Crystal structures of a novel, thermostable phytase in partially and fully calcium-loaded states

Characterization of a putative metal-dependent PTP-like phosphatase from Lactobacillus helveticus 2126

To date, there are very limited reports on sequence analysis and structure-based molecular modeling of phosphatases produced by probiotic bacteria. Therefore, a novel protein tyrosine-like phosphatase was characterized from L. helveticus 2126 in this study. The purified bacterial phosphatase was subjected to mass spectrometric analysis, and the identity of constructed sequence was analyzed using peptide mass fingerprint. The 3-D structure of protein was elucidated using homology modeling, while its stability was assessed using Ramachandran plot, VERIFY 3D, and PROCHECK. The bacterium produced an extracellular phosphatase of zone diameter 15 ± 0.8 mm on screening medium within 24 h of incubation. This bacterial phosphatase was highly specific towards sodium phytate as it yielded the lowest Km value of 299.50 ± 4.95 μM compared to other phosphorylated substrates. The activity was effectively stimulated in the presence of zinc, magnesium, and manganese ions thereby showing its PTP-like behavior. The phosphatase showed a molecular mass of 43 kDa, and the corresponding M/Z ratio data yielded 46% query coverage to Bacillus subtilis (3QY7). This showed a 61.1% sequence similarity to Ligilactobacillus ruminis (WP_046923835.1). The final sequence construct based on these bacteria showed a conserved motif "HCHILPGIDD" in their active site. In addition, homology modeling showed a distorted Tim barrel structure with a trinuclear metal center. The final model after energy minimization showed 90.9% of the residues in the favorable region of Ramachandran's plot. This structural information can be used in genetic engineering for improving the overall stability and catalytic efficiency of probiotic bacterial phosphatases.

Enhanced and suppressed phosphorus mineralization by Ca complexation: NMR and CD spectroscopy investigation

With the increasing demand for P fertilizer for world food production, the use of soil organic P fraction via mineralization could become an important P resource in agricultural soils. However, the predominant organic P species, phytic acid, has been considered rather recalcitrant to mineralization due to its active interaction with dissolved metals like Ca²⁺ in soil pore water. Calcium ions can be an inhibitor to many phytases, yet the mechanism was not clear. The objective of this study was to understand the effects of Ca²⁺(aq) on the phytase activity and inhibitory mechanisms using batch degradation kinetic experiments, Nuclear Magnetic Resonance (NMR) spectroscopy, Saturation Transfer Difference (STD) NMR, and Circular dichroism (CD) spectroscopy. The phytase activity followed Michaelis-Menten kinetics and increased Michaelis constant K_m and decreased V_max with Ca²⁺ addition were observed at pH 6. Therefore, mixed inhibition was the inhibition mechanism which was likely a result of the allosteric effect of Ca²⁺. The near-UV CD spectra supported phytase secondary conformational change upon the interaction between Ca²⁺ and the enzyme. It was found that phytase initially reacted with the D/L-3 phosphate of phytic acid at pH 6. At pH 8, the overall phytase activity decreased, yet the effect of Ca²⁺ on phytase activity was the opposite of that of pH 6. Enhanced phytase activity with Ca²⁺ addition was attributed to the structural change of phytic acid upon the Ca²⁺ complexation, which was confirmed by NOE spectra. The Ca²⁺-phytic acid complex might be a more favorable substrate than the free phytic acid. Unlike the findings from pH 6, Ca²⁺ didn't induce significant changes in either the near- or far-UV region of the CD spectra at pH 8. Furthermore, P5 was found to be the target of phytase at pH 8. The study revealed the pH-specific effects of Ca²⁺ on the mineralization of phytic acid.

Research status of Bacillus phytase

Phytic acid is abundant in seeds, roots and stems of plants, it acts as an anti-nutrient in food and feed industry, since it affects the absorption of nutrients by humans and monogastric animals. Furthermore, phosphorus produced through its decomposition by microorganisms can cause environmental pollution. Phytase degrades phytic acid generating precursors of inositol that can be used in clinical practice; in addition, phytase treatment can minimize the anti-nutritional effect of phytic acid. The use of phytase synthesized from Bacillus is more advantageous due to its high activity. Additionally, its good heat resistance under neutral conditions greatly fills the gap of commercial utilization of acid phytase. In this review, we summarize the latest research results on Bacillus phytase, including its physiological and biochemical characteristics, molecular structure information, calcium effects on its catalytic activity and stability, its catalytic mechanism and molecular modification.

