Lactate dehydrogenase encapsulated in a metal-organic framework: A novel stable and reusable biocatalyst for the synthesis of D-phenyllactic acid

A two-enzyme system in an amorphous metal-organic framework for the synthesis of D-phenyllactic acid

In this study, we synthesized an amorphous metal-organic framework by adjusting the concentration of precursors, and established a two-enzyme system consisting of lactate dehydrogenase (LDH) and glucose dehydrogenase (GDH), which successfully achieved coenzyme recycling, and applied it to the synthesis of D-phenyllactic acid (D-PLA). The prepared two-enzyme-MOF hybrid material was characterized using XRD, SEM/EDS, XPS, FT-IR, TGA, CLSM, etc. In addition, reaction kinetic studies indicated that the MOF-encapsulated two-enzyme system exhibited faster initial reaction velocities than free enzymes due to its amorphous ZIF-generated mesoporous structure. Furthermore, the pH stability and temperature stability of the biocatalyst were evaluated, and the results indicated a significant improvement compared to the free enzymes. Moreover, the amorphous structure of the mesopores still maintained the shielding effect and protected the enzyme structure from damage by proteinase K and organic solvents. Finally, the remaining activity of the biocatalyst for the synthesis of D-PLA reached 77% after 6 cycles of use, and the coenzyme regeneration still maintained at 63%, while the biocatalyst also retained 70% and 68% residual activity for the synthesis of D-PLA after 12 days of storage at 4 °C and 25 °C, respectively. This study provides a reference for the design of MOF-based multi-enzyme biocatalysts.

One-pot encapsulation of lactate dehydrogenase and Fe3O4 nanoparticles into a metal-organic framework: A novel magnetic recyclable biocatalyst for the synthesis of D-phenyllactic acid

The main challenges in bio-catalysis of d-phenyllactic acid (D-PLA) are poor tolerance of lactate dehydrogenase (LDH) to harsh environmental conditions and inability to recycle the catalyst. A novel magnetic framework composite was prepared as solid support for the immobilization of enzymes via one-pot encapsulation in this study. LDH/MNPs@MAF-7 was synthesized by the one-pot encapsulation of both LDH and magnetic nanoparticles (MNPs) in MAF-7. The LDH/MNPs@MAF-7 showed stable biological activity for the efficient biosynthesis of D-PLA. The structure and morphology of LDH/MNPs@MAF-7 were systematically characterized by SEM, FT-IR, XRD, VSM, XPS, TGA and N₂ sorption. These indicated that LDH/MNPs@MAF-7 was successfully synthesized, exhibiting enhanced resistance to acid and alkali, temperature and organic solvents. Furthermore, the bio-catalyst could be separated easily using a magnet, and the reusability was once considerably expanded with 80% of enzyme activity last after eight rounds of recycling. Therefore, LDH/MNPs@MAF-7 could be used as a potential biocatalyst for the biosynthesis of D-PLA due to its good stability and recovery properties.

Coenzyme self-sufficiency system-recent advances in microbial production of high-value chemical phenyllactic acid

Phenyllactic acid (PLA), a natural antimicrobial substance, has many potential applications in the food, animal feed, pharmaceutical and cosmetic industries. However, its production is limited by the complex reaction steps involved in its chemical synthesis. Through advances in metabolic engineering and synthetic biology strategies, enzymatic or whole-cell catalysis was developed as an alternative method for PLA production. Herein, we review recent developments in metabolic engineering and synthetic biology strategies that promote the microbial production of high-value PLA. Specially, the advantages and disadvantages of the using of the three kinds of substrates, which includes phenylpyruvate, phenylalanine and glucose as starting materials by natural or engineered microbes is summarized. Notably, the bio-conversion of PLA often requires the consumption of expensive coenzyme NADH. To overcome the issues of NADH regeneration, efficiently internal cofactor regeneration systems constructed by co-expressing different enzyme combinations composed of lactate dehydrogenase with others for enhancing the PLA production, as well as their possible improvements, are discussed. In particular, the construction of fusion proteins with different linkers can achieve higher PLA yield and more efficient cofactor regeneration than that of multi-enzyme co-expression. Overall, this review provides a comprehensive overview of PLA biosynthesis pathways and strategies for increasing PLA yield through biotechnology, providing future directions for the large-scale commercial production of PLA and the expansion of downstream applications.

Redefining methods for augmenting lactic acid bacteria robustness and phenyllactic acid biocatalysis: Integration valorizes simplicity

The production of phenyllactic acid (PLA) has been reported by several researchers, but so far, no mention has been made of augmented PLA production using an orchestrated assembly of simple techniques integrated to improve lactic acid bacteria (LAB) metabolism for the same. This review summarizes sequentially tailoring LAB growth and metabolism for augmented PLA catalysis through several strategies like monitoring LAB sustenance by choosing appropriate starter PLA-producing LAB strains isolated from natural environments, with desirably fastidious growth rates, properties like acidification, proteolysis, bacteriophage-resistance, aromatic/texturing-features, etc.; entrapping chosen LAB strains in novel cryogels and/or co-cultivating two/more LAB strains to improve their biotransformation potential and promote growth dependency/sustainability; adopting adaptive evolution methods designed to improve LAB strains under selection pressure inducing desired phenotypes tolerant to stress factors like heat, salt, acid, and solvent; monitoring physico-chemical LAB fermentation factors like temperature, pH, dissolved oxygen content, enzymes, and cofactors for PLA biosynthesis; and modulating purification/downstream processes to extract substantial PLA yields. This review paper serves as a comprehensive preliminary guide that can evoke a strategic experimental plan to produce industrial-scale PLA yields using simple techniques orchestrated together in the pursuit of conserving time, effort, and resources.

Enzyme-immobilized metal-organic frameworks: From preparation to application

As a class of widely used biocatalysts, enzymes possess advantages including high catalytic efficiency, strong specificity and mild reaction condition. However, most free enzymes have high requirements on the reaction environment and are easy to deactivate. Immobilization of enzymes on nanomaterial-based substrates is a good way to solve this problem. Metal-organic framework (MOFs), with ultra-high specific surface area and adjustable porosity, can provide a large space to carry enzymes. And the tightly surrounded protective layer of MOFs can stabilize the enzyme structure to a great extent. In addition, the unique porous network structure enables selective mass transfer of substrates and facilitates catalytic processes. Therefore, these enzyme-immobilized MOFs have been widely used in various research fields, such as molecule/biomolecule sensing and imaging, disease treatment, energy and environment protection. In this review, the preparation strategies and applications of enzymes-immobilized MOFs are illustrated and the prospects and current challenges are discussed.