Discovery of a novel class of rosmarinic acid derivatives as antibacterial agents: Synthesis, structure-activity relationship and mechanism of action.

Twenty-seven rosmarinic acid derivatives were synthesized, among which compound RA-N8 exhibited the most potent antibacterial ability. The minimum inhibition concentration of RA-N8 against both S. aureus (ATCC 29213) and MRSA (ATCC BAA41 and ATCC 43300) was found to be 6 µg/mL, and RA-N8 killed E. coli (ATCC 25922) at 3 µg/mL in the presence of polymyxin B nonapeptide (PMBN) which increased the permeability of E. coli. RA-N8 exhibited a weak hemolytic effect at the minimum inhibitory concentration. SYTOX Green assay, SEM, and LIVE/DEAD fluorescence staining assay proved that the mode of action of RA-N8 is targeting bacterial cell membranes. Furthermore, no resistance in wildtype S. aureus developed after incubation with RA-N8 for 20 passages. Cytotoxicity studies further demonstrated that RA-N8 is non-toxic to the human normal cell line (HFF1). RA-N8 also exerted potent inhibitory ability against biofilm formation of S. aureus and even collapsed the shaped biofilm.

Fluorescently Modified NDM-1: A Versatile Drug Sensor for Rapid In Vitro ß-Lactam Antibiotic and Inhibitor Screening.

We successfully developed a fluorescent drug sensor from clinically relevant New Delhi metallo-ß-lactamase-1 (NDM-1). The F70 residue was chosen to be replaced with a cysteine for conjugation with thiol-reactive fluorescein-5-maleimide to form fluorescent F70Cf, where "f" refers to fluorescein-5-maleimide. Our proteolytic studies of unlabeled F70C and labeled F70Cf monitored by electrospray ionization-mass spectrometry (ESI-MS) revealed that fluorescein-5-maleimide was specifically linked to C70 in 1:1 mole ratio (F70C:fluorophore). Our drug sensor (F70Cf) can detect the ß-lactam antibiotics cefotaxime and cephalothin by giving stronger fluorescence in the initial binding phase and then declining fluorescence signals as a result of the hydrolysis of the antibiotics into acid products. F70Cf can also detect non-ß-lactam inhibitors (e.g., l-captopril, d-captopril, dl-thiorphan, and thanatin). In all cases, F70Cf exhibits stronger fluorescence due to inhibitor binding and subsequently sustained fluorescence signals in a later stage. Native ESI-MS results show that F70Cf can bind to all four inhibitors. Moreover, our drug sensor is compatible with a high-throughput microplate reader and has the capability to perform in vitro drug screening.

Development of a bioengineered Erwinia chrysanthemi asparaginase to enhance its anti-solid tumor potential for treating gastric cancer.

Asparaginase has been traditionally applied for only treating acute lymphoblastic leukemia due to its ability to deplete asparagine. However, its ultimate anticancer potential for treating solid tumors has not yet been unleashed. In this study, we bioengineered Erwinia chrysanthemi asparaginase (ErWT), one of the US Food and Drug Administration-approved types of amino acid depleting enzymes, to achieve double amino acid depletions for treating a solid tumor. We constructed a fusion protein by joining an albumin binding domain (ABD) to ErWT via a linker (GGGGS)5 to achieve ABD-ErS5. The ABD could bind to serum albumin to form an albumin-ABD-ErS5 complex, which could avoid renal clearance and escape from anti-drug antibodies, resulting in a remarkably prolonged elimination half-life of ABD-ErS5. Meanwhile, ABD-ErS5 did not only deplete asparagine but also glutamine for ∼2 weeks. A biweekly administration of ABD-ErS5 (1.5 mg/kg) significantly suppressed tumor growth in an MKN-45 gastric cancer xenograft model, demonstrating a novel approach for treating solid tumor depleting asparagine and glutamine. Multiple administrations of ABD-ErS5 did not cause any noticeable histopathological abnormalities of key organs, suggesting the absence of acute toxicity to mice. Our results suggest ABD-ErS5 is a potential therapeutic candidate for treating gastric cancer.

