Optimizing Protein-Glutaminase Expression in Bacillus subtilis

Pickering emulsion stabilized by protein-glutaminase modified soybean isolated proteins as a new delivery system

Plant protein-based Pickering emulsions have garnered significant attention for their natural, stable, and efficient properties. However, the aggregation and sedimentation of plant proteins have restricted their applications in the food industry. To address this challenge, the current study explored the effect of protein-glutaminase on the structural characteristics of soy protein isolate (SPI) and assessed the potential of emulsions prepared from deamidated SPI as carriers for bioactive compounds. Structural characterization of SPI at varying degrees of deamidation (DD) revealed that deamidation notably enhanced the solubility, emulsifying ability, and surface charge density of SPI, while preserving its higher-order structure. Moreover, SPI Pickering emulsions with moderate deamidation (5 % DD) demonstrated increased droplet density, a more compact microstructure, improved rheological properties, and enhanced light stability. Additionally, in vitro digestion studies showed that deamidated SPI Pickering emulsions could effectively deliver bioactive compounds. This study offers new insights into developing legume protein-based Pickering emulsions with superior performance.

Rational design of DAHP synthase and prephenate dehydrogenase for metabolic engineering of Bacillus amyloliquefaciens to produce L-tyrosine

The rational design of enzymes represents a critical strategy for achieving efficient and sustainable biocatalysis. In this study, enzyme evolution guided by rational design was utilized to engineer two key enzymes, DAHP synthase (AroA) and prephenate dehydrogenase (TyrA), within the biosynthetic pathway of L-tyrosine. The beneficial mutants AroAR27A/K38A and TyrAI309A/E330V were identified, leading to a 102 % and 105 % increase in L-tyrosine yield, respectively. Molecular dynamics simulations further explained the possible mechanism underlying their improved catalytic efficiency. Co-expression of these two mutant genes resulted in a significant increase in L-tyrosine yield. Additionally, modifications in the branching metabolic pathways, which altered both material and energy flux, further enhanced L-tyrosine production. Ultimately, the L-tyrosine yield (0.14 g/g) from xylose was much higher than that from glucose, and the final L-tyrosine titer (9.39 g/L) and productivity (0.26 g/(L·h)) were achieved through fermentation optimization in shake flasks. This represents the highest reported yield in shake flasks. The strategies described here will contribute to the development of microbial strains for the efficient production of L-tyrosine from sustainable biomass resources.

L-glutaminase synthesis by Klebsiella pneumoniae (AS KP 23) isolated from clinical strain, and its efficacy against human hepatocellular and breast cancer cell lines

BACKGROUND

Cancer is a major cause of morbidity and mortality worldwide. The proliferation of cancer cells depends largely on glutamine for survival and proliferation. Glutamine serves as a carbon source for the synthesis of metabolites and lipids via the TCA cycle, as well as a source of nitrogen for the synthesis of amino acids and nucleotides. Recently, the role of glutamine metabolism in cancer has been explored in many studies. Therefore, it provides a scientific relationship for targeting glutamine metabolism for cancer treatment. L-glutaminase which is a powerful anticancer medication that is widely used around the world, works by removing L-glutamine from cancerous cells. L-glutaminase has been cited as the most potent molecule that inhibits the proliferation of cancer cells, which significantly raises the possible applicability of cancer therapy and the possibility of its application as an alternative drug to chemotherapy. The first investigation into the antitumor property of L-glutaminase revealed its inhibitory effect on the growth of Gardner lymphosarcoma (6C3HED) and L-1210 leukemia cells. In the same study, glutaminase from Pseudomonas spp., in combination with azaserine enhanced the degree of tumor growth inhibition. Subsequently, L-glutaminase was administered intravenously in patients with acute lymphoblastic leukemia and acute myeloid leukemia. Recently, a purified L-glutaminase from Streptomyces sp. D214 was shown to be the most effective, with an IC50 value of 10 mg/ml against the MCF-7 tumor cell line. Also, various in vitro studies have revealed that the activity of glutaminase against the proliferation of tumor cell lines using the MTT (3-(4,5- dimethylthiazol-2-yl)- 2, 5-diphenyltetrazolium bromide) cell proliferation assay. Alcaligenes faecalis KLU102 glutaminase was able to reduce the viability of HeLa cells in a dose-dependent manner, with an IC50 value of 12.5 mg/ml within 24 h.

