Construction of ATP-Switched Allosteric Antioxidant Selenoenzyme

Improving Catalytic Activity, Acid-Tolerance, and Thermal Stability of Glutathione Peroxidase by Systematic Site-Directed Selenocysteine Incorporation

Glutathione peroxidase (GPx) is an important antioxidant enzyme. Selenocysteine (Sec)-containing GPxs (Sec-GPxs) are usually superior to their conventional cysteine-containing counterparts (Cys-GPxs), which make up the majority of the natural GPxs but display unsuitable activity and stability for industrial applications. This study first heterologously expressed and characterized a Cys-GPx from Lactococcus lactis (LlGPx), systematically exchanged all the three Cys to Sec and introduced an extra Sec. The results showed that the insertion of Sec at the active site could effectively increase the enzyme activity and confer a lower optimal pH value on the mutants. The double mutant C36U/L157U increased by 2.65 times (5.12 U/mg). The thermal stability of the C81U mutant was significantly improved. These results suggest that site-directed Sec incorporation can effectively improve the enzymatic properties of LlGPx, which may be also used for the protein engineering of other industrial enzymes containing catalytic or other functional cysteine residues.

Chemical Modification for the "off-/on" Regulation of Enzyme Activity

Enzymes with excellent catalytic performance play important roles in living organisms. Advances in strategies for enzyme chemical modification have enabled powerful strategies for exploring and manipulating enzyme functions and activities. Based on the development of chemical enzyme modifications, incorporating external stimuli-responsive features-for example, responsivity to light, voltage, magnetic force, pH, temperature, redox activity, and small molecules-into a target enzyme to turn "on" and "off" its activity has attracted much attention. The ability to precisely control enzyme activity using different approaches would greatly expand the chemical biology toolbox for clarification and detection of signal transduction and in vivo enzyme function and significantly promote enzyme-based disease therapy. This review summarizes the methods available for chemical enzyme modification mainly for the off-/on control of enzyme activity and particularly highlights the recent progress regarding the applications of this strategy. This article is protected by copyright. All rights reserved.

Carbon dots as nanocatalytic medicine for anti-inflammation therapy

Aberrant reactive oxygen species (ROS) generation is one of the crucial mediators in the pathogenesis of inflammation. So, the development of nanocatalytic medicine to catalyze the ROS-scavenging reactions in pathological regions are promising for anti-inflammatory therapy. Herein, a type of biocompatible metal free carbon dots is prepared via a hydrothermal method which can exhibit peroxidase (POD)-like, catalase (CAT)-like and superoxide dismutase (SOD)-like activities. It has been found that the carbon dots have the capability to efficiently deplete the excessive ROS such as peroxide (H₂O₂)_, superoxide anion (O₂^-) and hydroxyl radical (OH) for their abundant functional groups. After the tail injection in mice with liver inflammation induced by lipopolysaccharide, the carbon dots efficiently reduced the excessive production of ROS and proinflammatory cytokines in vitro. Both in vitro and in vivo results endowed the biocompatible carbon dots with great potential in nanocatalytic medicine for the treatment of disease.

Synergistic Interactions Are Prevalent in Catalytic Amyloids

Interactions between multiple functional groups are key to catalysis. Previously, we reported synergistic interactions in catalytic amyloids formed by mixtures of heptameric peptides that lead to significant improvements in esterase activity. Herein, we describe the in-depth investigation of synergistic interactions within a family of amyloid fibrils, exploring the results of functional group interactions, the effects of chirality and the use of mixed enantiomers within fibrils. Remarkably, we find that synergistic interactions (either positive or negative) are found in the vast majority of binary mixtures of catalytic amyloid-forming peptides. The productive arrangements of functionalities rapidly identified by mixing different peptides will undoubtedly lead to the development of more active catalysts for a variety of different transformations.

Minimalist de novo Design of Protein Catalysts

The field of protein design has grown enormously in the past few decades. In this review we discuss the minimalist approach to design of artificial enzymes, in which protein sequences are created with the minimum number of elements for folding and function. This method relies on identifying starting points in catalytically inert scaffolds for active site installation. The progress of the field from the original helical assemblies of the 1980s to the more complex structures of the present day is discussed, highlighting the variety of catalytic reactions which have been achieved using these methods. We outline the strengths and weaknesses of the minimalist approaches, describe representative design cases and put it in the general context of the de novo design of proteins.

Catalytic antioxidants for therapeutic medicine

In this Review, we focus on catalytic antioxidant study based on transition metal complexes, organoselenium compounds, supramolecules and protein scaffolds.