Advances in rapid detection of SARS-CoV-2 by mass spectrometry.

COVID-19 has already been lasting for more than two years and it has been severely affecting the whole world. Still, detection of SARS-CoV-2 remains the frontline approach to combat the pandemic, and the reverse transcription polymerase chain reaction (RT-PCR)-based method is the well recognized detection method for the enormous analytical demands. However, the RT-PCR method typically takes a relatively long time, and can produce false positive and false negative results. Mass spectrometry (MS) is a very commonly used technique with extraordinary sensitivity, specificity and speed, and can produce qualitative and quantitative information of various analytes, which cannot be achieved by RT-PCR. Since the pandemic outbreak, various mass spectrometric approaches have been developed for rapid detection of SARS-CoV-2, including the LC-MS/MS approaches that could allow analysis of several hundred clinical samples per day with one MS system, MALDI-MS approaches that could directly analyze clinical samples for the detection, and efforts for the on-site detection with portable devices. In this review, these mass spectrometric approaches were summarized, and their pros and cons as well as further development were also discussed.

A multi-omics investigation into the mechanisms of hyper-virulence in Mycobacterium tuberculosis.

Clinical manifestations of tuberculosis range from asymptomatic infection to a life-threatening disease such as tuberculous meningitis (TBM). Recent studies showed that the spectrum of disease severity could be related to genetic diversity among clinical strains of Mycobacterium tuberculosis (Mtb). Certain strains are reported to preferentially invade the central nervous system, thus earning the label "hypervirulent strains".However, specific genetic mutations that accounted for enhanced mycobacterial virulence are still unknown. We previously identified a set of 17 mutations in a hypervirulent Mtb strain that was from TBM patient and exhibited significantly better intracellular survivability. These mutations were also commonly shared by a cluster of globally circulating hyper-virulent strains. Here, we aimed to validate the impact of these hypervirulent-specific mutations on the dysregulation of gene networks associated with virulence in Mtb via multi-omic analysis. We surveyed transcriptomic and proteomic differences between the hyper-virulent and low-virulent strains using RNA-sequencing and label-free quantitative LC-MS/MS approach, respectively. We identified 25 genes consistently differentially expressed between the strains at both transcript and protein level, regardless the strains were growing in a nutrient-rich or a physiologically relevant multi-stress condition (acidic pH, limited nutrients, nitrosative stress, and hypoxia). Based on integrated genomic-transcriptomic and proteomic comparisons, the hypervirulent-specific mutations in FadE5 (g. 295,746 C >T), Rv0178 (p. asp150glu), higB (p. asp30glu), and pip (IS6110-insertion) were linked to deregulated expression of the respective genes and their functionally downstream regulons. The result validated the connections between mutations, gene expression, and mycobacterial pathogenicity, and identified new possible virulence-associated pathways in Mtb.

The structural dynamics of full-length divisome transmembrane proteins FtsQ, FtsB, and FtsL in FtsQBL complex formation.

FtsQBL is a transmembrane protein complex in the divisome of Escherichia coli that plays a critical role in regulating cell division. Although extensive efforts have been made to investigate the interactions between the three involved proteins, FtsQ, FtsB, and FtsL, the detailed interaction mechanism is still poorly understood. In this study, we used hydrogen-deuterium exchange mass spectrometry to investigate these full-length proteins and their complexes. We also dissected the structural dynamic changes and the related binding interfaces within the complexes. Our data revealed that FtsB and FtsL interact at both the periplasmic and transmembrane regions to form a stable complex. Furthermore, the periplasmic region of FtsB underwent significant conformational changes. With the help of computational modeling, our results suggest that FtsBL complexation may bring the respective constriction control domains (CCDs) in close proximity. We show that when FtsBL adopts a coiled-coil structure, the CCDs are fixed at a vertical position relative to the membrane surface; thus, this conformational change may be essential for FtsBL's interaction with other divisome proteins. In the FtsQBL complex, intriguingly, we show only FtsB interacts with FtsQ at its C-terminal region, which stiffens a large area of the ß-domain of FtsQ. Consistent with this, we found the connection between the α- and ß-domains in FtsQ is also strengthened in the complex. Overall, the present study provides important experimental evidence detailing the local interactions between the full-length FtsB, FtsL, and FtsQ protein, as well as valuable insights into the roles of FtsQBL complexation in regulating divisome activity.