RESULTS

In this study, a bacterium extracellular from human stool samples was extracted and identified using morphological, biochemical, and molecular methods. The 16 S rRNA gene was 100% identical to the sequence from Klebsiella pneumoniae and was submitted to GenBank under accession number OQ703039. Thus, this strain was named Klebsiella pneumoniae AS KP 23. Further kinetic studies on the purified enzyme were performed. In addition, the pH stability of the L-glutaminase enzyme was slightly affected over the pH range of 7.0-9.0 after 2 h of pre-incubation, and the rate of thermal inactivation of the L-glutaminase enzyme increased with higher temperatures and longer preheating periods. In addition, the stability of the tested enzyme decreased with an increasing storage period at -20 °C. The SDS-PAGE revealed that the L-glutaminase subunits had a molecular weight of around 97 kDa. L-glutaminase was purified 1.33-fold with a final specific activity of 799.9 U/mg protein using gel filtration chromatography. The enzyme´s cytotoxic activity showed severe toxicity against the HepG-2 human hepatocellular and breast cancer cell lines. Klebsiella pneumoniae glutaminase was able to reduce the viability of HeLa cells in a dose-dependent manner, with an IC50 value of 305.78 µg/ml in human hepatocellular carcinoma and an IC50 value of 400.51 µg/ml in breast cancer cell lines.

CONCLUSION

Klebsiella pneumoniae AS KP 23 was a genetically determined microbial species isolated from human stool samples. The production of extracellular enzymes was examined. Additionally, purified L-glutaminase inhibited the growth of normal cells and showed potent anticancer activity against numerous cancer cell lines in the study. Its broad pH and temperature range, combined with its unique and highly stable catalytic activity, make it an excellent choice for use as an effective cancer inhibitor.

The effect of protein-glutaminase from Chryseobacterium proteolyticum on physicochemical and functional properties of high-temperature soybean meal protein

Protein-glutaminase (EC 3.5.1.44, PG) can significantly improve the functional properties of food proteins. However, the low yield of PG has limited industrial applications. Results showed that 0.02 % tea saponin could increase the PG yield by 18.93 %. The transcription level of the PG gene was significantly enhanced, which promoted the extracellular secretion of PG through an increase in membrane permeability. On this basis, PG was used to modify high-temperature soybean meal protein (HSMP) due to its poor properties. In this study, the deamidation degree (DD) of PG-modified HSMP was optimized to 58.61 % by the response surface method. HSMP with different DD was prepared and its physicochemical and functional properties were studied. After PG treatment, the intermolecular repulsive force of HSMP increased, the particle size distribution became uniform, and the solution system was more stable. In addition, the surface morphology of HSMP gradually became loose and porous. The solubility of HSMP significantly improved, reaching 11.34 times that of untreated HSMP at pH 5.00. Meanwhile, the emulsifying and foaming capacity of HSMP significantly improved, but the foaming stability was reduced.

Purified protein glutaminase from Chryseobacterium proteolyticum enhances the properties of wheat gluten

Protein glutaminase (PG), originating from Chryseobacterium proteolyticum, can catalyze the deamidation of glutamine residues in plant proteins into glutamic acid, thus enhancing its functional properties. However, the low yield of PG limits its industrial production. In this study, the yield of PG in C. proteolyticum TM1040 increased by 121 %, up to 7.30 U/mL in a 15 L fermenter after medium optimization. Subsequently, purified PG was obtained by cation exchange chromatography (CEX) coupled with hydrophobic interaction chromatography (HIC). The degree of deamidation (DD) of wheat gluten after purified PG deamidation was 87.11 %, which is superior to chemical deamidation in safety and DD. The emulsifying and foaming properties of deamidated wheat gluten were 2.67 and 18.86 times higher, and the water- and oil-holding properties were 4.23 and 18.77 times higher, respectively. The deamidated wheat gluten with enhanced functional properties was used to improve the flavor and texture in baking cakes.

