Aniline as a TICT rotor to derive methine fluorogens for biomolecules:A curcuminoid-BF2 compound for lighting up HSA/BSA

The unique structure of fluorescent proteins in which the fluorophore is encapsulated by the protein shell to restrict rotation and emit light inspired the screening of chromophores that selectively bind to biomolecules to generate fluorescence. In this paper, we report a curcuminoid-BF2-like fluorescent dye NBF2containing 4-dimethylaniline as an electron-donating group. When this dye is combined with HSA or BSA, the fluorescence is enhanced 90/112-fold, and the fluorescence quantum yield increases from <0.001to 0.16/0.19. Such a large change in fluorescence enhancement is due to the encapsulation of N-BF2in the protein cavity by HSA/BSA, which inhibits the intramolecular rotation of the aniline moiety caused by charge transfer after the fluorophore is excited by light. N-BF2has fast and strong binding to HSA or BSA and was found to be reversible in solution and intracellularly. Since N-BF2also has the ability to target lipid droplets, the complex of N-BF2/HSA realizes the regulation of reversible lipid droplet staining in cells.

Multiplexed imaging detection of live cell intracellular changes in early apoptosis with aggregation-induced emission fluorogens

Apoptosis is an important process for maintaining tissue homeostasis and eliminating abnormal cells in multicellular organisms.Abnormality in apoptosis often leads to severe diseases such as cancers. Better understanding of its mechanisms and processes is therefore important. Accompanying molecular biology events of apoptosis is a series of cellular morphology changes: nucleus condensation, cell shrinkage and rounding, cell surface blebbing, dynamic blebbing, apoptotic membrane protrusions and nucleus fragmentations and finally, the formation and release of apoptotic bodies. It is difficult to detect cellular changes in the early phase of apoptosis due to the subtle changes at this phase. In the current study, we induced apoptosis in He La cells with H2 O2 and used nuclear dye Hoechst 33258, mitochondria, lysosome and cytoplasmic protein specific aggregation-induced emission fluorogens(AIEgens), TPE-Ph-In, 2 M-DABS and BSPOTPE to successfully perform live cell multiplexed imaging to investigate early apoptosis cellular events. We showed the gradual dissipation of mitochondria membrane potential until it is nondetectable by TPE-Ph-In. Increased mitophagy detected by TPE-Ph-In and 2 M-DABS, condensed nucleus detected by Hoechst33258, increased permeability and/or reduced integrity of nuclear membrane, and increased intracellular vesicles detected by2 M-DABS are some of the early events of apoptosis.

Recent advances in chiral aggregation-induced emission fluorogens

Over the past decade,aggregation-induced emission(AIE)molecules have played a pivotal role in bioimaging,anti-microbial,and photodynamic therapy,and have been at the forefront of several disciplines worldwide.When combined with chiral moieties,they can easily collide with dazzling sparks and exhibit exceptional and unique advantages.In the application of chiral recognition and measurement of enantiomeric excess,it can identify chi-ral molecules visually based on color change and precipitation reaction,quantitatively analyze chiral molecules while determining the enantiomeric composition based on the fluorescence intensity change at different wave-lengths,and obtain two parameters about chiral molecules from one measurement,thereby demonstrating its high selectivity,sensitivity and accuracy in chiral identification.In the field of organic circularly polarized lu-minescent(CPL)materials,the asymmetry(g lum)of common organic light emitting elements is usually between 10−5 and 10−2,whereas the CPL asymmetry factor(g lum)of chiral AIE fluorogens(AIEgens)can reach 1.42,which is very close to the theoretical value of 2.Therefore,the combination of chiral elements and luminescent groups promotes their adoption in the field of organic CPL materials.Herein we have summarized the recent applications of chiral AIEgens in both chiral molecule recognition and circularly polarized organic light-emitting diode(CP-OLED)in order to provide future researchers with a more comprehensive and detailed understanding of chiral AIEgens and to encourage more scientists to contribute to the development of AIEgens.

