Prediction of mutation-induced protein stability changes based on the geometric representations learned by a self-supervised method.

BACKGROUND: Thermostability is a fundamental property of proteins to maintain their biological functions. Predicting protein stability changes upon mutation is important for our understanding protein structure-function relationship, and is also of great interest in protein engineering and pharmaceutical design. RESULTS: Here we present mutDDG-SSM, a deep learning-based framework that uses the geometric representations encoded in protein structure to predict the mutation-induced protein stability changes. mutDDG-SSM consists of two parts: a graph attention network-based protein structural feature extractor that is trained with a self-supervised learning scheme using large-scale high-resolution protein structures, and an eXtreme Gradient Boosting model-based stability change predictor with an advantage of alleviating overfitting problem. The performance of mutDDG-SSM was tested on several widely-used independent datasets. Then, myoglobin and p53 were used as case studies to illustrate the effectiveness of the model in predicting protein stability changes upon mutations. Our results show that mutDDG-SSM achieved high performance in estimating the effects of mutations on protein stability. In addition, mutDDG-SSM exhibited good unbiasedness, where the prediction accuracy on the inverse mutations is as well as that on the direct mutations. CONCLUSION: Meaningful features can be extracted from our pre-trained model to build downstream tasks and our model may serve as a valuable tool for protein engineering and drug design.

Chimeric virus-like particles of human norovirus constructed by structure-guided epitope grafting elicit cross-reactive immunity against both GI.1 and GII.4 genotypes.

IMPORTANCE: Human norovirus (HuNoV) is highly infectious and can result in severe illnesses in the elderly and children. So far, there is no effective antiviral drug to treat HuNoV infection, and thus, the development of HuNoV vaccines is urgent. However, NoV evolves rapidly, and currently, at least 10 genogroups with numerous genotypes have been found. The genetic diversity of NoV and the lack of cross-protection between different genotypes pose challenges to the development of broadly protective vaccines. In this study, guided by structural alignment between GI.1 and GII.4 HuNoV VP1 proteins, several chimeric-type virus-like particles (VLPs) were designed through surface-exposed loop grafting. Mouse immunization studies show that two of the designed chimeric VLPs induced cross-immunity against both GI.1 and GII.4 HuNoVs. To our knowledge, this is the first designed chimeric VLPs that can induce cross-immune activities across different genogroups of HuNoV, which provides valuable strategies for the development of cross-reactive HuNoV vaccines.

Anti-Inflammatory Phomalones from the Deep-Sea-Derived Fungus Trichobotrys effuse FS522.

Four new phomalones A-D (1-4), together with five known analogues (5-9) were isolated from the deep-sea-derived fungus Trichobotrys effuse FS522. Their structures of the new compounds established by analysis of their NMR and HR-ESI-MS spectroscopic data, and the absolute configurations of 2 was determined by electronic circular dichroism (ECD) calculations. compounds 4, 6 and 8 substantially inhibited the production of nitric oxide (NO) with IC50 values of 4.64, 13.90, and 34.07 µM.

Chromone-Derived Polyketides from the Deep-Sea Fungus Diaporthe phaseolorum FS431.

Five new chromone-derived polyketides phaseolorins A-F (1⁻5), together with nine known compounds, were isolated from the deep-sea derived fungus Diaporthe phaseolorum FS431. The structures of new compounds were determined by analysis of their NMR and high-resolution electrospray ionization mass spectroscopy (HRESIMS) spectroscopic data. The absolute configurations were confirmed by chemical transformations, extensively experimental electron capture detection (ECD) calculations, or X-ray crystallography. Among them, compound 2 represented the first example for a new family of chromone derivative possessing an unprecedented recombined five-member γ-lactone ring. Moreover, the new compounds (1⁻5) were evaluated for in vitro cytotoxic activities against a panel of human cancer cell lines.

Tersone A-G, New Pyridone Alkaloids from the Deep-Sea Fungus Phomopsis tersa.

