Site-Selective Oxidative Coupling Reactions for the Attachment of Enzymes to Glass Surfaces through DNA-Directed Immobilization

Artificial antibody-antigen-directed immobilization of lipase for consecutive catalytic synthesis of ester: Benzyl acetate case study

A strategy based on artificial antibody-antigen recognition was proposed for the specific directed immobilization of lipase. The artificial antibody was synthesized using catechol as a template, α-methacrylic acid as a functional monomer, and Fe3O4 as the matrix material. Lipase was modified with 3,4-dihydroxybenzaldehyde as an artificial antigen. The artificial antibody can specifically recognize catechol fragment in the enzyme structure to achieve the immobilization of lipase. The immobilization amount, yield, specific activity, and immobilized enzyme activity were 13.2 ± 0.2 mg/g, 78.9 ± 0.4 %, 7.9 ± 0.2 U/mgprotein, and 104.6 ± 1.7 U/gcarrier, respectively. Moreover, the immobilized lipase exhibited strong reusability and regeneration ability. Additionally, the immobilized lipase successfully catalyzed the synthesis of benzyl acetate and demonstrated robust continuous catalytic activity. These results fully demonstrate the feasibility of the proposed artificial antibody-antigen-directed immobilization of lipase.

Highly Efficient Carbon Dioxide Electroreduction via DNA-Directed Catalyst Immobilization

Electrochemical reduction of carbon dioxide (CO2) is a promising route to up-convert this industrial byproduct. However, to perform this reaction with a small-molecule catalyst, the catalyst must be proximal to an electrode surface. Efforts to immobilize molecular catalysts on electrodes have been stymied by the need to optimize the immobilization chemistries on a case-by-case basis. Taking inspiration from nature, we applied DNA as a molecular-scale "Velcro" to investigate the tethering of three porphyrin-based catalysts to electrodes. This tethering strategy improved both the stability of the catalysts and their Faradaic efficiencies (FEs). DNA-catalyst conjugates were immobilized on screen-printed carbon and carbon paper electrodes via DNA hybridization with nearly 100% efficiency. Following immobilization, a higher catalyst stability at relevant potentials is observed. Additionally, lower overpotentials are required for the generation of carbon monoxide (CO). Finally, high FE for CO generation was observed with the DNA-immobilized catalysts as compared to the unmodified small-molecule systems, as high as 79.1% FE for CO at -0.95 V vs SHE using a DNA-tethered catalyst. This work demonstrates the potential of DNA "Velcro" as a powerful strategy for catalyst immobilization. Here, we demonstrated improved catalytic characteristics of molecular catalysts for CO2 valorization, but this strategy is anticipated to be generalizable to any reaction that proceeds in aqueous solutions.

Strategies to improve the mass transfer in the CO2 capture process using immobilized carbonic anhydrase

High carbon dioxide (CO₂) concentration in the atmosphere urgently requires eco-friendly mitigation strategies. Carbonic anhydrase (CA) is a high-quality enzyme protein, available from a wide range of sources, which has an extremely high catalytic efficiency for the hydration of CO₂ compared with other catalytic CO₂ conversion systems. While free CA is costly and weakly stable, CA immobilization can significantly improve its stability and allow enzyme recycling. However, gaseous CO₂ is significantly different from traditional liquid substrates. Additionally, due to the presence of enzyme carriers, there is limited mass transfer between CO₂ and the active center of immobilized CA. Most of the available reviews provide an overview of the improvement in catalytic activity and stability of CA by different immobilization methods and substrates. However, they do not address the limited mass transfer between CO₂ and the active center of immobilized CA. Therefore, by focusing on the mass transfer process, this review presents CA immobilization strategies that are more efficient and of greater environmental tolerance by categorizing the methods of enhancing the mass transfer process at each stage of the enzymatic CO₂ capture reaction. Such improvements in this green and environmentally friendly biological carbon capture process can increase its efficiency for industrial applications.