A novel method for high level production of protein glutaminase by sfGFP tag in Bacillus subtilis

Protein glutaminase (PG; EC 3.5.1.44) is a novel deamidase that helps to improve functional properties of food proteins. Currently, the highest activated PG enzyme activity was 26 U/mg when recombinantly expressed via the twin-arginine translocation (Tat) pathway in Corynebacterium glutamicum. In this study, superfolder green fluorescent protein (sfGFP) was used to replace traditional signal peptides to facilitate efficient heterologous expression and secretion of Propeptide-Protein glutaminase (PP) in Bacillus subtilis. The fusion protein, sfGFP-PP, was secreted from 12 h of fermentation and reached its highest extracellular expression at 28 h, with a secretion efficiency of about 93 %. Moreover, when fusing sfGFP with PP at the N-terminus, it significantly enhances PG expression up to 26 U/mL by approximately 2.2-fold compared to conventional signal-peptides- guided PP with 11.9 U/mL. Finally, the PG enzyme activity increased from 26 U/mL to 36.9 U/mL after promoter and RBS optimization. This strategy not only provides a new approach to increase PG production as well as extracellular secretion but also offers sfGFP as an effective N-terminal tag for increased secreted production of difficult-to-express proteins.

An Efficient Prephenate Dehydrogenase Gene for the Biosynthesis of L-tyrosine: Gene Mining, Sequence Analysis, and Expression Optimization

L-tyrosine is a key precursor for synthesis of various functional substances, but the microbial production of L-tyrosine faces huge challenges. The development of new microbial chassis cell and gene resource is especially important for the biosynthesis of L-tyrosine. In this study, the optimal host strain Bacillus amyloliquefaciens HZ-12 was firstly selected by detecting the production capacity of L-tyrosine. Subsequently, the recombinant expression of 15 prephenate dehydrogenase genes led to the discovery of the best gene, Bao-tyrA from B. amyloliquefaciens HZ-12. After the overexpression of Bao-tyrA, the L-tyrosine yield of the recombinant strain HZ/P43-Bao-tyrA reach 411 mg/L, increased by 42% compared with the control strain (HZ/pHY300PLK). Moreover, the nucleic acid sequence and deduced amino acid sequence of the gene Bao-tyrA were analyzed, and their conservative sites and catalytic mechanisms were proposed. Finally, the expression of Bao-tyrA was regulated through a promoter and 5'-UTR sequence to obtain the optimal expression elements. Thereby, the maximum L-tyrosine yield of 475 mg/L was obtained from HZ/P43-UTR3-Bao-tyrA. B. amyloliquefaciens was applied for the first time to produce L-tyrosine, and the optimal prephenate dehydrogenase gene Bao-tyrA and corresponding expression elements were obtained. This study provides new microbial host and gene resource for the construction of efficient L-tyrosine chassis cells, and also lays a solid foundation for the production of various functional tyrosine derivatives.

Protein-Glutaminase Engineering Based on Isothermal Compressibility Perturbation for Enhanced Modification of Soy Protein Isolate

Protein-glutaminase plays a significant role in future food (e.g., plant-based meat) processing as a result of its ability to improve the solubility, foaming, emulsifying, and gel properties of plant-based proteins. However, poor stability, activity, high pressure, and high shear processing environments hinder its application. Therefore, we developed an application-oriented method isothermal compressibility perturbation engineering strategy to improve enzyme performance by simulating the high-pressure environment. The best variant with remarkable improvement in specific activity and half-time, N16M/Q21H/T113E, exhibited a 4.28-fold increase compared to the wild type in specific activity (117.18 units/mg) and a 1.23-fold increase in half-time (472 min), as one of the highest comprehensive performances ever reported. The solubility of the soy protein isolate deaminated by the N16M/Q21H/T113E mutant was 55.74% higher than that deaminated by the wild type, with a tinier particle size and coarser texture. Overall, this strategy has the potential to improve the functional performance of enzymes under complex food processing conditions.

