Identification of a novel phospholipase D with high transphosphatidylation activity and its application in synthesis of phosphatidylserine and DHA-phosphatidylserine

Whole-Cell Display of Phospholipase D in Escherichia coli for High-Efficiency Extracellular Phosphatidylserine Production

Phospholipids are widely utilized in various industries, including food, medicine, and cosmetics, due to their unique chemical properties and healthcare benefits. Phospholipase D (PLD) plays a crucial role in the biotransformation of phospholipids. Here, we have constructed a super-folder green fluorescent protein (sfGFP)-based phospholipase D (PLD) expression and surface-display system in Escherichia coli, enabling the surface display of sfGFP-PLDr34 on the bacteria. The displayed sfGFP-PLDr34 showed maximum enzymatic activity at pH 5.0 and 45 °C. The optimum Ca2+ concentrations for the transphosphatidylation activity and hydrolysis activity are 100 mM and 10 mM, respectively. The use of displayed sfGFP-PLDr34 for the conversion of phosphatidylcholine (PC) and L-serine to phosphatidylserine (PS) showed that nearly all the PC was converted into PS at the optimum conditions. The displayed enzyme can be reused for up to three rounds while still producing detectable levels of PS. Thus, Escherichia coli/sfGFP-PLD shows potential for the feasible industrial-scale production of PS. Moreover, this system is particularly valuable for quickly screening higher-activity PLDs. The fluorescence of sfGFP can indicate the expression level of the fused PLD and changes that occur during reuse.

Immobilization of Bio-imprinted Phospholipase D and Its Catalytic Behavior for Transphosphatidylation in the Biphasic System

Phospholipase D (PLD) with the higher transphosphatidylation activity was screened from Streptomyces sp. LD0501 basing on the protoplast mutagenesis technology. Then, it was successfully bio-imprinted to form a hyperactivated structure and rigidified by the intramolecular cross-linking, which was immobilized on the nonporous nanoscale silica. Characterization techniques were employed to investigate the structure and physicochemical properties of the catalysts, including Fourier transform infrared (FTIR) spectra and scanning electron microscopy (SEM) analysis. Transphosphatidylation activity and selectivity were improved significantly when immobilized PLD was used. The maximum yield for the production of phosphatidylserine (PS) reached 97% and the side reaction, the hydrolysis, was minimized. These results were further confirmed by the nuclear magnetic resonance (NMR) and mass spectrometry (MS) analysis. The imprint-induced characteristics of PLD was successfully "remembered" even in the present of much water. In addition, this immobilized hyperactivated PLD showed the excellent operational stabilities and environmental tolerances.

ARTP mutagenesis of phospholipase D-producing strain Streptomyces hiroshimensis SK43.001, and its enzymatic properties

Phospholipase D (PLD) is a group of enzymes that act on phospholipid molecules, which is widely used in the fields of food and medicine. PLD is extracted from animals and plants with low transesterification activity and high price. Therefore, it is benefit to screen an efficient PLD producing strain from microorganisms. A highly productive strain of PLD with transphosphatidylation activity, named Streptomyces hiroshimensis SK43.001, was screened from soil in our laboratory and mutated using atmospheric room temperature plasma (ARTP). A mutant strain SK43.001-11 with the highest enzyme activity and superior genetic stability was obtained, and its fermentation enzyme activity was 5.3 U/mL, which was 82% increased comparing to wild strain. The purification of PLD showed that the specific enzyme activity increased to 49.48 U/mg, which was 54.37-fold higher than that of the crude enzyme, with a recovery of 32.31%. In addition, enzymatic properties of PLD have revealed that the optimal pH and temperature were 7.0 and 60 °C, respectively. Metal ion Mg²⁺ and surfactant Triton X-100 made the enzymatic activity increased by 16% and 100%, respectively. The reaction kinetic parameters showed that the mutant PLD had higher affinity for the substrate of egg PC and better catalytic efficiency with K _m, V _max and K _cat of 30.20 mmol/L, 99.70 μmol/min and 76.33 s^-1, respectively. This study may provide important inspiration for obtaining high enzyme activity strains with PLD.

Immunomodulatory effects of vinegar-egg juice: Potential pharmacological effects of a traditional Chinese food remedy?

