avoided as prudent safety measures to avoid possible allergic responses. In expanding the use of phytase, another important consideration has been achieved. Conservation of the world's deposits of rock phosphate is recognized as important for future generations. Phosphorus is a basic component of life like nitrogen, but, unlike nitrogen, phosphorus does not have a cycle to constantly replenish its supply. It is very likely that the use of phytase will expand as the need to conserve the world's phosphate reserves increases.

Biochemical characterization of cloned Aspergillus fumigatus phytase (phyA)

The gene for Aspergillus fumigatus phytase (phyA) was cloned and expressed in Pichia pastoris. The enzyme expressed was purified to near homogeneity using sequential ion-exchange chromatography and was characterized biochemically. Although A. fumigatus phytase shows 66.2% sequence homology with A. ficuum phytase, the most widely studied enzyme, the cloned phytase showed identical molecular weight and temperature optima profile to the benchmark phytase. The pH profile of activity and kinetic parameters, however, differed from A. ficuum phytase. The cloned enzyme contains the septapeptide RHGARYP motif, which is also identical to the active site motif of A. ficuum phytase. Chemical probing of the active site Arg residues using both cyclohexanedione and phenylglyoxal resulted in the inactivation of phytase. The cloned A. fumigatus phytase, however, was more resistant to phenylglyoxal-induced inactivation. Both cloned A. fumigatus and A. ficuum phytases were identically affected by cyclohexanedione. Both the thermal characterization data and kinetic parameters of cloned and expressed A. fumigatus phytase indicate that this biocatalyst is not superior to the benchmark enzyme. The sequence difference between A. fumigatus and A. ficuum phytase may explain why the former enzyme catalyzes poorly compared to the benchmark enzyme. In addition, differential sensitivity toward the Arg modifier, phenylglyoxal, indicates a different chemical environment at the active site for each of the phytases.

Crystal structure of Aspergillus niger pH 2.5 acid phosphatase at 2. 4 A resolution

The crystal structure of Aspergillus niger pH 2.5 acid phosphatase (EC 3.1.3.2) has been determined at 2.4 A resolution. In the crystal, two dimers form a tetramer in which the active sites are easily accessible to substrates. The main contacts in the dimer come from the N termini, each lying on the surface of the neighbouring molecule. The monomer consists of two domains, with the active site located at their interface. The active site has a highly conserved catalytic center and a charge distribution, which explains the highly acidic pH optimum and the broad substrate specificity of the enzyme.

Comparison of the thermostability properties of three acid phosphatases from molds: Aspergillus fumigatus phytase, A. niger phytase, and A. niger PH 2.5 acid phosphatase

Enzymes that are used as animal feed supplements should be able to withstand temperatures of 60 to 90 degrees C, which may be reached during the feed pelleting process. The thermostability properties of three histidine acid phosphatases, Aspergillus fumigatus phytase, Aspergillus niger phytase, and A. niger optimum pH 2.5 acid phosphatase, were investigated by measuring circular dichroism, fluorescence, and enzymatic activity. The phytases of A. fumigatus and A. niger were both denatured at temperatures between 50 and 70 degrees C. After heat denaturation at temperatures up to 90 degrees C, A. fumigatus phytase refolded completely into a nativelike, fully active conformation, while in the case of A. niger phytase exposure to 55 to 90 degrees C was associated with an irreversible conformational change and with losses in enzymatic activity of 70 to 80%. In contrast to these two phytases, A. niger pH 2.5 acid phosphatase displayed considerably higher thermostability; denaturation, conformational changes, and irreversible inactivation were observed only at temperatures of >/=80 degrees C. In feed pelleting experiments performed at 75 degrees C, the recoveries of the enzymatic activities of the three acid phosphatases were similar (63 to 73%). At 85 degrees C, however, the recovery of enzymatic activity was considerably higher for A. fumigatus phytase (51%) than for A. niger phytase (31%) or pH 2.5 acid phosphatase (14%). These findings confirm that A. niger pH 2.5 acid phosphatase is irreversibly inactivated at temperatures above 80 degrees C and that the capacity of A. fumigatus phytase to refold properly after heat denaturation may favorably affect its pelleting stability.

