An updated view on horseradish peroxidases: recombinant production and biotechnological applications

A Cost-Effective Hemin-Based Artificial Enzyme Allows for Practical Applications

Nanomaterials excel in mimicking the structure and function of natural enzymes while being far more interesting in terms of structural stability, functional versatility, recyclability, and large-scale preparation. Herein, the story assembles hemin, histidine analogs, and G-quadruplex DNA in a catalytically competent supramolecular assembly referred to as assembly-activated hemin enzyme (AA-heminzyme). The catalytic properties of AA-heminzyme are investigated both in silico (by molecular docking and quantum chemical calculations) and in vitro (notably through a systematic comparison with its natural counterpart horseradish peroxidase, HRP). It is found that this artificial system is not only as efficient as HRP to oxidize various substrates (with a turnover number kcat of 115 s-1) but also more practically convenient (displaying better thermal stability, recoverability, and editability) and more economically viable, with a catalytic cost amounting to <10% of that of HRP. The strategic interest of AA-heminzyme is further demonstrated for both industrial wastewater remediation and biomarker detection (notably glutathione, for which the cost is decreased by 98% as compared to commercial kits).

Dual-Mode Virus Detection: Combining Electrochemical and Fluorescence Modalities for Enhanced Sensitivity and Reliability

This study introduces a dual-mode biosensor specifically designed for the quantitative detection of viruses in rapid analysis. The biosensor is unique in its use of both optical (fluorescence) and electrochemical (impedance) detection methods using the same nanocomposites, providing a dual confirmation system for virus (norovirus-like particles) quantification. The system is based on using two antibody-conjugated nanocomposites: CdSeS quantum dots and Au-N,S-GQD nanocomposites. For optical detection, the principle relies on the fluorescence quenching of CdSeS by Au-N,S-GQD in a sandwich structure with the target. Conversely, electrochemical detection is based on the change in impedance caused by the formation of the same sandwich structure. The biosensor demonstrated exceptional sensitivity, capable of detecting norovirus at concentrations of as low as femtomolar in the electrochemical method and picomolar in the optical method. In the dual-responsive concentration range from 10-13 to 10-10 M, the sensor is highly sensitive in both methods, creating significant changes in fluorescence intensity and impedance in the presence of virus. Furthermore, the biosensor exhibits a high degree of specificity, with a negligible response to nontarget proteins, even within complex test solutions. This work represents a significant advancement in the field of biosensor technology, offering a fast, accurate, and reliable method for diagnosing viral infections and diseases.

Immobilization of Thiol-Modified Horseradish Peroxidase on Gold Nanoparticles Enhances Enzyme Stability and Prevents Proteolytic Digestion

The specificity and efficiency of enzyme-mediated reactions have the potential to positively impact many biotechnologies; however, many enzymes are easily degraded. Immobilization on a solid support has recently been explored to improve enzyme stability. This study aims to gain insights and facilitate enzyme adsorption onto gold nanoparticles (AuNPs) to form a stable bioconjugate through the installation of thiol functional groups that alter the protein chemistry. In specific, the model enzyme, horseradish peroxidase (HRP), is thiolated via Traut's reagent to increase the robustness and enzymatic activity of the bioconjugate. This study compares HRP and its thiolated analog (THRP) to deduce the impact of thiolation and AuNP-immobilization on the enzyme activity and stability. HRP, THRP, and their corresponding bioconjugates, HRP-AuNP and THRP-AuNP, were analyzed via UV-vis spectrophotometry, circular dichroism, zeta potential, and enzyme-substrate kinetics assays. Our data show a 5-fold greater adsorption for THRP on the AuNP, in comparison to HRP, that translated to a 5-fold increase in the THRP-AuNP bioconjugate activity. The thiolated and immobilized HRP exhibited a substantial improvement in stability at elevated temperatures (50 °C) and storage times (1 month) relative to the native enzyme in solution. Moreover, HRP, THRP, and their bioconjugates were incubated with trypsin to assess the susceptibility to proteolytic digestion. Our results demonstrate that THRP-AuNP bioconjugates maintain full enzymatic activity after 18 h of incubation with trypsin, whereas free HRP, free THRP, and HRP-AuNP conjugates are rendered inactive by trypsin treatment. These results highlight the potential for protein modification and immobilization to substantially extend enzyme shelf life, resist protease digestion, and enhance biological function to realize enzyme-enabled biotechnologies.

Immobilized enzymatic membrane surfaces for biocatalytic organics removal and fouling resistance

This research reported on the immobilization of environmentally friendly enzymes, such as horseradish peroxidase (HRP) and laccase (L), along with the hydrophilic zwitterionic compound l-DOPA on nano-filtration (NF) membranes. This approach introduced biocatalytic membranes, leveraging combined effects between membranes and enzymes. The aim was to systematically assess the efficacy of the enzymatic modified membrane (HRP-NF) in degrading colors in the wastewater, as well as enhancing the membrane resistance toward organic fouling. The enzymatic immobilized membrane demonstrated 96.3 ± 1.8% to 96.6 ± 1.9% removal of colors, and 65.2 ± 1.3% to 67.2 ± 1.3% removal of TOC. This result was underpinned by the insights obtained from the radical scavenger coumarin, which was employed to trap and confirm the formation of PRs through the reaction of enzymes and H2O2. Furthermore, membranes modified with enzymes exhibited significantly improved antifouling properties. The HRP-NF membrane experienced an 8% decline in flux, while the co-immobilized HRP-L-NF membrane demonstrated as low as 6% flux decline, contributed by the synergistic effect of increased hydrophilicity and biocatalytic effects. These findings confirmed that the immobilized enzymatic surface has added function of degrading contaminants in addition to separation function of nanofiltration membrane. These l-DOPA-immobilized enzymatic membranes offered a promising hybrid biocatalytic membrane to eliminate dyes and mitigate membrane fouling, which can be applied in many industrial and domestic water and wastewater treatment.

Nanolevel of detection of ascorbic acid using horse-radish peroxidase inhibition assay

Ascorbic acid plays a significant role in regulation of various bodily functions with high concentrations in immune cells and being involved in connective tissue maintenance. Commonly it is detected through various colorimetric methods. In this study, we propose a one-step simple method based on the inhibitory activity of ascorbic acid on horseradish peroxidase and hydrogen peroxide. The detection is observed by colorimetric changes to TMB (3,3',5,5' tetramethylbenzidine). The enzyme inhibition unit was optimized with a high level of linearity (r2 = 0.9999) and the level of detection and level of quantification were found to be 1.35 nM and 4.08 nM, respectively with higher sensitive compared to the HPLC method (11 μM). Both intra and inter-assays showed high correlations at different AA concentrations. (r2 > 0.9999). Similar results were also observed for vitamin C tablets, ascorbate salts, fruits, and market products (r2 = 0.999). There was negligible effect of interference by citric acid, lactic acid, tartaric acids, and glucose with high recoveries (>98%) at 1 mg/mL to 0.0078 mg/mL concentration ranges. The recovery error (RE%) was found to be less than 10%. Our detection method is distinguished by its simplicity, nano-level of detection, reproducibility, and potential application and adaptability as a point-of-use test.

