Laser-Induced MoOx/Sulfur-Doped Graphene Hybrid Frameworks as Efficient Antibacterial Agents

Rational design and scalable construction of antibacterial mediators based on unique graphene architectures with highly efficient antibacterial ability and significant biocompatibility are challenging. Herein, sulfur-doped graphene skeletons uniformly decorated with metal oxide nanoparticles were designed and constructed via one-step laser-induced microexplosive techniques and demonstrated for the first time as highly efficient antibacterial agents. The optical density and flat colony counting methods demonstrated that the as-designed laser-induced MoO_x/sulfur-doped graphene hybrids exhibited exceptional activity inhibition of Escherichia coli and Staphylococcus aureus. Moreover, the bacteria were treated with an impressive laser-induced MoO_x/sulfur-doped graphene colloidal solution of concentration as low as 1 mg/mL for 4 h, leading to an excellent viability loss of 85% for the two bacteria. Cell toxicity experiments proved that the biological toxicity of laser-induced MoO_x/sulfur-doped graphene to pig sperm cells was negligible. The molecular dynamics calculations proposed that the intrinsic interaction with N-acetylglucosamine at the cell wall and the high-efficiency synergistic effect of sulfur-doped graphene and MoO_x played the key role in inhibiting the viability of bacteria. This work provides new insights for a novel structure design and opens up a potential route to construct antibacterial agents with high efficiency for clinical application.

Immobilization of Multi-Enzymes on Support Materials for Efficient Biocatalysis

Multi-enzyme biocatalysis is an important technology to produce many valuable chemicals in the industry. Different strategies for the construction of multi-enzyme systems have been reported. In particular, immobilization of multi-enzymes on the support materials has been proved to be one of the most efficient approaches, which can increase the enzymatic activity via substrate channeling and improve the stability and reusability of enzymes. A general overview of the characteristics of support materials and their corresponding attachment techniques used for multi-enzyme immobilization will be provided here. This review will focus on the materials-based techniques for multi-enzyme immobilization, which aims to present the recent advances and future prospects in the area of multi-enzyme biocatalysis based on support immobilization.

Establishment of a five-enzyme cell-free cascade for the synthesis of uridine diphosphate N-acetylglucosamine

In spite of huge endeavors in cell line engineering to produce glycoproteins with desired and uniform glycoforms, it is still not possible in vivo. Alternatively, in vitro glycoengineering can be used for the modification of glycans. However, in vitro glycoengineering relies on expensive nucleotide sugars, such as uridine 5'-diphospho-N-acetylglucosamine (UDP-GlcNAc) which serves as GlcNAc donor for the synthesis of various glycans. In this work, we present a systematic study for the cell-free de novo synthesis and regeneration of UDP-GlcNAc from polyphosphate, UMP and GlcNAc by a cascade of five enzymes (N-acetylhexosamine kinase (NahK), Glc-1P uridyltransferase (GalU), uridine monophosphate kinase (URA6), polyphosphate kinase (PPK3), and inorganic diphosphatase (PmPpA). All enzymes were expressed in E. coli BL21 Gold (DE3) and purified using immobilized metal affinity chromatography (IMAC). Results from one-pot experiments demonstrate the successful production of UDP-GlcNAc with a yield approaching 100%. The highest volumetric productivity of the cascade was about 0.81 g L^-1  h^-1 of UDP-GlcNAc. A simple model based on mass action kinetics was sufficient to capture the dynamic behavior of the multienzyme pathway. Moreover, a design equation based on metabolic control analysis was established to investigate the effect of enzyme concentration on the UDP-GlcNAc flux and to demonstrate that the flux of UDP-GlcNAc can be controlled by means of the enzyme concentrations. The effect of temperature on the UDP-GlcNAc flux followed an Arrhenius equation and the optimal co-factor concentration (Mg²⁺) for high UDP-GlcNAc synthesis rates depended on the working temperature. In conclusion, the study covers the entire engineering process of a multienzyme cascade, i.e. pathway design, enzyme expression, enzyme purification, reaction kinetics and investigation of the influence of basic parameters (temperature, co-factor concentration, enzyme concentration) on the synthesis rate. Thus, the study lays the foundation for future cascade optimization, preparative scale UDP-GlcNAc synthesis and for in situ coupling of the network with UDP-GlcNAc transferases to efficiently regenerate UDP-GlcNAc. Hence, this study provides a further step towards cost-effective in vitro glycoengineering of antibodies and other glycosylated proteins.

