Single Enzyme Nanoparticles with Improved Biocatalytic Activity through Protein Entrapment in a Surfactant Shell

Electrostatically Mediated In Situ Polymerization for Enzyme Immobilization and Activation

Enzyme immobilization in nanoparticles is of interest for boosting their catalytic applications, yet rational approaches to designs achieving both high enzyme loading and activation remain a challenge. Herein, we report an electrostatically mediated in situ polymerization strategy that simultaneously realizes enzyme immobilization and activation. This was achieved by copolymerizing cationic monomers with a cross-linker in the presence of the enzyme lipase (anionic) as the template, which produces enzyme-loaded nanogels. The effects of different control factors such as pH, lipase dosage, and cross-linker fraction on nanogel formation are investigated systematically, and optimal conditions for enzyme loading and activation have been determined. A central finding is that the cationic polymer network of the nanogel creates a favorable environment that not only protects the enzyme but also boosts enzymatic activity nearly 2-fold as compared to free lipase. The nanogels improve the stability of the lipase to tolerate a broader working range of pH (5.5-8.5) and temperature (25-70 °C) and allow recycling such that after six cycles of reaction, 70% of the initial activity is conserved. The established fabrication strategy can be applied generally to different cationic monomers, and most of these nanogels exhibit adequate immobilization and activation of lipase. Our study confirms that in situ polymerization based on electrostatic interaction provides a facile and robust strategy for enzyme immobilization and activation. The wide variety of ionic monomers, therefore, features great potential for developing functional platforms toward satisfying enzyme immobilization and demanding applications.

Tuning of Cationic Polymer Functionality in Complex Coacervate Artificial Cells for Optimized Enzyme Activity

Complex coacervates are a versatile platform to mimic the structure of living cells. In both living systems and artificial cells, a macromolecularly crowded condensate phase has been shown to be able to modulate enzyme activity. Yet, how enzyme activity is affected by interactions (particularly with cationic charges) inside coacervates is not well studied. Here, we synthesized a series of amino-functional polymers to investigate the effect of the type of amine and charge density on coacervate formation, stability, protein partitioning, and enzyme function. The polymers were prepared by RAFT polymerization using as monomers aminoethyl methacrylate (AEAM), 2-(dimethylamino)ethyl methacrylate (DMAEMA), imidazolepropyl methacrylamide (IPMAm), and [2-(methacryloyloxy)ethyl] trimethylammonium chloride (TMAEMA). Membranized complex coacervate artificial cells were formed with these polycations and an anionic amylose derivative. Results show that polycations with reduced charge density result in higher protein mobility in the condensates and also higher enzyme activity. Insights described here could help guide the use of coacervate artificial cells in applications such as sensing, catalysis, and therapeutic formulations.

Co-assembly-mediated biosupramolecular catalysis: thermodynamic insights into nucleobase specific (oligo)nucleotide attachment and cleavage

Gaining control over the stability and cleavage of phosphoester and phosphodiester remains a matter of interest for their application in biotechnology to oligonucleotide-based therapeutics. Herein, we report an efficient unactivated phosphoester hydrolysis (stable mono/di/tri/cyclic nucleotide to nucleoside conversion) via a biosupramolecular system comprising of a non-covalent complex of enzyme, alkaline phosphatase (ALP), and Zn(II)-metallosurfactant. We also demonstrate the nucleobase selective activation or inhibition of ALP-mediated oligonucleotide digestion process using that complex. The higher binding affinity of Zn(II)-containing headgroup with phosphate-containing substrate enhanced the effective substrate concentration surrounding the enzyme, which, in turn, results in a drastic decrease in the Michaelis constant (KM), along with an increase in the turnover (kcat). The catalytic activation or inhibition of nucleobase-specific oligonucleotide digestion depends on the hydration, localization of the substrates, and viscosity of the resultant co-assembly upon substrate binding with the enzyme-metallosurfactant complex. Additionally, through isothermal titration calorimetry experiment, we demonstrate enthalpy-entropy change during both the supramolecular binding of (oligo)nucleotides and simultaneous activation/inhibition in catalytic cleavage. Overall, it showed the possible modularity of Zn(II)-mediated biosupramolecular interaction, describing intrinsic thermodynamic aspects in developing complex biocatalytic circuits with nucleobase-specific oligonucleotides inputs, which are relevant in designing nucleic acid-based cargo for drug delivery and bioimaging.