Controllable Enzyme Immobilization via Simple and Quantitative Adsorption of Dendronized Polymer-Enzyme Conjugates Inside a Silica Monolith for Enzymatic Flow-Through Reactor Applications

Although many different methods are known for the immobilization of enzymes on solid supports for use in flow-through applications as enzyme reactors, the reproducible immobilization of predetermined amounts of catalytically active enzyme molecules remains challenging. This challenge was tackled using a macro- and mesoporous silica monolith as a support and dendronized polymer-enzyme conjugates. The conjugates were first prepared in an aqueous solution by covalently linking enzyme molecules and either horseradish peroxidase (HRP) or bovine carbonic anhydrase (BCA) along the chains of a water-soluble second-generation dendronized polymer using an established procedure. The obtained conjugates are stable biohybrid structures in which the linking unit between the dendronized polymer and each enzyme molecule is a bisaryl hydrazone (BAH) bond. Quantitative and reproducible enzyme immobilization inside the monolith is possible by simply adding a defined volume of a conjugate solution of a defined enzyme concentration to a dry monolith piece of the desired size. In that way, (i) the entire volume of the conjugate solution is taken up by the monolith piece due to capillary forces and (ii) all conjugates of the added conjugate solution remain stably adsorbed (immobilized) noncovalently without detectable leakage from the monolith piece. The observed flow-through activity of the resulting enzyme reactors was directly proportional to the amount of conjugate used for the reactor preparation. With conjugate solutions consisting of defined amounts of both types of conjugates, the controlled coimmobilization of the two enzymes, namely, BCA and HRP, was shown to be possible in a simple way. Different stability tests of the enzyme reactors were carried out. Finally, the enzyme reactors were applied to the catalysis of a two-enzyme cascade reaction in two types of enzymatic flow-through reactor systems with either coimmobilized or sequentially immobilized BCA and HRP. Depending on the composition of the substrate solution that was pumped through the two types of enzyme reactor systems, the coimmobilized enzymes performed significantly better than the sequentially immobilized ones. This difference, however, is not due to a molecular proximity effect with regard to the enzymes but rather originates from the kinetic features of the cascade reaction used. Overall, the method developed for the controllable and reproducible immobilization of enzymes in the macro- and mesoporous silica monolith offers many possibilities for systematic investigations of immobilized enzymes in enzymatic flow-through reactors, potentially for any type of enzyme.

Design of composite nanosupports and applications thereof in enzyme immobilization: A review

Enzyme immobilization techniques have developed dramatically over the past several decades. Support materials are key in shaping the function of a specific immobilized enzyme. Although they have large specific surface areas and functional active sites, single-component nanomaterials and their surface chemical modification derivatives struggle to meet increasing demand. Thus, composite materials, compounds of two or more materials, have been developed and applied in efficient immobilization through advances in materials science. More methods have been developed and employed to design composite nanomaterials in recent years. These novel composite nanomaterials often show superior physical, chemical, and biological performance as supports in enzyme immobilization, among other applications. In this review, immobilization techniques and their supports are stated first and methods to design and fabricate composite nanomaterials as nanosupports are also shown in the following section. Applications of composite nanosupports in laccase immobilization are discussed as models in the later sections of the paper. This review is intended to help readers gain insight into the design principles of composite nanomaterials for immobilization supports.

Two-point immobilization of a conformation-specific beta2-adrenoceptor for recognizing the receptor agonists or antagonists inspired by binding-induced DNA assembly

Immobilized protein has advanced in many areas like drug discovery. While this field evolved rapidly over the last three decades, the immobilization platform for the G-protein-coupled receptor (GPCR) remains unpromising due to its instability under the relatively harsh conditions of current methodologies. Taking beta₂-adrenoceptor (β₂-AR) as an example, we presented here a general strategy for immobilization of GPCRs by combining the His₆-tag trap system, conformation-specific aptamer, and target binding induced DNA hybridization. Morphology characterization by diverse assays confirmed a monolayer of β₂-AR on the microsphere surface. The radio-ligand binding assay and immuno-transmission electron microscopy showed desirable ligand- and antibody-binding activities. A case study of chromatography using the immobilized receptor as a stationary phase exhibited a demonstrable conformation specificity that enables the selective recognition of the receptor agonists or antagonists. Owing to the competitive strand displacement during the immobilization, the method proved to be capable of sensitively and directly determining the receptor density on the surface which enormously challenges most of the reported assays. This method is possible to turn into a general strategy for the immobilization of GPCRs with a defined orientation, conformation, function, and density, thus paving the way for precisely realizing the receptor-ligand binding interaction and screening the receptor agonist or antagonist with high efficiency.