Myo-inositol hexasulfate is a potent inhibitor of Aspergillus ficuum phytase

Myo-inositol hexasulfate (MIHS), a structural analog of the substrate myo-inositol hexaphosphate, is a potent competitive inhibitor of both phyA and phyB enzymes. The Ki of inhibition for the phyA and phyB proteins were estimated to be 4.6 and 0.2 microM, respectively. Thus, the phyB protein is 23-fold more sensitive to MIHS inhibition than the phyA protein. The active-site geometry of phyB protein is presumed to be very different from the phyA protein as deduced by chemical probing of the enzymes by Arg-specific modifiers, i.e., 1,2-cyclohexanedione and phenylglyoxal. Probing the catalytic site of the same proteins by this newly developed specific inhibitor also gives a similar conclusion.

Deglycosylation of proteins for crystallization using recombinant fusion protein glycosidases

Obtaining high quality protein crystals remains a rate-limiting step in the determination of three-dimensional X-ray structures. A frequently encountered problem in this respect is the high or heterogeneous carbohydrate content of many eukaryotic proteins. A number of reports have demonstrated the use of enzymatic deglycosylation in the crystallization of certain glycoproteins. Although this is an attractive tool, there are some problems that hinder the more widespread use of glycosidases in crystallization. First, commercially available glycosidases are relatively expensive, which virtually prohibits their use on a large scale. Second, the glycosidase must be removed from the glycoprotein of interest following deglycosylation, which is not always straightforward. To circumvent these problems we have cloned the two most generally useful glycosidases, peptide-N-glycosidase F and endoglycosidase F1 from Flavobacterium meningosepticum, as fusion proteins with glutathione S-transferase. The fusion not only allows rapid purification of these enzymes from Escherichia coli cell extracts, but also permits rapid removal from target proteins following deglycosylation. We have used these enzymes to obtain crystals of phytase from Aspergillus ficuum and acid phosphatase from Aspergillus niger and to obtain a new crystal form of recombinant human renin.

Phytase

Of all the sources of phytase that have been studied (plant, animal, and microorganisms), the highest yields are produced by a wild-type strain A. niger NRRL 3135 (12.7 mg P/hr/ml = 6.8 microns P/ml/min = 113.9 nKat/ml) in a mineral salt medium in which total phosphate (4 mg %) is limiting for growth and cornstarch and glucose are the carbon sources. Synthesis of the enzyme is repressed by phosphate in the wild-type strain. Aspergillus niger NRRL 3135 produces two phytases one with pH optima at 2.5 and 5.5 (phyA) and one with an optimum at pH 2.0 (phyB). It also produces a pH 6.0 optimum phosphatase that has no phytase activity. These three glycoproteins have been purified to homogeneity, characterized, sequenced, and cloned. The sequences have been compared to each other, other phytases, and to known phosphatases. Their homology has been determined. The active sites of phytases show remarkable homology to the active site residues of the members of a particular class of acid phosphatase (histidine phosphatase). The most conserved sequence is RHGXRXP. Phytase has been covalently immobilized on Fractogel TSK HW-75 F and glutaraldehyde-activated silicate. It has been immobilized on agarose. Losses of activity have been noted on immobilization but these may be minimized by future research. It should be possible to commercially produce and recover penta-, tetra-, tri-, di-, and monoinositol phosphates using immobilized phytase if markets develop for those products. Phytase (phyA) from A. niger NRRL 3135 has been cloned into an A. niger glucoamylase producing strain CBS 513.88 using a construct that has a glucoamylae promoter and an A. niger NRRL 3135 leader sequence, and that is devoid of phosphate repression. The yield of the secreted enzyme was increased 52-fold above that of wild-type A. niger NRRL 3135. The bioengineered organism produces 270 microns P/ml/min (4500 nKat/ml) which is approximately 7.9 g/liter in the medium. The yield of the secreted enzyme was increased 1440-fold above that of wild type CBS 513.88. Commercial preparations of the cloned enzyme are available. Phytase (phyA) has been cloned into tobacco and canola. The enzyme is localized in the seed and expressed at high levels. Feeding of the seed to animals has made the phytin-P in the commercial diets available to the animals. The efficacy of feeding phytase to monogastric animals (poultry and swine) has been established. The amount of enzyme that is necessary to be added to commercial diets has been titred for broilers, layers, turkeys, ducks, and swine. The units of enzyme required are related to the phytin-P content in the diet. The use of the enzyme as a feed additive has been cleared in 22 countries. If phytase were used in the diets of all of the monogastric animals reared in the U.S., it would release phosphorus that has a value of $1.68 x 10(8) per year. The FDA has approved the enzyme preparation as GRAS. The effect of feeding phytase to animals enables assimilation of the P found in feed ingredients and diminishes the amount of phosphate in the manure and subsequently entering the environment. The effect of feeding phytase to animals on pollution has been quantitatively determined. If phytase were used in the diets of all of the monogastric animals reared in the United States, it would preclude 8.23 x 10(7) kg P from entering the environment.

