Introducing a covalent thiol-based protected immobilized acetylcholinesterase with enhanced enzymatic performances for biosynthesis of esters

Developing a label-free full-range highly selective pH nanobiosensor using a novel high quantum yield pH-responsive activated-protein-protected gold nanocluster prepared by a novel ultrasonication-protein-assisted procedure

A novel, label-free, ultra-selective, reproducible, and reversible pH nanobiosensor was developed for analyzing biofluids, food samples, and real water media utilizing a novel activated-protein-protected gold nanocluster with an ultra-narrow emission band, termed as ABSA-AuNCs. The ABSA-AuNCs were synthesized via a novel ultrasonication-protein-assisted procedure, for the first time, using activated bovine serum albumin as both capping and reducing agents. The ABSA-AuNCs revealed a highly narrow symmetric emission spectrum (λmax = 330.0 nm upon excitation at 312-317 nm), and a highly narrow size distribution of 2.9-3.7 nm along with an enhanced quantum yield of 28.3 %. At present, with a full width at half maximum (FWHM) of 14.0 nm, ABSA-AuNCs have the narrowest bandwidth of fluorescent nanomaterials reported to date. The ABSA-AuNCs were characterized for their stability, size, morphology, crystallinity, structural, and optical properties. The ABSA-AuNCs were found to be appropriate for constructing a label-free ultraselective pH nanobiosensor. A linear range over 2.0-11.0, fast response time of less than 5 s, and long-term stability of 99.7 % after 500 min were achieved. The %RSD for repeatability, intra-day reproducibility, and inter-day reproducibility was found to be 1.4 %, 1.7 %, and 2.3 %, in order, to reveal high repeatable and reproducible results. The selectivity of the pH biosensor was evaluated upon the addition of different interferents, indicating an excellent pH selectivity for the ABSA-AuNCs. Real sample analysis proved the feasibility of the ABSA-AuNCs for accurate, precise, and reliable pH sensing in biofluids (undiluted blood and urine), a variety of food samples, and several real water samples.

Developing a novel ultraselective and ultrasensitive label-free direct spectrofluorimetric nanobiosensor for direct highly fast field detection of explosive triacetone triperoxide

BACKGROUND

Direct detection of the notorious explosive triacetone triperoxide (TATP) is very difficult because it lacks facile ionization and UV absorbance or fluorescence. Besides, the current indirect methods are time-consuming and need a pre-step for TATP cleavage to hydrogen peroxide. Moreover, they commonly show significant false-positive results in the presence of some camouflage which limits their field applications. Herein, for the first time, a novel label-free field-applicable spectrofluorimetric nanobiosensor was developed for direct TATP detection using a novel activated-protein protected gold nanocluster (ABSA-AuNCs; QY = 28.3 %) synthesized by a combined protein-assisted-ultrasonication procedure.

RESULTS

The ABSA-AuNCs revealed a fluorescence spectrum centered at 330.0 nm which was significantly quenched by TATP (binding constant = 154.06 M-1; ΔG = -12.5 kJ mol-1; E(%) = 88.5 %). This phenomenon was used as a basis for direct TATP quantification, providing a working range of 0.01-40.0 mg L-1 and a detection limit of 6.7 μg L-1 which is the lowest LOD provided for TATP detection up to now. A %RSD of 0.9 % and 1.56 % was obtained for repeatability and inter-day reproducibility, respectively. The selectivity was checked against a variety of camouflages, revealing ultra-selectivity. Several synthetic samples prepared by several camouflages and real samples (clay soil and real water media) were analyzed, revealing quantitative recoveries of TATP.

SIGNIFICANCE

During the production of the notorious explosive TATP, it can be discharged into water and soil. This novel method eliminated the false-positive results of traditional methods and is applicable for direct quantitative detection of camouflaged TATP and its residues in real soil and water samples in a highly short response time (2 min). The camouflaged TATP analysis is important for tracking the terrorist attacks in field conditions and analysis of soil and water can provide a first indication of the location of the production site.

