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

Discovery and mechanistic analysis of a novel source protein glutaminase PG5 and its potential application

In this study, we successfully obtained a novel source protein glutaminase PG5 with specific activity of 10.4 U/mg, good tolerance and broad substrate profile through big data retrieval. Structural analysis and site-directed mutagenesis revealed that the catalytic pocket of Mature-PG5 contained a large number of aromatic amino acids and hydrophobic amino acids, and that Ser72 greatly affects the properties of the catalytic pocket and the affinity of PG5 for the substrate. In addition, molecular dynamics analysis revealed that the opening and closing between amino acid residues Gly65 and Thr66 with Cys164 at the catalytic cleft could affect substrate binding and product release. In addition, PG5 effectively improved the solubility of fish myofibrillar proteins under low-salt conditions while enhancing their foaming and emulsification properties. This study offers valuable insights into the catalytic mechanism of PG5, which will contribute to its future directed evolution and application in the food industry.

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.

Engineering of protein glutaminase for highly efficient modification of fish myofibrillar protein through structure-based and computational-aided strategy

Protein glutaminase (PG; EC 3.5.1.44) is a class of food-grade enzyme with the potential to significantly improve protein functionality. However, its low catalytic activity and stability greatly hindered industrial application. In this study, we employed structural-based engineering and computational-aided design strategies to target the engineering of protein glutaminase PG5, which led to the development of a combinatorial mutant, MT8, exhibiting a specific activity of 31.1 U/mg and a half-life of 216.2 min at 55 °C. The results indicated that the flexible region in MT8 shifted from the C-terminus to the N-terminus, with increased N-terminal flexibility positively correlating with its catalytic activity. Additionally, MT8 notably boosted fish myofibrillar proteins (MPs) solubility under the absence of NaCl conditions and enhanced their foaming and emulsifying properties. Key residues like Asp31, Ser72, Asn121, Asp471, and Glu485 were crucial for maintaining PG5-myosin interaction, with Ser72 and Asn121 making significant energy contributions.

Molecular expression, purification and structural characterization of recombinant L-Glutaminase from Streptomyces roseolus

The present research reports the anti-cancer potential of recombinant L-Glutaminase from Streptomyces roseolus. L-Glutaminase gene was synthesized by codon-optimization, cloned and successfully expressed in E. coli BL21 (DE3). Affinity purified recombinant L-Glutaminase revealed a molecular mass of 32 kDa. Purified recombinant L-Glutaminase revealed stability at pH 7.0-8.0 with optimum activity at 70 °C further indicating its thermostable nature based on thermodynamic characterization. Recombinant L-Glutaminase exhibited profound stability in the presence of several biochemical parameters and demonstrated its metalloenzyme nature and was also found to be highly specific towards favorable substrate (l-Glutamine) based on kinetics. It demonstrated antioxidant property and pronounced cytotoxic effect against breast cancer (MCF-7 cell lines) in a dose dependent behavior with IC50 of 40.68 μg/mL. Matrix-assisted laser desorption ionization-time of flight-mass spectroscopy (MALDI-TOF-MS) analysis of desired mass peaks ascertained the recombinant L-Glutaminase identity. N-terminal amino acid sequence characterization through Edman degradation revealed highest resemblance for L-glutaminase within the Streptomyces sp. family. The purified protein was characterized structurally and functionally by employing spectroscopic methods like Raman, circular dichroism and nuclear magnetic resonance. The thermostability was assessed by thermogravimetric analysis. The outcomes of the study, suggests the promising application of recombinant L-Glutaminase as targeted therapeutic candidate for breast cancer.

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.

Enhancing the functionality of plant-based Yogurt: Integration of lycopene through dual-stage fermentation of soymilk

Well-defined compositional assemblies of plant-based yogurt are of fast-growing awareness for world population concerning environmental sustainability, economic burdens and health risks. Soybean is an attractive candidate for plant yogurt, suffering from poor flavor, limited nutrition, and undesired allergens to offer healthy-functional segments. Herein, we deciphered a novel lycopene-soy yogurt by efficient two-stage fermentation of engineered B. subtilis and LAB. The fortified sogurt was ensured with redundant lycopene of 22.67 ± 2.95 mg/g DCW by engineered B. subtilis and enriched soy isoflavone from synergistic effects of engineered B. subtilis and LAB, possessing strong antioxidant capacity for upgrading functionality. Moreover, the desired pH, accelerated protein hydrolysis, enhanced amino acid availability, and expected sensory attributes cooperatively conferred lycopene-soy yogurt as healthy functional food. High potential is firstly ascribed to sequential dual culture of engineered B. subtilis and LAB in lycopene-soy yogurt, in which flavorful, hypoallergenic and antioxidative ingredients enabled functionalities for plant-based yogurt.