Exogenous Enzymes as Zootechnical Additives in Animal Feed: A Review

Enzymes are widely used in the food industry. Their use as a supplement to the raw material for animal feed is a current research topic. Although there are several studies on the application of enzyme additives in the animal feed industry, it is necessary to search for new enzymes, as well as to utilize bioinformatics tools for the design of specific enzymes that work in certain environmental conditions and substrates. This will allow the improvement of the productive parameters in animals, reducing costs and making the processes more efficient. Technological needs have considered these catalysts as essential in many industrial sectors and research is constantly being carried out to optimize their use in those processes. This review describes the enzymes used in animal nutrition, their mode of action, their production and new sources of production as well as studies on different animal models to evaluate their effect on the productive performance intended for the production of animal feed.

A native conjugative plasmid confers potential selective advantages to plant growth-promoting Bacillus velezensis strain GH1-13

The conjugative plasmid (pBV71) possibly confers a selective advantage to Bacillus velezensis strain GH1-13, although a selective marker gene is yet to be identified. Here we show that few non-mucoid wild-type GH1-13 cells are spontaneously converted to mucoid variants with or without the loss of pBV71. Mucoid phenotypes, which contain or lack the plasmid, become sensitive to bacitracin, gramicidin, selenite, and tellurite. Using the differences in antibiotic resistance and phenotype, we isolated a reverse complement (COM) and a transconjugant of strain FZB42 with the native pBV71. Transformed COM and FZB42p cells were similar to the wild-type strain GH1-13 with high antibiotic resistance and slow growth rates on lactose compared to those of mucoid phenotypes. RT-PCR analysis revealed that the expression of plasmid-encoded orphan aspartate phosphatase (pRapD) was coordinated with a new quorum-sensing (QS) cassette of RapF2-PhrF2 present in the chromosome of strain GH1-13, but not in strain FZB42. Multi-omics analysis on wild-type and plasmid-cured cells of strain GH1-13 suggested that the conjugative plasmid expression has a crucial role in induction of early envelope stress response that promotes cell morphogenesis, biofilm formation, catabolite repression, and biosynthesis of extracellular-matrix components and antibiotics for protection of host cell during exponential phase.

Characterization and application of natural and recombinant butelase-1 to improve industrial enzymes by end-to-end circularization

Butelase-1, an asparaginyl endopeptidase or legumain, is the prototypical and fastest known Asn/Asp-specific peptide ligase that could be used for improving other enzymes by catalyzing simple and efficient end-to-end circularization.

High-phytate/low-calcium diet is a risk factor for crystal nephropathies, renal phosphate wasting, and bone loss

Phosphate overload contributes to mineral bone disorders that are associated with crystal nephropathies. Phytate, the major form of phosphorus in plant seeds, is known as an indigestible and of negligible nutritional value in humans. However, the mechanism and adverse effects of high-phytate intake on Ca²⁺ and phosphate absorption and homeostasis are unknown. Here, we show that excessive intake of phytate along with a low-Ca²⁺ diet fed to rats contributed to the development of crystal nephropathies, renal phosphate wasting, and bone loss through tubular dysfunction secondary to dysregulation of intestinal calcium and phosphate absorption. Moreover, Ca²⁺ supplementation alleviated the detrimental effects of excess dietary phytate on bone and kidney through excretion of undigested Ca²⁺-phytate, which prevented a vicious cycle of intestinal phosphate overload and renal phosphate wasting while improving intestinal Ca²⁺ bioavailability. Thus, we demonstrate that phytate is digestible without a high-Ca²⁺ diet and is a risk factor for phosphate overloading and for the development of crystal nephropathies and bone disease.

