Improving the thermostability of Escherichia coli phytase, appA, by enhancement of glycosylation

Functional expression, purification, biochemical and biophysical characterizations, and molecular dynamics simulation of a histidine acid phosphatase from Saccharomyces cerevisiae

A histidine acid phosphatase (HAP) (PhySc) with 99.50% protein sequence similarity with PHO5 from Saccharomyces cerevisiae was expressed functionally with the molecular mass of ∼110 kDa through co-expression along with the set of molecular chaperones dnaK, dnaJ, GroESL. The purified HAP illustrated the optimum activity of 28.75 ± 0.39 U/mg at pH 5.5 and 40 ˚C. The Km and Kcat values towards calcium phytate were 0.608 ± 0.09 mM and 650.89 ± 3.6 s- 1. The half-lives (T1/2) at 55 and 60 ˚C were 2.75 min and 55 s, respectively. The circular dichroism (CD) demonstrated that PhySc includes 30.5, 28.1, 21.3, and 20.1% of random coils, α-Helix, β-Turns, and β-Sheet, respectively. The Tm recorded by CD for PhySc was 56.5 ± 0.34˚C. The molecular docking illustrated that His59 and Asp322 act as catalytic residues in the PhySc. MD simulation showed that PhySc at 40 ˚C has higher structural stability over those of the temperatures 60 and 80 ˚C that support the thermodynamic in vitro investigations. Secondary structure content results obtained from MD simulation indicated that PhySc consists of 34.03, 33.09, 17.5, 12.31, and 3.05% of coil, helix, turn, sheet, and helix310, respectively, which is almost consistent with the experimental results.

Glycosylation Contributes to Thermostability and Proteolytic Resistance of rFIP-nha (Nectria haematococca)

Glycosylation is an important post-translational modification of proteins, contributing to protein function, stability and subcellular localization. Fungal immunomodulatory proteins (FIPs) are a group of small proteins with notable immunomodulatory activity, some of which are glycoproteins. In this study, the impact of glycosylation on the bioactivity and biochemical characteristics of FIP-nha (from Nectria haematococca) is described. Three rFIP-nha glycan mutants (N5A, N39A, N5+39A) were constructed and expressed in Pichia pastoris to study the functionality of the specific N-glycosylation on amino acid N5 and N39. Their protein characteristics, structure, stability and activity were tested. WT and mutants all formed tetramers, with no obvious difference in crystal structures. Their melting temperatures were 82.2 °C (WT), 81.4 °C (N5A), 80.7 °C (N39A) and 80.1 °C (N5+39A), indicating that glycosylation improves thermostability of rFIP-nha. Digestion assays showed that glycosylation on either site improved pepsin resistance, while 39N-glycosylation was important for trypsin resistance. Based on the 3D structure and analysis of enzyme cleavage sites, we conclude that glycosylation might interfere with hydrolysis via increasing steric hindrance. WT and mutants exerted similar bioactivity on tumor cell metabolism and red blood cells hemagglutination. Taken together, these findings indicate that glycosylation of FIP-nha impacts its thermostability and digestion resistance.

Enhancing the Thermostability of Phytase to Boiling Point by Evolution-Guided Design