A novelα-ketoamide reactivity-based two-photon fluorogenic probe for visualizing peroxynitrite in Parkinson's disease models

Peroxynitrite(ONOO^(-))contributes to oxidative stress and neurodegeneration in Parkinson's disease(PD).Developing a peroxynitrite probe would enable in situ visualization of the overwhelming ONOO^(-)flux and understanding of the ONOO^(-)stress-induced neuropathology of PD.Herein,a novelα-ketoamide-based fluorogenic probe(DFlu)was designed for ONOO^(-)
monitoring in multiple PD models.The results demonstrated that DFlu exhibits a fluorescence turn-on response to ONOO^(-)with high specificity and sensitivity.The efficacy of DFlu for intracellular ONOO^(-)
imaging was demonstrated systematically.The results showed that DFlu can successfully visualize endogenous and exogenous ONOO^(-)in cells derived from chemical and biochemical routes.More importantly,the two-photon excitation ability of DFlu has been well demonstrated by monitoring exogenous/endogenous ONOO^(-)production and scavenging in live zebraflsh PD models.This work provides a reliable and promising
α-ketoamide-based optical tool for identifying variations of ONOO^(-)in PD models.

A novel fluorogenic probe for monoamine oxidase assays

Monoamine oxidase is flavoenzymes, widely distributed in mammals. It is well recognized that MAOs serve an important role in metabolism that they have close relationship with health .Along with the discoveries between MAOs and neurotic disease, more and more studies have been jumped in .In this paper, we design a new probe for assaying the activities of MAOs. The results showed that the probe [7-（3-aminopropoxy）coumarin] is simple, effective and sensitive for MAOB.

Establishment of Real-Time TaqMan-Fluorescence Quantitative RT-PCR Assay for Detection and Quantification of Porcine Lipoprotein Lipase mRNA

Porcine lipoprotein lipase （LPL） cDNA was cloned as the standard for real-time quantifying LPL mRNA and the TaqMan-fluorescence quantitative PCR assay for detection was established. The total RNA extracted from Longissimus dorsi of porcine was reverse-transcribed to cDNA. LPL cDNA was ligated with pGM-T vector and transformed into Escherichia coli TOP10. Plasmid DNA extracted from positive clones was verified by PCR amplification and sequenced. LPL was amplified by real-time fluorescence quantitative PCR from the plasmid DNA. The concentration of DNA template purified was detected by analyzing absorbance in 260 nm and then the combined plasmid was diluted to series as standard for fluorescence quantitative PCR （FQ-PCR）. The method of LPL mRNA real-time PCR was well established, which detected as low as 103 with the linear range 10^3 to 10^10 copies. The standard curves showed high correlations （R2 = 0.9871）. A series of standards for real-time PCR analysis have been constructed successfially, and real-time TaqMan-fluorescence quantitative RT-PCR is reliable to quantitatively evaluate FQ-PCR mRNA in L. dorsi of porcine.

Gelatin degradation assay reveals MMP-9 inhibitors and function of O-glycosylated domain

AIM: To establish a novel, sensitive and high-throughput gelatinolytic assay to define new inhibitors and compare domain deletion mutants of gelatinase B/matrix metalloproteinase (MMP)-9. METHODS: Fluorogenic Dye-quenched (DQ)TM-gelatin was used as a substrate and biochemical parameters (substrate and enzyme concentrations, DMSO solvent concentrations) were optimized to establish a highthroughput assay system. Various small-sized libraries (ChemDiv, InterBioScreen and ChemBridge) of hetero-cyclic, drug-like substances were tested and compared with prototypic inhibitors. RESULTS: First, we designed a test system with gelatin as a natural substrate. Second, the assay was validated by selecting a novel pyrimidine-2,4,6-trione (barbitu- rate) inhibitor. Third, and in line with present structural data on collagenolysis, it was found that deletion of the O-glycosylated region significantly decreased gelatinolytic activity (kcat/kM ± 40% less than full-length MMP-9). CONCLUSION: The DQTM-gelatin assay is useful in high-throughput drug screening and exosite targeting. We demonstrate that flexibility between the catalytic and hemopexin domain is functionally critical for gelatinolysis.

Synthesis of New Near-infrared Fluorescent Dyes

A new near-infrared fluorescent dye, 9-N-(2-hydroxyethyl)-N-methylamino-6-carbethoxy-5H-benzo[a]phenoxazin-5-one 1, was prepared from the reaction of N-(2-hydroxyethyl)-N-methyl-4-nitrosoaniline hydrochloride and ethyl 1,3-dihydroxynaphthoate. Five more fluorescent compounds were synthesized by the reaction of the resulting dye 1 with appropriate amino acid or carboxylic acids.