Enzyme Activated Gold Nanoparticles for Versatile Site-Selective Bioconjugation

A new enzymatic method is reported for constructing protein- and DNA-AuNP conjugates. The strategy relies on the initial functionalization of AuNPs with phenols, followed by activation with the enzyme tyrosinase. Using an oxidative coupling reaction, the activated phenols are coupled to proteins bearing proline, thiol, or aniline functional groups. Activated phenol-AuNPs are also conjugated to a small molecule biotin and commercially available thiol-DNA. Advantages of this approach for AuNP bioconjugation include: (1) initial formation of highly stable AuNPs that can be selectively activated with an enzyme, (2) the ability to conjugate either proteins or DNA through a diverse set of functional handles, (3) site-specific immobilization, and (4) facile conjugation that is complete within 2 h at room temperature under aqueous conditions. The enzymatic oxidative coupling on AuNPs is applied to the construction of tobacco mosaic virus (TMV)-AuNP conjugates, and energy transfer between the AuNPs and fluorophores on TMV is demonstrated.

Probing Interactions between Metal-Organic Frameworks and Freestanding Enzymes in a Hollow Structure

It has been reported that the biological functions of enzymes could be altered when they are encapsulated in metal-organic frameworks (MOFs) due to the interactions between them. Herein, we probed the interactions of catalase in solid and hollow ZIF-8 microcrystals. The solid sample with confined catalase is prepared through a reported method, and the hollow sample is generated by hollowing the MOF crystals, sealing freestanding enzymes in the central cavities of hollow ZIF-8. During the hollowing process, the samples were monitored by small-angle X-ray scattering (SAXS) spectroscopy, electron microscopy, powder X-ray diffraction (PXRD), and nitrogen sorption. The interfacial interactions of the two samples were studied by infrared (IR) and fluorescence spectroscopy. IR study shows that freestanding catalase has less chemical interaction with ZIF-8 than confined catalase, and a fluorescence study indicates that the freestanding catalase has lower structural confinement. We have then carried out the hydrogen peroxide degradation activities of catalase at different stages and revealed that the freestanding catalase in hollow ZIF-8 has higher activity.

Fast surface immobilization of native proteins through catalyst-free amino-yne click bioconjugation

Surface immobilization provides a useful platform for biosensing, drug screening, tissue engineering and other chemical and biological applications. However, some of the used reactions are inefficient and/or complicated, limiting their applications in immobilization. Herein, we use a spontaneous and catalyst-free amino-yne click bioconjugation to generate activated ethynyl group functionalized surfaces for fast immobilization of native proteins and cells. Biomolecules, such as bovine serum albumin (BSA), human IgG and a peptide of C(RGDfK), could be covalently immobilized on the surfaces in as short as 30 min. Notably, the bioactivity of the anchored biomolecules remains intact, which is verified by efficiently capturing target antibodies and cells from the bulk solutions. This strategy represents an alternative for highly efficient surface biofunctionalization.

Metal-Organic Framework in Situ Post-Encapsulating DNA-Enzyme Composites on a Magnetic Carrier with High Stability and Reusability

In recent years, metal-organic frameworks (MOFs) have been extensively studied as candidate enzyme immobilization platforms. However, conventional MOF-enzyme composites usually exhibit low controllability and reusability. In this study, a novel and stable strategy for enzyme immobilization was designed by use of ZIF-8 to encapsulate in situ DNA-enzyme composites on the surface of magnetic particles (MPs). The mechanism of in situ encapsulation was discussed in detail. It was found that immobilized enzymes were involved in the growth of ZIF-8, and the DNA cross-linking agents promoted the growth of ZIF-8 on the surface of MP. The thermal, chemical, and physical stabilities of horseradish peroxidase (HRP) were all significantly enhanced after in situ encapsulation. Most importantly, this strategy was proven to be a general platform that can be used to stabilize various proteins. The in situ encapsulation strategy was expanded to immobilize a cascade of enzymes, and ZIF-8@MP_GOx-HRP possessed high selectivity and a wide linear range (25-500 μM) for glucose detection.