Four phenylfuropyridone racemates, (±)-tersones A-C and E (1-3, 5), one phenylpyridone racemate, (±)-tersone D (4), one new pyridine alkaloid, tersone F (6), single new phenylfuropyridone, tersone G (7) and two known analogs 8 and 9 were isolated from the deep-sea fungus Phomopsis tersa. Their structures and absolute configurations were characterized on the basis of comprehensive spectroscopic analyses, single-crystal X-ray diffraction experiments, and electronic circular dichroism (ECD) calculations. Moreover, compounds 1-9 were evaluated for in vitro antimicrobial and cytotoxic activity. Compounds 5b and 8b exhibited antibacterial activity against S. aureus with the MIC value of 31.5 µg/mL, while compound 5b showed cytoxic activities against SF-268, MCF-7, HepG-2 and A549 cell lines with IC50 values of 32.0, 29.5, 39.5 and 33.2 µM, respectively.

Transgenic expression of human cytoxic T-lymphocyte associated antigen4-immunoglobulin (hCTLA4Ig) by porcine skin for xenogeneic skin grafting.

Porcine skin is frequently used as a substitute of human skin to cover large wounds in clinic practice of wound care. In our previous work, we found that transgenic expression of human cytoxicT-lymphocyte associated antigen4-immunoglobulin (hCTLA4Ig) in murine skin graft remarkably prolonged its survival in xenogeneic wounds without extensive immunosuppression in recipients, suggesting that transgenic hCTLA4Ig expression in skin graft may be an effective and safe method to prolong xenogeneic skin graft survival. In this work, using a transgene construct containing hCTLA4Ig coding sequence under the drive of human Keratine 14 (k14) promoter, hCTLA4Ig transgenic pigs were generated by somatic nuclear transfer. The derived transgenic pigs were healthy and exhibited no signs of susceptibility to infection. The hCTLA4Ig transgene was stably transmitted through germline over generations, and thereby a transgenic pig colony was established. In the derived transgenic pigs, hCTLA4Ig expression in skin was shown to be genetically stable over generations, and detected in heart, kidney and corneal as well as in skin. Transgenic hCTLA4Ig protein in pigs exhibited expected biological activity as it suppressed human lymphocyte proliferation in human mixed lymphocyte culture to extents comparable to those of commercially purchased purified hCTLA4Ig protein. In skin grafting from pigs to rats, transgenic porcine skin grafts exhibited remarkably prolonged survival compared to the wild-type skin grafts derived from the same pig strain (13.33 ± 3.64 vs. 6.25 ± 2.49 days, P < 0.01), further indicating that the transgenic hCTLA4Ig protein was biologically active and capable of extending porcine skin graft survival in xenogeneic wounds. The transgenic pigs generated in this work can be used as a reproducible resource to provide porcine skin grafts with extended survival for wound coverage, and also as donors to investigate the impacts of hCTLA4Ig on xenotransplantation of other organs (heart, kidney and corneal) due to the ectopic transgenic hCTLA4Ig expression.

Design of hepadnavirus core protein-based chimeric virus-like particles carrying epitopes from respiratory syncytial virus.

Respiratory syncytial virus (RSV) is one of the most important pathogens causing respiratory tract infection in humans, especially in infants and the elderly. The identification and structural resolution of the potent neutralizing epitopes on RSV fusion (F) protein enable an "epitope-focused" vaccine design. However, the display of RSV F epitope II on the surface of the widely-used human hepatitis B virus core antigen (HBcAg) has failed to induce neutralizing antibody response in mice. Here, we used the hepadnavirus core protein (HcAg) from different mammalian hosts as scaffolds to construct chimeric virus-like particles (VLPs) presenting the RSV F epitope II. Mouse immunization showed that different HcAg-based chimeric VLPs elicited significantly different neutralizing antibody responses, among which the HcAg derived from roundleaf bat (RBHcAg) is the most immunogenic. Furthermore, RBHcAg was used as the scaffold platform to present multiple RSV F epitopes, and the immunogenicity was further improved in comparison to that displaying a single epitope II. The designed RBHcAg-based multiple-epitope-presenting VLP formulated with MF59-like adjuvant elicited a potent and balanced Th1/Th2 immune response, and offered substantial protection in mice against the challenge of live RSV A2 virus. The designed chimeric VLPs may serve as the potential starting point for developing epitope-focused vaccines against RSV. Our study also demonstrated that RBHcAg is an effective VLP carrier for presenting foreign epitopes, providing a promising platform for epitope-focused vaccine design.