Fluorogenic Detection of Duck Tembusu Virus( DTMUV ) by Loop-mediated Isothermal Amplification(LAMP)

This study was to develop an efficient and simple method for the detection of duck Tembusu virus( DTMUV) by loop-mediated isothermal amplification( LAMP). Six pairs of LAMP primers were designed according to the conserved region of the DTMUV E gene sequence in Gen Bank,which were then used for the optimization of various reaction components and reaction system of specific LAMP for DTMUV. Further the fluorescent reagent SYBR Green I and a certain proportion of calcium and manganese ion were used to determin the color development of products for visible analysis instead of agarose gel electrophoresis. The results showed that the sensitivity SYBR Green I as the fluorescent reagent was 10 copies viruses per μL,which is 100 times higher than normal PCR method,while the detection limit of combined use of calcium and manganese ion was 1 000 copies viruses per μL. Although the sensitivity of mixture of calcium and manganese ion is lower than SYBR Green I,it can avoid the aerosol contamination. The fluorogenic analysis-based LAMP system established in our study has a high sensitivity and avoid the cross contamination,which is of huge potential in research institutions,grass-roots laboratories and field testing and can provide effective means to completely curb the occurrence and spreading of DTMUV.

THE DETECTION OF MDR1 GENE EXPRESSION USING FLUOROGENIC PROBE QUANTITATIVE RT-PCR METHOD

Objective: To establish a fluoregenic probe quantitative RT-PCR (FQ-RT-PCR) method for detection of the expression of MDR1 gene in tumor cells and to investigate the expression of MDR1 gene in patients with lung cancer. Methods: The fluorogenic quantitative RT-PCR method for detection of the expression of MDR1 gene was established. K562/ADM and K562 cell lines or 45 tumor tissues from patients with lung cancer were examined on PE Applied Biosystems 7700 Sequence Detection machine. Results: the average levels of MDR1 gene expression in K562/ADM cells and K562 cells were (6.86±0.65)× 107 copies/μg RNA and (8.49±0.67)×105 copies/μg RNA, respectively. The former was 80.8 times greater than the latter. Each sample was measured 10 times and the coefficient variation (CV) was 9.5% and 7.9%, respectively. Various levels of MDR1 gene expression were detected in 12 of 45 patients with lung cancer. Conclusion: Quantitative detection of MDR1 gene expression in tumor cells was achieved by using FQ-RT-PCR. FQ-RT-PCR is an accurate, and sensitive method and easy to perform. Using this method, low levels of MDR1 gene expression could be detected in 24% of the patients with lung cancer.

Evaluation of the effect of compound aqueous solubility in cytochrome P450 inhibition assays

It is a common practice in drug discovery organizations to screen new chemical entities in order to predict future drug-drug interactions. For this purpose, there are two main assay strategies, one based on recombinant cytochrome P450 (rCYP) enzymes and fluorescent detection, and other on human liver microsomes (HLM) and liquid chromatography coupled to mass spectrometry. Many authors have reported a poor correlation between both technologies, giving rise to concerns about the usefulness of fluorometric methods for predicting drug-drug interactions. In this study, we investigated the role that compound aqueous kinetic solubility may play in this lack of correlation. We found that drug discovery compounds with unacceptable kinetic solubility, measured by a turbidimetric solutibility assay, tended to yield higher IC50 values in in vitro models based on human liver microsomes, whereas compounds with kinetic solubility values higher than 50 μM showed very similar IC50 values in both in vitro models. Our results show that the turbidimetric solubility assay is a useful tool to identify those discovery compounds that may require further investigation in order to avoid overlooking future drug-drug interactions.

Development of an active-site titrant for SARS-CoV-2 main protease as an indispensable tool for evaluating enzyme kinetics

A titrant for the SARS-CoV-2 main protease(M^(pro))was developed that enables,for the first time,the exact determination of the concentration of the enzymatically active M^(pro) by active-site titration.The covalent binding mode of the tetrapeptidic titrant was elucidated by the determination of the crystal structure of the enzyme–titrant complex.Four fluorogenic substrates of M^(pro),including a prototypical,internally quenched Dabcyl-EDANS peptide,were compared in terms of solubility under typical assay conditions.By exploiting the new titrant,key kinetic parameters for the M^(pro)-catalyzed cleavage of these substrates were determined.