The good thermostability of enzymes is an important basis for their wide application in industry. In this study, the phytase APPA from Yersinia intermedia was designed by evolution-guided design. Through the collection of homologous sequences in the NCBI database, we obtained a sequence set composed of 5,569 sequences, counted the number and locations of motif N-X-T/S, and selected the sites with high frequency in evolution as candidate sites for experiments. Based on the principle that N-glycosylation modification sites are located on the protein surface, 13 mutants were designed to optimize the number and location of N-glycosylation sites. Through experimental verification, 7 single mutants with improved thermostability were obtained. The best mutant, M14, with equal catalytic efficiency as the wild-type was obtained through combined mutation. The half-life (t_1/2) value of mutant M14 was improved from 3.32 min at 65°C to 25 min of at 100°C, allowing it to withstand boiling water treatment, retaining approximately 75% initial activity after a 10-min incubation at 100°C. Differential scanning calorimetry analysis revealed that while the mutants' thermodynamic stability was nearly unchanged, their kinetic stability was greatly improved, and the combined mutant exhibited strong refolding ability. The results of a in vitro digestibility test indicated that the application effect of mutant M14 was about 4.5 times that of wild-type APPA, laying a foundation for its industrial application. IMPORTANCE Due to the harsh reaction conditions of industrial production, the relative instability of enzymes limits their application in industrial production, such as for food, pharmaceuticals, and feed. For example, the pelleting process of feed includes a brief high temperature (80 to 85°C), which requires the enzyme to have excellent thermostability. Therefore, a simple and effective method to improve the thermostability of enzymes has important practical value. In this study, we make full use of the existing homologous sequences (5,569) in the database to statistically analyze the existence frequency of N-X-T/S motifs in this large sequence space to design the phytase APPA with improved thermostability and a high hit rate (~50%). We obtained the best combination mutant, M14, that can tolerate boiling water treatment and greatly improved its kinetic stability without damaging its specific activity. Simultaneously, we proved that its performance improvement is due to its enhanced refolding ability, which comes from N-glycan modification rather than amino acid replacement. Our results provide a feasible and effective method for the modification of enzyme thermostability.

Evolution of E. coli Phytase Toward Improved Hydrolysis of Inositol Tetraphosphate

Protein engineering campaigns are driven by the demand for superior enzyme performance under non-natural process conditions, such as elevated temperature or non-neutral pH, to achieve utmost efficiency and conserve limited resources. Phytases are industrial relevant feed enzymes that contribute to the overall phosphorus (P) management by catalyzing the stepwise phosphate hydrolysis from phytate, which is the main phosphorus storage in plants. Phosphorus is referred to as a critical disappearing nutrient, emphasizing the urgent need to implement strategies for a sustainable circular use and recovery of P from renewable resources. Engineered phytases already contribute today to an efficient phosphorus mobilization in the feeding industry and might pave the way to a circular P-bioeconomy. To date, a bottleneck in its application is the drastically reduced hydrolysis on lower phosphorylated reaction intermediates (lower inositol phosphates, ≤InsP4) and their subsequent accumulation. Here, we report the first KnowVolution campaign of the E. coli phytase toward improved hydrolysis on InsP4 and InsP3. As a prerequisite prior to evolution, a suitable screening setup was established and three isomers Ins(2,4,5)P3, Ins(2,3,4,5)P4 and Ins(1,2,5,6)P4 were generated through enzymatic hydrolysis of InsP6 and subsequent purification by HPLC. Screening of epPCR libraries identified clones with improved hydrolysis on Ins(1,2,5,6)P4 carrying substitutions involved in substrate binding and orientation. Saturation of seven positions and screening of, in total, 10,000 clones generated a dataset of 46 variants on their activity on all three isomers. This dataset was used for training, testing, and inferring models for machine learning guided recombination. The PyPEF method used allowed the prediction of recombinants from the identified substitutions, which were analyzed by reverse engineering to gain molecular understanding. Six variants with improved InsP4 hydrolysis of >2.5 were identified, of which variant T23L/K24S had a 3.7-fold improved relative activity on Ins(2,3,4,5)P4 and concomitantly shows a 2.7-fold improved hydrolysis of Ins(2,4,5)P3. Reported substitutions are the first published Ec phy variants with improved hydrolysis on InsP4 and InsP3.

Improved methanol tolerance of Rhizomucor miehei lipase based on N‑glycosylation within the α-helix region and its application in biodiesel production

BACKGROUND

Liquid lipases are widely used to convert oil into biodiesel. Methanol-resistant lipases with high catalytic activity are the first choice for practical production. Rhizomucor miehei lipase (RML) is a single-chain α/β-type protein that is widely used in biodiesel preparation. Improving the catalytic activity and methanol tolerance of RML is necessary to realise the industrial production of biodiesel.

RESULTS

In this study, a semi-rational design method was used to optimise the catalytic activity and methanol tolerance of ProRML. After N-glycosylation modification of the α-helix of the mature peptide in ProRML, the resulting mutants N218, N93, N115, N260, and N183 increased enzyme activity by 66.81, 13.54, 10.33, 3.69, and 2.39 times than that of WT, respectively. The residual activities of N218 and N260 were 88.78% and 86.08% after incubation in 50% methanol for 2.5 h, respectively. In addition, the biodiesel yield of all mutants was improved when methanol was added once and reacted for 24 h with colza oil as the raw material. N260 and N218 increased the biodiesel yield from 9.49% to 88.75% and 90.46%, respectively.