Thousands of years of historical practice have proven that the ancient Chinese food, vinegar-egg juice, has immune-boosting effects with the presence of many nutritional factors. However, its mechanism of action in the body remains unclear. In this research project, vinegar-egg juice was chosen to analyze its immune-enhancing effects on mice. The immune enhancing effects of egg, vinegar and vinegar egg juice on lymphocytes of mouse spleen were compared. The effects on immune function of mice were analyzed by studying the organ index, natural killer(NK) cell activity, lymphocyte transformation function and cytokine changes in immune organs after treatment with vinegar-egg juice. The mechanism of immune enhancement was speculated by analyzing the changes of total IKKα/β/IκBα/NF-κB and its phosphorylated protein kinase by Western blot. Experiments have shown that vinegar and eggs have less immune regulation than vinegar-egg juice. Vinegar-egg juice can regulate the cellular and humoral immunity of spleen lymphocytes, increase the phosphorylated kinases of IKKα/β, reduce the total protein expression of IκBα, and activate the signaling pathway of IKK/IκB/NF-κB. In addition, compared with the control group, vinegar-egg juice reduced the Firmicutes/Bacteroidetes ratio and increased the relative abundance of beneficial bacteria. Furthermore, vinegar-egg juice can raise phosphatidylserine (PS) and serotonin (5-HT) levels in the body. The results showed that the vinegar-egg juice had obvious immunomodulatory activity. It was speculated that the intake of vinegar-egg juice can increase the activity of NK cells, T lymphocytes and B lymphocytes by increasing 5-HT levels, ultimately enhancing the body's immune function. PRACTICAL APPLICATIONS: In this work, we evaluated the immune regulation of vinegar, egg and vinegar-egg juice in mice. In addition, we investigated the effects of vinegar-egg juice on gut microbiota. And combined with the composition of the vinegar-egg juice, it was found that the intake of vinegar-egg juice could increase the activity of NK cells, T lymphocytes and B lymphocytes by increasing 5-HT levels, ultimately enhancing the body's immune function. On the basis of the results of this study, we recommend vinegar-egg juice can be a potential health food to resist the epidemic and improve autoimmunity in special times of the novel coronavirus outbreak.

Advances in enzyme biocatalysis for the preparation of functional lipids

Functional lipids, mainly ω-3 polyunsaturated fatty acids (n-3 PUFAs) such as eicosapentaenoic (EPA; 20:5n-3) and docosahexaenoic (DHA; 22:6n-3), are known to have a variety of health benefits. Lipases and phospholipases are widely used to prepare different forms of structured lipids, since biocatalytic methods can be carried out under mild conditions, preserving the quality of the products. On the other hand, many processes still are conducted at high temperatures and with organic solvents, which are conditions unfavorable for the production of nutritional products. This article gives an updated overview of enzyme biocatalysis methods for the preparation of different derivatives containing n-3 PUFAs, including specific reactions, enzyme immobilization research for high-efficiency catalysis, and enzyme engineering technologies (higher selectivity, stability, and activity). Furthermore, advanced control strategies of biocatalytic processes and reactors are presented. The future prospect and opportunities for marine functional lipids are also discussed. Therefore, the obtainment of enzymes endowed with superior properties and the development of optimized processes, still have to be pursued to achieve greener bio-catalyzed processes.

Phospholipids (PLs) know-how: exploring and exploiting phospholipase D for its industrial dissemination

Owing to their numerous nutritional and bioactive functions, phospholipids (PLs), which are major components of biological membranes in all living organisms, have been widely applied as nutraceuticals, food supplements, and cosmetic ingredients. To date, PLs are extracted solely from soybean or egg yolk, despite the diverse market demands and high cost, owing to a tedious and inefficient manufacturing process. A microbial-based manufacturing process, specifically phospholipase D (PLD)-based biocatalysis and biotransformation process for PLs, has the potential to address several challenges associated with the soybean- or egg yolk-based supply chain. However, poor enzyme properties and inefficient microbial expression systems for PLD limit their wide industrial dissemination. Therefore, sourcing new enzyme variants with improved properties and developing advanced PLD expression systems are important. In the present review, we systematically summarize recent achievements and trends in the discovery, their structural properties, catalytic mechanisms, expression strategies for enhancing PLD production, and its multiple applications in the context of PLs. This review is expected to assist researchers to understand current advances in this field and provide insights for further molecular engineering efforts toward PLD-mediated bioprocessing.

Characterization of a phospholipase D from Streptomyces cinnamoneum SK43.003 suitable for phosphatidylserine synthesis

A phospholipase D high producing strain with transphosphatidylation activity that is suitable for phosphatidylserine synthesis was screened by our laboratory and named as Streptomyces cinnamoneum SK43.003. The enzyme structural and biochemical properties were investigated using the molecular biology method. A 1521-bp fragment of the phospholipase D gene from Streptomyces cinnamoneum SK43.003 was amplified by PCR and encoded for 506 amino acids. The primary structure contained two conserved HKD and GG/S motifs. The pld gene was cloned and expressed in Escherichia coli. The purified enzyme exhibited the highest activity at a pH value of 6.0 andtemperature of 60°C. The enzyme was stable within a pH range of 4-7 for 24 h or at temperatures below 50°C. In addition, Triton X-100, Fe²⁺ , and Al³⁺ were beneficial to the enzyme activity, whereas Zn²⁺ and Cu²⁺ dramatically inhibited its activity. In a two-phase system, the enzyme could convert phosphatidylcholine to phosphatidylserine with a 92% transformation rate.