Improving Bond Performance and Reducing Cross-Linker Dosage of Soy Protein Adhesive via Hyper-Branched and Organic-Inorganic Hybrid Structures

Eco-friendly soybean protein adhesives could be an ideal substitute for replacing traditional formaldehyde-based adhesives in wood industry. However, a large number of cross-linking agents are required in soy protein adhesive formulations to obtain sufficiently performing properties. Inspired by the high performance of nacre and branched structures, a hyper-branched amine (HBPA) was synthesized and grafted to graphene oxide (GO), generating a hyper-branched amine-functionalized GO (FGO). A novel soy protein-based adhesive was developed by mixing FGO with soy protein (SPI) and a low dose polyamidoamine-epichlorohydrin (PAE). Results showed that the addition of only 0.4 wt% FGO and 0.75 wt% PAE to the SPI adhesive formulation enhanced the wet shear strength of plywood to 1.18 MPa, which was 181% higher than that of the adhesive without enhancement. The enhanced performance is attributed to the denser cross-linking structure and improved toughness of the adhesive layer. Using FGO in the adhesive formulation also greatly reduced the concentration of the additive cross-linker by up to 78.6% when compared with values reported in the literature. Thus, using a hyper-branched functionalized nano-material to form an organic-inorganic hybrid structure is an effective and efficient strategy to reinforce the composites and polymers. It significantly reduces the chemical additive levels, and is a practical way to develop a sustainable product.

Photoenzymatic Activity of Artificial-Natural Bienzyme Applied in Biodegradation of Methylene Blue and Accelerating Polymerization of Dopamine

Enzymes as biocatalysts have attracted extensive attention. In addition to immobilizing or encapsulating various enzymes for combating the easy loss of enzymatic activity, strengthening the enzymatic activity upon light irradiation is a challenge. To the best of our knowledge, the work of spatiotemporally modulating the catalytic activity of artificial-natural bienzymes with a near-infrared light irradiation has not been reported. Inspired by immobilized enzymes and nanozymes, herein a platinum nanozyme was synthesized; subsequently, the platinum nanozyme was grafted on the body of laccase, thus successfully obtaining the artificial-natural bienzyme. The three-dimensional structure of the artificial-natural bienzyme was greatly different from that of the immobilized enzyme or the encapsulated enzyme. The platinum nanozyme possessed excellent laccase-like activity, which was 3.7 times higher than that of laccase. Meanwhile, the coordination between the platinum nanozyme and laccase was proved. Besides, the cascaded catalysis of artificial-natural bienzyme was verified with hydrogen peroxide as a mediator. The enzymatic activities of artificial-natural bienzyme with and without near-infrared light irradiation were, respectively, 46.2 and 29.5% higher than that of free laccase. Moreover, the reversible catalytic activity of the coupled enzyme could be manipulated with and without a near-infrared light at 808 nm. As a result, the degradation rates of methylene blue catalyzed by the coupled enzyme and the platinum nanozyme were higher than that of laccase. Furthermore, accelerating polymerization of the dopamine was also demonstrated. Briefly, this facile strategy may provide a universal approach to control the catalytic activity of other natural enzymes.

Tween® Preserves Enzyme Activity and Stability in PLGA Nanoparticles

Enzymes, as natural and potentially long-term treatment options, have become one of the most sought-after pharmaceutical molecules to be delivered with nanoparticles (NPs); however, their instability during formulation often leads to underwhelming results. Various molecules, including the Tween^® polysorbate series, have demonstrated enzyme activity protection but are often used uncontrolled without optimization. Here, poly(lactic-co-glycolic) acid (PLGA) NPs loaded with β-glucosidase (β-Glu) solutions containing Tween^® 20, 60, or 80 were compared. Mixing the enzyme with Tween^® pre-formulation had no effect on particle size or physical characteristics, but increased the amount of enzyme loaded. More importantly, NPs made with Tween^® 20:enzyme solutions maintained significantly higher enzyme activity. Therefore, Tween^® 20:enzyme solutions ranging from 60:1 to 2419:1 mol:mol were further analyzed. Isothermal titration calorimetry analysis demonstrated low affinity and unquantifiable binding between Tween^® 20 and β-Glu. Incorporating these solutions in NPs showed no effect on size, zeta potential, or morphology. The amount of enzyme and Tween^® 20 in the NPs was constant for all samples, but a trend towards higher activity with higher molar rapports of Tween^® 20:β-Glu was observed. Finally, a burst release from NPs in the first hour with Tween^®:β-Glu solutions was the same as free enzyme, but the enzyme remained active longer in solution. These results highlight the importance of stabilizers during NP formulation and how optimizing their use to stabilize an enzyme can help researchers design more efficient and effective enzyme loaded NPs.