Smart responsive in situ hydrogel systems applied in bone tissue engineering

The repair of irregular bone tissue suffers severe clinical problems due to the scarcity of an appropriate therapeutic carrier that can match dynamic and complex bone damage. Fortunately, stimuli-responsive in situ hydrogel systems that are triggered by a special microenvironment could be an ideal method of regenerating bone tissue because of the injectability, in situ gelatin, and spatiotemporally tunable drug release. Herein, we introduce the two main stimulus-response approaches, exogenous and endogenous, to forming in situ hydrogels in bone tissue engineering. First, we summarize specific and distinct responses to an extensive range of external stimuli (e.g., ultraviolet, near-infrared, ultrasound, etc.) to form in situ hydrogels created from biocompatible materials modified by various functional groups or hybrid functional nanoparticles. Furthermore, "smart" hydrogels, which respond to endogenous physiological or environmental stimuli (e.g., temperature, pH, enzyme, etc.), can achieve in situ gelation by one injection in vivo without additional intervention. Moreover, the mild chemistry response-mediated in situ hydrogel systems also offer fascinating prospects in bone tissue engineering, such as a Diels-Alder, Michael addition, thiol-Michael addition, and Schiff reactions, etc. The recent developments and challenges of various smart in situ hydrogels and their application to drug administration and bone tissue engineering are discussed in this review. It is anticipated that advanced strategies and innovative ideas of in situ hydrogels will be exploited in the clinical field and increase the quality of life for patients with bone damage.

Split Proteins and Reassembly Modules for Biological Applications

Split systems, modular entities enabling controlled biological processes, have become instrumental in biological research. This review highlights their utility across applications like gene regulation, protein interaction identification, and biosensor development. Covering significant progress over the last decade, it revisits traditional split proteins such as GFP, luciferase, and inteins, and explores advancements in technologies like Cas proteins and base editors. We also examine reassembly modules and their applications in diverse fields, from gene regulation to therapeutic innovation. This review offers a comprehensive perspective on the recent evolution of split systems in biological research.

Development and performance of NLISA for C-reactive protein detection based on Prussian blue nanoparticle conjugates

Prussian blue nanoparticles (PBNPs), also called nanozymes, are very attractive as an alternative to horseradish peroxidase in immunoassay development due to their simple and low-cost synthesis, stability and high catalytic activity. Today, there is a method for highly effective PBNP synthesis based on the reduction of an FeCl3/K3[Fe(CN)6] mixture by hydrogen peroxide. However, there is a lack of research showcasing the use of these highly effective PBNPs for specific target detection in clinical settings, as well as a lack of comprehensive comparisons with conventional methods. To address this gap, we prepared diagnostic reagents based on highly effective PBNPs by modifying them using gelatin and attaching anti-C-reactive protein (CRP) monoclonal antibodies through cross-linking with glutaraldehyde. As a result, a solid-phase colorimetric immunoassay in a sandwich format (nanozyme-linked immunosorbent assay [NLISA]) using highly effective PBNPs as a label for CRP detection has been demonstrated for the first time. The assay demonstrated a detection limit of 21.8 pg/mL, along with acceptable selectivity, precision (CV < 25%) and accuracy (the recovery index was within acceptable limits (75-125%) for LLOQ /ULOQ range. The analytical performance of this method is on par with sensitive assays developed in the last 5 years. Notably, the results obtained from NLISA align with those from an immunofluorescence assay conducted by a certified clinical laboratory. Furthermore, this study underscores the technological challenges involved in constructing an analysis that necessitate further exploration.

Atomic Force Microscopy Study of the Long-Term Effect of the Glycerol Flow, Stopped in a Coiled Heat Exchanger, on Horseradish Peroxidase

Glycerol is employed as a functional component of heat-transfer fluids, which are of use in both bioreactors and various biosensor devices. At the same time, flowing glycerol was reported to cause considerable triboelectric effects. Herein, by using atomic force microscopy (AFM), we have revealed the long-term effect of glycerol flow, stopped in a ground-shielded coiled heat exchanger, on horseradish peroxidase (HRP) adsorption on mica. Namely, the solution of HRP was incubated in the vicinity of the side of the cylindrical coil with stopped glycerol flow, and then HRP was adsorbed from this solution onto a mica substrate. This incubation has been found to markedly increase the content of aggregated enzyme on mica-as compared with the control enzyme sample. We explain the phenomenon observed by the influence of triboelectrically induced electromagnetic fields of non-trivial topology. The results reported should be further considered in the development of flow-based heat exchangers of biosensors and bioreactors intended for operation with enzymes.

Class III plant peroxidases: From classification to physiological functions

Peroxidases (EC 1.11.1.7) are involved in a wide range of physiological processes, hence their broad distribution across biological systems. These proteins can be classified as haem or non-haem enzymes. According to the RedOxiBase database, haem peroxidases are approximately 84 % of all known peroxidase enzymes. Class III plant peroxidases are haem-enzymes that share similar three-dimensional structures and a common catalytic mechanism for hydrogen peroxide degradation. They exist as large multigene families and are involved in metabolizing Reactive Oxygen Species (ROS), hormone synthesis and decomposition, fruit growth, defense, and cell wall synthesis and maintenance. As a result, plant peroxidases gained attention in research and became one of the most extensively studied groups of enzymes. This review provides an update on the database, classification, phylogeny, mechanism of action, structure, and physiological functions of class III plant peroxidases.

The Nanozyme Revolution: Enhancing the Performance of Medical Biosensing Platforms

Nanozymes represent a class of nanosized materials that exhibit innate catalytic properties similar to biological enzymes. The unique features of these materials have positioned them as promising candidates for applications in clinical sensing devices, specifically those employed at the point-of-care. They notably have found use as a means to amplify signals in nanosensor-based platforms and thereby improve sensor detection limits. Recent developments in the understanding of the fundamental chemistries underpinning these materials have enabled the development of highly effective nanozymes capable of sensing clinically relevant biomarkers at detection limits that compete with "gold-standard" techniques. However, there remain considerable hurdles that need to be overcome before these nanozyme-based sensors can be utilized in a platform ready for clinical use. An overview of the current understandings of nanozymes for disease diagnostics and biosensing applications and the unmet challenges that must be considered prior to their translation in clinical diagnostic tests is provided.

In vitro Production of Hemin-Based Artificial Metalloenzymes

Developing enzyme alternatives is pivotal to improving and enabling new processes in biotechnology and industry. Artificial metalloenzymes (ArMs) are combinations of protein scaffolds with metal elements, such as metal nanoclusters or metal-containing molecules with specific catalytic properties, which can be customized. Here, we engineered an ArM based on the consensus tetratricopeptide repeat (CTPR) scaffold by introducing a unique histidine residue to coordinate the hemin cofactor. Our results show that this engineered system exhibits robust peroxidase-like catalytic activity driven by the hemin. The expression of the scaffold and subsequent coordination of hemin was achieved by recombinant expression in bulk and through in vitro transcription and translation systems in water-in-oil drops. The ability to synthesize this system in emulsio paves the way to improve its properties by means of droplet microfluidic screenings, facilitating the exploration of the protein combinatorial space to discover improved or novel catalytic activities.

