Immobilization and enzymatic properties of glutamate decarboxylase from Enterococcus faecium by affinity adsorption on regenerated chitin

Purification, immobilization, evolution, and characterization of D-allulose 3-epimerase from Antarctic Microbacterium

D-allulose is a rare, low-calorie sugar substitute with multiple physiological functions and is widely used in food and pharmaceutical industries. D-allulose is primarily produced by the catalytic conversion of d-fructose via D-allulose 3-epimerase (DAEase). In this study, a DAEase gene, dpema4, was isolated from an Antarctic bacterium and expressed in Escherichia coli. The recombinant DAEase was a homotetramer with an optimal temperature of 60 °C and pH of 7.5. Its catalytic activity was not strictly dependent on metal ions, making it a safer alternative to the other reported DAEases. The recombinant DAEase showed exhibited the highest activity towards D-allulose, and the bioconversion rate was 29 %. For immobilization, the cellulose-binding domain (CBD) was fused to DAEase, and the fusion protein was immobilized on microcrystalline cellulose. The immobilized DAEase showed highly improved pH stability and maintained approximately 44 % of catalytic activity after 10 continuous reaction cycles. The single-point mutant A248H showed high thermal stability and catalytic activity at 60 °C, and the bioconversion rate of d-fructose reached 32 %. In summary, the recombinant DAEase can serve as a good candidate enzyme for the production of D-allulose, and the establishment of a one-step purification and immobilization of DAEase can facilitate its industrial application.

Advances in engineering and applications of microbial glutamate decarboxylases for gamma-aminobutyric acid production

Gamma-aminobutyric acid (GABA) is a key neurotransmitter with significant health benefits, including anxiolytic and anti-hypertensive effects, and potential use in biodegradable material synthesis. The increasing market demand for GABA has intensified the search for cost-effective production methods. The key enzyme involved in GABA production is glutamate decarboxylase (GAD), which catalyzes the conversion of L-glutamate to GABA. GAD plays a central role in various production approaches, such as enzyme-based catalysis, whole-cell catalysis, and microbial fermentation. Although microbial GADs are preferred for their high catalytic activity, their low pH and thermal stability present significant challenges for large-scale GABA production. Wild-type GADs typically have an optimal pH range of 4-5, and their activity sharply declines as the pH increases, thereby reducing production efficiency. Furthermore, GADs' poor thermal stability makes them vulnerable to temperature fluctuations during industrial processes, further limiting GABA production. Recent research has focused on engineering GAD variants with improved stability and performance through rational design, directed evolution, and semi rational approaches. These advancements not only expand the potential applications of GAD in biocatalysis but also offer promising solutions for sustainable GABA production. This paper provides an in-depth review of the engineering of GADs, applications of GAD in GABA production, and strategies to overcome limitations, offering a comprehensive overview of the current state and future prospects of GAD modification in enhancing GABA production.

The application of chitin materials in enzymatic catalysis: A review

Enzymatic catalysis offers notable advantages, including exceptional catalytic efficiency, selectivity, and the ability to operate under mild conditions. However, its widespread application is hindered by the high costs associated with enzymes and cofactors. Materials-mediated immobilization technology has proven effective in the recycling of enzymes and cofactors. An optimal carrier material for protein immobilization must be non-toxic, biocompatible, and should not compromise the biological activity or structure of the enzymes. Compared to synthetic polymers, chitin is a promising carrier given its low cost, renewability, abundance of functional groups, and notable biocompatibility and biodegradability. Although numerous reviews on chitosan and other polymers for immobilization have been published, few have addressed using chitin as supports. In this review, chitin-based materials mediated enzyme immobilization, the one-step purification and immobilization of enzymes, as well as co-immobilization of enzymes and cofactors were summarized. Particularly, the significance of chitin materials in the field of enzymatic catalysis was emphasized. This study has the potential to open new avenues for immobilized biocatalysts.