Enhancement of Phospholipid Binding and Catalytic Efficiency of Streptomyces klenkii Phospholipase D by Increasing Hydrophobicity of the Active Site Loop

The mechanism of active site loops of Streptomyces phospholipase D (PLD) binding to the lipid-water interface for catalytic reactions still remains elusive. A flexible loop (residues 376-382) in the active site of Streptomyces klenkii PLD (SkPLD) is conserved within PLDs in most of the Streptomyces species. The residue Ser380 was found to be essential for the enzyme's adsorption to the interface and its substrate recognition. The S380V mutant showed a 4.8 times higher catalytic efficiency and nearly seven times higher adsorption equilibrium coefficient compared to the wild-type SkPLD. The monolayer film technique has confirmed that the substitution of Ser380 with valine in the loop exhibited positive interaction between the enzyme and PCs with different acyl chain lengths. The results of the interfacial binding properties indicated that the S380V mutant might display suitable phosphatidylserine synthesis activity. The present study will be helpful to explain the role of residue 380 in the active site loops of Streptomyces PLD.

DHA-enriched phosphatidylserine ameliorates non-alcoholic fatty liver disease and intestinal dysbacteriosis in mice induced by a high-fat diet

Docosahexaenoic acid-enriched phosphatidylserine (DHA-PS) has attracted increasing attention because of its unique health benefits. In this study, DHA-PS was biosynthesized from DHA-enriched phosphatidylcholine (DHA-PC), which was extracted from herring roe, Clupea harengus. The ameliorating effect of DHA-PS on high-fat diet (HFD)-induced non-alcoholic fatty liver disease (NAFLD) was investigated using a mouse model. The DHA-PS treatment ameliorated NAFLD and effectively decreased the serum total cholesterol, triglyceride, non-esterified fatty acid, and low-density lipoprotein cholesterol levels and considerably increased the serum high-density lipoprotein cholesterol levels. Moreover, the DHA-PS treatment reduced the levels of liver-function enzymes and pro-inflammatory cytokines and also the oxidative stress indices. Furthermore, DHA-PS increased the diversity and richness of the beneficial intestinal microorganisms, suggesting its potential as a dietary supplement and functional food to combat HFD-induced NAFLD.

Design of amino-functionalized hollow mesoporous silica cube for enzyme immobilization and its application in synthesis of phosphatidylserine

In this study, hollow mesoporous silica cube (HMSC) modified with amino (-NH₂) were synthesized and applied in the immobilization of phospholipase D (PLD) via physical adsorption and chemical cross-linking strategy. The amino-functionalized nano carrier HMSC represented excellent immobilization ability and achieved 87.15 % immobilization rate. The immobilized PLD has wider pH application range and thermal stability, and maintained over 90% of the initial activity after incubation at 50 °C for 2 h. After 50 days of storage at 4 ℃, immobilized PLD retained 40.12 % of its initial activity while free PLD lost 88.28% of its initial activity. The modified HMSC with immobilized PLD (HMSC-NH₂-PLD) retained 50.73% activities after 9 consecutive reuses. Using the HMSC-NH₂-PLD, a high-efficient method for the conversion of phosphatidylserine (PS) from phosphatidylcholine (PC) and L-serine was proposed. The HMSC-NH₂-PLD exhibited prominent enzymatic activity for PS synthesis, the maximal conversion of PS was 90.40% with a catalytic efficiency (CE) of 31.95 μmol / (g h under the optimal conditions. The research in this paper provides a sustainable and efficient biocatalysis application for PS synthesis.

The Serine Carboxypeptidase-Like Gene SCPL41 Negatively Regulates Membrane Lipid Metabolism in Arabidopsis thaliana

The Arabidopsis has 51 proteins annotated as serine carboxypeptidase-like (SCPL) enzymes. Although biochemical and cellular characterization indicates SCPLs involved in protein turnover or processing, little is known about their roles in plant metabolism. In this study, we identified an Arabidopsis mutant, bis4 (1-butanol insensitive 4), that was insensitive to the inhibitory effect of 1-butanol on seed germination. We cloned the gene that was defective in bis4 and found that it encoded an SCPL41 protein. Transgenic Arabidopsis plants constitutively expressing SCPL41 were generated, oil body staining and lipidomic assays indicated that SCPL41-overexpressing plants showed a decrease in membrane lipid content, especially digalactosyl diglyceride (DGDG) and monogalactosyl diglyceride (MGDG) contents, while the loss of SCPL41 increased the membrane lipid levels compared with those in wild-type plants. These findings suggested that SCPL41 had acquired novel functions in membrane lipid metabolism.