One-pot synthesis of biomimetic glutathione peroxidase with temperature responsive catalytic behaviors

Excessive reactive oxygen free radicals (ROS) are the main cause of various oxidative diseases. It is of great significance to develop antioxidant drugs that can intelligently regulate free radical concentrations. The biomimetic simulation of glutathione peroxidase (GPx) can provide an important theoretical basis for the development of antioxidant drugs. In order to explore a simple and efficient strategy for constructing biomimetic GPx, a microgel biomimetic GPx (PNTegel) with temperature responsive catalytic activity was prepared by a one-pot synthesis method. The PNTegel, with typical enzymatic catalytic characteristics, exhibited a maximum catalytic activity at 37 °C (υ₀ = 11.51 mM min⁻¹). The investigation of the catalytic mechanism of PNTegel suggested that the binding of different hydrophobic substrates to PNTegel was altered by the change of hydrophobicity of poly(N-isopropylacrylamide) (PNIPAM) in the microgel scaffold of PNTegel during the temperature response process. The change of hydrophobicity was the main factor for regulating the catalytic activity of PNTegel, which resulted in a temperature responsive catalytic behavior of PNTegel. This new strategy for the simple and efficient construction of biomimetic GPx by a one-pot method provides important theoretical support for exploring the preparation of highly effective antioxidant drugs.

A microgel-based biomimetic glutathione peroxidase with temperature responsive catalytic behavior is synthesized by integrating atom transfer radical polymerization (ATRP) technology into one-pot synthesis.

Multi-trichothecene mycotoxin exposure activates glutathione-redox system in broiler chicken

Co-occurrence of mycotoxin contamination of feeds is a frequent problem, therefore the purpose of this study was to evaluate the combined effect of T-2 toxin and deoxynivalenol (DON) on lipid peroxidation, parameters and regulation of the glutathione redox system in broiler chickens in a sub-chronic (7 day) study. The applied doses were: low mix: 0.23 mg T-2 toxin and 4.96 mg DON/kg feed; medium mix: 1.21 mg T-2 toxin and 12.38 mg DON/kg feed; and high mix: 2.42 T-2 toxin and 24.86 mg DON/kg feed. Liver samples were taken on days 0, 1, 2, 3, and 7 of the feeding trial. Lipid peroxidation decreased significantly as compared to the control on days 3 and 7 as effect of low and high doses, which can be related to the activation of the antioxidant system, which is supported by the elevated glutathione peroxidase activity and reduced glutathione concentration as compared to the control on day 3 in the medium and high dose groups. Gene expression of glutathione peroxidase 4 (GPX4) elevated on day 1 in a dose dependent manner, and showed continuous elevation in the highest dose group thereafter. The results suggested that common exposure of T-2 toxin and DON induced oxidative stress in the liver of broiler chickens, which activated the enzymatic antioxidant system, and consequently decreased lipid peroxidation.

Changes in the regulation and activity of glutathione redox system, and lipid peroxidation processes in short-term aflatoxin B1 exposure in liver of laying hens

The purpose of this study was to investigate the short-term (48 hr) effects of feeding aflatoxin contaminated diet (170.3 μg/kg AFB1) in 49-week-old laying hens. Liver samples were taken at 12-hr intervals. Feed intake, body weight, absolute and relative liver weight were the same in groups. However, there was no feed intake during both dark periods (between 12nd to 24th and 36th to 48th hours of the experiment); therefore, aflatoxin intake was also negligible. Markers of initial phase of lipid peroxidation, conjugated dienes and trienes did not change as effect of aflatoxin, but terminal marker, malondialdehyde content was significantly higher at 12 hr as effect of aflatoxin. No significant difference was found in reduced glutathione concentration and glutathione peroxidase activity between the groups. Expression of glutathione peroxidase 4 gene (GPX4) was significantly reduced due to aflatoxin treatment at 12 and 24 hr, but induced later, while glutathione reductase gene (GSR) expression was significantly lower at 24 hr and glutathione synthetase gene (GSS) in aflatoxin-treated group at 12 hr. The results suggest that aflatoxin induced oxygen-free radical formation, but it did not reach critical level during this short period of time to cause activation of the expression of glutathione system.

Rational and Semirational Protein Design

This mini review gives an overview over different design approaches and methodologies applied in rational and semirational enzyme engineering. The underlying principles for engineering novel activities, enantioselectivity, substrate specificity, stability, and pH optimum are summarized.

The Small Glutathione Peroxidase Mimic 5P May Represent a New Strategy for the Treatment of Liver Cancer

Glutathione peroxidase (GPx) is an antioxidant protein containing selenium. Owing to the limitations of native GPx, considerable efforts have been made to develop GPx mimics. Here, a short 5-mer peptides (5P) was synthesized and characterized using matrix-assisted laser desorption ionization time-of-flight mass spectrometry. Enzyme coupled assays were used to evaluate GPx activity. The cell viability and apoptosis of H22 cells were tested, and mice bearing H22 cell-derived tumors were used to determine the effects of 5P on tumor inhibition. In comparison with other enzyme models, 5P provided a suitable substrate with proper catalytic site positions, resulting in enhanced catalytic activity. In our mouse model, 5P showed excellent inhibition of tumor growth and improved immunity. In summary, our findings demonstrated the design and synthesis of the small 5P molecule, which inhibited tumor growth and improved immunity. Notably, 5P could inhibit tumor growth without affecting normal growth. Based on these advantages, the novel mimic may have several clinical applications.