Mutating a flexible region of the RSV F protein can stabilize the prefusion conformation.

The respiratory syncytial virus (RSV) fusion (F) glycoprotein is highly immunogenic in its prefusion (pre-F) conformation. However, the protein is unstable, and its conformation must be stabilized for it to function effectively as an immunogen in vaccines. We present a mutagenesis strategy to arrest the RSV F protein in its pre-F state by blocking localized changes in protein structure that accompany large-scale conformational rearrangements. We generated a series of mutants and screened them in vitro to assess their potential for forming a stable pre-F. In animals, the immunogenicity of a representative mutant F protein, with a conformation confirmed by cryo-electron microscopy, elicited levels of neutralizing antibodies and protection against RSV-induced lung damage that were comparable to those of DS-Cav1, a pre-F used in a licensed vaccine.

Safety and immunogenicity of a mosaic vaccine booster against Omicron and other SARS-CoV-2 variants: a randomized phase 2 trial.

An ongoing randomized, double-blind, controlled phase 2 trial was conducted to evaluate the safety and immunogenicity of a mosaic-type recombinant vaccine candidate, named NVSI-06-09, as a booster dose in subjects aged 18 years and older from the United Arab Emirates (UAE), who had administered two or three doses of inactivated vaccine BBIBP-CorV at least 6 months prior to enrollment. The participants were randomly assigned with 1:1 to receive a booster dose of NVSI-06-09 or BBIBP-CorV. The primary outcomes were immunogenicity and safety against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) Omicron variant, and the exploratory outcome was cross-immunogenicity against other circulating strains. Between May 25 and 30, 2022, 516 adults received booster vaccination with 260 in NVSI-06-09 group and 256 in BBIBP-CorV group. Interim results showed a similar safety profile between two booster groups, with low incidence of adverse reactions of grade 1 or 2. For immunogenicity, by day 14 post-booster, the fold rises in neutralizing antibody geometric mean titers (GMTs) from baseline elicited by NVSI-06-09 were remarkably higher than those by BBIBP-CorV against the prototype strain (19.67 vs 4.47-fold), Omicron BA.1.1 (42.35 vs 3.78-fold), BA.2 (25.09 vs 2.91-fold), BA.4 (22.42 vs 2.69-fold), and BA.5 variants (27.06 vs 4.73-fold). Similarly, the neutralizing GMTs boosted by NVSI-06-09 against Beta and Delta variants were also 6.60-fold and 7.17-fold higher than those by BBIBP-CorV. Our findings indicated that a booster dose of NVSI-06-09 was well-tolerated and elicited broad-spectrum neutralizing responses against divergent SARS-CoV-2 variants, including Omicron and its sub-lineages.

Purification, structural characterization, and anticoagulant activity evaluation of chondroitin sulfate from codfish (Gadus macrocephalus) bones.