A novel fungal beta-propeller phytase from nematophagous Arthrobotrys oligospora: characterization and potential application in phosphorus and mineral release for feed processing

Phytases are widely utilized in feed industry to increase the utilization of phosphorus, minerals, and amino acids for improvement of animal and human nutrition. At present, all known β-propeller phytases (BPP) have been generated from bacteria, particularly Bacillus. In this work we report for the first time a new fungal-derived BPP phytase. We identified a phytase highly differentially expressed only in the parasitic stage of a nematophagous fungus, Arhtrobotrys oliogospora, during the development of the 3D traps. We found that this phytase was homologous to the known bacterial BPP phytase, thus we referred the new phytase to Aophytase. The heterologous expression of codon-optimized Aophytase gene in Pichia pastoris was successfully investigated to yield recombinant Aophytase (r-Aophytase) with high specific enzyme activity of 74.71 U/mg, much higher than those of recombinant BPP phytases derived bacteria. The kinetic parameters of the r-Aophytase, the optimum pH and temperature, as well as the effects of surfactant, EDTA and different ions on its enzyme activity were further investigated. The potential utilization of r-Aophytase in feed processing was finally explored. We found that the optimal pH value was about 7.5, and the optimal temperature was 50 °C.; r-Aophytase significantly increased the release of inorganic phosphorus from soybean meal, and improved the release of soluble minerals from the durum wheat flour and finger millet flour. The findings indicate its potential utilization in the feed processing to ameliorate nutritional value of cereals and animal feed in the future.

Probiotic Validation of a Non-native, Thermostable, Phytase-Producing Bacterium: Streptococcus thermophilus

Phytate-linked nutritional deficiency disorders have plagued poultry for centuries. The application of exogenous phytases in poultry feed has served as a solution to this problem. However, they are linked to certain limitations which include thermal instability during prolonged feed processing. Therefore, in this study, Streptococcus thermophilus 2412 based phytase stability was assessed at higher temperatures up to 90 °C. This was followed by probiotic validation of the same bacterium in an in vitro intestinal model. Bacterial phytase showed thermostability up to 70 °C with a recorded activity of 9.90 U. The bacterium was viable in the intestinal lumen as indicated by the cell count of 6.10 log(CFU/mL) after 16 h. It also showed acid tolerance with a stable cell count of 5.01 log(CFU/mL) after 16 h of incubation at pH 2. The bacterium displayed bile tolerance yielding a cell count of 6.36 log(CFU/mL) in the presence of 0.3% bile. Bacterial susceptibility was observed toward all tested antibiotics with a maximum zone of 20 mm against clindamycin. The maximum antagonistic activity was observed against Staphylococcus aureus, Serratia marcescens, and Escherichia coli with inhibition zone diameters up to 10 mm. The above characteristics prove that S. thermophilus 2412 can be used as an effective phytase-producing poultry probiotic.

Crystal Structure of LysB4, an Endolysin from Bacillus cereus-Targeting Bacteriophage B4

Endolysins are bacteriophage-derived enzymes that hydrolyze the peptidoglycan of host bacteria. Endolysins are considered to be promising tools for the control of pathogenic bacteria. LysB4 is an endolysin produced by Bacillus cereus-infecting bacteriophage B4, and consists of an N-terminal enzymatic active domain (EAD) and a C-terminal cell wall binding domain (CBD). LysB4 was discovered for the first time as an Lalanoyl-D-glutamate endopeptidase with the ability to breakdown the peptidoglycan among B. cereus-infecting phages. To understand the activity of LysB4 at the molecular level, this study determined the X-ray crystal structure of the LysB4 EAD, using the full-length LysB4 endolysin. The LysB4 EAD has an active site that is typical of LAS-type enzymes, where Zn2+ is tetrahedrally coordinated by three amino acid residues and one water molecule. Mutational studies identified essential residues that are involved in lytic activity. Based on the structural and biochemical information about LysB4, we suggest a ligand-docking model and a putative endopeptidase mechanism for the LysB4 EAD. These suggestions add insight into the molecular mechanism of the endolysin LysB4 in B. cereus-infecting phages.