CONCLUSIONS

These results indicate that optimising N-glycosylation modification in the α-helix structure is an effective strategy for improving the performance of ProRML. This study provides an effective approach to improve the design of the enzyme and the properties of lipase mutants, thereby rendering them suitable for industrial biomass conversion.

Thermostable lipases and their dynamics of improved enzymatic properties

Thermal stability is one of the most desirable characteristics in the search for novel lipases. The search for thermophilic microorganisms for synthesising functional enzyme biocatalysts with the ability to withstand high temperature, and capacity to maintain their native state in extreme conditions opens up new opportunities for their biotechnological applications. Thermophilic organisms are one of the most favoured organisms, whose distinctive characteristics are extremely related to their cellular constituent particularly biologically active proteins. Modifications on the enzyme structure are critical in optimizing the stability of enzyme to thermophilic conditions. Thermostable lipases are one of the most favourable enzymes used in food industries, pharmaceutical field, and actively been studied as potential biocatalyst in biodiesel production and other biotechnology application. Particularly, there is a trade-off between the use of enzymes in high concentration of organic solvents and product generation. Enhancement of the enzyme stability needs to be achieved for them to maintain their enzymatic activity regardless the environment. Various approaches on protein modification applied since decades ago conveyed a better understanding on how to improve the enzymatic properties in thermophilic bacteria. In fact, preliminary approach using advanced computational analysis is practically conducted before any modification is being performed experimentally. Apart from that, isolation of novel extremozymes from various microorganisms are offering great frontier in explaining the crucial native interaction within the molecules which could help in protein engineering. In this review, the thermostability prospect of lipases and the utility of protein engineering insights into achieving functional industrial usefulness at their high temperature habitat are highlighted. Similarly, the underlying thermodynamic and structural basis that defines the forces that stabilize these thermostable lipase is discussed. KEY POINTS: • The dynamics of lipases contributes to their non-covalent interactions and structural stability. • Thermostability can be enhanced by well-established genetic tools for improved kinetic efficiency. • Molecular dynamics greatly provides structure-function insights on thermodynamics of lipase.

A novel phytase from Citrobactergillenii: characterization and expression in Pichia pastoris (Komagataella pastoris)

The phyCg gene encoding a new phytase from Citrobacter gillenii was optimized, synthesized, cloned and expressed in Pichia pastoris. Analysis of the amino acid sequence of the enzyme showed that it belongs to the histidine acid phosphatase family. The amino acid sequence of the PhyCg phytase has the highest homology (73.49%) with a phytase sequence from Citrobacter braakii. The main characteristics for the purified recombinant phytase were established. The optimum pH and temperature were 4.5 and 50°C, respectively. The specific activity of the enzyme was 1577 U/mg. The Michaelis constant (Km) and the maximum reaction rate (Vmax) for sodium phytate were 0.185 mM and 2185 U/mg, respectively. The enzyme showed the pH and trypsin stability and had a high activity over a wide pH range.

Disulfide bond engineering of AppA phytase for increased thermostability requires co-expression of protein disulfide isomerase in Pichia pastoris

BACKGROUND

Phytases are widely used commercially as dietary supplements for swine and poultry to increase the digestibility of phytic acid. Enzyme development has focused on increasing thermostability to withstand the high temperatures during industrial steam pelleting. Increasing thermostability often reduces activity at gut temperatures and there remains a demand for improved phyases for a growing market.

RESULTS

In this work, we present a thermostable variant of the E. coli AppA phytase, ApV1, that contains an extra non-consecutive disulfide bond. Detailed biochemical characterisation of ApV1 showed similar activity to the wild type, with no statistical differences in k_cat and K_M for phytic acid or in the pH and temperature activity optima. Yet, it retained approximately 50% activity after incubations for 20 min at 65, 75 and 85 °C compared to almost full inactivation of the wild-type enzyme. Production of ApV1 in Pichia pastoris (Komagataella phaffi) was much lower than the wild-type enzyme due to the presence of the extra non-consecutive disulfide bond. Production bottlenecks were explored using bidirectional promoters for co-expression of folding chaperones. Co-expression of protein disulfide bond isomerase (Pdi) increased production of ApV1 by ~ 12-fold compared to expression without this folding catalyst and restored yields to similar levels seen with the wild-type enzyme.