Advances in exogenous docosahexaenoic acid-containing phospholipids: Sources, positional isomerism, biological activities, and advantages

In recent years, docosahexaenoic acid-containing phospholipids (DHA-PLs) have attracted much attention because of theirs unique health benefits. Compared with other forms of docosahexaenoic acid (DHA), DHA-PLs possess superior biological effects (e.g., anticancer, lipid metabolism regulation, visual development, and brain and nervous system biochemical reactions), more intricate metabolism mechanisms, and a stronger attraction to consumer. The production of DHA-PLs is hampered by several challenges associated with the limited content of DHA-PLs in natural sources, incomplete utilization of by-products, few microorganisms for DHA-PLs production, high cost, and complex process of artificial preparation of DHA-PLs. In this article, the sources, biological activities, and commercial applications of DHA-PLs were summarized, with intensive discussions on advantages of DHA-PLs over DHA, isomerism of DHA in phospholipids (PLs), and brain health. The excellent biological characteristics of DHA-PLs are primarily concerned with DHA and PLs. The metabolic fate of different DHA-PLs varies from the position of DHA in PLs to polar groups in DHA-PLs. Overall, well understanding of DHA-PLs about their sources and characteristics is critical to accelerate the production of DHA-PLs, economically enhance the value of DHA-PLs, and improve the applicability of DHA-PLs and the acceptance of consumers.

Combining Cell Surface Display and DNA-Shuffling Technology for Directed Evolution of Streptomyces Phospholipase D and Synthesis of Phosphatidylserine

Phospholipids have been widely used in food, medicine, cosmetics, and other fields because of their unique chemical structure and healthcare functions. Phospholipase D (PLD) is a key biocatalyst for the biotransformation of phospholipids. Here, an autodisplay expression system was constructed for rapid screening of mutants, and PLD variants were recombined using DNA shuffling technology and three beneficial mutations were obtained. The results of enzymatic performance and sequence information comparison indicated that C-terminal amino acids exerted a greater impact on the correct folding of PLDs, and N-terminal amino acids are more important for catalytic reaction. The best-performing recombinant enzyme in transphosphatidylation reactions was Recom-34, with a phosphatidylserine content accounting for 80.3% of total phospholipids and a 3.24-fold increased conversion rate compared to the parent enzyme. This study demonstrates great significance for screening ideal biocatalysts, facilitating soluble expression of inclusion body proteins, and identifying key amino acids.

A novel autolysis system for extracellular production and direct immobilization of a phospholipase D fused with cellulose binding domain

Background

Several types of phospholipases have been described in phospholipids modification. The majority of phospholipase D (PLD) superfamily members can catalyze two separate reactions: the hydrolysis of phospholipids to produce phosphatidic acid (PA) and the transphosphatidylation of phosphatidyl groups into various phosphatidyl alcohols to produce modified phospholipids. Transphosphatidylation is a useful biocatalytic method for the synthesis of functional phospholipids from lecithin or phosphatidylcholine (PC), which are both easily accessible. Different PLD coding genes have been cloned from various sources from viral, prokaryotic, and eukaryotic organisms. Despite the catalytic potential of PLD, their low productivity has hampered their practical applications, probably because PLD, which is highly toxic to the host cells, when transformation of the PLD genes into the host cells, degrade PLs in the cell membrane. In this study, we designed a novel two-step expression system to produce and secrete recombinant PLD in extracellular medium, cellulose-binding domains as an affinity fused with PLD for immobilization and purification proteins.

Results

The engineered BL21 (DE3) host strain, which harbored the final expression vector pET28a-PLD-CBD-araC-ESN, was induced by IPTG and L-arabinose, the cell density decreased rapidly over a 2 h period and the enzymes released into the extracellular medium accounts owned 81.75% hydrolytic activity. Scanning electron microscopy results showed that there were obvious structural changes on the cell surface. The extracellularly secreted PLD-CBD powder was used to catalyze the transphosphatidylation reaction synthesis of phosphatidylserine, 2.3 U enzymes reacted for 12 h, during which the conversion rate reached 99% with very few by-products being produced. When the fused protein PLD-CBD immobilized on microcrystalline cellulose, the enzymes can be cycle used five times with 26% conversion rate was preserved.