Structural analysis of human NHLRC2, mutations of which are associated with FINCA disease

NHLRC2 (NHL repeat-containing protein 2) is an essential protein. Mutations of NHLRC2, including Asp148Tyr, have been recently associated with a novel FINCA disease (fibrosis, neurodegeneration, cerebral angiomatosis), which is fatal in early childhood. To gain insight into the mechanisms of action of this essential protein, we determined the crystal structure of the Trx-like and NHL repeat β-propeller domains of human NHLRC2 to a resolution of 2.7 Å. The structure reveals two domains adjacent to each other that form a cleft containing a conserved CCINC motif. A SAXS structure of full-length NHLRC2 reveals that the non-conserved C-terminal domain does not pack against the N-terminal domains. Analysis of the surface properties of the protein identifies an extended negative electrostatic potential in the surface of the cleft formed by the two domains, which likely forms a binding site for a ligand or interaction partner(s). Bioinformatics analysis discovers homologs across a range of eukaryotic and prokaryotic species and conserved residues map mostly to the adjacent surfaces of the Trx-like and β-propeller domains that form the cleft, suggesting both that this forms the potential functional site of NHLRC2 and that the function is conserved across species. Asp148 is located in the Trx-like domain and is not conserved across species. The Asp148Tyr mutation destabilizes the structure of the protein by 2°C. The NHLRC2 structure, the first of any of its homologs, provides an important step towards more focused structure-function studies of this essential protein.

Crystallization and X-ray diffraction analysis of native and selenomethionine-substituted PhyH-DI from Bacillus sp. HJB17

Phytases are phosphatases that hydrolyze phytates to less phosphorylated myo-inositol derivatives and inorganic phosphate. β-Propeller phytases, which are very diverse phytases with improved thermostability that are active at neutral and alkaline pH and have absolute substrate specificity, are ideal substitutes for other commercial phytases. PhyH-DI, a β-propeller phytase from Bacillus sp. HJB17, was found to act synergistically with other single-domain phytases and can increase their efficiency in the hydrolysis of phytate. Crystals of native and selenomethionine-substituted PhyH-DI were obtained using the vapour-diffusion method in a condition consisting of 0.2 M sodium chloride, 0.1 M Tris pH 8.5, 25%(w/v) PEG 3350 at 289 K. X-ray diffraction data were collected to 3.00 and 2.70 Å resolution, respectively, at 100 K. Native PhyH-DI crystals belonged to space group C121, with unit-cell parameters a = 156.84, b = 45.54, c = 97.64 Å, α = 90.00, β = 125.86, γ = 90.00°. The asymmetric unit contained two molecules of PhyH-DI, with a corresponding Matthews coefficient of 2.17 Å3 Da-1 and a solvent content of 43.26%. Crystals of selenomethionine-substituted PhyH-DI belonged to space group C2221, with unit-cell parameters a = 94.71, b = 97.03, c = 69.16 Å, α = β = γ = 90.00°. The asymmetric unit contained one molecule of the protein, with a corresponding Matthews coefficient of 2.44 Å3 Da-1 and a solvent content of 49.64%. Initial phases for PhyH-DI were obtained from SeMet SAD data sets. These data will be useful for further studies of the structure-function relationship of PhyH-DI.

Molecular advancements in the development of thermostable phytases

Since the discovery of phytic acid in 1903 and phytase in 1907, extensive research has been carried out in the field of phytases, the phytic acid degradatory enzymes. Apart from forming backbone enzyme in the multimillion dollar-based feed industry, phytases extend a multifaceted role in animal nutrition, industries, human physiology, and agriculture. The utilization of phytases in industries is not effectively achieved most often due to the loss of its activity at high temperatures. The growing demand of thermostable phytases with high residual activity could be addressed by the combinatorial use of efficient phytase sources, protein engineering techniques, heterologous expression hosts, or thermoprotective coatings. The progress in phytase research can contribute to its economized production with a simultaneous reduction of various environmental problems such as eutrophication, greenhouse gas emission, and global warming. In the current review, we address the recent advances in the field of various natural as well as recombinant thermotolerant phytases, their significance, and the factors contributing to their thermotolerance.

