Thiol-ene click reaction-induced fluorescence enhancement by altering the radiative rate for assaying butyrylcholinesterase activity

The critical roles of propanethiol oxidoreductase and sulfide-quinone oxidoreductase in the propanethiol catabolism pathway in Pseudomonas putida S-1

Propanethiol (PT) is a hazardous pollutant that poses risks to both the environment and human well-being. Pseudomonas putida S-1 has been identified as a microorganism capable of utilizing PT as its sole carbon source. However, the metabolic pathway responsible for PT degradation in P. putida S-1 has remained poorly understood, impeding its optimization and practical application. In this study, we investigated the catabolic network involved in PT desulfurization with P. putida S-1 and identified key gene modules crucial to this process. Notably, propanethiol oxidoreductase (PTO) catalyzes the initial degradation of PT, a pivotal step for P. putida S-1's survival on PT. PTO facilitates the oxidation of PT, resulting H2S, H2O2, and propionaldehyde (PA). Catalase-peroxidase catalyzes the conversion of H2O2 to oxygen and water, while PA undergoes gradual conversion to Succinyl-CoA, which is subsequently utilized in the tricarboxylic acid cycle. H2S is digested in a comprehensive desulfurization network where sulfide-quinone oxidoreductase (SQOR) predominantly converts it to sulfane sulfur. The transcriptome analysis suggests that sulfur can be finally converted to sulfite or sulfate and exported out of the cell. The PT degradation capacity of P. putida S-1 was enhanced by increasing the transcription level of PTO and SQOR genes in vivo.IMPORTANCEThis work investigated the PT catabolism pathway in Pseudomonas putida S-1, a microorganism capable of utilizing PT as the sole carbon source. Critical genes that control the initiation of PT degradation were identified and characterized, such as pto and sqor. By increasing the transcription level of pto and sqor genes in vivo, we have successfully enhanced the PT degradation efficiency and growth rate of P. putida S-1. This work does not only reveal a unique PT degradation pathway but also highlights the potential of enhancing the microbial desulfurization process in the bioremediation of thiol-contaminated environment.

Optical imaging probes for selective detection of butyrylcholinesterase

Butyrylcholinesterase (BChE), a member of the human serine hydrolase family, is an essential enzyme for cholinergic neurotransmission as it catalyzes the hydrolysis of acetylcholine. It also plays central roles in apoptosis, lipid metabolism, and xenobiotic detoxification. On the other side, abnormal levels of BChE are directly associated with the formation of pathogenic states such as neurodegenerative diseases, psychiatric and cardiovascular disorders, liver damage, diabetes, and cancer. Thus, selective and sensitive detection of BChE level in living organisms is highly crucial and is of great importance to further understand the roles of BChE in both physiological and pathological processes. However, it is a very complicated task due to the potential interference of acetylcholinesterase (AChE), the other human cholinesterase, as these two enzymes share a very similar substrate scope. To this end, optical imaging probes have attracted immense attention in recent years as they have modular structures, which can be tuned precisely to satisfy high selectivity toward BChE, and at the same time they offer real time and nondestructive imaging opportunities with a high spatial and temporal resolution. Here, we summarize BChE selective imaging probes by discussing the critical milestones achieved during the development process of these molecular sensors over the years. We put a special emphasis on design principles and biological applications of highly promising new generation activity-based probes. We also give a comprehensive outlook for the future of BChE-responsive probes and highlight the ongoing challenges. This collection marks the first review article on BChE-responsive imaging agents.

Ratiometric imaging of butyrylcholinesterase activity in mice with nonalcoholic fatty liver using an AIE-based fluorescent probe

Butyrylcholinesterase (BChE) is an essential human biomarker which is related to liver and neurodegenerative diseases. It is of great significance to develop a fluorescent probe that can image BChE in vitro and in vivo. Unfortunately, most fluorescent probes that are based on a single change in fluorescence intensity are susceptible to environmental interference. Therefore, we reported an easily available ratiometric fluorescent probe, TB-BChE, with aggregation-induced emission (AIE) characteristics for ratiometric imaging of BChE. TB-BChE demonstrated excellent sensitivity (LOD = 39.24 ng mL^-1) and specificity for BChE. Moreover, we have successfully studied the ratiometric imaging of TB-BChE to BChE in a nonalcoholic fatty liver disease model. These results indicated that TB-BChE is expected to become a powerful analysis tool for butyrylcholinesterase research in basic medicine and clinical applications.

Rational construction of a novel probe for the rapid detection of butyrylcholinesterase stress changes in apoptotic cells

The occurrence of numerous neurodegenerative diseases is associated with abnormal levels of butyrylcholinesterase (BChE).

Fluorescent Determination of Butyrylcholinesterase Activity and Its Application in Biological Imaging and Pesticide Residue Detection

Butyrylcholinesterase (BChE) is an essential human cholinesterase relevant to liver conditions and neurodegenerative diseases, which makes it a pivotal biomarker of health. It therefore remains challenging and highly desired to elaborate efficient chemical tools for BChE with simple operations and satisfactory working performance. In this work, a background-free detection strategy was built by virtue of the judicious coupling of a specific BChE-enzymatic reaction and in situ cyclization. High sensitivity with a low limit of detection (LOD) of 0.075 μg/mL could be readily achieved from the blank background and the as-produced emissive indicators, and the specific reaction site contributed to the high selectivity over other bio-species even acetylcholinesterase (AChE). In addition to the multifaceted spectral experiments to verify the sensing mechanism, this work assumed comprehensive studies on the application. The bio-investigation ranged from cells to an organism, declaring a noteworthy prospect in disease diagnosis, especially for Alzheimer's disease (AD), a common neurodegenerative disease with over-expressed BChE. Moreover, its excellent work for inhibition efficacy elucidation was also proved with the accuracy IC₅₀ of tacrine for BChE (8.6 nM), giving rise to an expanded application for trace pesticide determination.