Crystal structure of urethanase from Candida parapsilosis and insights into the substrate-binding through in silico mutagenesis and improves the catalytic activity and stability

Ethyl carbamate (EC) is classified as a Class 2A carcinogen, and is present in various fermented foods, posing a threat to human health. Urethanase (EC 3.5.1.75) can catalyze EC to produce ethanol, CO2 and NH3. The urethanase (cpUH) from Candida parapsilosis can hydrolyze EC, but its low affinity and poor stability hinder its application. Here, the structure of cpUH from Candida parapsilosis was determined with a resolution of 2.66 Å. Through sequence alignment and site-directed mutagenesis, it was confirmed that cpUH contained the catalytic triad Ser-cisSer-Lys of the amidase family. Then, the structure-oriented engineering mutant N194V of urethanase was obtained. Its urethanase activity increased by 6.12 %, the catalytic efficiency (kcat/Km) increased by 21.04 %, and the enzyme stability was also enhanced. Modeling and molecular docking analysis showed that the variant N194V changed the number of hydrogen bonds between the substrate and the catalytic residue, resulting in enhanced catalytic ability. MD simulation also demonstrated that the introduction of hydrophobic amino acid Val reduced the RMSD value and increased protein stability. The findings of this study suggest that the N194V variant exhibits significant potential for industrial applications due to its enhanced affinity for substrate binding, improved catalytic efficiency, and increased enzyme stability.

Double domain fusion improves the reverse transcriptase activity and inhibitor tolerance of Bst DNA polymerase

To enhance the DNA/RNA amplification efficiency and inhibitor tolerance of Bst DNA polymerase, four chimeric Bst DNA polymerase by fusing with a DNA-binding protein Sto7d and/or a highly hydrophobic protein Hp47 to Bst DNA polymerase large fragment. One of chimeric protein HpStBL exhibited highest inhibitor tolerance, which retained high active under 0.1 U/μL sodium heparin, 0.8 ng/μL humic acid, 2.5× SYBR Green I, 8 % (v/v) whole blood, 20 % (v/v) tissue, and 2.5 % (v/v) stool. Meanwhile, HpStBL showed highest sensitivity (93.75 %) to crude whole blood infected with the African swine fever virus. Moreover, HpStBL showed excellent reverse transcriptase activity in reverse transcription loop-mediated isothermal amplification, which could successfully detect 0.5 pg/μL severe acute respiratory syndrome coronavirus 2 RNA in the presence of 1 % (v/v) stools. The fusion of two domains with different functions to Bst DNA polymerase would be an effective strategy to improve Bst DNA polymerase performance in direct loop-mediated isothermal amplification and reverse transcription loop-mediated isothermal amplification detection, and HpStBL would be a promising DNA polymerase for direct African swine fever virus/severe acute respiratory syndrome coronavirus 2 detection due to simultaneously increased inhibitor tolerance and reverse transcriptase activity.

Enzyme Immobilization using Covalent Organic Frameworks: From Synthetic Strategy to COFs Functional Role

Enzymes, a class of biocatalysts, exhibit remarkable catalytic efficiency, specificity, and selectivity, governing many reactions that are essential for various cascades within living cells. The immobilization of structurally flexible enzymes on appropriate supports holds significant importance in facilitating biomimetic transformations in extracellular environments. Covalent organic frameworks (COFs) have emerged as ideal candidates for enzyme immobilization due to high surface tunability, diverse chemical/structural designs, exceptional stability, and metal-free nature. Various immobilization techniques have been proposed to fabricate COF-enzyme biocomposites, offering significant enhancements in activity and reusability for COF-immobilized enzymes as well as new insights into developing advanced enzyme-based applications. In this review, we provide a comprehensive overview of state-of-the-art strategies for immobilizing enzymes within COFs by focusing on their applicability and versatility. These strategies are systematically summarized and compared by categorizing them into postsynthesis immobilization and in situ immobilization, where their respective strengths and limitations are thoroughly discussed. Combined with an overview of critical emerging applications, we further elucidate the multifaceted roles of COFs in enzyme immobilization and subsequent applications, highlighting the advanced biofunctionality achievable through COFs.