Integrated Mass Spectrometry Reveals Celastrol As a Novel Catechol-O-methyltransferase Inhibitor.

Natural product celastrol is known to have various biological activities, yet its molecular targets that correspond to many activities remain unclear. Here, we used multiple mass-spectrometry-based approaches to identify catechol-O-methyltransferase (COMT) as a major binding target of celastrol and characterized their interaction comprehensively. Celastrol was found to inhibit the enzymatic activity of COMT and increased the dopamine level in neuroendocrine chromaffin cells significantly. Our study not only revealed a novel binding target of celastrol but also provided a new scaffold and cysteine hot spot for developing new generation COMT inhibitors in combating neurological disorders.

Data storage using peptide sequences.

Humankind is generating digital data at an exponential rate. These data are typically stored using electronic, magnetic or optical devices, which require large physical spaces and cannot last for a very long time. Here we report the use of peptide sequences for data storage, which can be durable and of high storage density. With the selection of suitable constitutive amino acids, designs of address codes and error-correction schemes to protect the order and integrity of the stored data, optimization of the analytical protocol and development of a software to effectively recover peptide sequences from the tandem mass spectra, we demonstrated the feasibility of this method by successfully storing and retrieving a text file and the music file Silent Night with 40 and 511 18-mer peptides respectively. This method for the first time links data storage with the peptide synthesis industry and proteomics techniques, and is expected to stimulate the development of relevant fields.

Interdomain flexibility and interfacial integrity of ß-lactamase inhibitory protein (BLIP) modulate its binding to class A ß-lactamases.

ß-Lactamase inhibitory protein (BLIP) consists of a tandem repeat of αß domains conjugated by an interdomain loop and can effectively bind and inactivate class A ß-lactamases, which are responsible for resistance of bacteria to ß-lactam antibiotics. The varied ability of BLIP to bind different ß-lactamases and the structural determinants for significant enhancement of BLIP variants with a point mutation are poorly understood. Here, we investigated the conformational dynamics of BLIP upon binding to three clinically prevalent class A ß-lactamases (TEM1, SHV1, and PC1) with dissociation constants between subnanomolar and micromolar. Hydrogen deuterium exchange mass spectrometry revealed that the flexibility of the interdomain region was significantly suppressed upon strong binding to TEM1, but was not significantly changed upon weak binding to SHV1 or PC1. E73M and K74G mutations in the interdomain region improved binding affinity toward SHV1 and PC1, respectively, showing significantly increased flexibility of the interdomain region compared to the wild-type and favorable conformational changes upon binding. In contrast, more rigidity of the interfacial loop 135-145 was observed in these BLIP mutants in both free and bound states. Consistently, molecular dynamics simulations of BLIP exhibited drastic changes in the flexibility of the loop 135-145 in all complexes. Our results indicated for the first time that higher flexibility of the interdomain linker, as well as more rigidity of the interfacial loop 135-145, could be desirable determinants for enhancing inhibition of BLIP to class A ß-lactamases. Together, these findings provide unique insights into the design of enhanced inhibitors.

Stabilizer-free bismuth nanoparticles for selective polyol electrooxidation.