Production of γ-aminobutyric acid by immobilization of two Yarrowia lipolytica glutamate decarboxylases on electrospun nanofibrous membrane

This study harnesses glutamate decarboxylase (GAD) from Yarrowia lipolytica to improve the biosynthesis of γ-aminobutyric acid (GABA), focusing on boosting the enzyme's catalytic efficiency and stability by immobilizing it on nanofibrous membranes. Through recombinant DNA techniques, two GAD genes, YlGAD1 and YlGAD2, were cloned from Yarrowia lipolytica and then expressed in Escherichia coli. Compared to their soluble forms, the immobilized enzymes exhibited significant improvements in thermal and pH stability and increased resistance to chemical denaturants. The immobilization notably enhanced substrate affinity, as evidenced by reduced Km values and increased kcat values, indicating heightened catalytic efficiency. Additionally, the immobilized YlGAD1 and YlGAD2 enzymes showed substantial reusability, maintaining 50% and 40% of their activity, respectively, after six consecutive cycles. These results underscore the feasibility of employing immobilized YlGAD enzymes for cost-effective and environmentally sustainable GABA production. This investigation not only affirms the utility of YlGADs in GABA synthesis but also underscores the advantages of enzyme immobilization in industrial settings, paving the way for scalable biotechnological processes.

Preparation of magnetic polyacrylamide hydrogel with chitosan for immobilization of glutamate decarboxylase to produce γ-aminobutyric acid

Gamma-aminobutyric acid (GABA) is an vital neurotransmitter, and the reaction to obtain GABA through biocatalysis requires coenzymes, which are therefore limited in the production of GABA. In this study, polyacrylamide hydrogels doped with chitosan and waste toner were synthesized for glutamate decarboxylase (GAD) and coenzyme co-immobilization to realize the production of GABA and the recovery of coenzymes. Enzymatic properties of immobilized GAD were discussed. The immobilized enzymes have significantly improved pH and temperature tolerance compared to free enzymes. In terms of reusability, after 10 repeated reuses of the immobilized GAD, the residual enzyme activity of immobilized GAD still retains 100% of the initial enzyme activity, and the immobilized coenzyme can also be kept at about 32%, with better stability and reusability. And under the control of no exogenous pH, immobilized GAD showed good performance in producing GABA. Therefore, in many ways, the new composite hydrogel provides another way for the utilization of waste toner and promises the possibility of industrial production of GABA.

Research Progress on Lignocellulosic Biomass Degradation Catalyzed by Enzymatic Nanomaterials

Lignocellulose biomass (LCB) has extensive applications in many fields such as bioenergy, food, medicines, and raw materials for producing value-added products. One of the keys to efficient utilization of LCB is to obtain directly available oligo- and monomers (e.g., glucose). With the characteristics of easy recovery and separation, high efficiency, economy, and environmental protection, immobilized enzymes have been developed as heterogeneous catalysts to degrade LCB effectively. In this review, applications and mechanisms of LCB-degrading enzymes are discussed, and the nanomaterials and methods used to immobilize enzymes are also discussed. Finally, the research progress of lignocellulose biodegradation catalyzed by nano-enzymes was discussed.

Molecular Analysis of Glutamate Decarboxylases in Enterococcus avium

Enterococcus avium (E. avium) is a common bacterium inhabiting the intestines of humans and other animals. Most strains of this species can produce gamma-aminobutyric acid (GABA) via the glutamate decarboxylase (GAD) system, but the presence and genetic organization of their GAD systems are poorly characterized. In this study, our bioinformatics analyses showed that the GAD system in E. avium strains was generally encoded by three gadB genes (gadB1, gadB2, and gadB3), together with an antiporter gene (gadC) and regulator gene (gadR), and these genes are organized in a cluster. This finding contrasts with that for other lactic acid bacteria. E. avium SDMCC050406, a GABA producer isolated from human feces, was employed to investigate the contribution of the three gadB genes to GABA biosynthesis. The results showed that the relative expression level of gadB3 was higher than those of gadB1 and gadB2 in the exponential growth and stationary phases, and this was accompanied by the synchronous transcription of gadC. After heterologous expression of the three gadB genes in Escherichia coli BL21 (DE3), the K_m value of the purified GAD3 was 4.26 ± 0.48 mM, a value lower than those of the purified GAD1 and GAD2. Moreover, gadB3 gene inactivation caused decreased GABA production, accompanied by a reduction in resistance to acid stress. These results indicated that gadB3 plays a crucial role in GABA biosynthesis and this property endowed the strain with acid tolerance. Our findings provided insights into how E. avium strains survive the acidic environments of fermented foods and throughout transit through the stomach and gut while maintaining cell viability.