Conclusions

This study introduced an effective method for use in the expression of recombinant proteins and their extracellular secretion that simplifies the steps of sonication and purification and demonstrates great potential in the industrial application of enzymes. Cellulose as the most abundant renewable biomass resources in nature, and the cost is low, used for PLD immobilization make it more simple, effective and sustainable.

Microbial production of cyanophycin: From enzymes to biopolymers

Cyanophycin is an attractive biopolymer with chemical and material properties that are suitable for industrial applications in the fields of food, medicine, cosmetics, nutrition, and agriculture. For efficient production of cyanophycin, considerable efforts have been exerted to characterize cyanophycin synthetases (CphAs) and optimize fermentations and downstream processes. In this paper, we review the characteristics of diverse CphAs from cyanobacteria and non-cyanobacteria. Furthermore, strategies for cyanophycin production in microbial strains, including Escherichia coli, Pseudomonas putida, Ralstonia eutropha, Rhizopus oryzae, and Saccharomyces cerevisiae, heterologously expressing different cphA genes are reviewed. Additionally, chemical and material properties of cyanophycin and its derivatives produced through biological or chemical modifications are reviewed in the context of their industrial applications. Finally, future perspectives on microbial production of cyanophycin are provided to improve its cost-effectiveness.

Immobilization of Phospholipase D on Silica-Coated Magnetic Nanoparticles for the Synthesis of Functional Phosphatidylserine

In this study, silica-coated magnetic nanoparticles (Fe3O4/SiO2) were synthesized and applied in the immobilization of phospholipase D (PLDa2) via physical adsorption and covalent attachment. The immobilized PLDa2 was applied in the synthesis of functional phosphatidylserine (PS) through a transphophatidylation reaction. The synthesis process and characterizations of the carriers were examined by scanning electron microscope (SEM), transmission electron microscope (TEM), and Fourier-transform infrared spectroscopy (FT-IR). The optimum immobilization conditions were evaluated, and the thermal and pH stability of immobilized and free PLDa2 were measured and compared. The tolerance to high temperature of immobilized PLDa2 increased remarkably by 10°C. Furthermore, the catalytic activity of the immobilized PLDa2 remained at 40% after eight recycles, which revealed that silica-coated magnetic nanoparticles have potential application for immobilization and catalytic reactions in a biphasic system.

Reaction Specificity of Phospholipase D Prepared from Acinetobacter radioresistens a2 in Transphosphatidylation

Phospholipase D (PLD) can react with phospholipids as substrates, generally phosphatidylcholine (PtdCho), and the PLD-substrate intermediate can be cleaved by another alcohol, resulting in transphosphatidylation of the substrate, which can be used in the production of special lipids. In this study, the reaction conditions affecting the transphosphatidylation of PtdCho with serine were optimized and the reaction specificity of a novel PLD prepared from Acinetobacter radioresistens a2 was evaluated for transphosphatidylation with a variety of phospholipid substrates and head group donors. Based on the yield of phosphatidylserine, experimental kinetic data, maximum transphosphatidylation rate, and kinetic constant, the specificity of PLD in transphosphatidylation was found to be affected by unsaturated fatty-acid phospholipid substrates. The catalytic efficiency of PLD prepared from A. radioresistens a2 on the synthesis of natural phospholipids is on the order of l-serine > ethanolamine and glycerol ≫ inositol. Moreover, it was found that the transphosphatidylation of PtdCho with saccharides was related to the length of the carbon chain and the number of saccharide units.

High-Yield and Sustainable Production of Phosphatidylserine in Purely Aqueous Solutions via Adsorption of Phosphatidylcholine on Triton-X-100-Modified Silica

Triton X-100 was covalently bound to a surface of silica and acted as an anchor molecule to facilitate the adsorption of phosphatidylcholine (PC) in a purely aqueous solution. The silica-adsorbed PC obtained was successfully used for phospholipase D (PLD)-mediated transphosphatidylation in the production of phosphatidylserine (PS). Organic solvents were completely avoided in the whole production process. The PC loading and PS yield reached 98.9 and 99.0%, respectively. Two adsorption models were studied, and the relevant parameters were calculated to help us understand the adsorption and reaction processes deeply. In addition, the silica-adsorbed PC provides a promising way to continuously biosynthesize PS. A packed-bed reactor was employed to demonstrate the process flow of the continuous production of PS. The recyclability and stability of the Triton-X-100-modified silica were excellent, as demonstrated by its use 30 times during continuous operation without any loss of the productivity.