Use of polyethylene glycol and high-performance liquid chromatography for preparative separation of Aspergillus ficuum acid phosphatases

Proteins of Aspergillus ficuum culture filtrate were sequentially fractionated with 4, 9, 15, 19, 24, 30 and 36% polyethylene glycol (PEG) into seven acid phosphatases (APases) with 93% and 52% overall recoveries of activity and protein, respectively. Crude extract was also separated into seven APase peaks on a 30 cm x 2.5 cm I.D. anion-exchange column using 0.1 M Tris-HCl (pH 8.0) and a 0-0.4 M KCl gradient as the eluent, but their resolution was incomplete. However, when individual PEG precipitates were injected on to the column, each APase was eluted in a single, large peak resulting in 85% recovery and fifteen-fold purification of APase activity over the PEG precipitates. Use of PEG prior to HPLC separations also reduced the separation time to half and allowed a tenfold increase in sample load with complete resolution. The APases in PEG fractions and their corresponding HPLC peaks varied significantly in their kinetic parameters, including substrate specificity and pH optimum. The method developed is most beneficial for the isolation of these closely related APases from microbial or other sources for further molecular biology studies.

The cloning and sequencing of the genes encoding phytase (phy) and pH 2.5-optimum acid phosphatase (aph) from Aspergillus niger var. awamori

The genes encoding phytase (EC 3.1.3.8) and pH 2.5-optimum acid phosphatase (EC 3.1.3.2) have been cloned and sequenced from Aspergillus niger var. awamori. The translated nucleotide sequences yielded polypeptides of 467 and 479 amino acids (aa) for phytase and acid phosphatase, respectively. The genes were isolated using oligodeoxyribonucleotide probes based on the aa sequences of the purified proteins. Recombinant A. niger var. awamori strains carrying additional copies of the gene sequences demonstrated elevated enzyme activities.

Cloning, characterization and overexpression of the phytase-encoding gene (phyA) of Aspergillus niger

Phytase catalyzes the hydrolysis of phytate (myo-inositol hexakisphosphate) to myo-inositol and inorganic phosphate. A gene (phyA) of Aspergillus niger NRRL3135 coding for extracellular, glycosylated phytase was isolated using degenerate oligodeoxyribonucleotides deduced from phytase amino acid (aa) sequences. Nucleotide (nt) sequence analysis of the cloned region revealed the presence of an open reading frame coding for 467 aa and interrupted once by an intron of 102 bp in the 5' part of the gene. The start codon is followed by a sequence coding for a putative signal peptide. Expression of phyA is controlled at the level of mRNA accumulation in response to inorganic phosphate levels. After cell growth in low-phosphate medium, a transcript of about 1.8 kb was visualized. Transcription of phyA initiates at at least seven start points within a region located 45-25 nt upstream from the start codon. In transformants of A. niger, expression of multiple copies of phyA resulted in up to more than tenfold higher phytase levels than in the wild-type strain.