From DNA Nanotechnology to Material Systems Engineering

In the past 35 years, DNA nanotechnology has grown to a highly innovative and vibrant field of research at the interface of chemistry, materials science, biotechnology, and nanotechnology. Herein, a short summary of the state of research in various subdisciplines of DNA nanotechnology, ranging from pure "structural DNA nanotechnology" over protein-DNA assemblies, nanoparticle-based DNA materials, and DNA polymers to DNA surface technology is given. The survey shows that these subdisciplines are growing ever closer together and suggests that this integration is essential in order to initiate the next phase of development. With the increasing implementation of machine-based approaches in microfluidics, robotics, and data-driven science, DNA-material systems will emerge that could be suitable for applications in sensor technology, photonics, as interfaces between technical systems and living organisms, or for biomimetic fabrication processes.

Stable Immobilization of Enzymes in a Macro- and Mesoporous Silica Monolith

Horseradish peroxidase isoenzyme C (HRP) and Engyodontium album proteinase K (proK) were immobilized inside macro- and mesoporous silica monoliths. Stable immobilization was achieved through simple noncovalent adsorption of conjugates, which were prepared from a polycationic, water-soluble second generation dendronized polymer (denpol) and the enzymes. Conjugates prepared from three denpols with the same type of repeating unit (r.u.), but different average lengths were compared. It was shown that there is no obvious advantage of using denpols with very long chains. Excellent results were achieved with denpols having on average 750 or 1000 r.u. The enzyme-loaded monoliths were tested as flow reactors. Comparison was made with microscopy glass coverslips onto which the conjugates were immobilized and with glass micropipettes containing adsorbed conjugates. High enzyme loading was achieved using the monoliths. Monoliths containing immobilized denpol-HRP conjugates exhibited good operational stability at 25 °C (for at least several hours), and good storage stability at 4 °C (at least for weeks) was demonstrated. Such HRP-containing monoliths were applied as continuous flow reactors for the quantitative determination of hydrogen peroxide in aqueous solution between 1 μM (34 ng/mL) and 50 μM (1.7 μg/mL). Although many methods for immobilizing enzymes on silica surfaces exist, there are only a few approaches with porous silica materials for the development of flow reactors. The work presented is a promising contribution to this field of research toward bioanalytical and biosynthetic applications.

Advancing the Frontiers of Chemical Protein Synthesis-The 7th CPS Meeting, Haifa, Israel

The 7^th Chemical Protein Synthesis Meeting took place in September 2017 in Haifa, Israel, bringing together 100 scientists from 11 countries. The cutting-edge scientific program included new synthetic strategies and ligation auxiliaries, novel insights into protein signaling and post-translational modifications, and a range of promising therapeutic applications.

Photoactivatable Reaction for Covalent Nanoscale Patterning of Multiple Proteins

This article describes a photochemical approach for independently patterning multiple proteins to an inert substrate, particularly for studies of cell adhesion. A photoactivatable chloropyrimidine ligand was employed for covalent immobilization of SnapTag fusion proteins on self-assembled monolayers of alkanethiolates on gold. A two-step procedure was used: first, patterned UV illumination of the surface activated protein capture ligands, and second, incubation with a SnapTag fusion protein bound to the surface in illuminated regions. Two different fluorescent proteins were patterned in registry with features of 400 nm in size over a 1 mm2 area. An example is given wherein an anti-carcinoembryonic antigen (anti-CEA) scFv antibody was patterned to direct the selective attachment of a human cancer cell line that express the CEA antigen. This method enables the preparation of surfaces with control over the density and activity of independently patterned proteins.

Facile immobilization of DNA using an enzymatic his-tag mimic

Methods for immobilization of DNA on solid supports are in high demand. Herein, we present a generally applicable enzymatic method for the immobilization of DNA without any prior chemical derivatization. This strategy relies on the homopolymerization of the modified triphosphate dImTP by the TdT. The resulting enzymatic his-tag mimic ensures binding of DNA on Ni-NTA agarose. The usefulness of this method is highlighted by the immobilization of functional nucleic acids without impairing their specific activities.

