Noncovalent and covalent immobilization of oxygenase on single-walled carbon nanotube for enzymatic decomposition of aromatic hydrocarbon intermediates

Implementation of cytochrome c proteins and carbon nanotubes hybrids in bioelectrodes towards bioelectrochemical systems applications

Multiheme cytochrome c (Cyt c) can function as a redox protein on electrode to accomplish bioelectrocatalysis. However, the direct electron transfer (DET) between the redox site of Cyt c and electrode is low due to the large coupling distance. A close proximity or a connection pathway from the deeply buried active site to the protein surface can be established by modifying the electrode with carbon nanotubes (CNTs) to improve the DET. Therefore, the isolated Cyt c has been assembled or casted with CNTs by various processes to form Cyt c-CNTs bioelectrodes that can be further applied to biosensing and bioanalysis. These strategies can be transplanted to the fabrication of biofilm-CNTs based electrodes by complexing the out membrane (OM) Cyt c of natural electricigen with CNTs to realize the application of the electrochemical properties of "in vivo" Cyt c to bioelectrochemical systems (BESs). This review intends to highlight the preparation strategies of bioelectrodes that have been well studied in electrochemical biosensors and improving approaches of the DET from the CNTs surface to Cyt c in their hybrids. The efficient fabrication processes of the biofilm-CNTs based electrodes that can be considered as "in vivo" Cyt c-CNTs based electrodes for BES designs are also summarized, aiming to provide an inspiration source and a reference to the related studies of BES downstream.

Oxidoreductase enzymes: Characteristics, applications, and challenges as a biocatalyst

Oxidoreductases are enzymes with distinctive characteristics that favor their use in different areas, such as agriculture, environmental management, medicine, and analytical chemistry. Among these enzymes, oxidases, dehydrogenases, peroxidases, and oxygenases are very interesting. Because their substrate diversity, they can be used in different biocatalytic processes by homogeneous and heterogeneous catalysis. Immobilization of these enzymes has favored their use in the solution of different biotechnological problems, with a notable increase in the study and optimization of this technology in the last years. In this review, the main structural and catalytical features of oxidoreductases, their substrate specificity, immobilization, and usage in biocatalytic processes, such as bioconversion, bioremediation, and biosensors obtainment, are presented.

Covalent conjugation of proteins onto fluorescent single-walled carbon nanotubes for biological and medical applications

Single-walled carbon nanotubes (SWCNTs) have optical properties that are conducive for biological applications such as sensing, delivery, and imaging. These applications necessitate the immobilization of macromolecules that can serve as therapeutic drugs, molecular templates, or modulators of surface interactions. Although previous studies have focused on non-covalent immobilization strategies, recent advances have introduced covalent functional handles that can preserve or even enhance the SWCNT optical properties. This review presents an overview of covalent sidewall modifications of SWCNTs, with a focus on the latest generation of "sp³ defect" modifications. We summarize and compare the reaction conditions and the reported products of these sp³ chemistries. We further review the underlying photophysics governing SWCNT fluorescence and apply these principles to the fluorescence emitted from these covalently modified SWCNTs. Finally, we provide an outlook on additional chemistries that could be applied to covalently conjugate proteins to these chemically modified, fluorescent SWCNTs. We review the advantages of these approaches, emerging opportunities for further improvement, as well as their implications for enabling new technologies.

A comprehensive review on bio-mimicked multimolecular frameworks and supramolecules as scaffolds for enzyme immobilization

Immobilization depicts a propitious route to optimize the catalytic performances, efficient recovery, minimizing autocatalysis, and also augment the stabilities of enzymes, particularly in unnatural environments. In this opinion, supramolecules and multimolecular frameworks have captivated immense attention to achieve profound controllable interactions between enzyme molecules and well-defined natural or synthetic architectures to yield protein bioconjugates with high accessibility for substrate binding and enhanced enantioselectivities. This scholastic review emphasizes the possibilities of associating multimolecular complexes with biological entities via several types of interactions, namely covalent interactions, host-guest complexation, π - π ${\rm{\pi }}-{\rm{\pi }}$ interactions, intra/inter hydrogen bondings, electrostatic interactions, and so forth offers remarkable applications for the modulations of enzymes. The potential synergies between artificial supramolecular structures and biological systems are the primary concern of this pedagogical review. The majority of the research primarily focused on the dynamic biomolecule-responsive supramolecular assemblages and multimolecular architectures as ideal platforms for the recognition and modulation of proteins and cells. Embracing sustainable green demeanors of enzyme immobilizations in a quest to reinforce site-selectivity, catalytic efficiency, and structural integrality of enzymes are the contemporary requirements of the biotechnological sectors that instigate the development of novel biocatalytic systems.