Penicillium chrysogenum extracellular acid phosphatase: purification and biochemical characterization

An extracellular acid phosphatase (EC 3.1.3.2) from crude culture filtrate of Penicillium chrysogenum was purified to homogeneity using high-performance ion-exchange chromatography and size-exclusion chromatography. SDS-PAGE of the purified enzyme exhibited a single stained band at an Mr of approx. 57,000. The mobility of the native enzyme indicated the Mr to be 50,000, implying that the active form is a monomer. The isoelectric point of the enzyme was estimated to be 6.2 by isoelectric focusing. Like acid phosphatases from several yeasts and fungi the Penicillium enzyme was a glycoprotein. Removal of carbohydrate resulted in a protein band with an Mr of 50,000 as estimated by SDS-PAGE, suggesting that 12% of the mass of the enzyme was carbohydrate. The enzyme was catalytically active at temperatures ranging from 20 degrees C to 65 degrees C with a maximum activity at 60 degrees C and the pH optimum was at 5.5. The Michaelis constant of the enzyme for p-nitrophenyl phosphate was 0.11 mM and it was inhibited competitively by inorganic phosphate (ki = 0.42 mM).

Extracellular alpha galactosidase (E.C. 3.2.1.22) from Aspergillus ficuum NRRL 3135 purification and characterization

Extracellular alpha-galactosidase, a glycoprotein from the extracellular culture fluid of Aspergillus ficuum grown on glucose and raffinose in a batch culture system, was purified to homogeneity in five steps by ion exchange and hydrophobic interaction chromatography. The molecular mass of the enzyme was 70.8 Kd by SDS polyacrylamide gel electrophoresis and 74.1 Kd by gel permeation HPLC. On the basis of a molecular mass of 70.7 Kd, the molar extinction coefficient of the enzyme at 279 nm was estimated to be 6.1 X10(4) M-1 cm-1. The purified enzyme was remarkably stable at 0 degrees C. It had a broad temperature optimum and maximum catalytic activity was at 60 degrees C. It retained 33% of its activity after 10 min. at 65 degrees C. It had a pH optimum of 6.0. It retained 62% of its activity after 12 hours at pH 2.3. The Kms for p-nitrophenyl-alpha-D-galactopyranoside, o-nitrophenyl-alpha-D-galactopyranoside and m-nitrophenyl-alpha-D-galactopyranoside are: 1462, 839 and 718 microM. The enzyme was competitively inhibited by mercury (19.8 microM), silver (21.5 microM), copper (0.48 mM), zinc (0.11 mM), galactose (64.0 mM) and fructose (60.3 mM). It was inhibited non-competitively by glucose (83.2 mM) and uncompetitively by mannose (6.7 mM).

Aspergillus ficuum phytase: partial primary structure, substrate selectivity, and kinetic characterization

Purified Aspergillus ficuum phytase's partial primary structure and amino acid and sugar composition were elucidated. Determination of kinetic parameters of the enzyme at different pH values and temperatures indicated no significant alteration of the Km for phytate while the Kcat was affected. The enzyme was able to release more than 51% of the total available Pi from phytate in a 3.0 hr assay at 58 degrees C, but the Kcat dropped to 15% of the initial rate. Substrate selectivity studies revealed phytate to be the preferred substrate. The pH optima of phytase was 5.0, 4.0, and 3.0 for phytate, ATP, and polyphosphate, respectively. The enzyme had varied sensitivity towards cations. While Ca++ and Fe++ produced no effect on the catalytic rate of the enzyme, Cu+, Cu++, Zn++, and Fe were found to be inhibitory. Mn++ was observed to enhance enzyme activity by 33% at 50 microM. Known inhibitors of acid phosphatases e.g. L (+)-tartrate, phosphomycin, and sodium fluoride had no effect on enzyme activity.

Extracellular PH 2.5 optimum acid phosphatase from Aspergillus ficuum: immobilization on modified fractogel

Aspergillus ficuum pH 2.5 optimum acid phosphatase (orthophosphoric monoesters phosphohydrolase, E.C.3.1.3.2) was covalently immobolized on 2-fluoro-1-methylpyridinium toluene-4-sulfonate (FMP)-activated Fractogel TSK HW-50F. The catalytic parameters and stability of the immobilized enzyme were compared with those of the free enzyme. While the Km and the temperature optima were unchanged, the Ki for orthophosphate was changed from 185 microM to 422 microM and greater stability was observed against heat treatment.