Cell-Free Biosynthesis System: Methodology and Perspective of in Vitro Efficient Platform for Pyruvate Biosynthesis and Transformation

The modification of intracellular metabolic pathways by metabolic engineering has generated many engineered strains with relatively high yields of various target products in the past few decades. However, the unpredictable accumulation of toxic products, the cell membrane barrier, and competition between the carbon flux of cell growth and product synthesis have severely retarded progress toward the industrial-scale production of many essential chemicals. On the basis of an in-depth understanding of intracellular metabolic pathways, scientists intend to explore more sustainable methods and construct a cell-free biosynthesis system in vitro. In this review, the synthesis and application of pyruvate as a platform compound is used as an example to introduce cell-free biosynthesis systems. We systematically summarize a proposed methodology workflow of cell-free biosynthesis systems, including pathway design, enzyme mining, enzyme modification, multienzyme assembly, and pathway optimization. Some new methods, such as machine learning, are also mentioned in this review.

Oxidation-Induced "One-Pot" Click Chemistry

Click chemistry has been established rapidly as one of the most valuable methods for the chemical transformation of complex molecules. Due to the rapid rates, clean conversions to the products, and compatibility of the reagents and reaction conditions even in complex settings, it has found applications in many molecule-oriented disciplines. From the vast landscape of click reactions, approaches have emerged in the past decade centered around oxidative processes to generate in situ highly reactive synthons from dormant functionalities. These approaches have led to some of the fastest click reactions know to date. Here, we review the various methods that can be used for such oxidation-induced "one-pot" click chemistry for the transformation of small molecules, materials, and biomolecules. A comprehensive overview is provided of oxidation conditions that induce a click reaction, and oxidation conditions are orthogonal to other click reactions so that sequential "click-oxidation-click" derivatization of molecules can be performed in one pot. Our review of the relevant literature shows that this strategy is emerging as a powerful approach for the preparation of high-performance materials and the generation of complex biomolecules. As such, we expect that oxidation-induced "one-pot" click chemistry will widen in scope substantially in the forthcoming years.

Increased Flame Retardancy of Enzymatic Functionalized PET and Nylon Fabrics via DNA Immobilization

Poly(ethylene terephthalate) (PET) and nylon find their main applications in working clothes, domestic furniture and as indoor decoration (curtains and carpets). The increasing attention on healthy lifestyle, together with protection and safety, gained a strong interest in today's society. In this context, reducing the flammability of textiles has been tackled by designing flame retardants (FRs) able to suppress or delay the flame propagation. Commercially available FRs for textiles often consist of brominated, chlorinated and organo-phosphorus compounds, which are considered a great concern for human health and for the environment. In this study, Deoxyribose Nucleic Acid (DNA) was investigated as a green and eco-friendly alternative to halogen-containing FRs. DNA is in fact able to provide flame retardant properties due to its intrinsically intumescent building blocks (deoxyribose, phosphoric-polyphosphoric acid, and nitrogen-containing bases). In a first step, anchor groups (i.e., carboxyl groups) for subsequent coupling of DNA were introduced to PET and nylon-6 fabrics via limited surface hydrolysis with Humicola insolens cutinase (HiC). Released monomer/oligomers were measured via HPLC (1 mM of BHET for PET and 0.07 mM of caprolactam from nylon after 72 h). In a next step, DNA immobilization on the activated polymers was studied by using three different coupling systems, namely: EDC/NHS, dopamine, and tyrosine. DNA coupling was confirmed via FT-IR that showed typical bands at 1,220, 970, and 840 cm⁻¹. The tyrosine/DNA coupling on nylon fabrics resulted to be the most effective as certified by the lowest burning rate and total burning time (35 s, 150 mm, and 4.3 mm^*s⁻¹ for the blank and 3.5 s, 17.5 mm, and 5 mm^* s⁻¹ for nylon/tyrosine/DNA) which was also confirmed by FT-IR and ESEM/EDS measurements. Thermogravimetric analysis (TGA) further confirmed that tyrosine/DNA coated nylon showed a lower thermal degradation between 450 and 625°C when compared to the untreated samples.