Enhanced protein glutaminase production from Chryseobacterium proteolyticum combining physico-chemical mutagenesis and resistance screening and its application to soybean protein isolates

BACKGROUND

Protein glutaminase (PG) is a novel protein modification biotechnology that is increasingly being used in the food industry. However, the current level of fermentation of PG-producing strains still does not meet the requirements of industrial production. To obtain the mutant strains with high PG production, the atmospheric and room temperature plasma (ARTP) combined with LiCl chemical mutagen were used in mutagenesis of a PG producing Chryseobacterium proteolyticum 1003.

RESULTS

A mutant strain (WG15) was successfully obtained based on malonic acid resistance screening after compound mutagenesis of the starting strain C. proteolyticum 1003 using ARTP with LiCl, and it was confirmed to be genetically stable in PG synthesis after 15 generations. The protein glutaminase production of WG15 was 2.91 U mL^-1 after optimization of fermentation conditions, which is 48.69% higher than the original strain C. proteolyticum 1003. The PG obtained from fermentation showed good activities in deamidation of soy protein isolate. The solubility and foaming properties of the PG-treated soy protein isolate were significantly increased by 36.50% and 10.03%, respectively, when PG was added at the amount of 100 U mL^-1 . In addition, the emulsifying activity and emulsion stability of the treated soy protein isolate were improved by 12.44% and 10.34%, respectively, on the addition of 10 U mL^-1 PG. The secondary structure of the soy protein isolate changed after PG treatment, with an increased proportion of glutamate.

CONCLUSION

The results of the present study indicate that the PG produced by this mutant strain could improve the functional properties of soybean protein isolate and the C. proteolyticum mutant WG15 has great potential in food industry. © 2023 Society of Chemical Industry.

Effect of fermentation on structural properties and antioxidant activity of wheat gluten by Bacillus subtilis

Bacillus subtilis has been extensively studied for its ability to inhibit the growth of harmful microorganisms and its high protease activity. In this study, Bacillus subtilis was used to ferment gluten and assess the effects of the fermentation process on the physicochemical, microstructure and antioxidant properties of gluten. The results of Fourier infrared spectroscopy (FT-IR) and circular chromatography (CD) showed a significant decrease in the content of α-helix structures and a significant increase in the content of β-sheet structures in gluten after fermentation (p < 0.05). Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) showed that glutenin was degraded into small molecular peptides with a molecular weight of less than 26 kDa after 24 h of fermentation; meanwhile, the fermentation process significantly increased the free amino acid content of the samples (p < 0.05), reaching 1923.38 μg/mL at 120 h of fermentation, which was 39.46 times higher than that at 24 h of fermentation (p < 0.05). In addition, the fermented back gluten has higher free radical scavenging activity and iron reduction capacity. Therefore, fermented gluten may be used as a functional food to alleviate oxidative stress. This study provides a reference for the high-value application of gluten.

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.

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.

Cis-Element Engineering Promotes the Expression of Bacillus subtilis Type I L-Asparaginase and Its Application in Food

Type I L-asparaginase from Bacillus licheniformis Z-1 (BlAase) was efficiently produced and secreted in Bacillus subtilis RIK 1285, but its low yield made it unsuitable for industrial use. Thus, a combined method was used in this study to boost BlAase synthesis in B. subtilis. First, fifteen single strong promoters were chosen to replace the original promoter P43, with PyvyD achieving the greatest BlAase activity (436.28 U/mL). Second, dual-promoter systems were built using four promoters (PyvyD, P43, PaprE, and PspoVG) with relatively high BlAase expression levels to boost BlAase output, with the engine of promoter PaprE-PyvyD reaching 502.11 U/mL. The activity of BlAase was also increased (568.59 U/mL) by modifying key portions of the PaprE-PyvyD promoter. Third, when the ribosome binding site (RBS) sequence of promoter PyvyD was replaced, BlAase activity reached 790.1 U/mL, which was 2.27 times greater than the original promoter P43 strain. After 36 h of cultivation, the BlAase expression level in a 10 L fermenter reached 2163.09 U/mL, which was 6.2 times greater than the initial strain using promoter P43. Moreover, the application potential of BlAase on acrylamide migration in potato chips was evaluated. Results showed that 89.50% of acrylamide in fried potato chips could be removed when combined with blanching and BlAase treatment. These findings revealed that combining transcription and translation techniques are effective strategies to boost recombinant protein output, and BlAase can be a great candidate for controlling acrylamide in food processing.