Enhanced activity and stability of protein-glutaminase by Hofmeister effects

Unlocking the Anion Effect on Steerable Production of 5-Hydroxymethylfurfural

Homogeneous metal salt catalysts play a pivotal role in industrial production of 5-hydroxymethylfurfural (HMF). Herein, we first proposed the anion effect on steerable production of HMF using metal salts with different anions as catalyst in a biphasic system of tetrahydrofuran (THF)/NaCl aqueous solution (NaCl aq). Notably, the anions affected the catalytic activity of the metal salts, leading to an order of magnitude difference in the HMF yields, i.e., AlBr3 (74.0 mol %)>AlCl3 (60.8 mol %)>Al2(SO4)3 (35.2 mol %)>Al(NO3)3 (14.9 mol %). The anion effect on steerable production of HMF could be attributed to the proximity effect and electron tension. Anions form close-range interactions with glucose molecules by proximity effect to promote electron transfer, facilitating the isomerization of glucose to fructose. Besides, anions induce a reduction of the electron cloud density of glucose carbon atoms, generating electron tension that rapidly transforms glucose from the ground state to the transition state, thereby increasing the HMF yield. Based on the revelation of anions effect and evaluation of techno-economic process, we expect to provides theoretical guidance for high-throughput screening of metal salt catalysts in industrial biorefinery.

Optimizing skim milk yogurt properties: Combined impact of transglutaminase and protein-glutaminase

The lack of fat in yogurt can lead to alterations in taste and whey separation, reducing consumer acceptance. In this study, the feasibility of enhancing the quality of skim milk yogurt through a combination of transglutaminase (TG) and protein-glutaminase (PG) was investigated. The combination of TG and PG resulted in simultaneous cross-linking and deamidation of CN micelles, with PG deamidation taking priority over TG cross-linking, leading to higher solubility and lower turbidity of milk proteins compared with TG alone. When 0.06 U/mL TG and 0.03 U/mL PG were added, firmness and viscosity indexes significantly increased by 38.26% and 78.59%, respectively, as compared with the control. Microscopic images revealed increased cross-linking with CN and filling of cavities by smaller submicelles in the combination of TG and PG treatment. Furthermore, the combination of TG and PG resolved issues of rough taste and whey separation, leading to improved overall liking. This study highlights the benefits of using both enzymes in dairy production and has important implications for future research.

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.

Functional and Mechanistic Dissection of Protein Glutaminase PG3 and Its Rational Engineering for Enhanced Modification of Myofibrillar Proteins

Protein glutaminases (PG; EC = 3.5.1.44) are enzymes known for enhancing protein functionality. In this study, we cloned and expressed the gene chryb3 encoding protein glutaminase PG3, exhibiting 39.4 U/mg specific activity. Mature-PG3 featured a substrate channel surrounded by aromatic and hydrophobic amino acids at positions 38-45 and 78-84, with Val81 playing a pivotal role in substrate affinity. The dynamic opening and closing motions between Gly65, Thr66, and Cys164 at the catalytic cleft greatly influence substrate binding and product release. Redesigning catalytic pocket and cocatalytic region produced combinatorial mutant MT6 showing a 2.69-fold increase in specific activity and a 2.99-fold increase at t65 °C1/2. Furthermore, MT6 boosted fish myofibrillar protein (MP) solubility without NaCl. Key residues such as Thr3, Asn54, Val81, Tyr82, Asn107, and Ser108 were vital for PG3-myosin interaction, particularly Asn54 and Asn107. This study sheds light on the catalytic mechanism of PG3 and guided its rational engineering and utilization in low-salt fish MP product production.