CONCLUSIONS

Overall, the results show that protein engineering for enhanced enzymatic properties like thermostability may result in folding complexity and decreased production in microbial systems. Hence parallel development of improved production strains is imperative to achieve the desirable levels of recombinant protein for industrial processes.

Synergistic optimisation of expression, folding, and secretion improves E. coli AppA phytase production in Pichia pastoris

Background

Pichia pastoris (Komagataella phaffii) is an important platform for heterologous protein production due to its growth to high cell density and outstanding secretory capabilities. Recent developments in synthetic biology have extended the toolbox for genetic engineering of P. pastoris to improve production strains. Yet, overloading the folding and secretion capacity of the cell by over-expression of recombinant proteins is still an issue and rational design of strains is critical to achieve cost-effective industrial manufacture. Several enzymes are commercially produced in P. pastoris, with phytases being one of the biggest on the global market. Phytases are ubiquitously used as a dietary supplement for swine and poultry to increase digestibility of phytic acid, the main form of phosphorous storage in grains.

Results

Potential bottlenecks for expression of E. coli AppA phytase in P. pastoris were explored by applying bidirectional promoters (BDPs) to express AppA together with folding chaperones, disulfide bond isomerases, trafficking proteins and a cytosolic redox metabolism protein. Additionally, transcriptional studies were used to provide insights into the expression profile of BDPs. A flavoprotein encoded by ERV2 that has not been characterised in P. pastoris was used to improve the expression of the phytase, indicating its role as an alternative pathway to ERO1. Subsequent AppA production increased by 2.90-fold compared to the expression from the state of the AOX1 promoter.

Discussion

The microbial production of important industrial enzymes in recombinant systems can be improved by applying newly available molecular tools. Overall, the work presented here on the optimisation of phytase production in P. pastoris contributes to the improved understanding of recombinant protein folding and secretion in this important yeast microbial production host.

Exploiting the activity-stability trade-off of glucose oxidase from Aspergillus niger using a simple approach to calculate thermostability of mutants

Glucose oxidase (Gox) is a biocatalyst that is widely applied in the food industry, as well as other biotechnological industries. However, the industrial application of Gox is hampered by its low thermostability and activity. Here, we aimed to improve the thermostability of GoxM4 from Aspergillus niger without reducing its activity due to the activity-stability trade-off. A simple and effective approach combining enzyme activity and structure stability was adopted to evaluate the thermostability of GoxM4 and its mutants. After four rounds of computer-aided rational design, the best mutant, GoxM8, was obtained. The melting temperature (T_m) of GoxM8 was increased by 9 °C compared with GoxM4. The catalytic efficiency of GoxM8 was similar to GoxM4, suggesting that the enzyme activity-stability trade-off was counteracted. To explore its mechanism, we performed molecular dynamics simulations of GoxM4 and its mutants. Our findings provided a typical example for researching the enzyme activity-stability trade-off.

A multistrategy approach for improving the expression of E. coli phytase in Pichia pastoris

Phytase is an additive in animal feed that degrades phytic acid in plant material, reducing feeding costs, and pollution from fecal phosphorus excretion. A multistrategy approach was adopted to improve the expression of E. coli phytase in Pichia pastoris. We determined that the most suitable signal peptide for phytase secretion was an α-factor secretion signal with an initial enzyme activity of 153.51 U/mL. Increasing the copy number of this gene to four increased phytase enzyme activity by 234.35%. PDI overexpression and Pep4 gene knockout increased extracellular phytase production by 35.33% and 26.64%, respectively. By combining favorable factors affecting phytase expression and secretion, the enzyme activity of the phytase-engineered strain was amplified 384.60% compared with that of the original strain. We also evaluated the potential for the industrial production of the engineered strain using a 50-L fed-batch fermenter and achieved a total activity of 30,246 U/mL after 180 h of fermentation.