Chondroitin sulfate (CCS) was purified from discarded codfish (Gadus macrocephalus) bones, and its chemical structure and anticoagulant activity were assessed. CCS was obtained via enzymatic lysis and ion-exchange column chromatography, with a yield of approximately 0.15%. High-performance gel performance chromatography revealed CCS to be a largely homogeneous polysaccharide with a relatively low molecular weight of 12.3 kDa. FT-IR spectroscopy, NMR spectroscopy, and SAX-HPLC indicated that CCS was composed of monosulfated disaccharides (ΔDi4S 73.85% and ΔDi6S 19.06%) and nonsulfated disaccharides (ΔDi0S 7.09%). In vitro anticoagulation analyses revealed that CCS was able to significantly prolong activated partial thromboplastin time (APTT) and thrombin time (TT) (p < 0.05). At a CCS concentration of 5 µg/mL and 25 µg/mL, APTT and TT were approximately 1.08 and 1.12 times higher, respectively, compared to the negative control group. The results indicated that CCS might offer value as a dietary fiber supplement with the potential to prevent the incidence of coagulation-related thrombosis.

A mosaic-type trimeric RBD-based COVID-19 vaccine candidate induces potent neutralization against Omicron and other SARS-CoV-2 variants.

Large-scale populations in the world have been vaccinated with COVID-19 vaccines, however, breakthrough infections of SARS-CoV-2 are still growing rapidly due to the emergence of immune-evasive variants, especially Omicron. It is urgent to develop effective broad-spectrum vaccines to better control the pandemic of these variants. Here, we present a mosaic-type trimeric form of spike receptor-binding domain (mos-tri-RBD) as a broad-spectrum vaccine candidate, which carries the key mutations from Omicron and other circulating variants. Tests in rats showed that the designed mos-tri-RBD, whether used alone or as a booster shot, elicited potent cross-neutralizing antibodies against not only Omicron but also other immune-evasive variants. Neutralizing antibody ID50 titers induced by mos-tri-RBD were substantially higher than those elicited by homo-tri-RBD (containing homologous RBDs from prototype strain) or the BIBP inactivated COVID-19 vaccine (BBIBP-CorV). Our study indicates that mos-tri-RBD is highly immunogenic, which may serve as a broad-spectrum vaccine candidate in combating SARS-CoV-2 variants including Omicron.

The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pandemic continues to pose a serious threat to public health and has so far resulted in over six million deaths worldwide. Mass vaccination programs have reduced the risk of serious illness and death in many people, but the virus continues to persist and circulate in communities across the globe. Furthermore, the current vaccines may be less effective against the new variants of the virus, such as Omicron and Delta, which are continually emerging and evolving. Therefore, it is urgent to develop effective vaccines that can provide broad protection against existing and future forms of SARS-CoV-2. There are several different types of SARS-CoV-2 vaccine, but they all work in a similar way. They contain molecules that induce immune responses in individuals to help the body recognize and more effectively fight SARS-CoV-2 if they happen to encounter it in the future. These immune responses may be so specific that new variants of a virus may not be recognized by them. Therefore, a commonly used strategy for producing vaccines with broad protection is to make multiple vaccines that each targets different variants and then mix them together before administering to patients. Here, Zhang et al. took a different approach by designing a new vaccine candidate against SARS-CoV2 that contained three different versions of part of a SARS-CoV2 protein ­ the so-called spike protein ­ all linked together as one molecule. The different versions of the spike protein fragment were designed to include key features of the fragments found in Omicron and several other SARS-CoV-2 variants. The experiments found that this candidate vaccine elicited a much higher immune response against Omicron and other SARS-CoV-2 variants in rats than an existing SARS-CoV-2 vaccine. It was also effective as a booster shot after a first vaccination with the existing SARS-CoV-2 vaccine. These findings demonstrate that the molecule developed by Zhang et al. induces potent and broad immune responses against different variants of SARS-CoV-2 including Omicron in rats. The next steps following on from this work are to evaluate the safety and immunogenicity of this vaccine candidate in clinical trials. In the future, it may be possible to use a similar approach to develop new broad-spectrum vaccines against other viruses.

Design of a mutation-integrated trimeric RBD with broad protection against SARS-CoV-2.