Designing Configurable Soft Microgelsomes as a Smart Biomimetic Protocell

Self-assembly is an intriguing aspect of primitive cells. The construction of a semipermeable compartment with a robust framework of soft material capable of housing an array of functional components for chemical changes is essential for the fabrication of synthetic protocells. Microgels, loosely cross-linked polymer networks, are suitable building blocks for protocell capsule generation due to their porous structure, tunable properties, and assembly at the emulsion interface. Here, we present an interfacial assembly of microgel-based microcompartments (microgelsomes, MGC) that are defined by a semipermeable, temperature-responsive elastic membrane formed by densely packed microgels in a monolayer. The water-dispersible microgelsomes can thermally shuttle between 10 and 95 °C while retaining their structural integrity. Importantly, the microgelsomes exhibited distinct properties of protocells, such as cargo encapsulation, semipermeable membrane, DNA amplification, and membrane-gated compartmentalized enzymatic cascade reaction. This versatile approach for the construction of biomimetic microcompartments augments the protocell library and paves the way for programmable synthetic cells.

Nanocellulose/Fe3O4/Ag Nanozyme with Robust Peroxidase Activity for Enhanced Antibacterial and Wound Healing Applications

Peroxidase memetic nanozymes with their free radical-mediated catalytic actions proved as efficacious antibacterial agents for combating bacterial resistance. Herein, nanocellulose (NC) extracted from Eragrostis teff straw was used to prepare NC/Fe3O4/Ag peroxidase nanozyme as an antibacterial and wound healing agent. Characterization of the nanozyme with XRD, FTIR, SEM-EDX, and XPS confirmed the presence of silver NPs and the magnetite phase of iron oxide dispersed on nanocellulose. The peroxidase activity of the prepared nanozyme was examined using TMB and H2O2 as substrates which turned blue in acidic pH (λmax = 652 nm). With a lower Km (0.387 mM), the nanozyme showed a comparable affinity for TMB with that reported for the HRP enzyme. Furthermore, the nanozyme remained efficient over a broader temperature range while maintaining 61.53% of its activity after the fourth cycle. In vitro, antibacterial tests against Escherichia coli (Gram-negative) and Staphylococcus aureus (Gram-positive) bacterial strains showed that NC/Fe3O4/Ag exhibits concentration-dependent and enhanced antibacterial effect for Escherichia coli compared to NC and NC-Fe3O4 and negative control. Furthermore, the wound-healing performance of the NC-Fe3O4-Ag nanozyme was investigated in vivo using an animal model (mice). The nanozyme showed 30% higher wound healing performance compared to the control base ointment and is comparable with the commercial nitrofurazone ointment. The results show the potential of the prepared nanozyme for wound-healing purposes.

Aptasensors Based on Non-Enzymatic Peroxidase Mimics: Current Progress and Challenges

Immunoassays based on antibodies as recognizing elements and enzymes as signal-generating modules are extensively used now in clinical lab diagnostics, food, and environmental analyses. However, the application of natural enzymes and antibodies has some drawbacks, such as relatively high manufacturing costs, thermal instability, and lot-to-lot variations that lower the reproducibility of results. Oligonucleotide aptamers are able to specifically bind their targets with high affinity and selectivity, so they represent a prospective alternative to protein antibodies for analyte recognition. Their main advantages include thermal stability and long shelf life, cost-efficient chemical synthesis, and negligible batch-to-batch variations. At the same time, a wide variety of non-protein peroxidase mimics are now available that show strong potential to replace protein enzymes. Here, we review and analyze non-protein biosensors that represent a nexus of these two concepts: aptamer-based sensors (aptasensors) with optical detection (colorimetric, luminescent, or fluorescent) based on different peroxidase mimics, such as DNAzymes, nanoparticles, or metal-organic frameworks.

Mechanisms and Opportunities for Rational In Silico Design of Enzymes to Degrade Per- and Polyfluoroalkyl Substances (PFAS)

Per and polyfluoroalkyl substances (PFAS) present a unique challenge to remediation techniques because their strong carbon-fluorine bonds make them difficult to degrade. This review explores the use of in silico enzymatic design as a potential PFAS degradation technique. The scope of the enzymes included is based on currently known PFAS degradation techniques, including chemical redox systems that have been studied for perfluorooctanesulfonic acid (PFOS) and perfluorooctanoic acid (PFOA) defluorination, such as those that incorporate hydrated electrons, sulfate, peroxide, and metal catalysts. Bioremediation techniques are also discussed, namely the laccase and horseradish peroxidase systems. The redox potential of known reactants and enzymatic radicals/metal-complexes are then considered and compared to potential enzymes for degrading PFAS. The molecular structure and reaction cycle of prospective enzymes are explored. Current knowledge and techniques of enzyme design, particularly radical-generating enzymes, and application are also discussed. Finally, potential routes for bioengineering enzymes to enable or enhance PFAS remediation are considered as well as the future outlook for computational exploration of enzymatic in situ bioremediation routes for these highly persistent and globally distributed contaminants.

Annotation of GC-MS Data of Antimicrobial Constituents in the Antarctic Seaweed Phaeurus antarcticus by Molecular Networking

Phaeurus antarcticus is a member of the Desmarestiaceae family endemic to the Antarctic Peninsula. Reports addressing its chemical composition and biological activities are scarce. Herein, bioactive non-polar compounds of P. antarcticus against pathogenic bacteria, Leishmania amazonensis and Neospora caninum parasites were targeted through GC-MS Molecular Networking and multivariate analysis (OPLS-DA). The effects on horseradish peroxidase (HRP) were also evaluated. P. antarcticus exhibited selective bacteriostatic and bactericidal activities against Staphylococcus aureus with MIC and MBC values from 6.25-100 μg mL-1 . Fractions HX-FC and HX-FD were the most active against L. amazonensis with EC50 ranging from 18.5-62.3 μg mL-1 . Additionally, fractions HX-FC and HX-FD showed potent inhibition of N. caninum at EC50 values of 2.8 and 6.3 μg mL-1 , respectively. All fractions inhibited HRP activity, indicating possible interactions with Heme proteins. It was possible to annotate compounds from tree mains clusters, containing terpenoids, steroids, fatty acids, and alcohols by correlating the spectral data of the GC-MS analysis with Molecular Networking and the OPLS-DA results.

Multifaceted personality and roles of heme enzymes in industrial biotechnology

Heme enzymes are the most prominent category of iron-containing metalloenzymes with the capability of catalyzing an astonishingly wide range of reactions like epoxidation, hydroxylation, demethylation, desaturation, reduction, sulfoxidation, and decarboxylation. Various enzymes in this category are P450s, heme peroxidases, catalases, myoglobin, cytochrome C, and others. Besides this, the natural promiscuity and amenability of these enzymes to protein engineering and evolution have also added several non-native reactions such as C-H, N-H, S-H insertions, cyclopropanation, and other industrially important reactions to their capabilities. Surprisingly, all of these reactions and their wide substrate scopes are attributed to changes in the active site scaffold of different heme enzymes as the center of all enzymes is constituted by a porphyrin ring containing iron. Multiple prominent research groups across the world, including 2018, Nobel Laureate Frances Arnold's group, have shown keen interest in engineering and evolving these enzymes for utilizing their industrial potential. Besides engineering the active site, researchers have also explored the possibility of these enzymes catalyzing non-native reactions by replacing the center porphyrin ring with other cofactors or by changing the iron in the porphyrin ring with other metal ions along with engineering the active site and thereby creating novel artificial metalloenzymes. Thus, in this mini-review from our group, for the first time, we are trying to catalog various activities catalyzed by heme enzymes and their engineered variants and their active usage in various industries along with shedding light on their potential for use in various applications in the future.