Heterologous Expression of Histidine Acid Phytase From Pantoea sp. 3.5.1 in Methylotrophic Yeast Pichia Pastoris

Background and Objective:

The major storage form of phosphorus in plant-derived feed is presented by phytates and not digested by animals. Phytases are able to hydrolyze phytates and successfully used as feed additives. Nevertheless, nowadays, there is a constant search of new phytases and expression systems for better production of these enzymes. In this study, we describe cloning and expression of gene encoding histidine acid phytase fromPantoeasp. 3.5.1 using methylotrophic yeastPichia pastorisas the host.

Methods:

The phytase gene was placed under the control of the methanol-inducible AOX1 promoter and expressed inP. pastoris. Experiments of small-scale phytase expression and activity assays were used to test recombinant colonies. Four different signal peptides were screened for better secretion of phytase byP. pastoris. After 36 h of methanol induction in shake flasks, the maximum extracellular phytase activity (3.2 U/ml) was observed inP. pastorisstrain with integrated construct based on pPINK-HC vector andKluyveromyces maxianusinulinase gene signal sequence. This phytase was isolated and purified using affinity chromatography.

Results:

Recombinant phytase was a glycosylated protein, had a molecular weight of around 90 kDa and showed maximum activity at pH 4.0 and at 50°C. Recombinant phytase had excellent thermal stability – it retained high residual activity (100% ± 2%) after 1 hour of heat treatment at 70°C.

Conclusion:

The enhanced thermostability of the recombinant phytase, its expression provided by strong inducible promotor and the effectively designed expression cassette, the simple purification procedure of the secreted enzyme, and the possibility of large-scale expression make the foundation for further production of this bacterial phytase inP. pastorisat an industrial scale.

Integrative Structural and Computational Biology of Phytases for the Animal Feed Industry

Resistance to high temperature, acidic pH and proteolytic degradation during the pelleting process and in the digestive tract are important features of phytases as animal feed. The integration of insights from structural and in silico analyses into factors affecting thermostability, acid stability, proteolytic stability, catalytic efficiency and specific activity, as well as N-glycosylation, could improve the limitations of marginal stable biocatalysts with trade-offs between stability and activity. Synergistic mutations give additional benefits to single substitutions. Rigidifying the flexible loops or inter-molecular interactions by reinforcing non-bonded interactions or disulfide bonds, based on structural and roof mean square fluctuation (RMSF) analyses, are contributing factors to thermostability. Acid stability is normally achieved by targeting the vicinity residue at the active site or at the neighboring active site loop or the pocket edge adjacent to the active site. Extending the positively charged surface, altering protease cleavage sites and reducing the affinity of protease towards phytase are among the reported contributing factors to improving proteolytic stability. Remodeling the active site and removing steric hindrance could enhance phytase activity. N-glycosylation conferred improved thermostability, proteases degradation and pH activity. Hence, the integration of structural and computational biology paves the way to phytase tailoring to overcome the limitations of marginally stable phytases to be used in animal feeds.

Mutational analysis of a catalytically important loop containing active site and substrate-binding site in Escherichia coli phytase AppA

A phytase from Escherichia coli, AppA, has been the target of protein engineering to reduce the amount of undigested phosphates from livestock manure by making phosphorous from phytic acid available as a nutrient. To understand the contribution of each amino acid in the active site loop to the AppA activity, alanine and glycine scanning mutagenesis was undertaken. The results of phytase activity assay demonstrated loss of activity by mutations at charged residues within the conserved motif, supporting their importance in catalytic activity. In contrast, both conserved, non-polar residues and non-conserved residues tended to be tolerant to Ala and/or Gly mutations. Correlation analyses of chemical/structural characteristics of each mutation site against mutant activity revealed that the loop residues located closer to the substrate have greater contribution to the activity of AppA. These results may be useful in efficiently engineering AppA to improve its catalytic activity.

