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.

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.

Cu-Co Dual-Atom Catalysts Supported on Hierarchical USY Zeolites for an Efficient Cross-Dehydrogenative C(sp2)-N Coupling Reaction.

A cross-coupling reaction via the dehydrogenative route over heterogeneous solid atomic catalysts offers practical solutions toward an economical and sustainable elaboration of simple organic substrates. The current utilization of this technology is, however, hampered by limited molecular definition of many solid catalysts. Here, we report the development of Cu-M dual-atom catalysts (where M = Co, Ni, Cu, and Zn) supported on a hierarchical USY zeolite to mediate efficient dehydrogenative cross-coupling of unprotected phenols with amine partners. Over 80% isolated yields have been attained over Cu-Co-USY, which shows much superior reactivity when compared with our Cu1 and other Cu-M analogues. This amination reaction has hence involved simple and non-forceful reaction condition requirements. The superior reactivity can be attributed to (1) the specifically designed bimetallic Cu-Co active sites within the micropore for "co-adsorption-co-activation" of the reaction substrates and (2) the facile intracrystalline (meso/micropore) diffusion of the heterocyclic organic substrates. This study offers critical insights into the engineering of next-generation solid atomic catalysts with complex reaction steps.

C-terminal modification of a de novo designed antimicrobial peptide via capping of macrolactam rings.

In this work, by capping a macrolactam ring at the C-terminus of a de novo-designed peptide, namely zp80, we have constructed a small peptide library via the solid phase peptide synthesis for screening. Eight peptides bearing different aspartic acid-rich macrolactam rings but the same linear (IIRR)4 unit exhibited improved antibacterial activities, hemolytic activity, and selectivity index. Mechanistic studies revealed that they could destroy the integrity of bacterial envelope, leading to cytoplasm leakage and rapid dissipation of membrane potential. One of these peptides, zp90 with a macrolactam ring of (KaDGD), demonstrated preferential interaction with calcium ions at a stoichiometric ratio of 1:1, promoting the affinity of designed peptides to bacterial membrane. Overall, this work provides a feasible strategy for medicinal chemists to further develop potent, selective, and multifunctional de novo-designed antimicrobial peptides.

The crystal structure of the H116Q mutant of NDM-1: An enzyme devoid of zinc ions.

New Delhi metallo-ß-lactamase 1 (NDM-1) is an important causative factor of antimicrobial resistance due to its efficient hydrolysis of a broad range of ß-lactam compounds. The two zinc ions at the active site play essential roles in the NDM-1 catalytic activities. In a previous work, H116, one of the three ligands at the Zn1 site, was mutated in order to investigate the nature of zinc ion chelation. We report here the crystal structure of the NDM-1 H116Q mutant, that was designed to convert a B1 di-zinc enzyme into a B3 type, which either still binds two zinc ions or binds only one at the Zn2 site. The effect of mutation on the overall structure is minimal. Unexpectedly, no zinc ion was observed in the crystal structure. The Zn2-site ligating residue C221 forms a covalent bond with the nearby K121, a residue important in maintaining the active-site structure. The largest conformational changes were found at main-chain and side-chain atoms at residues 232-236 (loop 10), the proper configuration of which is known to be essential for substrate binding. The catalytic-site mutation caused little local changes, yet the effects were amplified and propagated to the substrate binding residues. There were big changes in the ψ angles of residues G232 and L234, which resulted in the side chain of N233 being displaced away from the substrate-binding site. In summary, we failed in turning a B1 enzyme into a B3 enzyme, yet we produced a zinc-less NDM-1 with residual activities.

High-Q localized surface plasmon resonance based on bound states in the continuum for enhanced refractive index sensing.

Nanophotonics based on localized surface plasmon resonance (LSPR) has emerged as a vibrant arena for research into enhanced light-matter interactions with potential applications in imaging, sensing, and computing. However, the low quality (Q) factor of LSPR is a significant barrier to comprehensive device applications. Here, we demonstrate that coupling the LSPR of a gold nanowire array with the optical bound states in the continuum (BIC) of a dielectric double-layer grating can significantly increase the Q factor of LSPR. We realize two hybrid modes with Q factors of up to 111 at 558 nm and 83 at 582 nm, which are about 14 and 10 times larger than those of an uncoupled gold nanowire array. Based on temporal coupled-mode theory, we further show that the resonance frequencies and Q factors of the hybrid modes can be modulated and optimized by varying relevant structural parameters. This coupled system provides a new platform for improving the figures of merit (FoMs) of LSPR-based refractive index sensors, and the concept of LSPR-BIC coupling can be extended to other similar nanosystems.