User-friendly one-step disposable signal-on bioassay for glyphosate detection in water samples

The onsite detection of glyphosate requires an easy-to-handle, low-cost and disposable assay for untrained users as requested by the ASSURED guidelines. A new strategy based on the expression of fusion proteins is proposed here. A glyphosate oxidase derived from Bacillus subtilis and the 6E10 variant of the dye peroxidase from Pseudomonas putida, both fused with the carbohydrate binding module (CBM) 3a from Clostridium thermocellum, were designed and expressed, leading to GlyphOx-CBM and 6E10-CBM. Cell lysates were used to immobilise both enzymes on cotton buds' heads without any purification. The cotton buds exhibit glyphosate oxidase activity when dipped into a glyphosate-contaminated water sample containing the 6E10-CBM chromogenic substrates. The chromophore could be quantified both in the solution and on the cotton buds' heads. Photography followed by image analysis allows to detect glyphosate with a linear range of 0.25-2.5 mM and a limit of detection (LoD) of 0.12 mM. When the chromogenic substrates are replaced by luminol, the chemiluminescence reaction allows the detection of glyphosate with a linear range of 2-500 μM and a LoD of 0.45 μM. No interference was observed using glyphosate analogues (glycine, sarcosine, aminomethylphosphonic acid) or other herbicides used in a mixture. Only cysteine was found to inhibit 6E10-CBM. Two river waters spiked with glyphosate lead to recoveries of 64-131%. This work describes a very easy-to-handle and inexpensive signal-on bioassay for glyphosate detection in real surface water samples.

Antioxidant Activity and Skin Sensitization of Eugenol and Isoeugenol: Two Sides of the Same Coin?

Eugenol and isoeugenol are well acknowledged to possess antioxidant and thus cytoprotective activities. Yet both compounds are also important skin sensitizers, compelling the cosmetics and fragrance industries to notify their presence in manufactured products. While they are structurally very similar, they show significant differences in their sensitization properties. Consequently, eugenol and isoeugenol have been the subject of many mechanistic studies where the final oxidation forms, electrophilic ortho-quinone and quinone methide, are blamed as the reactive species forming an antigenic complex with nucleophilic residues of skin proteins, inducing skin sensitization. However, radical mechanisms could compete with such an electrophilic-nucleophilic pathway. The antioxidant activity results from neutralizing reactive oxygen radicals by the release of the phenolic hydrogen atom. The so-formed phenoxyl radicals can then fully delocalize upon the structure, becoming potentially reactive toward skin proteins at several positions. To obtain in-depth insights into such reactivity, we investigated in situ the formation of radicals from eugenol and isoeugenol using electron paramagnetic resonance combined with spin trapping in reconstructed human epidermis (RHE), mimicking human skin and closer to what may happen in vivo. Two modes of radical initiation were used, exposing RHE to (i) horseradish peroxidase (HRP), complementing RHE metabolic capacities, and mimicking peroxidases present in vivo or (ii) solar light using a AM 1.5 solar simulator. In both experimental approaches, where the antioxidant character of both compounds is revealed, oxygen- and carbon-centered radicals were formed in RHE. Our hypothesis is that such carbon radicals are relevant candidates to form antigenic entities prior to conversion into electrophilic quinones. On this basis, these studies suggest that pro- or prehapten fingerprints could be advanced depending on the radical initiation method. The introduction of HRP suggested that eugenol and isoeugenol behave as prohaptens, while when exposed to light, a prehapten nature could be highlighted.

Optimizing the Composition of the Substrate Enhances the Performance of Peroxidase-like Nanozymes in Colorimetric Assays: A Case Study of Prussian Blue and 3,3'-Diaminobenzidine

One of the emerging trends in modern analytical and bioanalytical chemistry involves the substitution of enzyme labels (such as horseradish peroxidase) with nanozymes (nanoparticles possessing enzyme-like catalytic activity). Since enzymes and nanozymes typically operate through different catalytic mechanisms, it is expected that optimal reaction conditions will also differ. The optimization of substrates for nanozymes usually focuses on determining the ideal pH and temperature. However, in some cases, even this step is overlooked, and commercial substrate formulations designed for enzymes are utilized. This paper demonstrates that not only the pH but also the composition of the substrate buffer, including the buffer species and additives, significantly impact the analytical signal generated by nanozymes. The presence of enhancers such as imidazole in commercial substrates diminishes the catalytic activity of nanozymes, which is demonstrated herein through the use of 3,3'-diaminobenzidine (DAB) and Prussian Blue as a model chromogenic substrate and nanozyme. Conversely, a simple modification to the substrate buffer greatly enhances the performance of nanozymes. Specifically, in this paper, it is demonstrated that buffers such as citrate, MES, HEPES, and TRIS, containing 1.5-2 M NaCl or NH4Cl, substantially increase DAB oxidation by Prussian Blue and yield a higher signal compared to commercial DAB formulations. The central message of this paper is that the optimization of substrate composition should be an integral step in the development of nanozyme-based assays. Herein, a step-by-step optimization of the DAB substrate composition for Prussian Blue nanozymes is presented. The optimized substrate outperforms commercial formulations in terms of efficiency. The effectiveness of the optimized DAB substrate is affirmed through its application in several commonly used immunostaining techniques, including tissue staining, Western blotting assays of immunoglobulins, and dot blot assays of antibodies against SARS-CoV-2.

Diversifying the functions of heme proteins with non-porphyrin cofactors

Heme proteins perform diverse biochemical functions using a single iron porphyrin cofactor. This versatility makes them attractive platforms for the development of new functional proteins. While directed evolution and metal substitution have expanded the properties, reactivity, and applications of heme proteins, the incorporation of porphyrin analogs remains an underexplored approach. This review discusses the replacement of heme with non-porphyrin cofactors, such as porphycene, corrole, tetradehydrocorrin, phthalocyanine, and salophen, and the attendant properties of these conjugates. While structurally similar, each ligand exhibits distinct optical and redox properties, as well as unique chemical reactivity. These hybrids serve as model systems to elucidate the effects of the protein environment on the electronic structure, redox potentials, optical properties, or other features of the porphyrin analog. Protein encapsulation can confer distinct chemical reactivity or selectivity of artificial metalloenzymes that cannot be achieved with the small molecule catalyst alone. Additionally, these conjugates can interfere with heme acquisition and uptake in pathogenic bacteria, providing an inroad to innovative antibiotic strategies. Together, these examples illustrate the diverse functionality that can be achieved by cofactor substitution. The further expansion of this approach will access unexplored chemical space, enabling the development of superior catalysts and the creation of heme proteins with emergent properties.