Abbreviations: AppA: pH 2.5 acid phosphatase; CSU: contacts of structural units; HAPs: histidine acid phosphatases; SASA: solvent accessible surface area; SDS-PAGE: sodium dodecyl sulfate-polyacrylamide gel electrophoresis; SSM: site-saturation mutagenesis; WT: wild type

Thermostable phytase in feed and fuel industries

Phytase with wide ranging biochemical properties has long been utilized in a multitude of industries, even so, thermostability plays a crucial factor in choosing the right phytase in a few of the sectors. Mesophilic phytases are not considered to be a viable option in the feed industry owing to its limited stability in the required feed processing temperature. In the recent past, inclusion of thermostable phytase in fuel ethanol production from starch based raw material has been demonstrated with economic benefits. Therefore, considerable emphasis has been placed on using complementary approaches such as mining of extremophilic microbial wealth, encapsulation and using enzyme engineering for obtaining stable phytase variants. This article means to give an insight on role of thermostable phytases in feed and fuel industries and methods for its development, highlighting molecular determinants of thermostability.

A bifunctional cellulase-xylanase of a new Chryseobacterium strain isolated from the dung of a straw-fed cattle

A new cellulolytic strain of Chryseobacterium genus was screened from the dung of a cattle fed with cereal straw. A putative cellulase gene (cbGH5) belonging to glycoside hydrolase family 5 subfamily 46 (GH5_46) was identified and cloned by degenerate PCR plus genome walking. The CbGH5 protein was overexpressed in Pichia pastoris, purified and characterized. It is the first bifunctional cellulase-xylanase reported in GH5_46 as well as in Chryseobacterium genus. The enzyme showed an endoglucanase activity on carboxymethylcellulose of 3237 μmol min-1  mg-1 at pH 9, 90 °C and a xylanase activity on birchwood xylan of 1793 μmol min-1  mg-1 at pH 8, 90 °C. The activity level and thermophilicity are in the front rank of all the known cellulases and xylanases. Core hydrophobicity had a positive effect on the thermophilicity of this enzyme. When similar quantity of enzymatic activity units was applied on the straws of wheat, rice, corn and oilseed rape, CbGH5 could obtain 3.5-5.0× glucose and 1.2-1.8× xylose than a mixed commercial cellulase plus xylanase of Novozymes. When applied on spent mushroom substrates made from the four straws, CbGH5 could obtain 9.2-15.7× glucose and 3.5-4.3× xylose than the mixed Novozymes cellulase+xylanase. The results suggest that CbGH5 could be a promising candidate for industrial lignocellulosic biomass conversion.

Thermal stabilization of the deglycating enzyme Amadoriase I by rational design

Amadoriases are a class of FAD-dependent enzymes that are found in fungi, yeast and bacteria and that are able to hydrolyze glycated amino acids, cleaving the sugar moiety from the amino acidic portion. So far, engineered Amadoriases have mostly found practical application in the measurement of the concentration of glycated albumin in blood samples. However, these engineered forms of Amadoriases show relatively low absolute activity and stability levels, which affect their conditions of use. Therefore, enzyme stabilization is desirable prior to function-altering molecular engineering. In this work, we describe a rational design strategy based on a computational screening method to evaluate a library of potentially stabilizing disulfide bonds. Our approach allowed the identification of two thermostable Amadoriase I mutants (SS03 and SS17) featuring a significantly higher T₅₀ (55.3 °C and 60.6 °C, respectively) compared to the wild-type enzyme (52.4 °C). Moreover, SS17 shows clear hyperstabilization, with residual activity up to 95 °C, whereas the wild-type enzyme is fully inactive at 55 °C. Our computational screening method can therefore be considered as a promising approach to expedite the design of thermostable enzymes.

Microbial phytase: Impact of advances in genetic engineering in revolutionizing its properties and applications

Phytases are enzymes that increase the availability of phosphorous in monogastric diet and reduces the anti-nutrition effect of phytate. This review highlights contributions of recombinant technology to phytase research during the last decade with specific emphasis on new generation phytases. Application of modern molecular tools and genetic engineering have aided the discovery of novel phytase genes, facilitated its commercial production and expanded its applications. In future, by adopting most recent gene improvement techniques, more efficient next generation phytases can be developed for specific applications.