β-Propeller phytases: Diversity, catalytic attributes, current developments and potential biotechnological applications

Phytases are phosphatases which stepwise remove phosphates from phytic acid or its salts. β-Propeller phytase (BPPhy) belongs to a special class of microbial phytases that is regarded as most diverse, isolated and characterized from different microbes, mainly from Bacillus spp. BPPhy class is unique for its Ca²⁺-dependent catalytic activity, strict substrate specificity, active at neutral to alkaline pH and high thermostability. Numerous sequence and structure based studies have revealed unique attributes and catalytic properties of this class, as compared to other classes of phytases. Recent studies including cloning and expression and genetic engineering approaches have led to improvements in BPPhy which provide an opportunity for extended utilization of this class of phytases in improving animal nutrition, human health, plant growth promotion, and environmental protection, etc. This review describes the sources and diversity of BPPhy genes, biochemical properties, Ca²⁺ dependence, current developments in structural elucidation, heterogeneous expression and catalytic improvements, and multifarious applications of BPPhy.

Structural Characteristics and Catalytic Mechanism of Bacillus β-Propeller Phytases

β-Propeller phytases of Bacillus are unique highly conservative and highly specific enzymes capable of cleaving insoluble phytate compounds. In this review, we analyzed data on the properties of these enzymes, their differences from other phytases, and their unique spatial structures and substrate specificities. We considered influences of different factors on the catalytic activity and thermostability of these enzymes. There are few data on the hydrolysis mechanism of these enzymes, which makes it difficult to analyze their mechanism of action and their final products. We analyzed the available data on hydrolysis by β-propeller phytases of calcium complexes with myo-inositol hexakisphosphate.

Polarity Alteration of a Calcium Site Induces a Hydrophobic Interaction Network and Enhances Cel9A Endoglucanase Thermostability

Structural calcium sites control protein thermostability and activity by stabilizing native folds and changing local conformations. Alicyclobacillus acidocaldarius survives in thermal-acidic conditions and produces an endoglucanase Cel9A (AaCel9A) which contains a calcium-binding site (Ser465 to Val470) near the catalytic cleft. By superimposing the Ca(2+)-free and Ca(2+)-bounded conformations of the calcium site, we found that Ca(2+) induces hydrophobic interactions between the calcium site and its nearby region by driving a conformational change. The hydrophobic interactions at the high-B-factor region could be enhanced further by replacing the surrounding polar residues with hydrophobic residues to affect enzyme thermostability and activity. Therefore, the calcium-binding residue Asp468 (whose side chain directly ligates Ca(2+)), Asp469, and Asp471 of AaCel9A were separately replaced by alanine and valine. Mutants D468A and D468V showed increased activity compared with those of the wild type with 0 mM or 10 mM Ca(2+) added, whereas the Asp469 or Asp471 substitution resulted in decreased activity. The D468A crystal structure revealed that mutation D468A triggered a conformational change similar to that induced by Ca(2+) in the wild type and developed a hydrophobic interaction network between the calcium site and the neighboring hydrophobic region (Ala113 to Ala117). Mutations D468V and D468A increased 4.5°C and 5.9°C, respectively, in melting temperature, and enzyme half-life at 75°C increased approximately 13 times. Structural comparisons between AaCel9A and other endoglucanases of the GH9 family suggested that the stability of the regions corresponding to the AaCel9A calcium site plays an important role in GH9 endoglucanase catalysis at high temperature.

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.

Preparation, purification, crystallization and preliminary crystallographic analysis of dual-domain β-propeller phytase from Bacillus sp. HJB17

β-Propeller phytases (BPPs) are abundant in nature. Recently, dual-domain BPPs have been found in which the typical BPP domain is responsible for phytate hydrolysis. The dual-domain BPP (PhyH) from Bacillus sp. HJB17 was obtained with an incomplete N-terminal BPP domain (PhyH-DI; residues 41-318) and a typical BPP domain (PhyH-DII; residues 319-644) at the C-terminus. PhyH-DI was found to act synergistically (with a 1.2-2.5-fold increase in phosphate release) with PhyH-DII, other BPPs (PhyP and 168PhyA) and a histidine acid phosphatase. The structure of PhyH was therefore studied with the aim of explaining these functions. PhyH with the secreted signal peptide of the first 40 amino acids deleted (PhyHT) was cloned and expressed in Escherichia coli. Purified and active PhyHT protein was obtained by refolding from the precipitant. PhyHT was crystallized using the vapour-diffusion method. The crystal grew in a condition consisting of 0.2 M sodium acetate trihydrate, 0.1 M Tris-HCl pH 9.5, 25%(w/v) polyethylene glycol 4000 using 1 mg ml(-1) protein solution at 289 K. A complete data set was collected from a crystal to 2.85 Å resolution using synchrotron radiation at 100 K. The crystal belonged to space group P1211, with unit-cell parameters a = 46.82, b = 140.19, c = 81.94 Å, α = 90.00, β = 92.00, γ = 90.00°. The asymmetric unit was estimated to contain one molecule of PhyHT.