Efficient and novel biosynthesis of myricetin α-triglucoside with improved solubility using amylosucrase from Deinococcus deserti

Although myricetin (3,3',4',5,5',7-hexahydroxyflavone, MYR) has a high antioxidant capacity and health functions, its use as a functional food material is limited owing to its low stability and water solubility. Amylosucrase (ASase) is capable of biosynthesizing flavonol α-glycoside using flavonols as acceptor molecules and sucrose as a donor molecule. Here, ASase from Deinococcus deserti (DdAS) efficiently biosynthesizes a novel MYR α-triglucoside (MYRαG3) using MYR as the acceptor molecule. Comparative homology analysis and computational simulation revealed that DdAS has a different active pocket for the transglycosylation reaction. DdAS produced MYRαG3 with a conversion efficiency of 67.4 % using 10 mM MYR and 50 mM sucrose as acceptor and donor molecules, respectively. The structure of MYRαG3 was identified as MYR 4'-O-4″,6″-tri-O-α-D-glucopyranoside using NMR and LC-MS. In silico analysis confirmed that DdAS has a distinct active pocket compared to other ASases. In addition, molecular docking simulations predicted the synthetic sequence of MYRαG3. Furthermore, MYRαG3 showed a similar DPPH radical scavenging activity of 49 %, comparable to MYR, but with significantly higher water solubility, which increased from 0.03 μg/mL to 511.5 mg/mL. In conclusion, this study demonstrated the efficient biosynthesis of a novel MYRαG3 using DdAS and highlighted the potential of MYRαG3 as a functional material.

Targeted delivery of 5-fluorouracil and shikonin by blended and coated chitosan/pectin nanoparticles for treatment of colon cancer

Herein, 5-fluorouracil and shikonin (extracted from Fusarium tricinctum) were loaded in chitosan/pectin nanoparticle (CS/PEC-NPs), prepared by blending (B-CS/PEC-NPs) and coating (C-CS/PEC-NPs) methods. The nanoparticles characterized by Fourier Transform Infrared (FTIR), X-ray diffraction (XRD), Energy-dispersive X-ray (EDX), Scanning Electron Microscope (SEM) and Differential Light Scattering (DLS). Then, some properties of the nanoparticles such as drug release rate and the nanoparticles cytotoxicity were studied. The FTIR, XRD, EDX, SEM and DLS results showed that the nanoparticles synthesized properly with an almost spherical morphology, an average size of 82-93 nm for B-CS/PEC-NPs, an average diameter of below 100 nm (mostly 66-89 nm) for C-CS/PEC-NPs, and hydrodynamic diameter of 310-817 nm. The drug release results indicated the lower release rate of drugs for B-CS/PEC-NPs relative to C-CS/PEC-NPs at different pHs, high release rate of drugs for the nanoparticles in the simulated large intestinal fluids containing pectinase, and Korsmeyer-Peppas model for release of the drugs. The results showed more cytotoxicity of B-CS/PEC-NPs containing drugs, especially B-CS/PEC-NPs containing both drugs (B-CS/PEC/5-FU/SHK-NPs) after treating with pectinase (IC50 of 18.6 μg/mL). In conclusion, despite the limitation of C-CS/PEC-NPs for simultaneous loading of hydrophilic and hydrophobic drugs, B-CS/PEC-NPs showed suitable potency for loading and targeted delivery of the drugs.

Multiple strategies to improve extracellular secretion and activity of feruloyl esterase

Feruloyl esterase has a wide range of applications, but there are still problems with low enzyme yield and activity, and complex purification steps. Our previous research found Lactobacillus amylovorus feruloyl esterase could be secreted extracellular in Escherichia coli. In this study, multiple strategies were implemented to maximize the extracellular production of feruloyl esterase with improved activity in E. coli. Firstly, codon-optimized feruloyl esterase was obtained based on the preference of E. coli, resulting in 41.97 % increase in extracellular secretion. Furthermore, by cascading T7 promoters, replacing the 5' UTR, randomly mutating the N-terminal sequence, and co-expressing secretory cofactors, the extracellular secretion was increased by 36.46 %, 31.25 %, 20.66 % and 25.75 %, respectively. Moreover, the feruloyl esterase were mutated to improve the substrate affinity and activity. The catalytic efficiency of Fae-Q134T and Fae-Q198A increased by 4.62-fold and 5.42-fold. Combining above strategies, extracellular feruloyl esterase activity was increased from 2013.70 U/L to 10,349.04 U/L. These results indicated that the activity and yield of feruloyl esterase secreted by E. coli were significantly increased, which laid a foundation for its industrial application.