Structural insights into pH-responsive drug release of self-assembling human serum albumin-silk fibroin nanocapsules

Inflammation processes are associated with significant decreases in tissue or lysosomal pH from 7.4 to 4, a fact that argues for the application of pH-responsive drug delivery systems. However, for their design and optimization a full understanding of the release mechanism is crucial. In this study we investigated the pH-depending drug release mechanism and the influence of silk fibroin (SF) concentration and SF degradation degree of human serum albumin (HSA)-SF nanocapsules. Sonochemically produced nanocapsules were investigated regarding particle size, colloidal stability, protein encapsulation, thermal stability and drug loading properties. Particles of the monodisperse phase showed average hydrodynamic radii between 438 and 888 nm as measured by DLS and AFM and a zeta potential of -11.12 ± 3.27 mV. Together with DSC results this indicated the successful production of stable nanocapsules. ATR-FTIR analysis demonstrated that SF had a positive effect on particle formation and stability due to induced beta-sheet formation and enhanced crosslinking. The pH-responsive release was found to depend on the SF concentration. In in-vitro release studies, HSA-SF nanocapsules composed of 50% SF showed an increased pH-responsive release for all tested model substances (Rhodamine B, Crystal Violet and Evans Blue) and methotrexate at the lowered pH of 4.5 to pH 5.4, while HSA capsules without SF did not show any pH-responsive drug release. Mechanistic studies using confocal laser scanning microscopy (CLSM) and small angle X-ray scattering (SAXS) analyses showed that increases in particle porosity and decreases in particle densities are directly linked to pH-responsive release properties. Therefore, the pH-responsive release mechanism was identified as diffusion controlled in a novel and unique approach by linking scattering results with in-vitro studies. Finally, cytotoxicity studies using the human monocytic THP-1 cell line indicated non-toxic behavior of the drug loaded nanocapsules when applied in a concentration of 62.5 µg mL^-1. Based on the obtained release properties of HSA-SF nanocapsules formulations and the results of in-vitro MTT assays, formulations containing 50% SF showed the highest requirements arguing for future in vivo experiments and application in the treatment of inflammatory diseases.

Latent and active aurone synthase from petals of C. grandiflora: a polyphenol oxidase with unique characteristics

Aurone synthase belongs to the novel group 2 polyphenol oxidases and the presented kinetic characterization suggests a differing aurone biosynthesis in Asteraceae species compared to snapdragon. Aurone synthases (AUS) are polyphenol oxidases (PPO) physiologically involved in the formation of yellow aurone pigments in petals of various Asteraceae species. They catalyze the oxidative conversion of chalcones into aurones. Latent (58.9 kDa) and active (41.6 kDa) aurone synthase from petals of C. grandiflora was purified by a quantitative removal of pigments using aqueous two-phase separation and several subsequent chromatographic steps. The purified enzymes were identified as cgAUS1 (A0A075DN54) and sequence analysis revealed that cgAUS1 is a member of a new group of plant PPOs. Mass determination experiments of intact cgAUS1 gave evidence that the C-terminal domain, usually shielding the active site of latent polyphenol oxidases, is linked to the main core by a disulfide bond. This is a novel and unique structural feature of plant PPOs. Proteolytic activation in vivo leads to active aurone synthase possessing a residual peptide of the C-terminal domain. Kinetic characterization of purified cgAUS1 strongly suggests a specific involvement in 4-deoxyaurone biosynthesis in Coreopsis grandiflora (Asteraceae) that differs in various aspects compared to the 4-hydroxyaurone formation in Antirrhinum majus (Plantaginaceae): cgAUS1 is predicted to be localized in the thylakoid lumen, it possesses exclusively diphenolase activity and the results suggest that aurone formation occurs at the level of chalcone aglycones. The latent enzyme exhibits allosteric activation which changes at a specific product concentration to a constant reaction rate. The presented novel structural and functional properties of aurone synthase provide further insights in the diversity and role of plant PPOs.

Cellobiose dehydrogenase functionalized urinary catheter as novel antibiofilm system

Urinary catheters expose patients to a high risk of acquiring nosocomial infections. To prevent this risk of infection, cellobiose dehydrogenase (CDH), an antimicrobial enzyme able to use various oligosaccharides as electron donors to produce hydrogen peroxide using oxygen as an electron acceptor, was covalently grafted onto plasma-activated urinary polydimethylsiloxane (PDMS) catheter surfaces. Successful immobilization of CDH on PDMS was confirmed by Fourier transformed-infrared spectrometry and production of H2 O2 . The CDH functionalized PDMS surfaces reduced the amount of viable Staphylococcus aureus by 60%, total biomass deposited on the surface by 30% and 70% of biofilm formation. The immobilized CDH was relatively stable in artificial urine over 16 days, retaining 20% of its initial activity. The CDH coated PDMS surface did not affect the growth and physiology of HEK 239 and RAW 264,7 mammalian cells. Therefore this new CDH functionalized catheter system shows great potential for solving the current problems associated with urinary catheters. © 2015 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 104B: 1448-1456, 2016.