Recent advances in the synthesis and applications of single-atom nanozymes in food safety monitoring

Nanozymes are synthetic compounds with enzyme-like tunable catalytic properties. The success of nanozymes for catalytic applications can be attributed to their small dimensions, cost-effective synthesis, appreciable stability, and scalability to molecular dimensions. The emergence of single atom nanozymes (SANzymes) has opened up new possibilities in bioanalytical applications. In this regard, this review outlines enzyme-mimicking features of SANzymes for food safety applications in relation to the key variables controlling their catalytic performance. The discussion is extended further to cover the applications of SANzymes for the monitoring of various compounds/biomaterials of significance with respect to food safety (e.g., pesticides, veterinary drug residues, foodborne pathogenic bacteria, mycotoxins/bacterial endotoxin, antioxidant residues, hydrogen peroxide residues, and heavy metal ions). Furthermore, the performance of SANzymes is evaluated in terms of various performance metrics such as limit of detection (LOD), linear dynamic range, and figure of merit (FoM). The challenges and future road map for the applications of SANzymes are also addressed along with their upscaling in the area of food safety.

Assessment of the Environmental Impact of Solid Oil Materials Based on Pyrolysis Oil

One method of managing used car tires is decomposition by thermochemical conversion methods. By conducting the process at temperatures of 450-750 °C, three fractions are obtained from tires: oil, gas, and solid. The liquid product of the pyrolysis of used car tires is pyrolysis oil, which consists of aromatic, polyaromatic, and aliphatic hydrocarbons. Unconventional building materials were obtained from tire pyrolysis oil and the environmental impact was evaluated. Blocks made from pyrolysis oil showed mechanical strength of up to about 1700 N. No heavy metals or polycyclic aromatic hydrocarbons, which were found in the crude heavy-PO fraction, were detected in the filtrates after incubation of the block obtained from the heavy-PO fraction at 240 °C. The highest inhibition of Sorghum saccharatum shoot (74.4%) and root (57.5%) growth was observed for solid materials from the medium-PO fraction obtained at 240 °C. The most favorable values of the parameters for the process of obtaining blocks based on post-PO were an annealing temperature of 180 °C, time of 20 h, and mass ratio of catalyst to catalyzed oil of 0.045.

The allotetraploid horseradish genome provides insights into subgenome diversification and formation of critical traits

Polyploidization can provide a wealth of genetic variation for adaptive evolution and speciation, but understanding the mechanisms of subgenome evolution as well as its dynamics and ultimate consequences remains elusive. Here, we report the telomere-to-telomere (T2T) gap-free reference genome of allotetraploid horseradish (Armoracia rusticana) sequenced using a comprehensive strategy. The (epi)genomic architecture and 3D chromatin structure of the A and B subgenomes differ significantly, suggesting that both the dynamics of the dominant long terminal repeat retrotransposons and DNA methylation have played critical roles in subgenome diversification. Investigation of the genetic basis of biosynthesis of glucosinolates (GSLs) and horseradish peroxidases reveals both the important role of polyploidization and subgenome differentiation in shaping the key traits. Continuous duplication and divergence of essential genes of GSL biosynthesis (e.g., FMO_GS-OX, IGMT, and GH1 gene family) contribute to the broad GSL profile in horseradish. Overall, the T2T assembly of the allotetraploid horseradish genome expands our understanding of polyploid genome evolution and provides a fundamental genetic resource for breeding and genetic improvement of horseradish.

Affinity-based and in a single step purification of recombinant horseradish peroxidase A2A isoenzyme produced by Pichia pastoris

Horseradish peroxidase (HRP) is an oxidoreductase enzyme and oxidizes various inorganic and organic compounds. It has wide application areas such as immunological tests, probe-based test techniques, removal of phenolic pollutants from wastewater and organic synthesis. HRP is found in the root of the horseradish plant as a mixture of different isoenzymes, and it is very difficult to separate these enzymes from each other. In this regard, recombinant production is a very advantageous method in terms of producing the desired isoenzyme. This study was performed to produce HRP A2A isoenzyme extracellularly in Pichia pastoris and to purify this enzyme in a single step using a 3-amino-4-chloro benzohydrazide affinity column. First, codon-optimized HRP A2A gene was amplified and inserted into pPICZαC. So, obtained pPICZαC-HRPA2A was cloned in E. coli cells. Then, P. pastoris X-33 cells were transformed with linearized recombinant DNA and a yeast clone was cultivated for extracellular recombinant HRP A2A (rHRP A2A) enzyme production. Then, the purification of this enzyme was performed in a single step by affinity chromatography. The molecular mass of purified rHRP A2A enzyme was found to be about 40 kDa. According to characterization studies of the purified enzyme, the optimum pH and ionic strength for the rHRP A2A isoenzyme were determined to be 6.0 and 0.04 M, respectively, and o-dianisidine had the highest specificity with the lowest Km and Vmax values. Thus, this is an economical procedure to purify HRP A2A isoenzyme without time-consuming and laborious isolation from an isoenzyme mixture.

Stepwise Optimization of Inducible Expression System for the Functional Secretion of Horseradish Peroxidase in Saccharomyces cerevisiae

Horseradish peroxidase (HRP) is a plant-derived glycoprotein that can be developed as a food additive to cross-link proteins or biopolymers. Although Saccharomyces cerevisiae has advantages in the production of food-grade HRP, the low expressional level and inefficient secretion hindered its application values. After comparing the effects of constitutive and inducible expression on cell growth, the strength of HRP expression was roughly tuned by replacing core regions of the promoter in the GAL80-knockout strain and further finely tuned by terminator screening. Additionally, the most suitable signal peptide was selected, and the pre-peptide with pro-peptides was modified to balance the transport of HRP in the endoplasmic reticulum. The extracellular HRP activity of the best strain reached 13 506 U/L at the fermenter level, 330-fold higher than the previous result of 41 U/L in S. cerevisiae. The strategy can be applied to alleviate the inhibition of cell growth caused by the expression of toxic proteins and improve their secretion.

ELISA Essentials: Surfaces, Antibodies, Enzymes, and Substrates

The enzyme-linked immunosorbent assay is a powerful analytical tool for the assessment of the kind and quantity of specific analytes found within a biological sample. It is based upon the exceptional specificity of antibody recognition of its cognate antigen and the power of enzyme-mediated signal amplification for sensitivity. However, development of the assay is not without challenges. Here, we describe the essential components and features necessary to successfully prepare and carry out the ELISA format.

Determination of lysophosphatidylcholine using peroxidase-mimic PVP/PtRu nanozyme

Lysophosphatidylcholine (LPC) can be used as a biomarker for diseases such as cancer, diabetes, atherosclerosis, and sepsis. In this study, we demonstrated the ability of nanozymes to displace the natural derived enzyme in enzyme-based assays for the measurement of LPC. Synthesized polyvinylpyrrolidone-stabilized platinum-ruthenium nanozymes (PVP/PtRu NZs) had a uniform size of 2.48 ± 0.24 nm and superb peroxidase-mimicking activity. We demonstrated that the nanozymes had high activity over a wide pH and temperature range and high stability after long-term storage. The LPC concentration could be accurately analyzed through the absorbance and fluorescence signals generated by the peroxidation reaction using the synthesized nanozyme with substrates such as 3,3',5,5'-tetramethylbenzidine (TMB) and 10-acetyl-3,7-dihydroxyphenoxazine (Ampliflu™ Red). LPC at a concentration of 0-400 µM was used for the analysis, and the coefficient of determination (R²) was 0.977, and the limit of detection (LOD) was 23.1 µM by colorimetric assay. In the fluorometric assay, the R² was 0.999, and the LOD was 8.97 µM. The spiked recovery values for the determination of LPC concentration in human serum samples were 102-115%. Based on these results, we declared that PVP/PtRu NZs had an ability comparable to that of the native enzyme horseradish peroxidase (HRP) in the enzyme-based LPC detection method.