[Isolation and characterisation of a new bacillar phytase]

Bacillus ginsengihumi phytase has been firstly isolated and studied from the recombinant Escherichia coli strain cellular lysates. The enzyme was obtained from the cellular lysate, purified till homogeneous condition, primary structure was determined. It's concluded that phytase relates to beta-propeller class of phosphatases. The molecular weight of the protein was 41 kDa, pI was 4.8. Some physical and chemical properties of the enzyme were studied.

Cloning, Sequencing, and In Silico Analysis of β-Propeller Phytase Bacillus licheniformis Strain PB-13

β-Propeller phytases (BPPhy) are widely distributed in nature and play a major role in phytate-phosphorus cycling. In the present study, a BPPhy gene from Bacillus licheniformis strain was expressed in E. coli with a phytase activity of 1.15 U/mL and specific activity of 0.92 U/mg proteins. The expressed enzyme represented a full length ORF “PhyPB13” of 381 amino acid residues and differs by 3 residues from the closest similar existing BPPhy sequences. The PhyPB13 sequence was characterized in silico using various bioinformatic tools to better understand structural, functional, and evolutionary aspects of BPPhy class by multiple sequence alignment and homology search, phylogenetic tree construction, variation in biochemical features, and distribution of motifs and superfamilies. In all sequences, conserved sites were observed toward their N-terminus and C-terminus. Cysteine was not present in the sequence. Overall, three major clusters were observed in phylogenetic tree with variation in biophysical characteristics. A total of 10 motifs were reported with motif “1” observed in all 44 protein sequences and might be used for diversity and expression analysis of BPPhy enzymes. This study revealed important sequence features of BPPhy and pave a way for determining catalytic mechanism and selection of phytase with desirable characteristics.

A general method for artificial metalloenzyme formation through strain-promoted azide-alkyne cycloaddition

Strain-promoted azide-alkyne cycloaddition (SPAAC) can be used to generate artificial metalloenzymes (ArMs) from scaffold proteins containing a p-azido-L-phenylalanine (Az) residue and catalytically active bicyclononyne-substituted metal complexes. The high efficiency of this reaction allows rapid ArM formation when using Az residues within the scaffold protein in the presence of cysteine residues or various reactive components of cellular lysate. In general, cofactor-based ArM formation allows the use of any desired metal complex to build unique inorganic protein materials. SPAAC covalent linkage further decouples the native function of the scaffold from the installation process because it is not affected by native amino acid residues; as long as an Az residue can be incorporated, an ArM can be generated. We have demonstrated the scope of this method with respect to both the scaffold and cofactor components and established that the dirhodium ArMs generated can catalyze the decomposition of diazo compounds and both Si-H and olefin insertion reactions involving these carbene precursors.

Optimization of five environmental factors to increase beta-propeller phytase production in Pichia pastoris and impact on the physiological response of the host

Recently, we engineered Pichia pastoris Mut(s) strains to produce several beta-propeller phytases, one from Bacillus subtilis and the others designed by a structure-guided consensus approach. Furthermore, we demonstrated the ability of P. pastoris to produce and secrete these phytases in an active form in shake-flask cultures. In the present work, we used a design of experiments strategy (Simplex optimization method) to optimize five environmental factors that define the culture conditions in the induction step to increase beta-propeller phytase production in P. pastoris bioreactor cultures. With the optimization process, up to 347,682 U (82,814 U/L or 6.4 g/L culture medium) of phytase at 68 h of induction was achieved. In addition, the impact of the optimization process on the physiological response of the host was evaluated. The results indicate that the increase in extracellular phytase production through the optimization process was correlated with an increase in metabolic activity of P. pastoris, shown by an increase in oxygen demand and methanol consumption, that increase the specific growth rate. The increase in extracellular phytase production also occurred with a decrease in extracellular protease activity. Moreover, the optimized culture conditions increased the recombinant protein secretion by up to 88%, along with the extracellular phytase production efficiency per cell.