Enhancing the stability of a novel D-allulose 3-epimerase from Ruminococcus sp. CAG55 by interface interaction engineering and terminally attached a self-assembling peptide

D-allulose, a highly desirable sugar substitute, is primarily produced using the D-allulose 3-epimerase (DAE). However, the availability of usable DAE enzymes is limited. In this study, we discovered and engineered a novel DAE Rum55, derived from a human gut bacterium Ruminococcus sp. CAG55. The activity of Rum55 was strictly dependent on the presence of Co2+, and it exhibited an equilibrium conversion rate of 30.6 % and a half-life of 4.5 h at 50 °C. To enhance its performance, we engineered the interface interaction of Rum55 to stabilize its tetramer structure, and the best variant E268R was then attached with a self-assembling peptide to form active enzyme aggregates as carrier-free immobilization. The half-life of the best variant E268R-EKL16 at 50 °C was dramatically increased 30-fold to 135.3 h, and it maintained 90 % of its activity after 13 consecutive reaction cycles. Additionally, we identified that metal ions played a key role in stabilizing the tetramer structure of Rum55, and the dependence on metal ions for E268R-EKL16 was significantly reduced. This study provides a useful route for improving the thermostability of DAEs, opening up new possibilities for the industrial production of D-allulose.

Construction and Application of Nanozyme Sensor Arrays

Compared with traditional "lock-key mode" biosensors, a sensor array consists of a series of sensing elements based on intermolecular interactions (typically hydrogen bonds, van der Waals forces, and electrostatic interactions). At the same time, sensor arrays also have the advantages of fast response, high sensitivity, low energy consumption, low cost, rich output signals, and imageability, which have attracted widespread attention from researchers. Nanozymes are nanomaterials which own enzyme-like properties. Because of the adjustable activity, high stability, and cost effectiveness of nanozymes, they are potential candidates for construction of sensor arrays to output different signals from analytes through the chemoresponse of colorants, which solves the shortcomings of traditional sensors that they cannot support multiple detection and lack universality. Recently, a sensor array based on nanozymes as nonspecific recognition receptors has attracted much more attention from researchers and has been applied to precise recognition of proteins, bacteria, and heavy metals. In this perspective, attention is given to nanozymes and the regulation of their enzyme-like activity. Particularly, the building principles and methods for sensor arrays based on nanozymes are analyzed, and the applications are summarized. Finally, the approaches to overcome the challenges and perspectives are also presented and analyzed for facilitating further research and development of nanozyme sensor arrays. This perspective should be helpful for gaining insight into research ideas within the field of nanozyme sensor arrays.

Apple pectin-based active films to preserve oil: Effects of naturally branched phytoglycogen-curcumin host

Pectin has excellent film-forming properties, but its functional properties need to be enhanced. Therefore, we constructed naturally branched phytoglycogen (PG) nanoparticles to solubilize curcumin (CCM) and further enhance the properties of apple pectin-based active films. The size of the PG spherical particles ranged from 30 to 100 nm with some aggregates. The branch density of the PG was 6.02 %. These PG nanoparticles increased the solubility of CCM nearly 1742-fold and a nanosized phytoglycogen-curcumin (PG-CCM) host was formed via hydrogen bonding and hydrophobic interaction. This host promoted the formation of pectin-based films with a dense structure and increased their tensile strength to 23.51 MPa. The coefficient to water vapor permeability, oxygen permeability and carbon dioxide permeability were all decreased indicating their barrier performance were improved. Among them, the oxygen permeability coefficient decreased most, from 1.14 × 10-7 g·m-1·s-1 to 0.8 × 10-7 g·m-1·s-1. Also, the transmittance of the active film at 280 nm and 660 nm decreased to 0.65 % and 72.10 %. Antioxidant and antibacterial properties were significantly enhanced (P < 0.05). And the results showed this film was an excellent oil packaging material. The active film incorporating PG-CCM host can replace heat-sealed plastic bags/pouch made from polyethylene and polypropylene synthetic plastics, and solve the problem that plastic packaging is difficult to degrade and cannot be squeezed clean. This provides a new conceptual framework for developing pectin-based active films by incorporating of PG and CCM.