Bioprocess for the production of recombinant HAP phytase of the thermophilic mold Sporotrichum thermophile and its structural and biochemical characteristics

Thermophilc mold Sporotrichum thermophile secretes an acidstable and thermostable phytase, which finds application as a food and feed additive because of its adequate thermostability, acid stability, protease insensitivity and broad substrate spectrum. Low extracellular phytase production by the mold is a major bottleneck for its application on a commercial scale. We have successfully overcome this problem by constitutive secretary expression of codon optimized rStPhy under glyceraldehyde phosphate dehydrogenase (GAP) promoter in Pichia pastoris. A ∼41-fold improvement in rStPhy production has been achieved. Circular Dichroism (CD) spectra revealed that rStPhy is composed of 26.65% α-helices, 5.26% β-sheets and 68.09% random coils at pH 5.0 and 60°C, the optima for the enzyme activity. The melting temperature (T_m) of the enzyme is ∼73°C. The 3D structure of rStPhy displayed characteristic signature sequences (RHGXRXP and HD) of HAP phytase. The catalytically important amino acids (Arg74, His75, Arg78, His368 and Asp369) were identified by docking and site directed mutagenesis. Fluorescence quenching by N-bromosuccinimide (NBS) and CsCl exposed tryptophan residues surrounded by negative charges, which play a key role in maintaining structural integrity of rStPhy.

A Novel Phytase Derived from an Acidic Peat-Soil Microbiome Showing High Stability under Acidic Plus Pepsin Conditions

Four novel phytases of the histidine acid phosphatase family were identified in two publicly available metagenomic datasets of an acidic peat-soil microbiome in northeastern Bavaria, Germany. These enzymes have low similarity to all the reported phytases. They were overexpressed in <i>Escherichia coli</i> and purified. Catalytic efficacy in simulated gastric fluid was measured and compared among the four candidates. The phytase named rPhyPt4 was selected for its high activity. It is the first phytase identified from unculturable Acidobacteria. The phytase showed a longer half-life than all the gastric-stable phytases that have been reported to date, suggesting a strong resistance to low pH and pepsin. A wide pH profile was observed between pH 1.5 and 5.0. At the optimum pH (2.5) the activity was 2,790 μmol/min/mg at the physiological temperature of 37°C and 3,989 μmol/min/mg at the optimum temperature of 60°C. Due to the competent activity level as well as the high gastric stability, the phytase could be a potential candidate for practical use in livestock and poultry feeding

Cloning and Expression of Phytase appA Gene from Shigella sp. CD2 in Pichia pastoris and Comparison of Properties with Recombinant Enzyme Expressed in E. coli

The phytase gene appA_S was isolated from Shigella sp. CD2 genomic library. The 3.8 kb DNA fragment contained 1299 bp open reading frame encoding 432 amino acid protein (AppA_S) with 22 amino acid signal peptide at N-terminal and three sites of N-glycosylation. AppA_S contained the active site RHGXRXP and HDTN sequence motifs, which are conserved among histidine acid phosphatases. It showed maximum identity with phytase AppA of Escherichia coli and Citrobacter braakii. The appA_S was expressed in Pichia pastoris and E. coli to produce recombinant phytase rAppA_P and rAppA_E, respectively. Purified glycosylated rAppA_P and nonglycosylated rAppA_E had specific activity of 967 and 2982 U mg^-1, respectively. Both had pH optima of 5.5 and temperature optima of 60°C. Compared with rAppA_E, rAppA_P was 13 and 17% less active at pH 3.5 and 7.5 and 11 and 18% less active at temperature 37 and 50°C, respectively; however, it was more active at higher incubation temperatures. Thermotolerance of rAppA_P was 33% greater at 60°C and 24% greater at 70°C, when compared with rAppA_E. Both the recombinant enzymes showed high specificity to phytate and resistance to trypsin. To our knowledge, this is the first report on cloning and expression of phytase from Shigella sp.