Carbon Electrode-Based Biosensing Enabled by Biocompatible Surface Modification with DNA and Proteins

Modification of electrodes with biomolecules is an essential first step for the development of bioelectrochemical systems, which are used in a variety of applications ranging from sensors to fuel cells. Gold is often used because of its ease of modification with thiolated biomolecules, but carbon screen-printed electrodes (SPEs) are gaining popularity due to their low cost and fabrication from abundant resources. However, their effective modification with biomolecules remains a challenge; the majority of work to-date relies on nonspecific adhesion or broad amide bond formation to chemical handles on the electrode surface. By combining facile electrochemical modification to add an aniline handle to electrodes with a specific and biocompatible oxidative coupling reaction, we can readily modify carbon electrodes with a variety of biomolecules. Importantly, both proteins and DNA maintain bioactive conformations following coupling. We have then used biomolecule-modified electrodes to generate microbial monolayers through DNA-directed immobilization. This work provides an easy, general strategy to modify inexpensive carbon electrodes, significantly expanding their potential as bioelectrochemical systems.

Polyaniline Entrapped Water-Dispersible 3MPA-ZnSe Quantum Dots and Their Application for the Development of an Enzymatic Electrochemical Nanobiosensor for the Detection of 17β-Estradiol, an Endocrine-Disrupting Compound

17β-estradiol is used as a growth and fertility stimulant in the agronomic sector to induce fertility and manipulate reproductive characteristics in animals. However, unintended or unregulated distribution and exposure to even significant low levels of 17β-estradiol estrogen have detrimental health implication that can lead to reproductive abnormalities and even cancer. This could have severe effect on the ecosystem imbalance, food safety, to such a degree that its health impact necessitates rapid methods to probe for its prevalence and occurrence in the environment. Herein a simple, robust, sensitive and once-off use electrochemical biosensor to detect 17β-estradiol is developed, using 3-mercaptopropionic acid capped zinc selenide quantum dots trapped within the polyaniline (PANI) framework structure. The biosensor's interaction with the substrate was based on the capability of the hemeprotein, horseradish peroxidase (HRP) enzyme (i.e., baroreceptor) to alternatively catalyze phenolic alcohols. The biosensor displayed a significantly low limit of detection limit (LOD) of value 0.2 × 10^-6 M towards 17β-estradiol. The Mechaelis-Menten constant (K_m) with the magnitude of 0.64 × 10^-6 M was obtained; this indicates an outstanding affinity of the biosensing films towards 17β-estradiol. Subsequently, the developed biosensor was able to accurately and efficiently measure successive concentrations of 17β-estradiol from 0.2 × 10 to 4 × 10^-6 M. The fabricated biosensor showed good selectivity towards 17β-estradiol compared to the other estrogenic endocrine-disrupting compounds such as estrone (E1), ethnylstradiol (EE2), and estriol (E3). The biosensor was capable of detecting 17β-estradiol in spiked tap water samples with good recoveries, thus affirming its potential to be applied for real electro-analysis of 17β-estradiol in treated wastewater.

The Purification of Heme Peroxidases from Escherichia coli Inclusion Bodies: A Success Story Shown by the Example of Horseradish Peroxidase

In the following chapter a purification process for recombinant Horseradish peroxidase (HRP) produced in Escherichia coli is described. This enzyme is a secretory plant oxidoreductase belonging to the large peroxidase family III within the peroxidase-catalase superfamily of enzymes. It has high biotechnological significance, however, the isolation of the enzyme from its natural source, the horseradish root, has several shortcomings, which makes the development of a recombinant production strategy interesting. The presented protocol covers all process steps from isolation to the final chromatography step; the enzyme is solubilized from insoluble inclusion bodies, refolded and concentrated to yield a high purity enzyme preparation which is comparable to the commercially available plant-derived HRP. Moreover, we believe that this procedure can also be used to process other peroxidases of family II and III of the plant peroxidase superfamily, as they all share the same relevant features like disulfide bonds and a heme group.

Bioprospecting of novel peroxidase from Streptomyces coelicolor strain SPR7 for carcinogenic azo dyes decolorization

Peroxidase (POX) is a heme-containing oxidoreductase, its voluminous immuno-diagnostic and bioremediatory intuitions have incited optimization and large scale-generation from novel microbial repertoires. Azo dyes are the most detrimental classes of synthetic dyes and they are the common ecotoxic industrial pollutants in wastewater. In addition, azo dyes are refractory to degradation owing to their chemical nature, comprising of azoic linkages, amino moieties with recalcitrant traits. Moreover, they are major carcinogenic and mutagenic on humans and animals, whereby emphasizing the need for decolorization. In the present study, a novel POX from Streptomyces coelicolor strain SPR7 was investigated for the deterioration of ecotoxic dyestuffs. The initial medium component screening for POX production was achieved using, One Factor at a Time and Placket-Burman methodologies with starch, casein and temperature as essential parameters. In auxiliary, Response Surface Methodology (RSM) was recruited and followed by model validation using Back propagation algorithm (BPA). RSM-BPA composite approach prophesied that combination of starch, casein, and temperature at optimal values 2.5%, 0.035% and 35 °C respectively, has resulted in 7 folds enhancement of POX outturn (2.52 U/mL) compared to the unoptimized media (0.36 U/mL). The concentrated enzyme decolorized 75.4% and 90% of the two azo dyes with lignin (10 mM), respectively. Hence, this investigation confirms the potentiality of mangrove actinomycete derived POX for elimination of noxious azo dyes to overcome their carcinogenic, mutagenic and teratogenic effects on humans and aquatic organisms.

The Influence of Isoenzyme Composition and Chemical Modification on Horseradish Peroxidase@ZIF-8 Biocomposite Performance

Many articles in the literature deal with horseradish peroxidase (HRP) biomineralization, but none pay attention to the isoenzyme composition of commercial HRP or the influence of the carbohydrate component of the protein molecule on the biomineralization process. To study the impact of these factors, we performed periodate oxidation of commercial HRP and a purified HRP-C isoform for biomineralization within ZIF-8. With purified HRP, enzyme@ZIF-8 biocomposites with higher activity were obtained, while periodate oxidation of the carbohydrate component of both commercial HRP and purified HRP-C yields biocomposites with very high activity in acetate buffer that does not degrade the ZIF-8 structure. Using acetate instead of phosphate buffer can prevent the false high activity of HRP@ZIF-8 biocomposites caused by the degradation of ZIF-8 coating. At the same time, purification and especially oxidation of the carbohydrate component of enzymes prior to biomineralization lead to significantly improved activity of the biocomposites.

Towards Solving the PFAS Problem: The Potential Role of Metal-Organic Frameworks

Per- and polyfluoroalkyl substances (PFAS) are a group of recalcitrant molecules that have been used since the 1940s in a variety of applications. They are now linked to a host of negative health outcomes and are extremely resistant to degradation under environmental conditions. Currently, membrane technologies or adsorbents are used to remediate contaminated water. These techniques are either inefficient at capturing smaller PFAS molecules, have high energy demands, or result in concentrated waste that must be incinerated at high temperatures. This Review focuses on what role metal-organic frameworks (MOFs) may play in addressing the PFAS problem. Specifically, how the unique properties of MOFs such as their well-defined pore sizes, ultra-high internal surface area, and tunable surface chemistry may be a sustainable solution for PFAS contamination.