The continuous emergence of SARS-CoV-2 variants highlights the need of developing vaccines with broad protection. Here, according to the immune-escape capability and evolutionary convergence, the representative SARS-CoV-2 strains carrying the hotspot mutations were selected. Then, guided by structural and computational analyses, we present a mutation-integrated trimeric form of spike receptor-binding domain (mutI-tri-RBD) as a broadly protective vaccine candidate, which combined heterologous RBDs from different representative strains into a hybrid immunogen and integrated immune-escape hotspots into a single antigen. When compared with a homo-tri-RBD vaccine candidate in the stage of phase II trial, of which all three RBDs are derived from the SARS-CoV-2 prototype strain, mutI-tri-RBD induced significantly higher neutralizing antibody titers against the Delta and Beta variants, and maintained a similar immune response against the prototype strain. Pseudo-virus neutralization assay demonstrated that mutI-tri-RBD also induced broadly strong neutralizing activities against all tested 23 SARS-CoV-2 variants. The in vivo protective capability of mutI-tri-RBD was further validated in hACE2-transgenic mice challenged by the live virus, and the results showed that mutI-tri-RBD provided potent protection not only against the SARS-CoV-2 prototype strain but also against the Delta and Beta variants.

Complete genome sequence of Micromonospora craniellae LHW63014T, a potential metal ion-chelating agent producer.

Micromonospora craniellae LHW63014T is a novel marine Micromonospora, isolated from a Craniella species sponge collected in the South China Sea. In this study, we report the complete genome sequence of M. craniellae LHW63014T, which is comprised of a circular chromosome of 6,839,926 bp with the G + C content of 70.9 mol%. The complete genome contained 6572 protein-coding genes, 48 tRNA genes, and 9 rRNA genes. Genomic annotations revealed that 79.09% of the protein-coding genes were assigned to the COG database, among which, the abundant genes were predicted to be involved in transcription, replication, recombination and repair, and amino acid transport and metabolism. Secondary metabolites prediction using antiSMASH revealed that 22 biosynthetic gene clusters (BGC) of secondary metabolites were located in the genome of M. craniellae LHW63014T, 19 of which showed low similarity (<50%) to known BGCs and 5 of which showed the closest homology with BGCs encoding metal ion-chelating agents, indicating the immense potential of M. craniellae LHW63014T to produce a wide variety of novel antibiotics, especially for metal ion-chelating agents.

Cytotoxic diaporindene and tenellone derivatives from the fungus Phomopsis lithocarpus.

Nine new compounds, including five natural rarely-occurring 2, 3-dihydro-1H-indene derivatives named diaporindenes E-I (1-5), and four new benzophenone analogues named tenellones J-M (6-9) were isolated from the deep-sea sediment-derived fungus Phomopsis lithocarpus FS508. All the structures for these new compounds were fully characterized on the basis of spectroscopic data, NMR spectra, and ECD calculation and single-crystal X-ray diffraction analysis. The potential anti-tumor activities of compounds 1-9 against four tumor cell lines SF-268, MCF-7, HepG-2, and A549 were evaluated using the SRB method. Compound 7 exhibited cytotoxic activity against the SF-268 cell line with an IC50 value of 11.36 µmol·L-1.

[In vitro metabolic interconversion between baicalin and baicalein in the liver, kidney, intestine and bladder of rat].