Recent Advances in Electrocatalytic Hydrogen Evolution Using Nanoparticles.

Hydrogen fuel is considered as the cleanest renewable resource and the primary alternative to fossil fuels for future energy supply. Sustainable hydrogen generation is the major prerequisite to realize future hydrogen economy. The electrocatalytic hydrogen evolution reaction (HER), as the vital step of water electrolysis to H2 production, has been the subject of extensive study over the past decades. In this comprehensive review, we first summarize the fundamentals of HER and review the recent state-of-the-art advances in the low-cost and high-performance catalysts based on noble and non-noble metals, as well as metal-free HER electrocatalysts. We systemically discuss the insights into the relationship among the catalytic activity, morphology, structure, composition, and synthetic method. Strategies for developing an effective catalyst, including increasing the intrinsic activity of active sites and/or increasing the number of active sites, are summarized and highlighted. Finally, the challenges, perspectives, and research directions of HER electrocatalysis are featured.

Discrete metal nanoparticles with plasmonic chirality.

From a geometrical perspective, a chiral object does not have mirror planes or inversion symmetry. It exhibits the same physical properties as its mirror image (enantiomer), except for the chiroptical activity, which is often the opposite. Recent advancements have identified particularly interesting implications of chirality on the optical properties of metal nanoparticles, which are intimately related to localized surface plasmon resonance phenomena. Although such resonances are usually independent of the circular polarization of light, specific strategies have been applied to induce chirality, both in assemblies and at the single-particle level. In this tutorial review, we discuss the origin of plasmonic chirality, as well as theoretical models that have been proposed to explain it. We then summarise recent developments in the synthesis of discrete nanoparticles with plasmonic chirality by means of wet-chemistry methods. We conclude with a discussion of promising applications for discrete chiral nanoparticles. We expect this tutorial review to be of interest to researchers from a wide variety of disciplines where chiral plasmonics can be exploited at the nanoparticle level, such as chemical sensing, photocatalysis, photodynamic or photothermal therapies, etc.

Specific Amino Acid Substitutions in OXA-51-Type ß-Lactamase Enhance Catalytic Activity to a Level Comparable to Carbapenemase OXA-23 and OXA-24/40.

The chromosomal blaOXA-51-type gene encodes carbapenem-hydrolyzing class D ß-lactamases (CHDLs), specific variants shown to mediate carbapenem resistance in the Gram-negative bacterial pathogen Acinetobacter baumannii. This study aims to characterize the effect of key amino acid substitutions in OXA-51 variants of carbapenem-hydrolyzing class D ß-lactamases (CHDLs) on substrate catalysis. Mutational and structural analyses indicated that each of the L167V, W222G, or I129L substitutions contributed to an increase in catalytic activity. The I129L mutation exhibited the most substantial effect. The combination of W222G and I129L substitutions exhibited an extremely strong catalytic enhancement effect in OXA-66, resulting in higher activity than OXA-23 and OXA-24/40 against carbapenems. These findings suggested that specific arrangement of residues in these three important positions in the intrinsic OXA-51 type of enzyme can generate variants that are even more active than known CHDLs. Likewise, mutation leading to the W222M change also causes a significant increase in the catalytic activity of OXA-51. blaOXA-51 gene in A. baumannii may likely continue to evolve, generating mutant genes that encode carbapenemase with extremely strong catalytic activity.

Bioisosteric investigation of ebselen: Synthesis and in vitro characterization of 1,2-benzisothiazol-3(2H)-one derivatives as potent New Delhi metallo-ß-lactamase inhibitors.

Carbapenem-resistant Enterobacteriaceae (CRE) producing New Delhi metallo-ß-lactamase (NDM-1) cause untreatable bacterial infections, posing a significant threat to human health. In the present study, by employing the concept of bioisosteric replacement of the selenium moiety of ebselen, we have designed, synthesized and characterized a small compound library of 2-substituted 1,2-benzisothiazol-3(2H)-one derivatives and related compounds for evaluating their cytotoxicity and synergistic activity in combination with meropenem against the E. coli Tg1 (NDM-1) strain. The most promising compound 3a demonstrated potent synergistic activity against a panel of clinically isolated NDM-1 positive CRE strains with FICI as low as 0.09. Moreover, its IC50 value and inhibition mechanism were also confirmed by using the enzyme inhibition assay and the ESI-MS analysis respectively. Importantly, compound 3a has acceptable toxicity and is not a PAINS. Because of its structural simplicity and potent synergistic activity in combination with meropenem, we propose that compound 3a may be a promising meropenem adjuvant and a new series of such compounds may worth further investigations.