Bismuth is the least toxic element among heavy metals, an outstanding advantage for environmental and health considerations. Yet, utilizing bismuth as anodic electrocatalyst is hindered by the formation of a spreading Bi(OH)3 inhibitor layer during the anodic process. Herein, we report that bismuth nanoparticles, produced using laser ablation, can avoid such drawbacks. The production of Bi(V) species assists polyol electrooxidation. For glucose, instead of the commonly reported gluconic acid as the product, the Bi(V) species enables highly selective oxidation and C-C bond cleavage to produce arabinonic acid, erythronic acid, and eventually glyceric acid. We not only generate high-valent Bi(V) species for catalytic applications, especially for bioelectrocatalysis where the less toxic bismuth is highly appreciated, but also present Bi nanoparticle as a highly selective electrocatalyst that can break C-C bond. We believe that Bi electrocatalyst can find broader applications in electrochemical biomass conversion and electrosynthesis.

Structure of mouse cytosolic sulfotransferase SULT2A8 provides insight into sulfonation of 7α-hydroxyl bile acids.

Cytosolic sulfotransferases (SULTs) catalyze the transfer of a sulfonate group from the cofactor 3'-phosphoadenosine 5'-phosphosulfate to a hydroxyl (OH) containing substrate and play a critical role in the homeostasis of endogenous compounds, including hormones, neurotransmitters, and bile acids. In human, SULT2A1 sulfonates the 3-OH of bile acids; however, bile acid metabolism in mouse is dependent on a 7α-OH sulfonating SULT2A8 via unknown molecular mechanisms. In this study, the crystal structure of SULT2A8 in complex with adenosine 3',5'-diphosphate and cholic acid was resolved at a resolution of 2.5 Å. Structural comparison with human SULT2A1 reveals different conformations of substrate binding loops. In addition, SULT2A8 possesses a unique substrate binding mode that positions the target 7α-OH of the bile acid close to the catalytic site. Furthermore, mapping of the critical residues by mutagenesis and enzyme activity assays further highlighted the importance of Lys44 and His48 for enzyme catalysis and Glu237 in loop 3 on substrate binding and stabilization. In addition, limited proteolysis and thermal shift assays suggested that the cofactor and substrates have protective roles in stabilizing SULT2A8 protein. Together, the findings unveil the structural basis of bile acid sulfonation targeting 7α-OH and shed light on the functional diversity of bile acid metabolism across species.

Dynamic cross-linking of an alginate-acrylamide tough hydrogel system: time-resolved in situ mapping of gel self-assembly.

Hydrogels are a popular class of biomaterial that are used in a number of commercial applications (e.g.; contact lenses, drug delivery, and prophylactics). Alginate-based tough hydrogel systems, interpenetrated with acrylamide, reportedly form both ionic and covalent cross-links, giving rise to their remarkable mechanical properties. In this work, we explore the nature, onset and extent of such hybrid bonding interactions between the complementary networks in a model double-network alginate-acrylamide system, using a host of characterisation techniques (e.g.; FTIR, Raman, UV-vis, and fluorescence spectroscopies), in a time-resolved manner. Further, due to the similarity of bonding effects across many such complementary, interpenetrating hydrogel networks, the broad bonding interactions and mechanisms observed during gelation in this model system, are thought to be commonly replicated across alginate-based and broader double-network hydrogels, where both physical and chemical bonding effects are present. Analytical techniques followed real-time bond formation, environmental changes and re-organisational processes that occurred. Experiments broadly identified two phases of reaction; phase I where covalent interaction and physical entanglements predominate, and; phase II where ionic cross-linking effects are dominant. Contrary to past reports, ionic cross-linking occurred more favourably via mannuronate blocks of the alginate chain, initially. Evolution of such bonding interactions was also correlated with the developing tensile and compressive properties. These structure-property findings provide mechanistic insights and future synthetic intervention routes to manipulate the chemo-physico-mechanical properties of dynamically-forming tough hydrogel structures according to need (i.e.; durability, biocompatibility, adhesion, etc.), allowing expansion to a broader range of more physically and/or environmentally demanding biomaterials applications.

Lipidomic Analysis Reveals the Protection Mechanism of GLP-1 Analogue Dulaglutide on High-Fat Diet-Induced Chronic Kidney Disease in Mice.