In Situ Generation of Prussian Blue by MIL-53 (Fe) for Point-of-Care Testing of Butyrylcholinesterase Activity Using a Portable High-Throughput Photothermal Device

Butyrylcholinesterase (BuChE), the primary source of serum cholinesterase activity, is an indispensable biochemical marker for clinical diagnosis of liver function and organophosphorus poisoning. The requirement for bulky and expensive instruments represents a huge hindrance for point-of-care testing (POCT) of BuChE, especially in resource-limited settings. Herein, an easy-operated, economic, and portable photothermal (PT) biosensing platform for high-throughput BuChE detection was rationally designed. BuChE could "light up" the PT signal through in situ generation of Prussian blue (PB) by MIL-53 (Fe), which allowed us to translate biological signals into temperature signals. Such temperature change signals could be monitored at high throughput (six samples for a single measurement) by a miniature self-made integrated PT device via combining separable 96-well plates, a three-dimensional (3D) printed sample bracket, 808 nm lasers, and thermometers, satisfying the requirement for rapid on-site detection in a large batch with low cost. In addition, the large specific surface area, 3D network structure, and high porosity of MIL-53 (Fe) offered a beneficial platform for its reaction with enzymatic hydrolysate, resulting in high sensing sensitivity and low detection limit (0.3 U L^-1), which was at least 20 000 times lower than the normal human serum BuChE activity. This facile, affordable, and broad applicability PT sensing platform provides a beneficial reference for the rational design of other disease diagnostic approaches suitable for POCT.

A Bioorthogonally Synthesized and Disulfide-Containing Fluorescence Turn-On Chemical Probe for Measurements of Butyrylcholinesterase Activity and Inhibition in the Presence of Physiological Glutathione

Butyrylcholinesterase (BChE) is a biomarker in human blood. Aberrant BChE activity has been associated with human diseases. Here we developed a fluorescence resonance energy transfer (FRET) chemical probe to specifically quantify BChE activity in serum, while simultaneously discriminating against glutathione (GSH). The FRET chemical probe 11 was synthesized from a key trifunctional bicyclononyne exo-6 and derivatives of 5-(2-aminoethylamino)-1-naphthalenesulfonic acid (EDANS) and 4-[4-(dimethylamino)phenylazo]benzoic acid (DABCYL). EDANS fluorescence visualization and kinetic analysis of 11 in the presence of diverse compounds confirmed the outstanding reactivity and specificity of 11 with thiols. The thiol-dependent fluorescence turn-on property of 11 was attributed to a general base-catalyzed SN2 nucleophilic substitution mechanism and independent of metal ions. Moreover, all thiols, except GSH, reacted swiftly with 11. Kinetic studies of 11 in the presence of covalently modified GSH derivatives corroborated that the steric hindrance of 11 imposing on GSH was the likely cause of the distinguished reactivity. Since GSH commonly interferes in assays measuring BChE activity in blood samples, the 11-based fluorescent assay was employed to directly quantify BChE activity without GSH interference, and delivered a linear range of 4.3–182.2 U L−1 for BChE activity with detection limit of 4.3 U L−1, and accurately quantified serum BChE activity in the presence of 10 μM GSH. Finally, the 11-based assay was exploited to determine Ki of 5 nM for tacrine inhibition on BChE catalysis. We are harnessing the modulated characteristics of 6 to synthesize advanced chemical probes able to more sensitively screen for BChE inhibitors and quantify BChE activity in serum.

Detection, identification, and quantification of oxidative protein modifications

Exposure of biological molecules to oxidants is inevitable and therefore commonplace. Oxidative stress in cells arises from both external agents and endogenous processes that generate reactive species, either purposely (e.g. during pathogen killing or enzymatic reactions) or accidentally (e.g. exposure to radiation, pollutants, drugs, or chemicals). As proteins are highly abundant and react rapidly with many oxidants, they are highly susceptible to, and major targets of, oxidative damage. This can result in changes to protein structure, function, and turnover and to loss or (occasional) gain of activity. Accumulation of oxidatively-modified proteins, due to either increased generation or decreased removal, has been associated with both aging and multiple diseases. Different oxidants generate a broad, and sometimes characteristic, spectrum of post-translational modifications. The kinetics (rates) of damage formation also vary dramatically. There is a pressing need for reliable and robust methods that can detect, identify, and quantify the products formed on amino acids, peptides, and proteins, especially in complex systems. This review summarizes several advances in our understanding of this complex chemistry and highlights methods that are available to detect oxidative modifications-at the amino acid, peptide, or protein level-and their nature, quantity, and position within a peptide sequence. Although considerable progress has been made in the development and application of new techniques, it is clear that further development is required to fully assess the relative importance of protein oxidation and to determine whether an oxidation is a cause, or merely a consequence, of injurious processes.

A fluorescent probe for butyrylcholinesterase activity in human serum based on a fluorophore with specific binding affinity for human serum albumin

Non-specific binding of a fluorescent probe to human serum albumin is problematic because it induces signal interference when the probe detects the target biomarker in human serum. To eliminate this problem, we used intrinsically problematic non-specific fluorescence in designing a fluorescent probe for butyrylcholinesterase activity in serum. The probe containing a fluorophore with specific binding affinity for albumin could sensitively detect butyrylcholinesterase activity in serum with high selectivity to acetylcholinesterase and screen the efficiency of butyrylcholinesterase inhibitors.