The present study is aimed to investigate the in vitro metabolic interconversion between baicalin (BG) and baicalein (B) in rat liver, kidney, intestine and bladder. BG and B were separately incubated with rat hepatic, renal, and intestinal microsomes, as well as bladder homogenates, for 30 min. The metabolites were identified and quantified by HPLC and metabolic kinetic parameters were obtained by fitting the data to the Michaelis-Menten equation. In hepatic microsomes, renal microsomes and bladder homogenates, but not in intestinal microsomes, BG was transformed into B, the hydrolysis metabolite of BG, with K(m) values being (44.65 +/- 6.01), (92.73 +/- 11.41), (74.60 +/- 3.68) micromol x L(-1), respectively, and V(max) values being (12.32 +/- 0.56), (3.30 +/- 0.18), (5.93 +/- 0.12) micromol x min(-1) x g(-1) (protein), respectively. In incubations with hepatic, renal, and intestinal microsomes and bladder homogenates, B was also transformed into BG, the glucuronidation metabolite of B, with K(m) values being (67.46 +/- 10.49), (226.7 +/- 71.59), (177.3 +/- 35.85), and (18.33 +/- 2.53) micromol x L(-1), respectively, and V(max) values being (14.74 +/- 0.97), (5.91 +/- 1.03), (38.14 +/- 3.60), and (1.22 +/- 0.05) micromol x min(-1) x g(-1) (protein), respectively. The results showed that the activity of UDP-glucuronosyltranferase (UGT) in intestinal microsomes was the highest among the four organs, and the activities of UGT were higher than that of glucuronidase (GUS) in hepatic, renal and intestinal microsomes, but the activity of GUS was higher than that of UGT in bladder homogenates.

[Pharmacokinetics of flavonoids from xiexin decoction in rats].

To study the pharmacokinetics of flavonoids from Xiexin decoction in rats. SD rats were given a single ig dose of Xiexin decoction 12 g x kg(-1), plasma and urine were collected before and after dosing. Flavonoids components in plasma and urine were measured by HPLC. Pharmacokinetic parameters were determined from the plasma concentration-time data and urinary excretion-time data with the DAS software package. Baicalin was incubated with the rat renal homogenate to investigate its metabolism in vitro. After oral administration of Xiexin decoction baicalin and wogonoside were quickly absorbed and exhibited double peak phenomena in their plasma concentrations. The first peaks in plasma concentrations of baicalin and wogonoside reached Cmax1 of (10 +/- 8) and (1.5 +/- 0.5) mg x L(-1) at Tmax1 of (0.27 +/- 0.09) and (0.17 +/- 0.00) h, while the second peaks reached Cmax2 of (3. 9 0. 5) and (0. 74 +/- 0.11) mg x L(-1) at Tmax2 of (7.6 +/- 2.6) and (16.0 +/- 0.0) h, respectively. The T(1/2) of baicalin and wogonoside were (7 +/- 3) and (6.4 +/- 2.1) h, AUC(0-infinity) were (57 +/- 12) and (15 +/- 3) mg x h x L(-1), respectively. After oral administration of Xiexin decoction, not only baicalin and wogonoside but also baicalein and wogonin can be detected in the urine. The amounts of baicalin, wogonoside, baicalein and wogonin excreted from urine during 0-72 h were (1.4 +/- 0.3), (3.4 +/- 1.3), (2.2 +/- 0.97), (10 +/- 4)% of dose given in rats, respectively. The excretion T(1/2) of the four flavonoids were (6.9 +/- 2.1), (9 +/- 4) , (8.2 +/- 2.0) and (7.2 +/- 1.8) h, respectively. Baicalin was metabolized into baicalein in the rat renal homogenate in vitro, and the kinetic parameters were measured as Vmax = 702 nmol x min(-1) x g(-1) (protein) and Km=135 micromol x L(-1). After oral administration of Xiexin decoction, flavonoids can be absorbed quickly. Only a small quantity of baicalin, wogonoside, baicalein and wogonin were excreted from urine. Baicalin may be metabolized into baicalein in the rat kidney.

[Effects of exhaustive exercise on the expression of PHB1 and the function of mitochondria in rats].