Bacterial Peroxidase on Electrochemically Reduced Graphene Oxide for Highly Sensitive H2 O2 Detection

Peroxidase enzymes enable the construction of electrochemical sensors for highly sensitive and selective quantitative detection of various molecules, pathogens and diseases. Herein, we describe the immobilization of a peroxidase from Bacillus s. (BsDyP) on electrochemically reduced graphene oxide (ERGO) deposited on indium tin oxide (ITO) and polyethylene terephthalate (PET) layers. XRD, SEM, AFM, FT-IR and Raman characterization of the sensor confirmed its structural integrity and a higher enzyme surface occupancy. The BsDyP-ERGO/ITO/PET electrode performed better than other horseradish peroxidase-based electrodes, as evinced by an improved electrochemical response in the nanomolar range (linearity 0.05-280 μM of H2 O2 , LOD 32 nM). The bioelectrode was mechanically robust, active in the 3.5-6 pH range and exhibited no loss of activity upon storage for 8 weeks at 4 °C.

Peroxidase enzymes as green catalysts for bioremediation and biotechnological applications: A review

The fast-growing consumer demand drives industrial process intensification, which subsequently creates a significant amount of waste. These products are discharged into the environment and can affect the quality of air, degrade water streams, and alter soil characteristics. Waste materials may contain polluting agents that are especially harmful to human health and the ecosystem, such as the synthetic dyes, phenolic agents, polycyclic aromatic hydrocarbons, volatile organic compounds, polychlorinated biphenyls, pesticides and drug substances. Peroxidases are a class oxidoreductases capable of performing a wide variety of oxidation reactions, ranging from reactions driven by radical mechanisms, to oxygen insertion into CH bonds, and two-electron substrate oxidation. This versatility in the mode of action presents peroxidases as an interesting alternative in cleaning the environment. Herein, an effort has been made to describe mechanisms governing biochemical process of peroxidase enzymes while referring to H₂O₂/substrate stoichiometry and metabolite products. Plant peroxidases including horseradish peroxidase (HRP), soybean peroxidase (SBP), turnip and bitter gourd peroxidases have revealed notable biocatalytic potentialities in the degradation of toxic products. On the other hand, an introduction on the role played by ligninolytic enzymes such as manganese peroxidase (MnP) and lignin peroxidase (LiP) in the valorization of lignocellulosic materials is addressed. Moreover, sensitivity and selectivity of peroxidase-based biosensors found use in the quantitation of constituents and the development of diagnostic kits. The general merits of peroxidases and some key prospective applications have been outlined as concluding remarks.

Structure and activity of a novel robust peroxidase from Alkanna frigida cell culture

Demands for peroxidases (POX)s with diverse physicochemical properties have steadily grown as more applications of POXs are demonstrated. Plants are among the best sources of versatile POXs, and plant biotechnology, as an agricultural hassle-free technology, promises to circumvent the limitations of natural resource exploitation and to address the demands. Following this trend, it was shown that POX production steadily increased during the 31-day subculture of Alkanna frigida (from Boraginaceae) callus on Murashige-Skoog medium containing 2,4-dichlorophenoxyacetic acid (10^-6 M) and kinetin (10^-5 M). The purified cationic enzyme (POX_alf) maintained its optimal activity over pH 4-7 for 2 years. It was resistant to H₂O₂ high concentrations (IC50 = 543.7 mM) and showed high specific activity in the reaction with phenol (4320.5 AU mg^-1 > 20-fold of HRP AU). Furthermore, the specificity constant ratio of guaiacol to phenol indicated a 100 times faster reaction of POX_alf with guaiacol. However, in contrast to HRP, it had little effect on diazo derivatives of aniline and meta-diaminobenzene. Based on the resulting primary structure from the tandem mass analysis, the POX_alf 3D structure was constructed via homology modelling. Despite the high topological similarity between the HRP and POX_alf structures, there were important differences between the active site pockets that could explain the observed differences in the corresponding substrate spectra and the specific activities. Considering the dynamics of POX_alf production, its inactivity towards IAA and its high affinity for guaiacol, POX_alf may have associated roles with A. frigida cell wall construction and monolignol metabolism.

Horseradish Peroxidase-Functionalized Gold Nanoconjugates for Breast Cancer Treatment Based on Enzyme Prodrug Therapy

Introduction

Breast cancer has the highest mortality rate among cancers in women. Patients suffering from certain breast cancers, such as triple-negative breast cancer (TNBC), lack effective treatments. This represents a clinical concern due to the associated poor prognosis and high mortality. As an approach to succeed over conventional therapy limitations, we present herein the design and evaluation of a novel nanodevice based on enzyme-functionalized gold nanoparticles to efficiently perform enzyme prodrug therapy (EPT) in breast cancer cells.

Results

In particular, the enzyme horseradish peroxidase (HRP) – which oxidizes the prodrug indole-3-acetic acid (IAA) to release toxic oxidative species – is incorporated on gold nanoconjugates (HRP-AuNCs), obtaining an efficient nanoplatform for EPT. The nanodevice is biocompatible and effectively internalized by breast cancer cell lines. Remarkably, co-treatment with HRP-AuNCs and IAA (HRP-AuNCs/IAA) reduces the viability of breast cancer cells below 5%. Interestingly, 3D tumor models (multicellular tumor spheroid-like cultures) co-treated with HRP-AuNCs/IAA exhibit a 74% reduction of cell viability, whereas the free formulated components (HRP, IAA) have no effect.

Conclusion

Altogether, our results demonstrate that the designed HRP-AuNCs nanoformulation shows a remarkable therapeutic performance. These findings might help to bypass the clinical limitations of current tumor enzyme therapies and advance towards the use of nanoformulations for EPT in breast cancer.

Conversion of lignin-derived 3-methoxycatechol to the natural product purpurogallin using bacterial P450 GcoAB and laccase CueO

Purpurogallin is a natural benzotropolone extracted from Quercus spp, which has antioxidant, anticancer, and anti-inflammatory properties. Purpurogallin is typically synthesized from pyrogallol using enzymatic or metal catalysts, neither economically feasible nor environmentally friendly. 3-Methoxycatechol (3-MC) is a lignin-derived renewable chemical with the potential to be a substrate for the biosynthesis of purpurogallin. In this study, we designed a pathway to produce purpurogallin from 3-MC. We first characterized four bacterial laccases and identified the laccase CueO from Escherichia coli, which converts pyrogallol to purpurogallin. Then, we used CueO and the P450 GcoAB reported to convert 3-MC to pyrogallol, to construct a method for producing purpurogallin directly from 3-MC. A total of 0.21 ± 0.05 mM purpurogallin was produced from 5 mM 3-MC by whole-cell conversion. This study provides a new method to enable efficient and sustainable synthesis of purpurogallin and offers new insights into lignin valorization. KEY POINTS: • Screening four bacterial laccases for converting pyrogallol to purpurogallin. • Laccase CueO from Escherichia coli presenting the activity for purpurogallin yield. • A novel pathway for converting lignin-derived 3-methoxycatechol to purpurogallin.