Efficient chemoenzymatic synthesis of uridine 5'-diphosphate N-acetylglucosamine and uridine 5'-diphosphate N-trifluoacetyl glucosamine with three recombinant enzymes

Uridine 5'-diphosphate N-acetylglucosamine (UDP-GlcNAc) is a natural UDP-monosaccharide donor for bacterial glycosyltransferases, while uridine 5'-diphosphate N-trifluoacetyl glucosamine (UDP-GlcNTFA) is its synthetic mimic. The chemoenzymatic synthesis of UDP-GlcNAc and UDP-GlcNTFA was attempted by three recombinant enzymes. Recombinant N-acetylhexosamine 1-kinase was used to produce GlcNAc/GlcNTFA-1-phosphate from GlcNAc/GlcNTFA. N-acetylglucosamine-1-phosphate uridyltransferase from Escherichia coli K12 MG1655 was used to produce UDP-GlcNAc/GlcNTFA from GlcNAc/GlcNTFA-1-phosphate. Inorganic pyrophosphatase from E. coli K12 MG1655 was used to hydrolyze pyrophosphate to accelerate the reaction. The above enzymes were expressed in E. coli BL21 (DE3) and purified, respectively, and finally mixed in one-pot bioreactor. The effects of reaction conditions on the production of UDP-GlcNAc and UDP-GlcNTFA were characterized. To avoid the substrate inhibition effect on the production of UDP-GlcNAc and UDP-GlcNTFA, the reaction was performed with fed batch of substrate. Under the optimized conditions, high production of UDP-GlcNAc (59.51 g/L) and UDP-GlcNTFA (46.54 g/L) were achieved in this three-enzyme one-pot system. The present work is promising to develop an efficient scalable process for the supply of UDP-monosaccharide donors for oligosaccharide synthesis.

NahK/GlmU fusion enzyme: characterization and one-step enzymatic synthesis of UDP-N-acetylglucosamine

The availability of uridine 5'-diphosphate N-acetylglucosamine (UDP-GlcNAc) is a prerequisite for the GlcNAc-transferase-catalyzed glycosylation reaction. UDP-GlcNAc has already been synthesized using an N-acetylhexosamine 1-kinase (NahK) and a GlcNAc-1-P uridyltransferase (truncated GlmU) and here, a fusion enzyme was constructed with truncated GlmU and NahK. After determination of the optimum catalytic condition (pH 8.0 at 40 °C), the fusion enzyme was used to synthesize UDP-GlcNAc in a single step with a yield of 88 % from GlcNAc, ATP and UTP. Furthermore, a simplified purification method was demonstrated using separation by gel filtration after by-product digestion with alkaline phosphatase. An overall yield of 77 % and a purity of over 90 % were achieved.

Systematic study on the broad nucleotide triphosphate specificity of the pyrophosphorylase domain of the N-acetylglucosamine-1-phosphate uridyltransferase from Escherichia coli K12

N-Acetylglucosamine-1-phosphate uridyltransferase (GlmU) from Escherichia coli K12 is a bifunctional enzyme that catalyzes both the acetyltransfer and uridyltransfer reactions in the prokaryotic UDP-GlcNAc biosynthetic pathway. In this study, we report the broad substrate specificity of the pyrophosphorylase domain of GlmU during its uridyltransfer reaction and the substrate priority is ranked in the following order: UTP > dUTP > dTTP >> CTP > dATP/dm(6) ATP. This pyrophosphorylase domain of GlmU is also a tool to synthesize UDP-GlcNAc analogs, two examples of which were synthesized herein in multiple mg scale in vitro.

Pyrimidine as constituent of natural biologically active compounds

This review describes the various manifestations of the pyrimidine system (alkylated, glycosylated, benzo-annelated.). These comprise pyrimidine nucleosides as well as alkaloids and antibiotics--some of them have been discovered and isolated from natural sources already long time ago, others have been reported very recently. A short overview on pyrimidine syntheses (prebiotic synthesis, biosynthesis, and metabolism) is given. The biological activities of most of the pyrimidine analogs are briefly described, and, in some cases, syntheses are formulated.

Enzymes in the synthesis of bioactive compounds: the prodigious decades

The growing demand for enantiomerically pure pharmaceuticals has impelled research on enzymes as catalysts for asymmetric synthetic transformations. However, the use of enzymes for this purpose was rather limited until the discovery that enzymes can work in organic solvents. Since the advent of the PCR the number of available enzymes has been growing rapidly and the tailor-made biocatalysts are becoming a reality. Thus, it has been possible the use of enzymes for the synthesis of new innovative medicines such as carbohydrates and their incorporation to modern methods for drug development, such as combinatorial chemistry. Finally, the genomic research is allowing the manipulation of whole genomes opening the door to the combinatorial biosynthesis of compounds. In this review, our intention is to highlight the main landmarks that have led to transfer the chemical efficiency shown by the enzymes in the cell to the synthesis of bioactive molecules in the lab during the last 20 years.