Hydrophobic substituents on isatin derivatives enhance their inhibition against bacterial peptidoglycan glycosyltransferase activity.

Moenomycin A, the well-known natural product inhibitor of peptidoglycan glycosyltransferase (PGT), is a large amphiphilic molecule of molecular mass of 1583 g/mol and its bioavailablity as a drug is relatively poor. In searching for small-molecule ligands with high inhibition ability targeting the enzyme, we found that the addition of hydrophobic groups to an isatin-based inhibitor of bacterial PGT significantly improves its inhibition against the enzyme, as well as its antibacterial activity. The improvement in enzymatic inhibition can be attributed to a better binding of the small molecule inhibitor to the hydrophobic region of the membrane-bound bacterial cell wall synthesis enzyme and the plasma membrane. In the present study, a total of 20 new amphiphilic compounds were systematically designed and the relationship between molecular hydrophobicity and the antibacterial activity by targeting at PGT was demonstrated. The in vitro lipid II transglycosylation inhibitory effects (IC50) against E. coli PBP1b and MICs of the compounds were investigated. Optimized results including MIC values of 6 µg/mL for MSSA, MRSA, B. subtilis and 12 µg/mL for E. coli were obtained with an isatin derivative 5m which has a molecular mass of 335 g/mol.

A bioengineered arginine-depleting enzyme as a long-lasting therapeutic agent against cancer.

L-Arginine (L-Arg) depletion has attracted great attention in cancer therapy. Although two types of arginine-depleting enzymes, arginine deiminase (ADI) and human arginase I, are undergoing clinical trials, random site of PEGylation, low efficacy of heavy metal as co-factor, and immunogenicity limit the performance of these drugs and cause difficulty in a homogeneous production. Here we screened ten catalytic metal ions and have successfully produced a site-specific mono-PEGylated human arginase I mutant by conjugating the Cys45 residue to PEG-maleimide to minimize the decrease in activity and produce a homogeneous product. The catalytic efficiency trend of metal ion-enriched human arginase I mutant (HAI) was Co2+ > Ni2+ ≫ Mn2+. The overall kcat/KM values of Co-HAI and Ni-HAI were higher than Mn-HAI by ~ 8.7- and ~ 5.2-folds, respectively. Moreover, the results of enzyme kinetics and circular dichroism spectrometry demonstrated that the 20 or 40 kDa linear and branched PEG attached on the HAI surface did not affect the enzyme activity and the protein secondary structures. In vitro studies showed that both Co-HAI-PEG20L and Ni-HAI-PEG20L inhibited the growth of eight types of cancer cell lines. The pharmacodynamic study in mice demonstrated that the i.p. administration of Co-HAI-PEG20L at 13 mg/kg and Ni-HAI-PEG20L at 15 mg/kg was able to maintain a L-Arg level below its detection limit for over 120 h after one injection. The body weights of mice could return to normal levels within 5 days after injection, showing that the doses were well-tolerated. Therefore, both the Ni-HAI-PEG20L and Co-HAI-PEG20L are promising candidates for cancer therapy. KEY POINTS: • Mono-PEGylation applied on human arginase I mutant (HAI) successfully. • The catalytic efficiency of Co- and Ni-enriched HAI was higher than the wild type. • At least eight types of cancer cell lines were inhibited by Co- and Ni-HAI-PEG20L. • Co- and Ni-HAI-PEG20L were able to achieve weekly depletion of L-Arg. Graphical abstract.

Mono-PEGylation of a Thermostable Arginine-Depleting Enzyme for the Treatment of Lung Cancer.