OBJECTIVE: To observe the changes of Prohibitin1(PHB1) contents in rat brain, heart, skeletal muscle tissue and mitochondria with acute exhaustive exercise and the effects of acute exhaustive exercise on mitochondrial function in rats, to explore the relationship among PHB1 and mitochondrial function and energy metabolism. METHODS: Acute exhaustive exercise model:The rats carried acute exhaustive exercise after 8 weeks of feeding. The heart, brain and skeletal muscle samples were collected and the mitochondria were collected to detect the changes of respiratory function and reactive oxygen species(ROS). The expression of PHB1 protein in tissues and mitochondria was detected by Western blot. The ATP content in the organs and the activity of complexes (ATP synthase activity) in mitochondria were measured by spectrophotometer. RESULTS: ① The ATP contents of brain, myocardium and skeletal muscle were decreased significantly after acute exhaustive exercise. ②The activities of complex V, respiratory control rates (RCR) and ROS in mitochondria of brain, myocardium and skeletal muscle were decreased significantly after acute exhaustive exercise, respiration rate state 4(ST4) was increased significantly, at the same time, respiration rate state 3(ST3) had no significant difference. ③ The expression of PHB1 in mitochondria of skeletal muscle was decreased significantly after acute exhaustive exercise, while there was no significant change in PHB1 in myocardial tissue and mitochondria. ④ The correlation analysis showed that the ATP contents in the brain, myocardium and skeletal muscle were positively correlated with the activity of complex V and the expression of PHB1 after acute exhaustive exercise. CONCLUSIONS: After acute exhaustive exercise, the mitochondrial oxidative phosphorylation was reduced, the ROS production was increased, the expression of PHB1 was decreased, the ATP content and the activity of complex V were decreased in the brain and skeletal muscle of rats. Acute exhaustive exercise reduced the expression of PHB1 in mitochondria, decreased mitochondrial function, and reduced energy metabolism.

A novel substrate-inspired fluorescent probe to monitor native albumin in human plasma and living cells.

Human albumin (HA) displays crucial roles in maintaining health and fighting diseases. Accurate determination of native HA in plasma or non-plasma samples are of immense significance in both basic research and clinical practice. Herein, a novel ratiometric two-photon fluorescent probe (N-butyl-4-(4-phenyl-benzoyloxy) 1,8-naphthalimide, BPBN) has been designed and developed for highly selective and sensitive sensing the enzymatic activities of HA, on the basis of its unique pseudo-esterase feature. BPBN exhibits excellent selectivity, high sensitivity and good reactivity under physiological conditions. As an enzymatic activity-based probe, BPBN can distinguish between native HA and denatured HA, while the currently used dye-binding method cannot. The probe has been successfully applied to measure native HA in plasma samples and the secreted HA in the hepatocyte culture supernatant. BPBN has also been used for two-photon imaging of HA reabsorption in living renal cells, and the results demonstrate that this probe exhibits good cell permeability, low cytotoxicity and high imaging resolution. All these findings suggest that BPBN can be reliably used for the highly selective and sensitive detection of native HA in complex biological samples, as well as for exploring HA-associated biological processes and the physiological functions of native HA in living cells.

A highly selective fluorescent ESIPT probe for the detection of Human carboxylesterase 2 and its biological applications.

A new ratiometric florescence probe derived from 3-hydroxyflavone (3-HF) has been developed for selective and sensitive detection of human carboxylesterase 2 (CE2). The probe is designed by modulating the excited state intramolecular proton transfer (ESIPT) emission of 3-HF via introducing of 4-ethylbenzoyloxy group. Under physiological conditions, probe 1 displays satisfying stability with very low background signal, but it can be selectively hydrolyzed by CE2 to release free 3-HF which brings remarkable changes in fluorescence spectrum. Both reaction phenotyping and chemical inhibition assays demonstrate that probe 1 is highly selective for CE2 over other human hydrolases including carboxylesterase 1, cholinesterases and paraoxonases. Probe 1 has been applied successfully to measure the real activities of CE2 in human biological samples, as well as to screen CE2 inhibitors by using tissue preparations as the enzymes sources. Additionally, probe 1 is cell membrane permeable and can be used for cellular imaging of endogenous CE2 in living cells. All of these features make it possible to serve as a promising tool for exploring the individual differences in biological function of CE2, as well as for rapid screening of selective and potent inhibitors of CE2 for further clinical use.