Identification and characterization of a mesophilic phytase highly resilient to high-temperatures from a fungus-garden associated metagenome

Phytases are enzymes degrading phytic acid and thereby releasing inorganic phosphate. While the phytases reported to date are majorly from culturable microorganisms, the fast-growing quantity of publicly available metagenomic data generated in the last decade has enabled bioinformatic mining of phytases in numerous data mines derived from a variety of ecosystems throughout the world. In this study, we are interested in the histidine acid phosphatase (HAP) family phytases present in insect-cultivated fungus gardens. Using bioinformatic approaches, 11 putative HAP phytase genes were initially screened from 18 publicly available metagenomes of fungus gardens and were further overexpressed in Escherichia coli. One phytase from a south pine beetle fungus garden showed the highest activity and was then chosen for further study. Biochemical characterization showed that the phytase is mesophilic but possesses strong ability to withstand high temperatures. To our knowledge, it has the longest half-life time at 100 °C (27 min) and at 80 °C (2.1 h) as compared to all the thermostable phytases publicly reported to date. After 100 °C incubation for 15 min, more than 93 % of the activity was retained. The activity was 3102 μmol P/min/mg at 37 °C and 4135 μmol P/min/mg at 52.5 °C, which is higher than all the known thermostable phytases. For the high activity level demonstrated at mesophilic temperatures as well as the high resilience to high temperatures, the phytase might be promising for potential application as an additive enzyme in animal feed.

Isolation and molecular characterization of thermostable phytase from Bacillus subtilis (BSPhyARRMK33)

The thermostable phytase gene was isolated from Bacillus subtilis ARRMK33 (BsPhyARRMK33). The gene has an ORF of 1152 bp and that encodes a protein of 383 amino acids. Sequence analysis showed high homology with Bacillus sp. phytase proteins, but no similarity was found with other phytases. SDS-PAGE analysis exhibited a predicted molecular mass of 42 kDa. Homology modeling of BsPhyARRMK33 protein based on Bacillus amyloliquefaciens crystal structure disclosed its β-propeller structure. BsPhyARRMK33 recombinant plasmid in pET-28a(+) was expressed in Rosetta gami B DE3 cells and the maximum phytase activity 15.3 U mg(-1) obtained. The enzyme exhibits high thermostability at various temperatures and broad pH ranges. The recombinant protein retained 74% of its original activity after incubation at 95 °C for 10 min. In the presence of Ca(2+), the recombinant phytase activity was maximal where as it was inhibited by EDTA. The optimal pH and temperature for the recombinant phytase activity is achieved at 7.0 and 55 °C, respectively. Thermostable nature and wide range of pH are promising features of recombinant BsPhyARRMK33 protein that may be employed as an efficient alternative to commercially known phytases and thereby alleviate environmental eutrophication.

Enzymology and thermal stability of phytase appA mutants

(A) The comparison of different melting temperature (T_m) of appA (), appAM8 () and appAM10 (). TheT_mvalues were 60 °C for appA, 64.1 °C for appAM8, and 67.5 °C for appAM10. (B) Titration curves of the addition TNS to appAM10 (a) and appA (b).

Overexpression and functional characterization of an Aspergillus niger phytase in the fat body of transgenic silkworm, Bombyx mori

In a previous study, we isolated 1,119 bp of upstream promoter sequence from Bmlp3, a gene encoding a member of the silkworm 30 K storage protein family, and demonstrated that it was sufficient to direct fat body-specific expression of a reporter gene in a transgenic silkworm, thus highlighting the potential use of this promoter for both functional genomics research and biotechnology applications. To test whether the Bmlp3 promoter can be used to produce recombinant proteins in the fat body of silkworm pupae, we generated a transgenic line of Bombyx mori which harbors a codon-optimized Aspergillus niger phytase gene (phyA) under the control of the Bmlp3 promoter. Here we show that the Bmlp3 promoter drives high levels of phyA expression in the fat body, and that the recombinant phyA protein is highly active (99.05 and 54.80 U/g in fat body extracts and fresh pupa, respectively). We also show that the recombinant phyA has two optimum pH ranges (1.5-2.0 and 5.5-6.0), and two optimum temperatures (55 and 37 °C). The activity of recombinant phyA was lost after high-temperature drying, but treating with boiling water was less harmful, its residual activity was approximately 84% of the level observed in untreated samples. These results offer an opportunity not only for better utilization of large amounts of silkworm pupae generated during silk production, but also provide a novel method for mass production of low-cost recombinant phytase using transgenic silkworms.