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.

Crucial role of Pro 257 in the thermostability of Bacillus phytases: biochemical and structural investigation

We have previously cloned and characterized the thermostable phytase (PHY US417) from Bacillus subtilis US417. It differs with PhyC from B. subtilis VTTE-68013 by the R257P substitution. PHY US417 was shown to be more thermostable than PhyC. To elucidate the mechanism of how the Pro 257 changes the thermostability of Bacillus phytases, this residue was mutated to Arg and Ala. The experimental results revealed that the thermostability of the P257A mutants and especially P257R was significantly decreased. The P257R and P257A mutants recovered, respectively, 64.4 and 81.5% of the wild-type activity after incubation at 75 °C for 30 min in the presence of 5mM CaCl(2). The P257R mutation also led to a severe reduction in the specific activity and catalytic efficiency of the enzyme. Structural investigation, by molecular modeling of PHY US417 and PhyC focused on the region of the 257 residue, revealed that this residue was present in a surface loop connecting two of the six characteristic β sheets. The P257 residue is presumed to reduce the local thermal flexibility of the loop, thus generating a higher thermostability.

Characterization and application of calcium-dependent β-propeller phytase from Bacillus amyloliquefaciens DS11

The enzyme phytase has broad biotechnological applications, especially in the reduction of phytate, antinutritional factors that chelate essential minerals, in human and animal food. We investigated the enzymatic properties of β-propeller phytase (BPP) from Bacillus amyloliquefaciens DS11. Thermal refolding analysis demonstrated that BPP can remarkably restore its enzymatic activity in the presence of 5 mM Ca(2+) to 87% of its original activity after heating to 100 °C and subsequent cooling, indicating that the enzyme requires Ca(2+) for appropriate refolding. Furthermore, pH-dependent kinetic studies showed that BPP required excess Ca(2+) for its enzymatic activity as the pH decreased, suggesting that the optimal Ca(2+)-phytate ratio for enzymatic catalysis depends on the pH value of the environment. Finally, we verified the practical application of BPP at two different pH's using soybean meal as a natural source of phytate. As compared to a commercial phytase, BPP efficiently hydrolyzed food phytate over neutral pH ranges.

Site-directed mutagenesis of an alkaline phytase: influencing specificity, activity and stability in acidic milieu

Site-directed mutagenesis of a thermostable alkaline phytase from Bacillus sp. MD2 was performed with an aim to increase its specific activity and activity and stability in an acidic environment. The mutation sites are distributed on the catalytic surface of the enzyme (P257R, E180N, E229V and S283R) and in the active site (K77R, K179R and E227S). Selection of the residues was based on the idea that acid active phytases are more positively charged around their catalytic surfaces. Thus, a decrease in the content of negatively charged residues or an increase in the positive charges in the catalytic region of an alkaline phytase was assumed to influence the enzyme activity and stability at low pH. Moreover, widening of the substrate-binding pocket is expected to improve the hydrolysis of substrates that are not efficiently hydrolysed by wild type alkaline phytase. Analysis of the phytase variants revealed that E229V and S283R mutants increased the specific activity by about 19% and 13%, respectively. Mutation of the active site residues K77R and K179R led to severe reduction in the specific activity of the enzyme. Analysis of the phytase mutant-phytate complexes revealed increase in hydrogen bonding between the enzyme and the substrate, which might retard the release of the product, resulting in decreased activity. On the other hand, the double mutant (K77R-K179R) phytase showed higher stability at low pH (pH 2.6-3.0). The E227S variant was optimally active at pH 5.5 (in contrast to the wild type enzyme that had an optimum pH of 6) and it exhibited higher stability in acidic condition. This mutant phytase, displayed over 80% of its initial activity after 3h incubation at pH 2.6 while the wild type phytase retained only about 40% of its original activity. Moreover, the relative activity of this mutant phytase on calcium phytate, sodium pyrophosphate and p-nitro phenyl phosphate was higher than that of the wild type phytase.