Comparative analysis of multi-angle structural alterations and cold-water solubility of kudzu starch modifications using different methods

Kudzu, a plant known for its medicinal value and health benefits, is typically consumed in the form of starch. However, the use of native kudzu starch is limited by its high pasting temperature and low solubility, leading to a poor consumer experience. In this study, kudzu starch was treated using six modification techniques: ball milling, extrusion puffing, alcoholic-alkaline, urea-alkaline, pullulanase, and extrusion puffing-pullulanase. The results of the Fourier transform infrared spectrum showed that the intensity ratio of 1047/1022 cm-1 for the modified starches (1.02-1.21) was lower than that of the native kudzu starch (1.22). The relative crystallinity of modified kudzu starch significantly decreased, especially after ball milling, extrusion puffing, and alcoholic-alkaline treatment. Furthermore, scanning electron microscopy and confocal laser scanning microscopy revealed significant changes in the granular structures of the modified starches. After modification, the pasting temperature of kudzu starch decreased (except for the urea-alkaline treatment), and the apparent viscosity of kudzu starch decreased from 517.95 Pa·s to 0.47 Pa·s. The cold-water solubility of extrusion-puffing and extrusion puffing-pullulanase modified kudzu starch was >70 %, which was significantly higher than that of the native starch (0.11 %). These findings establish a theoretical basis for the potential development of instant kudzu powder.

Introducing a portable electrochemical biosensor for Mycobacterium avium subsp. paratuberculosis detection using graphene oxide and chitosan

In this contribution, a novel, low-cost, high throughput, and ultra-selective electrochemical DNA nanobiosensor was developed for accurate on-site detection of Mycobacterium avium subspecies paratuberculosis (MAP) in real media for practical diagnosis of Johne's disease (JD). The method was designed based on the immobilization of graphene oxide and chitosan biopolymer on the surface of a glassy carbon electrode, modified by electrochemical immobilization of graphene oxide and chitosan biopolymer, followed by activation of biopolymer via 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride and N-hydroxy succinimide (EDC/NHS) coupling system. Afterward, the commercial probe DNA (ssDNA) was stabilized on the activated electrode surface to prepare an ultra-selective ssDNA-stabilized nanobiosensor for MAP sensing called "ssDNA-stabilized GO-CH-EDC/NHS-modified electrode". Several characterization methods distinguished the bioelectrode. The DNA hybridization between the nanobiosensor and target DNA was confirmed by cyclic voltammetry and differential pulse voltammetry. "At optimal experimental conditions, the nanobiosensor showed a linear range of 1.0 × 10-15-1.0 × 10-12 mol L-1, a detection limit as low as 1.53 × 10-13 mol L-1, and a repeatability with a relative standard deviation (%RSD) of 4.7%. The reproducibility was also appropriate, with a %RSD of about 10%. It was used to diagnose MAP in real samples with highly accurate results. Therefore, the developed nanobiosensor can be used for clinical diagnosis of MAP.

Highly sensitive enantioselective spectrofluorimetric determination of R-/S-mandelic acid using l-tryptophan-modified amino-functional silica-coated N-doped carbon dots as novel high-throughput chiral nanoprobes