A mitochondria-targeted H_(2)S-activatable fluorogenic probe for tracking hepatic ischemia-reperfusion injury

Hepatic ischemia-reperfusion injury(HIRI)is the cause of postoperative hepatic dysfunction and failure,and even death.As an important biological effector molecule,hydrogen sulfide(H_(2)S)of mitochondria as a gasotransmitter that is usually used to protect against acute HIRI injury.However,the exact relationship between HIRI and mitochondrial H_(2)S remains tangled due to the lack of an effective analytical method.Herein,we have fabricated a mitochondria-targeted H_(2)S-activatable fluorogenic probe(Mito-GW)to explore the stability of mitochondrial H_(2)S and track the changes of mitochondrial H_(2)S during the HIRI.By virtue of pyridinium electropositivity and its amphiphilicity,Mito-GW could accumulate in mitochondria.It goes through an analyte-prompted immolation when reacts with H_(2)S,resulting in the releasing of the fluorophore(GW).Therefore,the extent of Mito-GW conversion to GW can be used to evaluate the changes of mitochondrial H_(2)S level in living cells and tissues.As proof-of-principle,we have used MitoGW to demonstrate the mitochondria H_(2)S-levels increase and then decrease during HIRI in vitro and in vivo.Our research highlights the tremendous potential of Mito-GW as a mitochondrial H_(2)S fluorogenic probe in elucidating the pathogenesis of HIRI,providing a powerful tool for promoting future research on hepatology.

A fluorogenic probe for SNAP-tag protein based on ESPT ratiometric signals

Protein self-labeling tags achieve selective fusion and labeling of target proteins through genetic coding technology,but require exogenous fluorescent probes with fluorogenicity for protein tag binding to have the performance of wash-free fluorescence imaging in live cells.In this paper,we reported a fluorogenic probe 1 capable of ratiometric fluorescence recognition of SNAP-tag proteins.In this probe,the O6-benzylguanine derivative of 3-hydroxy-1,8-naphthalimide underwent a selective covalent linkage reaction with SNAP-tag protein.The hydroxyl group on the naphthalimide fluorophore formed a hydrogen bond with the functional group near the protein cavity.The excited state proton transfer occurred after illumination,to obtain the ratio fluorescence signal from blue emission to red emission,realizing the wash-free fluorescence imaging of the target proteins.

Modulation of dynamic aggregation in fluorogenic SNAP-tag probes for long-term super-resolution imaging

The combination of super-resolution microscopy and synthetic fluorescence probes has emerged as a universal tool to monitor dynamic biological events at the nanometer scale.However,the limited site-specificity and fluorogenicity of synthetic fluorescent probes make it still difficult to realize long-term super-resolution imaging.Herein,we introduce a dynamic aggregation mediated SNAP-tag fluorogenic probe,BGAN-Aze,which can specifically bind to various SNAP-tag fusion proteins with 41-fold fluorescence enhancement.The equilibrium between the non-fluorescent aggregate/dimer(A–D)and the fluorescent monomer(M)of BGAN-Aze acts as an effective method to reduce the fluorescence background and endow BGAN-Aze with the capability of conducting washing-free super-resolution imaging of various intracellular and extracellular proteins.Using this probe,we monitored multiple dynamic biological events,such as MMC,mitophagy,the fusion of nucleolus,and the growth and contact of filopodia.We expect that BGAN-Aze will become a widely used SNAP-tag for super-resolution imaging of dynamic biological events and the A-D-M equilibrium can be a general strategy for designing fluorogenic probes.

RNA Imaging in Live Cells

Traditional molecular biology tools have elucidated the identities and functions of RNA molecules,which are essential to the understanding of gene transcription and protein translation.Deepening this research field would further require the direct visualization of RNA dynamics such as the DNA-RNA interactions and RNA-protein interactions.Towards this goal,the rise of RNA imaging tools over the past 15 years has reformed how we looked at these processes.In this Emerging Topic,we first highlighted recent advances on three main RNA imaging tools based on the species of interacting molecules:RNA-RNA pairing,RNA-protein binding,and small molecule-RNA complex.We introduced the advantages of these tools from a technical viewpoint,including binding affinity,fluorescent turn-on ratio,stability,and impacts on targeted RNA.Next,we discussed new rising opportunities and future directions,echoing the state-of-the-art imaging tools in the fields of fluorescent proteins and small fluorescent molecules.Together,we believe this emerging field will bring new insights on how we study RNA biology in living systems.

