Fusion enzyme design based on the "channelization" cascade theory and homogenous dextran product improvement

Bifunctional chimeras of myeloperoxidase and glucose oxidase. Antimicrobial, topological and enzymatic properties

Enhancing the local substrate concentration is a crucial strategy in nature for facilitating the proximity of two enzymes. The substrate of the first enzyme is transformed into a by-product that travels to the active site of the second enzyme without external diffusion, then transformed into a product and eventually expelled from the complex. In an effort to optimize the antimicrobial properties of myeloperoxidase from Rhodopirellula baltica (RbMPO), we created a library of fused chimeras between a glucose oxidase (GOx) and RbMPO so that H2O2 could be continuously perfused in the vicinity RbMPO, enabling the production of HOCl or HOSCN, well-known antimicrobial agents. The enzymes were characterized biochemically, enzymatically, and physically using low-resolution techniques such as AFM, SAXS, and cryofracture. SAXS experiments revealed that the chimeras were properly folded and existed in different oligomeric states. The kinetic parameters of the chimeras were determined and used for classification, revealing that all chimeras exhibited varying levels of activity and were microbicidal. The mixture of different oligomeric states of LEGGEAEA displayed both activity and microbicidal properties. AFM was used to visualize the chimeras in different oligomeric states, with their overall shapes ranging from round, oblong, to hooked, depending on the linker used.

Synthesis of dextran of different molecular weights by recombinant dextransucrase DsrB

Leuconostoc citreum JZ-002 was extracted from artisanal orange wine. This strain was used to synthesize dextran with a purification extraction of 27.9 g/L. The resulting dextran had a molecular weight of 2.45 × 106 Da. A significant portion, amounting to 64 % of the structure, is constituted by the main chain, with α-(1,6) glycosidic bonds acting as the linkages. In contrast, the branched chain, comprising 34 % of the entire molecule, is characterized by the presence of α-(1,3) glycosidic bonds. The dextransucrase DsrB, believed to be accountable for the formation of the dextran backbone, was successfully cloned into the pET-28a-AcmA vector. The recombinant expression of the enzyme was achieved. Purified recombinant enzymes and immobilized in a single go using the gram-positive enhancer matrix (GEM). The maximum yield of dextran produced by suchimmobilized enzyme was 191.9 g/L. The composition featured a dextran connected via α-(1,6) glycosidic linkages. Molecular weight controlled synthesis was achieved with sucrose concentrations of 100-2000 mM and enzyme concentrations of 320-1280 U. The Mw of the synthesized dextran extended from 4680 to 1,320,000 Da. By controlling the ratio between enzyme concentration and sucrose concentration, dextrans with diverse Mw can be enzymatically generated.

Temperature-regulated cascade reaction for homogeneous oligo-dextran synthesis using a fusion enzyme

Based on the principle of cascade reaction, a fusion enzyme of dextransucrase and dextranase was designed without linker to catalyze the production of oligo-dextran with homogeneous molecular weight from sucrose in one catalytic step. Due to the different effects of temperature on the two components of the fusion enzyme, temperature served as the "toggle switch" for the catalytic efficiency of the two-level fusion enzyme, regulating the catalytic products of the fusion enzyme. Under optimal conditions, the fusion enzyme efficiently utilized 100 % of the sucrose, and the yield of oligo-dextran with a homogeneous molecular weight reached 70 %. The product has been purified and characterized. The probiotic potential of the product was evaluated by analyzing the growth of 10 probiotic species. Its cytotoxic and anti-inflammatory activities were also determined. The results showed that the long-chain oligo-dextran in this study had significantly better probiotic potential and anti-inflammatory activity compared to other oligosaccharides. This study provides a strategy for the application of oligo-dextran in the food and pharmaceutical industries.

Leucine zipper as a bridge for transaminase self-assembly: A fusion enzyme for efficient chiral conversion of d-phenylglycine

Amino acid transferase is a family of enzymes used to catalyze and separate chiral amino acids. However, due to the low efficiency, by-products and reverse reactions occur in cascade reactions. Therefore, in the research, phenylglycine aminotransferase and aspartate aminotransferase were self-assembled in vitro by leucine zipper. The self-assembled enzyme system with d-phenylglycine and α-ketoglutarate as substrates were used for the chiral transformation reaction. By studying the enzyme combination, kinetic reaction stability and catalytic efficiency, it was found that the self-assembled enzyme showed improved stability and better affinity to the substrate than the control and achieved only ee value of 17.86% for the control at the substrate ratio was 1:2. In contrast, the self-assembled enzyme basically catalyzed the complete conversion of d-Phg to l-Phg, with the ee value as 99%. These results demonstrated the feasibility of the leucine zipper and the conversion of d-phenylglycine to the l-type by fusion enzyme.

Self-cascade deoxynivalenol detoxification by an artificial enzyme with bifunctions of dehydrogenase and aldo/keto reductase from genome mining

Due to the severe health risks for human and animal caused by the intake of toxic deoxynivalenol (DON) derived from Fusarium species, elimination DON in food and feed has been initiated as a critical issue. Enzymatic cascade catalysis by dehydrogenase and aldo-keto reductase represents a fascinating strategy for DON detoxification. Here, one quinone-dpendent alcohol dehydrogenase DADH oxidized DON into less-toxic 3-keto-DON and NADPH-dependent aldo-keto reductase AKR13B3 reduced 3-keto-DON into relatively non-toxic 3-epi-DON were identified from Devosia strain A6-243, indicating that degradation of DON on C3 are two-step sequential cascade processes. To establish the bifunctions, fusion enzyme linking DADH and AKR13B3 was successfully assembled to promote one-step DON degradations with accelerated specific activity and efficiency, resulting 93.29 % of DON removal rate in wheat sample. Three-dimensional simulation analysis revealed that the bifunctional enzyme forms an artificial intramolecular channel to minimize the distance of intermediate from DADH to AKR13B3 for two-step enzymatic reactions, and thereby accelerates this enzymatic process. As the first report of directing single step DON detoxification by an interesting bifunctional artificial enzyme, this work revealed a facile and eco-friendly approach to detoxify DON with application potential and gave valuable insights into execute other mycotoxin detoxification for ensuring food safety.