Lignocellulosic residues as supports for enzyme immobilization, and biocatalysts with potential applications

Growing demand for agricultural production means a higher quantity of residues produced. The reuse and recycling of agro-industrial wastes reduce worldwide greenhouse emissions. New opportunities are derived from this kind of residuals in the biotechnological field generating valuable products in growing sectors such as transportation, bioenergy, food, and feedstock. The use of natural macromolecules towards biocatalysts offers numerous advantages over free enzymes and friendliness with the environment. Enzyme immobilization improves enzyme properties (stability and reusability), and three types of supports are discussed: inorganic, organic, and hybrid. Several examples of agro-industrial wastes such as coconut wastes, rice husks, corn residues and brewers spent grains (BSG), their properties and potential as supports for enzyme immobilization are described in this work. Before the immobilization, biological and non-biological pretreatments could be performed to enhance the waste potential as a carrier. Additionally, immobilization methods such as covalent binding, adsorption, cross-linking and entrapment are compared to provide high efficiency. Enzymes and biocatalysts for industrial applications offer advantages over traditional chemical processes with respect to sustainability and process efficiency in food, energy, and bioremediation fields. The wastes reviewed in this work demonstrated a high affinity for lipases and laccases and might be used in biodiesel production and textile wastewater treatment, among other applications.

Characterization of Gentisate 1,2-Dioxygenase from Pseudarthrobacter phenanthrenivorans Sphe3 and Its Stabilization by Immobilization on Nickel-Functionalized Magnetic Nanoparticles

The aim of this study was the biochemical and kinetic characterization of the gentisate 1,2-dioxygenase (GDO) from Pseudarthrobacter phenanthrenivorans Sphe3 and the development of a nanobiocatalyst by its immobilization on Ni2+-functionalized Fe3O4-polydopamine magnetic nanoparticles (Ni2+-PDA-MNPs). This is the first GDO to be immobilized. The gene encoding the GDO was cloned with an N-terminal His-tag and overexpressed in E. coli. The nanoparticles showed a high purification efficiency of GDO from crude cell lysates with a maximum activity recovery of 97%. The immobilized enzyme was characterized by Fourier transform infrared spectroscopy (FTIR). The reaction product was identified by 1H NMR. Both free and immobilized GDO exhibited Michaelis–Menten kinetics with Km values of 25.9 ± 4.4 and 82.5 ± 14.2 μM and Vmax values of 1.2 ± 0.1 and 0.03 ± 0.002 mM*s−1, respectively. The thermal stability of the immobilized GDO was enhanced at 30 °C, 40 °C, and 50 °C, compared to the free GDO. Stored at −20 °C, immobilized GDO retained more than 60% of its initial activity after 30 d, while the free enzyme completely lost its activity after 10 d. Furthermore, the immobilized nanoparticle–enzyme conjugate retained more than 50% enzyme activity up to the fifth cycle.

Recent advances in carbon nanotubes-based biocatalysts and their applications

Enzymes have been incorporated into a wide variety of fields and industries as they catalyze many biochemical and chemical reactions. The immobilization of enzymes on carbon nanotubes (CNTs) for generating nano biocatalysts with high stability and reusability is gaining great attention among researchers. Functionalized CNTs act as excellent support for effective enzyme immobilization. Depending on the application, the enzymes can be tailored using the various surface functionalization techniques on the CNTs to extricate the desirable characteristics. Aiming at the preparation of efficient, stable, and recyclable nanobiocatalysts, this review provides an overview of the methods developed to immobilize the various enzymes. Various applications of carbon nanotube-based biocatalysts in water purification, bioremediation, biosensors, and biofuel cells have been comprehensively reviewed.

Enrichment and purification of red pigments from defective mulberry fruits using biotransformation in a liquid-liquid-solid three-phase system

A large number of defective mulberries are discarded each year because mulberries are easy to break. The red pigments from defective mulberries are recognized as the sustainable sources of anthocyanins extracted from nature. Cyanidin-3-O-rutinoside and cyanidin-3-O-glucoside are the main components of mulberry red pigments, accounting for 50% and 40% of the total, respectively. Cyanidin-3-O-glucoside exhibits anticancer, hypoglycemic, and liver and visceral protection properties. Cyanidin-3-O-glucoside can be prepared by enzymatically hydrolyzing the rhamnosidase bond of cyanidin-3-O-rutinoside. To obtain mulberry red pigment with a high purity of cyanidin-3-O-glucoside, immobilized α-L-rhamnosidase was added to the aqueous two-phase system to construct a liquid-liquid-solid three-phase enzyme catalytic system. After optimization, the three-phase system was composed of 27.12% (w/w) ethanol, 18.10% (w/w) ammonium sulfate, 15% (w/w) mulberry juice, 4.24% (w/w) immobilized α-L-rhamnosidase, and 35.54% (w/w) pure water. The three-phase system was employed to enrich and purify cyanidin-3-O-glucoside at pH 5 and 45 °C for 1 h. The purity of cyanidin-3-O-glucoside was increased from 40 to 82.42% with cyanidin-3-O-rutinoside conversion of 60.68%. The immobilized α-L-rhamnosidase could be reused seven times, maintaining a relative activity of over 50%. Overall, the developed system provided an efficient and simple approach for high purity mulberry red pigment production and recycling in the field of sustainable agriculture. Graphical abstract.