Wafer-scale bioactive substrate patterning by chemical lift-off lithography

The creation of bioactive substrates requires an appropriate interface molecular environment control and adequate biological species recognition with minimum nonspecific attachment. Herein, a straightforward approach utilizing chemical lift-off lithography to create a diluted self-assembled monolayer matrix for anchoring diverse biological probes is introduced. The strategy encompasses convenient operation, well-tunable pattern feature and size, large-area fabrication, high resolution and fidelity control, and the ability to functionalize versatile bioarrays. With the interface-contact-induced reaction, a preformed alkanethiol self-assembled monolayer on a Au surface is ruptured and a unique defect-rich diluted matrix is created. This post lift-off region is found to be suitable for insertion of a variety of biological probes, which allows for the creation of different types of bioactive substrates. Depending on the modifications to the experimental conditions, the processes of direct probe insertion, molecular structure change-required recognition, and bulky biological species binding are all accomplished with minimum nonspecific adhesion. Furthermore, multiplexed arrays via the integration of microfluidics are also achieved, which enables diverse applications of as-prepared substrates. By embracing the properties of well-tunable pattern feature dimension and geometry, great local molecular environment control, and wafer-scale fabrication characteristics, this chemical lift-off process has advanced conventional bioactive substrate fabrication into a more convenient route.

Surface functional DNA density control by programmable molecular defects

Spatially programmable molecular-level defects via straightforward chemical lift-off manipulation leads to the direct regulation of complex surface DNA densities.

ortho-Quinones and Analogues Thereof: Highly Reactive Intermediates for Fast and Selective Biofunctionalization

Fast, selective and facile functionalization of biologically relevant molecules is a pursuit of ever‐growing importance. A promising approach in this regard employs the high reactivity of quinone and quinone analogues for fast conjugation chemistry by nucleophilic addition or cycloadditions. Combined with in situ generation of these compounds, selective conjugation on proteins and surfaces can be uniquely induced in a time and spatially resolved manner: generation of a quinone can often be achieved by simple addition of an enzyme or stoichiometric amounts of chemoselective oxidant, or by exposure to light. In this Minireview, we discuss the generation and subsequent functionalization of quinones, iminoquinones, and quinone methides. We also discuss practical applications regarding these conjugation strategies.

Facile Oriented Immobilization of Histidine-Tagged Proteins on Nonfouling Cobalt Polyphenolic Self-Assembly Surfaces

In this study, a completely green and facile protocol to oriented immobilization of histidine-tagged (His-tagged) proteins based on plant polyphenolic tannic acid (TA) is described. This is the first time that TA has been applied as ionic chelators to immobilize His-tagged proteins. To reduce the nonspecific interactions between the TA and immobilized proteins, we assembled nonfouling zwitterionic poly(sulfobetaine methacrylate) (PSBMA) on the TA surface. The use of PSBMA could maintain the high activity of the His-tagged proteins and inhibit the adsorption of untagged protein to the TA surface. Subsequently, the obtained TA/PSBMA film was further chelated with Co^II for specific binding to a His-tagged protein. As Co^III is more stable and inert than Co^II, the chelated Co^II was oxidized to Co^III. Using this approach, His-tagged Chitinase was anchored to TA/PSBMA/Co^III film as a catalyst for the hydrolysis of chitin. The loading capacity of the film for the His-tagged Chitinase can reach ∼4.0 μg/cm². Moreover, the oriented immobilized Chitinase had high catalytic activity and excellent thermal and storage stability as well as being more resistant to proteolytic digestion by papain. This low-cost and green protein-oriented immobilization strategy may serve as a versatile platform for a range of applications, such as biomaterials, biocatalysis, sensors, drug delivery, and so on.

A Nanostructured Microfluidic Immunoassay Platform for Highly Sensitive Infectious Pathogen Detection

Rapid and simultaneous detection of multiple potential pathogens by portable devices can facilitate early diagnosis of infectious diseases, and allow for rapid and effective implementation of disease prevention and treatment measures. The development of a ZnO nanorod integrated microdevice as a multiplex immunofluorescence platform for highly sensitive and selective detection of avian influenza virus (AIV) is described. The 3D morphology and unique optical property of the ZnO nanorods boost the detection limit of the H5N2 AIV to as low as 3.6 × 103 EID50 mL-1 (EID50 : 50% embryo infectious dose), which is ≈22 times more sensitive than conventional enzyme-linked immunosorbent assay. The entire virus capture and detection process could be completed within 1.5 h with excellent selectivity. Moreover, this microfluidic biosensor is capable of detecting multiple viruses simultaneously by spatial encoding of capture antibodies. One prominent feature of the device is that the captured H5N2 AIV can be released by simply dissolving ZnO nanorods under slightly acidic environment for subsequent off-chip analyses. As a whole, this platform provides a powerful tool for rapid detection of multiple pathogens, which may extent to the other fields for low-cost and convenient biomarker detection.