Production of Recombinant Horseradish Peroxidase in an Engineered Cell-free Protein Synthesis System

One of the main advantages of a cell-free synthesis system is that the synthetic machinery of cells can be modularized and re-assembled for desired purposes. In this study, we attempted to combine the translational activity of Escherichia coli extract with a heme synthesis pathway for the functional production of horseradish peroxidase (HRP). We first optimized the reaction conditions and the sequence of template DNA to enhance protein expression and folding. The reaction mixture was then supplemented with 5-aminolevulinic acid synthase to facilitate co-synthesis of the heme prosthetic group from glucose. Combining the different synthetic modules required for protein synthesis and cofactor generation led to successful production of functional HRP in a cell-free synthesis system.

A Ready-to-Use Metal-Supported Bilayer Lipid Membrane Biosensor for the Detection of Phenol in Water

This work presents a novel metal-supported bilayer lipid membrane (BLM) biosensor built on tyrosinase to quantitate phenol. The detection strategy is based on the enzyme-analyte initial association and not the commonly adopted monitoring of the redox cascade reactions; such an approach has not been proposed in the literature to date and offers many advantages for environmental monitoring with regard to sensitivity, selectivity, reliability and assay simplicity. The phenol sensor developed herein showed good analytical and operational characteristics: the detection limit (signal-to-noise ratio = 3) was 1.24 pg/mL and the sensitivity was 33.45 nA per pg/mL phenol concentration. The shelf life of the tyrosinase sensor was 12 h and the lifetime (in consecutive assays) was 8 h. The sensor was reversible with bathing at pH 8.5 and could be used for eight assay runs in consecutive assays. The validation in real water samples showed that the sensor could reliably detect 2.5 ppb phenol in tap and river water and 6.1 ppb phenol in lake water, without sample pretreatment. The prospects and applicability of the proposed biosensor and the underlying technology are also discussed.

Nanoencapsulation as a General Solution for Lyophilization of Labile Substrates

Protein macromolecules occur naturally at the nanoscale. The use of a dedicated nanoparticle as a lyophilization excipient, however, has not been reported. Because biopolymeric and lipid nanoparticles often denature protein macromolecules and commonly lack the structural rigidity to survive the freeze-drying process, we hypothesized that surrounding an individual protein substrate with a nanoscale, thermostable exoshell (tES) would prevent aggregation and protect the substrate from denaturation during freezing, sublimation, and storage. We systematically investigated the properties of tES, including secondary structure and its homogeneity, throughout the process of lyophilization and found that tES have a near 100% recovery following aqueous reconstitution. We then tested the hypothesis that tES could encapsulate a model substrate, horseradish peroxidase (HRP), using charge complementation and pH-mediated controlled assembly. HRP were encapsulated within the 8 nm internal tES aqueous cavity using a simplified loading procedure. Time-course experiments demonstrated that unprotected HRP loses 95% of activity after 1 month of lyophilized storage. After encapsulation within tES nanoparticles, 70% of HRP activity was recovered, representing a 14-fold improvement and this effect was reproducible across a range of storage temperatures. To our knowledge, these results represent the first reported use of nanoparticle encapsulation to stabilize a functional macromolecule during lyophilization. Thermostable nanoencapsulation may be a useful method for the long-term storage of labile proteins.

Enzyme prodrug therapy: cytotoxic potential of paracetamol turnover with recombinant horseradish peroxidase

Targeted cancer treatment is a promising, less invasive alternative to chemotherapy as it is precisely directed against tumor cells whilst leaving healthy tissue unaffected. The plant-derived enzyme horseradish peroxidase (HRP) can be used for enzyme prodrug cancer therapy with indole-3-acetic acid or the analgesic paracetamol (acetaminophen). Oxidation of paracetamol by HRP in the presence of hydrogen peroxide leads to N-acetyl-p-benzoquinone imine and polymer formation via a radical reaction mechanism. N-acetyl-p-benzoquinone imine binds to DNA and proteins, resulting in severe cytotoxicity. However, plant HRP is not suitable for this application since the foreign glycosylation pattern is recognized by the human immune system, causing rapid clearance from the body. Furthermore, plant-derived HRP is a mixture of isoenzymes with a heterogeneous composition. Here, we investigated the reaction of paracetamol with defined recombinant HRP variants produced in E. coli, as well as plant HRP, and found that they are equally effective in paracetamol oxidation at a concentration ≥ 400 µM. At low paracetamol concentrations, however, recombinant HRP seems to be more efficient in paracetamol oxidation. Yet upon treatment of HCT-116 colon carcinoma and FaDu squamous carcinoma cells with HRP-paracetamol no cytotoxic effect was observed, neither in the presence nor absence of hydrogen peroxide.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s00706-021-02848-x.

Multicommutated Flow Analysis System for Determination of Horseradish Peroxidase and Its Inhibitors

A fully mechanized multicommutated flow analysis (MCFA) system dedicated to determining horseradish peroxidase (HRP) activity was developed. Detection was conducted using a flow-through optoelectronic detector-constructed of paired LEDs operating according to the paired emitter-detector diode (PEDD) principle. The PEDD-MCFA system is dedicated to monitoring the enzyme-catalyzed oxidation of p-phenylenediamine (pPD) by a hydrogen peroxide. Under optimized conditions, the presented bioanalytical system was characterized by a linear response range (33.47-200 U/L) with a detection limit at 10.54 U/L HRP activity and 1.66 mV·L/U sensitivity, relatively high throughput (12 signals recordings per hour), and acceptable precision (RSD below 6%). Additionally, the utility of the developed PEDD-MCFA system for the determination of HRP inhibitors allowing the detection of selected thiols at micromolar levels, is demonstrated. The practical utility of the flow system was illustrated by the analysis of some dietary supplements containing L-cysteine, N-acetylcysteine, and L-glutathione.

Potential of unglycosylated horseradish peroxidase variants for enzyme prodrug cancer therapy

Fighting cancer still relies on chemo- and radiation therapy, which is a trade-off between effective clearance of malignant cells and severe side effects on healthy tissue. Targeted cancer treatment on the other hand is a promising and refined strategy with less systemic interference. The enzyme horseradish peroxidase (HRP) exhibits cytotoxic effects on cancer cells in combination with indole-3-acetic acid (IAA). However, the plant-derived enzyme is out of bounds for medical purposes due to its foreign glycosylation pattern and resulting rapid clearance and immunogenicity. In this study, we generated recombinant, unglycosylated HRP variants in Escherichia coli using random mutagenesis and investigated their biochemical properties and suitability for cancer treatment. The cytotoxicity of the HRP-IAA enzyme prodrug system was assessed in vitro with HCT-116 human colon, FaDu human nasopharyngeal squamous cell carcinoma and murine colon adenocarcinoma cells (MC38). Extensive cytotoxicity was shown in all three cancer cell lines: the cell viability of HCT-116 and MC38 cells treated with HRP-IAA was below 1% after 24 h incubation and the surviving fraction of FaDu cells was ≤ 10% after 72 h. However, no cytotoxic effect was observed upon in vivo intratumoral application of HRP-IAA on a MC38 tumor model in C57BL/6J mice. However, we expect that targeting of HRP to the tumor by conjugation to specific antibodies or antibody fragments will reduce HRP clearance and thereby enhance therapy efficacy.