Trends in the development of innovative nanobiocatalysts and their application in biocatalytic transformations

The ever-growing demand for cost-effective and innocuous biocatalytic transformations has prompted the rational design and development of robust biocatalytic tools. Enzyme immobilization technology lies in the formation of cooperative interactions between the tailored surface of the support and the enzyme of choice, which result in the fabrication of tremendous biocatalytic tools with desirable properties, complying with the current demands even on an industrial level. Different nanoscale materials (organic, inorganic, and green) have attracted great attention as immobilization matrices for single or multi-enzymatic systems. Aiming to unveil the potentialities of nanobiocatalytic systems, we present distinct immobilization strategies and give a thorough insight into the effect of nanosupports specific properties on the biocatalysts' structure and catalytic performance. We also highlight the development of nanobiocatalysts for their incorporation in cascade enzymatic processes and various types of batch and continuous-flow reactor systems. Remarkable emphasis is given on the application of such nanobiocatalytic tools in several biocatalytic transformations including bioremediation processes, biofuel production, and synthesis of bioactive compounds and fine chemicals for the food and pharmaceutical industry.

Development of biocatalysts immobilized on coal ash-derived Ni-zeolite for facilitating 4-chlorophenol degradation

A new type of biocatalyst was developed to facilitate the biochemical decomposition of 4-chlorophenol (4-CP) in this study. Oxydoreductases that catalyze the initial steps of 4-CP biodegradation were immobilized on a synthetic inorganic enzyme support. Type-X zeolite, a high-surface area support, was synthesized from coal fly ash, on which nickel ions were plated by impregnation (Ni-zeolite), followed by the effective immobilization (77.5% immobilization yield) of recombinant monooxygenase (CphC-I), dioxygenase (CphA-I), and flavin reductase (Fre) isolated from Pseudarthrobacter chlorophenolicus A6 and Escherichia coli K-12, respectively. The retained catalytic activity of the enzymes immobilized on Ni-zeolite was as high as 64% of the value for the corresponding free enzymes. The Michaelis-Menten kinetic parameters v_max and K_M of the immobilized enzymes were determined to be 0.20 mM·min^-1 and 0.44 mM, respectively. These results are expected to provide useful information with respect to the development of novel enzymatic treatments for phenolic hydrocarbon contaminants.

Organic micropollutants paracetamol and ibuprofen-toxicity, biodegradation, and genetic background of their utilization by bacteria

Currently, analgesics and nonsteroidal anti-inflammatory drugs (NSAIDs) are classified as one of the most emerging group of xenobiotics and have been detected in various natural matrices. Among them, monocyclic paracetamol and ibuprofen, widely used to treat mild and moderate pain are the most popular. Since long-term adverse effects of these xenobiotics and their biological and pharmacokinetic activity especially at environmentally relevant concentrations are better understood, degradation of such contaminants has become a major concern. Moreover, to date, conventional wastewater treatment plants (WWTPs) are not fully adapted to remove that kind of micropollutants. Bioremediation processes, which utilize bacterial strains with increased degradation abilities, seem to be a promising alternative to the chemical methods used so far. Nevertheless, despite the wide prevalence of paracetamol and ibuprofen in the environment, toxicity and mechanism of their microbial degradation as well as genetic background of these processes remain not fully characterized. In this review, we described the current state of knowledge about toxicity and biodegradation mechanisms of paracetamol and ibuprofen and provided bioinformatics analysis concerning the genetic bases of these xenobiotics decomposition.

Identification of the upstream 4-chlorophenol biodegradation pathway using a recombinant monooxygenase from Arthrobacter chlorophenolicus A6

This study aimed to clarify the initial 4-chlorophenol (4-CP) biodegradation pathway promoted by a two-component flavin-diffusible monooxygenase (TC-FDM) consisting of CphC-I and CphB contained in Arthrobacter chlorophenolicus A6 and the decomposition function of CphC-I. The TC-FDM genes were cloned from A. chlorophenolicus A6, and the corresponding enzymes were overexpressed. Since CphB was expressed in an insoluble form, Fre, a flavin reductase obtained from Escherichia coli, was used. These enzymes were purified using Ni²⁺-NTA resin. It was confirmed that TC-FDM catalyzes the oxidation of 4-CP and the sequential conversion of 4-CP to benzoquinone (BQN)→hydroquinone (HQN)→HQL. This indicated that CphC-I exhibits substrate specificity for 4-CP, BQN, and HQN. The activity of CphC-I for 4-CP was 63.22U/mg-protein, and the Michaelis-Menten kinetic parameters were v_max=0.21mM/min, K_M=0.19mM, and k_cat/K_M=0.04mM^-1min^-1. These results would be useful for the development of a novel biochemical treatment technology for 4-CP and phenolic hydrocarbons.

Advances in biotechnological synthetic applications of carbon nanostructured systems

In the last few years carbon nanostructures have been applied for the immobilization of enzymes and biomimetic organo-metallic species useful for biotechnological applications. The nature of the support and the method of immobilization are responsible for the stability, reactivity and selectivity of the system. In this review, we focus on the recent advances in the use of carbon nanostructures, carbon nanotubes, carbon nanorods, fullerene and graphene for the preparation of biocatalytic and biomimetic systems and for their application in the development of green chemical processes.