Many clinical studies have suggested that glucagon-like peptide-1 receptor agonists (GLP-1RAs) have renoprotective properties by ameliorating albuminuria and increasing glomerular filtration rate in patients with type 2 diabetes mellitus (T2DM) and chronic kidney disease (CKD) by lowering ectopic lipid accumulation in the kidney. However, the mechanism of GLP-1RAs was hitherto unknown. Here, we conducted an unbiased lipidomic analysis using ultra-high-performance liquid chromatography/electrospray ionization-quadrupole time-of-flight mass spectrometry (UHPLC/ESI-Q-TOF-MS) and matrix-assisted laser desorption/ionization mass spectrometry imaging (MALDI-MSI) to reveal the changes of lipid composition and distribution in the kidneys of high-fat diet-fed mice after treatment with a long-acting GLP-1RA dulaglutide for 4 weeks. Treatment of dulaglutide dramatically improved hyperglycemia and albuminuria, but there was no substantial improvement in dyslipidemia and ectopic lipid accumulation in the kidney as compared with controls. Intriguingly, treatment of dulaglutide increases the level of an essential phospholipid constituent of inner mitochondrial membrane cardiolipin at the cortex region of the kidneys by inducing the expression of key cardiolipin biosynthesis enzymes. Previous studies demonstrated that lowered renal cardiolipin level impairs kidney function via mitochondrial damage. Our untargeted lipidomic analysis presents evidence for a new mechanism of how GLP-1RAs stimulate mitochondrial bioenergetics via increasing cardiolipin level and provides new insights into the therapeutic potential of GLP-1RAs in mitochondrial-related diseases.

Rational structural modification of the isatin scaffold to develop new and potent antimicrobial agents targeting bacterial peptidoglycan glycosyltransferase.

A series of isatin derivatives bearing three different substituent groups at the N-1, C-3 and C-5 positions of the isatin scaffold were systematically designed and synthesized to study the structure-activity relationship of their inhibition of bacterial peptidoglycan glycosyltransferase (PGT) activity and antimicrobial susceptibility against S. aureus, E. coli and methicillin-resistant Staphylococcus aureus (MRSA (BAA41)) strains. The substituents at these sites are pointing towards three different directions from the isatin scaffold to interact with the amino acid residues in the binding pocket of PGT. Comparative studies of their structure-activity relationship allow us to gain better understanding of the direction of the substituents that contribute critical interactions leading to inhibition activity against the bacterial enzyme. Our results indicate that the modification of these sites is able to maximize the antimicrobial potency and inhibitory action against the bacterial enzyme. Two compounds show good antimicrobial potency (MIC = 3 µg mL-1 against S. aureus and MRSA; 12-24 µg mL-1 against E. coli). Results of the inhibition study against the bacterial enzyme (E. coli PBP 1b) reveal that some compounds are able to achieve excellent in vitro inhibitions of bacterial enzymatic activity (up to 100%). The best half maximal inhibitory concentration (IC50) observed among the new compounds is 8.9 µM.

Hydrogen-Deuterium Exchange Mass Spectrometry for Probing Changes in Conformation and Dynamics of Proteins.

Hydrogen-deuterium exchange mass spectrometry (HDX-MS) is, nowadays, an increasingly important technique in studying protein conformation and dynamics. This technique possesses the advantages of low sample consumption, less limitation in protein size, and relatively simple experimental workflow. An HDX-MS experiment typically includes the steps of sample preparation, HDX reaction, quenching of HDX reaction, protease digestion, and LC-MS analysis. Although HDX-MS has been an established technique and automatic sample handling devices are commercially available nowadays, proper experimental conditions of each step are crucial for a successful HDX-MS experiment. This chapter is to provide a general guideline for each step in the HDX-MS workflow and highlight some precautions needed to be taken in order to acquire useful conformational and dynamic information.

N-Acetyl-D-Glucosamine Acts as Adjuvant that Re-Sensitizes Starvation-Induced Antibiotic-Tolerant Population of E. Coli to ß-Lactam.