Amino-functional silica-coated N-doped carbon dots (NH2-SiO2-CDs) were covalently modified by l-tryptophan (chiral selector) by producing an amide bond between carboxyl groups of L-try and amino groups of NH2-SiO2-CDs to develop a novel high throughput chiral nanoprobes (L-try-CONH-SiO2-CDs) for highly sensitive and enantioselective quantification of S-/R-mandelic acid (S-/R-Man). The method showed a great difference between S- and R-isomers (enantioselectivity coefficient = 4.17) due to the ultra-stability of the Meisenheimer complex that was formed between S-isomer and nanoprobe (KS-Man/KR-man = 2122.7, where K is the binding-constant). At optimal experimental conditions, two linear ranges of 0.5-25.0 (LOD of 0.05 μM) and 0.5-22.0 μM (LOD of 0.27 μM) for S- and R-Man, respectively, along with an enhanced sensitivity toward S-isomer (about 5.7-fold higher than R-isomer) were attained. High selectivity for the determination of mandelic acid was achieved compared to metal ions, amino acids, and sugars that commonly coexist with it. Intra-day as well as inter-day assays, respectively, showed RSD values of about 3.2 and 3.9%. The mechanistic studies were performed for proving the enantioselective behavior of the developed nanoprobe. The method was then used for S-/R-mandelic acid determination in bio-samples. The figures of merit for the method were found to be better than those already reported for enantioselective detection of R-/S-Man.

Fabrication of lignin-based sub-micro hybrid particle as a novel support for adenylate cyclase immobilization

This study developed a surface functionalized lignin-based sub-microsphere as an innovative support for enzyme immobilization. Lignin was first modified with a silane reagent leading to lignin/SiO2 (LS) organic/inorganic hybrid particles, displayed as regular sub-micro spheres with a SiO2 shell as demonstrated in SEM images. The LS particles were further modified to introduce nickel ions, as evidenced in XPS spectra, facilitating affinity adsorption with a his-tagged enzyme. The immobilization of adenylate cyclase from Haloactinopolyspora alba (HaAC), expressed in Escherichia coli, was conducted on the surface functionalized LS (LS-G-NTA-Ni). The immobilization conditions were optimized to achieve the highest relative activity, which were determined to be using a Ni2+ concentration of 62.5 mM, at pH=9.5 and 25 °C, with an enzyme-to-support ratio of 4.0 for a duration of 2 h. The immobilized HaAC shows maximum relative activity at pH=9.5 and 40 °C, and exhibits significantly improved thermal stability compared to the free enzyme. After undergoing five reusing cycles, the immobilized HaAC maintains a satisfactory activity (54.15%), which is due to the surface chemistry and the structural stability of the functionalized LS. This work provides a valuable exploration for high-value application of industrial lignin.

A Review on Recent Approaches on Molecular Docking Studies of Novel Compounds Targeting Acetylcholinesterase in Alzheimer Disease

Alzheimer's disease (AD), a neurodegenerative brain disorder that affects millions of people worldwide, is characterized by memory loss and cognitive decline. Low levels of acetylcholine and abnormal levels of beta-amyloid, T protein aggregation, inflammation, and oxidative stress, have been associated with AD, and therefore, research has been oriented towards the cholinergic system and primarily on acetylcholinesterase (AChE) inhibitors. In this review, we are focusing on the discovery of AChE inhibitors using computer-based modeling and simulation techniques, covering the recent literature from 2018-2022. More specifically, the review discusses the structures of novel, potent acetylcholinesterase inhibitors and their binding mode to AChE, as well as the physicochemical requirements for the design of potential AChE inhibitors.

Sustainable Biosynthesis of Esterase Enzymes of Desired Characteristics of Catalysis for Pharmaceutical and Food Industry Employing Specific Strains of Microorganisms

Reactions catalysed by sustainably produced enzymes can contribute to the bioeconomy supporting several industries. Low-value compounds can be transformed into added-value products or high-resolution chemicals could be prepared in reactions catalysed by biocatalyst esterase enzymes. These enzymes can be synthesised by purposely isolated or genetically modified strains of microorganisms. Enzymes belonging to the hydrolase family catalyse the formation and hydrolysis of ester bonds to produce the desired esterified molecule. The synthesis of homo-chiral compounds can be accomplished either by chemical or biocatalytic processes, the latter being preferred with the use of microbial esterases. For varied applications, esterases with high stability and retained activity at lower and higher temperatures have been produced with strains isolated from extreme environments. For sustainable production of enzymes, higher productivity has been achieved by employing fast-growing Escherichia coli after incorporating plasmids of required characteristics from specific isolates. This is a review of the isolated and engineered strains used in the biosynthesis of esterase of the desired property, with the objective of a sustainable supply of enzymes, to produce products of industrial importance contributing to the economy.