High electrolyte concentration effect on enzymatic oxygen reduction

The nature, the composition and the concentration of electrolytes is essential for electrocatalysis involving redox enzymes. Here, we discuss the effect of various electrolyte compositions with increasing ionic strengths on the stability and activity towards O₂ reduction of the bilirubin oxidase from Myrothecium verrucaria (Mv BOD). Different salts, Na₂SO₄, (NH₄)₂SO₄, NaCl, NaClO₄, added to a phosphate buffer (PB) were evaluated with concentrations ranging from 100 mM up to 1.7 M. On functionalized carbon nanotube-modified electrodes, it was shown that the catalytic current progressively decreased with increasing salt concentrations. The process was reversible suggesting it was not related to enzyme leakage. The enzyme was then immobilized on gold electrodes modified by self-assembling of thiols. When the enzyme was simply adsorbed, the catalytic current decreased in a reversible way, thus behaving similarly as on carbon nanotubes. Enzyme mobility at the interface induced by a modification in the interactions between the protein and the electrode upon salt addition may account for this behavior. When the enzyme was covalently attached, the catalytic current increased. Enzyme compaction is proposed to be at the origin of such catalytic current increase because of shorter distances between the first copper site electron acceptor and the electrode.

Decolorization and detoxication of plant-based proteins using hydrogen peroxide and catalase

The gap between the current supply of meat and its predicted future demand is widening, increasing the need to produce plant-based meat analogs. Despite ongoing technical developments, one of the unresolved challenges of plant-based meat analogs is to safely and effectively decolor plant proteins that originally exhibit yellow-brown or strong brown color. This study aimed to develop an effective and safe decoloring system for soy-based protein products using food-grade hydrogen peroxide and catalase. First, soy-based protein isolate (PI) and textured vegetable protein (TVP) were treated with hydrogen peroxide, and then the residual hydrogen peroxide was degraded using catalase. This process caused notable decolorization of PI and TVP, and residual hydrogen peroxide was not detected in these products. These findings indicate that this process could safely and effectively decolorize soy-based proteins. Interestingly, this decoloring process enhanced the solubility, water- and oil-holding capacities, foaming capacity, and emulsifying stability of decolored soy-based PI. Additionally, cooking loss and juiciness of decolored TVP-based foods were improved compared to those of non-treated foods. These findings indicate that the decoloring process also enhances the physical properties of soy-based protein products.

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.

Effects of Temperature and Nitrogen Application on Carbon and Nitrogen Accumulation and Bacterial Community Composition in Apple Rhizosphere Soil

Malus sieversii grows on the slopes of the Tianshan Mountains in Xinjiang where the difference in daily temperature is significant. In recent years, the rhizosphere soil health of Malus sieversii has been severely impacted by anthropogenic disturbance and pathogenic infestation. The soil nutrient content and soil microorganism diversity are the main components of soil health. Low temperature has negative effects on soil bacterial community structure by inhibiting the accumulation of carbon and nitrogen. However, the effects of temperature and nitrogen application on soil carbon and nitrogen accumulation and the bacterial community composition in the rhizosphere soil of Malus sieversii are unclear. We set two temperature levels, i.e., low temperature (L) and room temperature (R), combined with no nitrogen (N0) and nitrogen application (N1) to explore the response of plant carbon and nitrogen uptake, rhizosphere soil carbon and nitrogen accumulation and bacterial community composition to temperature and nitrogen fertilization. At the same temperature level, plant 13C abundance (P-Atom13C), plant 15N absolute abundance (P-Con15N), soil 15N abundance (S-Atom15N) and soil urease, protease and glutaminase activities were significantly higher under nitrogen application compared with the no-nitrogen application treatment. The bacterial community diversity and richness indices of the apple rhizosphere soil in the N1 treatment were higher than those in the N0 treatment. The relative abundances of Actinobacteria, Rhodopseudomonas, and Bradyrhizobium were higher in the LN1 treatment than in the LN0 treatment. Redundancy analysis (RDA) showed that plant 13C absolute abundance (P-Con13C) and plant 15N absolute abundance (P-Con15N) were the main factors affecting the soil bacterial community composition. In summary, Nitrogen application can alleviate the effects of low temperature stress on the soil bacterial community and is of benefit for the uptakes of carbon and nitrogen in Malus sieversii plants.