Bacterial tolerance to antibiotics causes reduction in efficacy in antimicrobial treatment of chronic and recurrent infections. Nutrient availability is one major factor that determines the degree of phenotypic antibiotic tolerance. In an attempt to test if specific nutrients can reverse phenotypic tolerance, we identified N-acetyl-D-glucosamine (GlcNAc) as a potent tolerance-suppressing agent and showed that it could strongly re-sensitize a tolerant population of E. coli to ampicillin. Such re-sensitization effect was attributable to two physiology-modulating effects of GlcNAc. First, uptake of GlcNAc by the tolerant population triggers formation of the peptidoglycan precursor UDP-N-acetyl-D-glucosamine (UDP-GlcNAc) and subsequently re-activates the peptidoglycan biosynthesis process, rendering the organism susceptible to ß-lactam antibiotics. Second, activation of glycolysis by-products of GlcNAc catabolism drives the re-sensitization process. Our findings imply that GlcNAc may serve as a non-toxic ß-lactam adjuvant that enhances the efficacy of treatment of otherwise hard-to-treat bacterial infections due to phenotypic antibiotic tolerance.

BADAN-conjugated ß-lactamases as biosensors for ß-lactam antibiotic detection.

ß-Lactam antibiotic detection has significant implications in food safety control, environmental monitoring and pharmacokinetics study. Here, we report the development of two BADAN-conjugated ß-lactamases, E166Cb and E166Cb/N170Q, as sensitive biosensors for ß-lactam antibiotic detection. These biosensors were constructed by coupling an environment-sensitive BADAN probe onto location 166 at the active site of the PenP ß-lactamase E166C and E166C/N170Q mutants. They gave fluorescence turn-on signals in response to ß-lactam antibiotics. Molecular dynamics simulation of E166Cb suggested that the turn-on signal might be attributed to a polarity change of the microenvironment of BADAN and the removal of the fluorescence quenching effect on BADAN exerted by a nearby Tyr-105 upon the antibiotic binding. In the detection of four ß-lactams (penicillin G, penicillin V, cefotaxime and moxalactam), both E166Cb and E166Cb/N170Q delivered signal outputs in an antibiotic-concentration dependent manner with a dynamic range spanning from 10 nM to 1 µM. Compared to E166Cb, E166Cb/N170Q generally exhibited more stable signals owing to its higher deficiency in hydrolyzing the antibiotic analyte. The overall biosensor performance of E166Cb and E166Cb/N170Q was comparable to that of their respective fluorescein-modified counterparts, E166Cf and E166Cf/N170Q. But comparatively, the BADAN-conjugated enzymes showed a higher sensitivity, displayed a faster response in detecting moxalactam and a more stable fluorescence signals towards penicillin G. This study illustrates the potential of BADAN-conjugated ß-lactamases as biosensing devices for ß-lactam antibiotics.

Design of a structure-based fluorescent biosensor from bioengineered arginine deiminase for rapid determination of L-arginine.

Rationally designed mutations on recombinant arginine deiminase (ADI) could act as a 'turn-off' L-arginine (L-Arg) fluorescent biosensor and provide an alternative method for rapid determination of L-Arg. Double mutations were introduced on the Cys251➔Ser251 and Thr265➔Cys265 of recombinant ADI, rendering a single cysteine present on the protein surface for the site-specific attachment of a fluorophore, fluorescein-5-maleimide. The double mutations on ADI (265C) and its fluorescein-labelled form (265Cf) conserved the catalytic efficiency of wild-type ADI. Upon binding to L-Arg, 265Cf induced structural conformational changes and rendered the fluorescein moiety to move closer to Trp264, resulting in fluorescence quenching. The duration of fluorescence quenching was dependant on the L-Arg concentration. A linear relationship between the time at the maximum rate of fluorescence change and L-Arg concentrations, which ranged from 2.5 to 100 µM, was found with R2 = 0.9988. The measurement time was within 0.15-4 min. Determination of L-Arg concentration in fetal bovine serum could be achieved by the standard addition method and without sample pre-treatment. The result showed a good agreement with the one determined by mass spectrometry, suggesting our biosensor as a promising tool for the detection of L-Arg in biological samples.