Genetic engineering for enhanced production of a novel alkaline protease BSP-1 in Bacillus amyloliquefaciens

Alkaline protease has been widely applied in food, medicine, environmental protection and other industrial fields. However, the current activity and yield of alkaline protease cannot meet the demand. Therefore, it is important to identify new alkaline proteases with high activity. In this study, we cloned a potential alkaline protease gene bsp-1 from a Bacillus subtilis strain isolated in our laboratory. BSP-1 shows the highest sequence similarity to subtilisin NAT (S51909) from B. subtilis natto. Then, we expressed BSP-1 in Bacillus amyloliquefaciens BAX-9 and analyzed the protein expression level under a collection of promoters. The results show that the P43 promoter resulted in the highest transcription level, protein level and enzyme activity. Finally, we obtained a maximum activity of 524.12 U/mL using the P43 promoter after fermentation medium optimization. In conclusion, this study identified an alkaline protease gene bsp-1 from B. subtilis and provided a new method for high-efficiency alkaline protease expression in B. amyloliquefaciens.

L-Glutamine-, peptidyl- and protein-glutaminases: structural features and applications in the food industry

L-Glutaminases are enzymes that catalyze the cleavage of the gamma-amido bond of L-glutamine residues, producing ammonia and L-glutamate. These enzymes have several applications in food and pharmaceutical industries. However, the L-glutaminases that hydrolyze free L-glutamine (L-glutamine glutaminases, EC 3.5.1.2) have different structures and properties with respect to the L-glutaminases that hydrolyze the same amino acid covalently bound in peptides (peptidyl glutaminases, EC 3.5.1.43) and proteins (protein-glutamine glutaminase, EC 3.5.1.44). In the food industry, L-glutamine glutaminases are applied to enhance the flavor of foods, whereas protein glutaminases are useful to improve the functional properties of proteins. This review will focus on structural backgrounds and differences between these enzymes, the methodology available to measure the activity as well as strengths and limitations. Production methods, applications, and challenges in the food industry will be also discussed. This review will provide useful information to search and identify the suitable L-glutaminase that best fits to the intended application.

The characteristics of protein-glutaminase from an isolated Chryseobacterium cucumeris strain and its deamidation application

Protein-glutaminase (PG), a deamidation enzyme commercially derived from Chryseobacterium proteolyticum, is used to improve the solubility and other functional properties of food proteins. In this study, a new PG-producing strain, Chryseobacterium cucumeris ZYF120413-7, was isolated from soil, and it had a high PG yield and a short culture time. It gave the maximum PG activity with 0.557 U/ml on Cbz-Gln-Gly after 12 h of culture, indicating that it was more suitable for PG production. The enzyme activity recovery and purification fold were 32.95% and 161.95-fold, respectively, with a specific activity of 27.37 U/mg. The PG was a pre-pro-protein with a 16 amino acids putative signal peptide, a pro-PG of 118 amino acids, and a mature PG of 185 amino acids. The amino acid sequence identity of PG from strain ZYF120413-7 was 74 and 45%, respectively, to that of PG from C. proteolyticum 9670T and BH-PG. The optimum reaction pH and temperature of PG was 6 and 60°C, respectively. Enzyme activity was inhibited by Cu2+. The optimum PG substrate was Cbz-Gln-Gly, and the Km and Vmax values were 1.68 mM and 1.41 μM mg protein−1 min−1, respectively. Degree of deamidation (DD) of soy protein isolate (SPI) treated by purified PG was 40.75% within the first 2 h and 52.35% after 18 h. These results demonstrated that the PG from C. cucumeris ZYF120413-7 was a promising protein-deamidating enzyme for improving the functionality of food proteins.

Combinatorial engineering for efficient production of protein-glutaminase in Bacillus subtilis

Protein-glutaminase (EC 3.5.1.44, PG) converts protein glutamine residues in proteins and peptides into glutamic acid residue, and markedly improves the solubility, emulsification, and foaming properties of food proteins. However, the source bacteria, Chryseobacterium proteolyticum, have low enzyme production ability, inefficient genetic operation, and high production cost. Therefore, it is critical to establish an efficient expression system for active PG. Here, combinatorial engineering was developed for high-yield production of PG in Bacillus subtilis. First, we evaluated different B. subtilis strains for PG self-activation. Then, combinatorial optimization involving promoters, signal peptides, and culture medium was applied to produce active recombinant PG in a B. subtilis expression system. Through combinatorial engineering, PG enzyme activity reached 3.23 U/mL in shaken-flask cultures. Active PG with the yield of 7.07 U/mL was obtained at 40 h by the P_SecA-YdeJ combination in fed-batch fermentation, which is the highest yield of PG in existing reports.