L-arginine (L-Arg) depletion induced by randomly PEGylated arginine deiminase (ADI-PEG20) can treat arginosuccinate synthase (ASS)-negative cancers, and ADI-PEG20 is undergoing phase III clinical trials. Unfortunately, ASS-positive cancers are resistant to ADI-PEG20. Moreover, the yield of ADI production is low because of the formation of inclusion bodies. Here, we report a thermostable arginine-depleting enzyme, Bacillus caldovelox arginase mutant (BCA-M: Ser161->Cys161). An abundant amount of BCA-M was easily obtained via high cell-density fermentation and heat treatment purification. Subsequently, we prepared BCA-M-PEG20, by conjugating a single 20 kDa PEG monomer onto the Cys161 residue via thio-chemistry. Unlike ADI-PEG20, BCA-M-PEG20 significantly inhibited ASS-positive lung cancer cell growth. Pharmacodynamic studies showed that a single intraperitoneal injection (i.p). administration of 250 U/mouse of BCA-M-PEG20 induced low L-Arg level over 168 h. The mono-PEGylation of BCA-M prolonged its elimination half-life from 6.4 to 91.4 h (a 14-fold increase). In an A549 lung cancer xenograft model, a weekly administration of 250 U/mouse of BCA-M-PEG20 suppressed tumor growth significantly. We also observed that BCA-M-PEG20 did not cause any significant safety issue in mouse models. Overall, BCA-M-PEG20 showed excellent results in drug production, potency, and stability. Thereby, it has great potential to become a promising candidate for lung cancer therapy.

Differential Adsorption of l- and d-Lysine on Achiral MFI Zeolites as Determined by Synchrotron X-Ray Powder Diffraction and Thermogravimetric Analysis.

Reported here is the first crystallographic observation of stereospecific bindings of l- and d-lysine (Lys) in achiral MFI zeolites. The MFI structure offers inherent geometric and internal confinement effects for the enantiomeric difference in l- and d-Lys adsorption. Notable differences have been observed by circular dichroism (CD) spectroscopy and thermogravimetric analysis (TGA). Distinct l- and d-Lys adsorption behaviours on the H-ZSM-5 framework have been revealed by the Rietveld refinement of high-resolution synchrotron X-ray powder diffraction (SXRD) data and the density-functional theory (DFT) calculations. Despite demonstrating the approach for l- and d-Lys over MFI zeolites at an atomistic resolution, the differential adsorption study sheds light on the rational engineering of molecular interaction(s) with achiral microporous materials for chiral separation purposes.

Antibacterial activity of indolyl-quinolinium derivatives and study their mode of action.

Filamenting temperature-sensitive mutant Z (FtsZ) is recognized as a promising target for new antibiotics development because of its high conservatism and pivotal role in the bacteria cell division. The aromatic heterocyclic scaffold of indole is known showing merit medical functions in antiviral and antimicrobial. In the present study, a series of 1-methylquinolinium derivatives, which were integrated with an indole fragment at its 2-position and a variety of amino groups (cyclic or linear, mono- or di-amine) at the 4-position were synthesized and their antibacterial activities were evaluated. The results of antibacterial study show that the representative compounds can effectively inhibit the growth of testing strains including MRSA and VRE, with MIC values of 1-4 µg/mL by bactericidal mode. The mode of action assays revealed that c2 can effectively disrupt the rate of GTP hydrolysis and dynamic polymerization of FtsZ, and thus inhibits bacterial cell division and then causes bacterial cell death. In addition, the result of resistance generation experiment reveals that c2 is not likely to induce resistance in S. aureus.

Fluorometric determination of the activity of inorganic pyrophosphatase and its inhibitors by exploiting the peroxidase mimicking properties of a two-dimensional metal organic framework.

A copper(II)-based two-dimensional metal-organic framework with nanosheet structure (CuBDC NS) that possesses peroxidase (POx) mimicking activity was prepared. In the presence of hydrogen peroxide, the system catalyses the oxidation of terephthalic acid to a blue-fluorescent product (excitation = 315 nm; emission = 425 nm). Pyrophosphate has a very strong affinity for Cu2+ ion and blocks the POx-mimicking activity of the CuBDC NS. If, however, inorganic pyrophosphatase is present, the POx mimicking activity is gradually restored because pyrophosphate is hydrolyzed. The findings were used to design a method for the determination of the activity of inorganic pyrophosphatase by fluorometry. Fluorescence increases linearly in the 1-50 mU·mL-1 inorganic pyrophosphatase activity range. The limit of detection is 0.6 mU·mL-1 (S/N = 3). Graphical abstract A copper(II)-based two-dimensional metal-organic framework (CuBDC NS) is described that possesses POx-mimicking activity. Inorganic pyrophosphate (PPi) was hydrolyzed to phosphate in the presence of inorganic pyrophosphatase (PPase). Hence, it cannot coordinate with Cu2+ in CuBDC NS, its structure was well-conserved to catalyses the oxidation of terephthalic acid (H2BDC) to produce a blue fluorescent product (oxBDC) in the presence of hydrogen peroxide (H2O2).