Fluorogen-activating proteins: beyond classical fluorescent proteins

Fluorescence imaging is a powerful technique for the real-time noninvasive monitoring of protein dynamics. Recently, fluorogen activating proteins(FAPs)/fluorogen probes for protein imaging were developed. Unlike the traditional fluorescent proteins(FPs), FAPs do not fluoresce unless bound to their specific small-molecule fluorogens. When using FAPs/fluorogen probes, a washing step is not required for the removal of free probes from the cells, thus allowing rapid and specific detection of proteins in living cells with high signal-to-noise ratio. Furthermore, with different fluorogens, living cell multi-color proteins labeling system was developed. In this review, we describe about the discovery of FAPs, the design strategy of FAP fluorogens, the application of the FAP technology and the advances of FAP technology in protein labeling systems.

Sensing cytochrome P4501A1 activity by a resorufin-based isoform-specific fluorescent probe

Cytochrome P4501 A1(CYP1A1),a heme-containing monooxygenase,is of particular importance for human health because of its vital roles in the metabolic activation of pro-carcinogenic compounds to the carcinogens.Deciphering the relevance of CYP1A1 to human diseases and screening of CYP1A1 modulators require reliable tool(s)for probing this key enzyme in complex biological matrices.Herein,a practical and ultrasensitive fluorescence-based assay for real-time sensing CYP1A1 activities in biological systems has been developed,via designing an isoform-specific fluorogenic sensor for CYP1A1(CHPO).The newly developed fluorogenic substrate for CYP1A1 has been carefully investigated in terms of specificity,sensitivity,precision,quantitative linear range and the anti-interference ability.The excellent selectivity,strong anti-interference ability and fast response kinetics,making the practicability of CHPObased CYP1A1 activity assay is better than that of most reported CYP1A1 activity assays.Furthermore,CHPO has been successfully used for imaging CYP1A1 activities in living cells and human tissues,as well as for high-throughput screening of CYP1A1 inhibitors using tissue preparations as enzyme sources.Collectively,this study provided a practical fluorogenic sensor for real-time sensing CYP1A1 in complex biological systems,which would strongly facilitate the investigations on the relevance of CYP1A1 to human diseases and promote high-throughput screening of CYP1A1 modulators for biomedical applications.

A self-assembly/disassembly two-photo ratiometric fluorogenic probe for bacteria imaging

Fluorescence imaging has facilitated fluorescent probes to analyze the subcellular localization and dynamics of biological targets. In this paper, we reported a fluorogenic probe for bacteria imaging. The probe was an imidazolium-derived pyrene compound, which self-assembled to form nano-particles and the pyrene fluorescence was quenched by the aggregation effects. When the self-assembly nanoparticles interacted with anionic bacteria surfaces, synergistic effects of electrostatic interaction and hydrophobic force caused competing binding between bacteria surfaces and imidazoliums. This binding resulted in the disassembly of the aggregates to give fluorescence turn-on signal. Meanwhile, the probe bound bacteria surfaces and displayed both pyrene-excimer and pyrene-monomer fluorescence, which gave ratiometric signal. Then, fluorescent labeling by the probe enabled the two-photo ratiometric imaging of bacteria.

Recent progress in two-photon small molecule fluorescent probes for enzymes

Enzymes are macromolecular biological catalysts which can accelerate chemical reactions in living organisms. Almost all the physiological metabolism activities in the cell need enzymes to sustain life via rapid catalysis. Currently, medical research has proved that abnormal enzyme activity is associated with numerous diseases, such as Parkinson’s disease(PD), Alzheimer’s disease(AD) and cancers. On the other hand, early diagnosis of those diseases is of great significance to improve the survival rate and cure rate.In the current diagnostic tools, two-photon fluorescent probes(TPFPs) are developing rapidly due to their unique advantages, such as higher spatial resolution, deeper imaging depth, and lower biotoxicity.Therefore, the design and synthesis of two-photon(TP) small molecule enzymatic probes have broad prospects for early diagnosis and treatment of diseases. As of now, scientists have developed many TP small molecule enzymatic probes. This review aims to summarize the TP small molecule enzymatic probes and expound the reaction mechanism.