Effect of Lactamase Inhibitors on the Biosensor Penp during the Measurement of Lactam Antibiotics Concentration.

PenP is a fluorescent biosensor of lactam antibiotics (LA). It is structurally derived from the mutant lactamase TEM-1 comprising the substitution E166C, where fluorescein is covalently linked to cysteine. The presence of LA in the medium produces a change in the intrinsic fluorescence level of the biosensor, and the integral of the fluorescence level over time correlates directly with the LA concentration. Previously, we have successfully used PenP to determine the concentration of lactam antibiotics in clinical samples. The use of lactamase inhibitors (LI) is a common strategy to enhance the effect of LA due to the inhibition of an important resistance mechanism of pathogenic microorganisms. Structurally, LI and LA share the common element of recognition of lactamases (the lactam ring), but they differ in the reversibility of the mechanism of interaction with said enzyme. Because the biological recognition domain of PenP is derived from a lactamase, LI is expected to interfere with the PenP detection capabilities. Surprisingly, this work provides evidence that the effect of LI is marginal in the determination of LA concentration mediated by PenP.

A quinoline-based FtsZ inhibitor for the study of antimicrobial activity and synergistic effects with ß-lactam antibiotics.

The antibacterial activity and the synergistic effect with ß-lactam antibiotics of a new 1-methylquinolinium iodide derivative were investigated. The experimental results indicate that the compound possesses a strong antibacterial activity against a panel of bacteria including methicillin-resistant Staphylococcus aureus, vancomycin-resistant Enterococcus and NDM-1 Escherichia coli with the MIC values from 0.75 µg/mL to 6 µg/mL. In addition, this compound combined with ß-lactam antibiotics shows strong synergistic antimicrobial activities against antibiotic-resistant strains of S. aureus. The results of biochemical studies also reveal that this compound can effectively disrupt GTPase activity, polymerization of FtsZ, and cell division to cause cell death. The compound shows high potential for further development as a new generation of antibacterial agents to fight against the emergence of multidrug-resistant bacteria.

Influences of disulfide connectivity on structure and antimicrobial activity of tachyplesin I.

Tachyplesin I is a potent antimicrobial peptide with broad spectrum of antimicrobial activity. It has 2 disulfide bonds and can form 3 disulfide bond isomers. In this study, the structure and antimicrobial activity of 3 tachyplesin I isomers (tachyplesin I, 3C12C, 3C7C) were investigated using molecular dynamic simulations, circular dichroism structural study, as well as antimicrobial activity and hemolysis assay. Our results suggest that in comparison to the native peptide, the 2 isomers (3C12C, 3C7C) have substantial structural and activity variations. The native peptide is in the ribbon conformation, while 3C12C and 3C7C possess remarkably different secondary structures, which are referred as "globular" and "beads" isomers, respectively. The substantially decreased hemolysis effects for these 2 isomers is accompanied by significantly decreased anti-gram-positive bacterial activity.

Antibacterial activity of 3-methylbenzo[d]thiazol-methylquinolinium derivatives and study of their action mechanism.

The increasing incidence of multidrug resistant bacterial infection renders an urgent need for the development of new antibiotics. To develop small molecules disturbing FtsZ activity has been recognized as promising approach to search for antibacterial of high potency systematically. Herein, a series of novel quinolinium derivatives were synthesized and their antibacterial activities were investigated. The compounds show strong antibacterial activities against different bacteria strains including MRSA, VRE and NDM-1 Escherichia coli. Among these derivatives, a compound bearing a 4-fluorophenyl group (A2) exhibited a superior antibacterial activity and its MICs to the drug-resistant strains are found lower than those of methicillin and vancomycin. The biological results suggest that these quinolinium derivatives can disrupt the GTPase activity and dynamic assembly of FtsZ, and thus inhibit bacterial cell division and then cause bacterial cell death. These compounds deserve further evaluation for the development of new antibacterial agents targeting FtsZ.