Search

Copyright of Journal of Food Science & Biotechnology is the property of Journal of Food Science & Biotechnology Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Type II fatty acid synthases are promising drug targets against major bacterial pathogens. Platensimycin (PTM) is a potent inhibitor against β-ketoacyl-[acyl carrier protein] synthase II (FabF) and β-ketoacyl-[acyl carrier protein] synthase I (FabB), while the poor pharmacokinetics has prevented its further development. In this work, thirty-two PTM derivatives were rapidly prepared via Heck, Sonogashira, and one-pot Sonogashira/cycloaddition cascade reactions based on the Gram-scale synthesis of 6-iodo PTM (4). About half of the synthesized compounds were approximately equipotent to PTM against the tested Staphylococcus aureus strains. Among them, the representative compounds 4, A4, and B8 exhibited different plasma protein binding affinity or stability in the human hepatic microsome assay and showed improved in vivo efficacy over PTM in a mouse peritonitis model. In addition, A4 was also effective in an S. aureus-infected skin mouse model. Our study not only significantly expands the known PTM derivatives with improved antibacterial activities in vivo, but showcased that C–C cross-coupling reactions are useful tools to functionalize natural product drug leads. [ABSTRACT FROM AUTHOR]

Time‐of‐flight secondary ion mass spectrometry (ToF‐SIMS) using a primary ion beam of (CO2)6k+ was used to analyse chemical changes in the bacterial envelope of a fabF knock‐out Escherichia coli strain. fabF is the gene coding for FabF, the enzyme involved in the elongation of FA(16:1) to FA(18:1) and has been associated with plasmid transfer that can lead to acquired multiantibiotic resistance. Comparison of the membrane composition between fabF mutant E. coli and wild type E. coli during the logarithmic and stationary growth phases at two culture temperatures (37°C and 30°C) revealed substantial depletion of FA(18:1) in the fabF mutant during logarithmic growth that resulted in a correlated reduction in FA(cp19:0) during stationary phase. While no clear temperature dependence on the effect of the fabF mutation was found, a reduction in cyclopropanation was observed at lower culture temperature in the wild type strain. Additionally, depth profile analysis revealed a 'thickening' of the lipid A layer on the surface of the bacteria during stationary phase and also the appearance of cyclic enterobacterial common antigen (ECACYC) below the surface of the bacteria upon the shift from logarithmic to stationary growth phase. [ABSTRACT FROM AUTHOR]

Type II fatty acid synthases are promising drug targets against major bacterial pathogens. Platensimycin (PTM) is a potent inhibitor against β-ketoacyl-[acyl carrier protein] synthase II (FabF) and β-ketoacyl-[acyl carrier protein] synthase I (FabB), while the poor pharmacokinetics has prevented its further development. In this work, thirty-two PTM derivatives were rapidly prepared via Heck, Sonogashira, and one-pot Sonogashira/cycloaddition cascade reactions based on the Gram-scale synthesis of 6-iodo PTM (4). About half of the synthesized compounds were approximately equipotent to PTM against the tested Staphylococcus aureus strains. Among them, the representative compounds 4, A4, and B8 exhibited different plasma protein binding affinity or stability in the human hepatic microsome assay and showed improved in vivo efficacy over PTM in a mouse peritonitis model. In addition, A4 was also effective in an S. aureus-infected skin mouse model. Our study not only significantly expands the known PTM derivatives with improved antibacterial activities in vivo, but showcased that C–C cross-coupling reactions are useful tools to functionalize natural product drug leads.

Phage-resistant bacteria often emerge rapidly when performing phage therapy. However, the relationship between the emergence of phage-resistant bacteria and improvements in clinical symptoms is still poorly understood. An inpatient developed a pulmonary infection caused by multidrug-resistant Klebsiella pneumoniae. He received a first course of treatment with a single nebulized phage (ΦKp_GWPB35) targeted at his bacterial isolate of Kp 7450. After 14 days, he received a second course of treatment with a phage cocktail (ΦKp_GWPB35+ΦKp_GWPA139). Antibiotic treatment was continued throughout the course of phage therapy. Whole-genome analysis was used to identify mutations in phage-resistant strains. Mutated genes associated with resistance were further analysed by generating knockouts of Kp 7450 and by measuring phage adsorption rates of bacteria treated with proteinase K and periodate. Bacterial virulence was evaluated in mouse and zebrafish infection models. Phage-resistant Klebsiella pneumoniae strains emerged after the second phage treatment. Comparative genomic analyses revealed that fabF was deleted in phage-resistant strains. The fabF knockout strain (Kp 7450 ΔfabF) resulted in an altered structure of lipopolysaccharide (LPS), which was identified as the host receptor for the therapeutic phages. Virulence evaluations in mice and zebrafish models showed that LPS was the main determinant of virulence in Kp 7450 and alteration of LPS structure in Kp 7450Δ fabF , and the bacteriophage-resistant strains reduced their virulence at cost. This study may shed light on the mechanism by which some patients experience clinical improvement in their symptoms post phage therapy, despite the incomplete elimination of pathogenic bacteria. [ABSTRACT FROM AUTHOR]

Bacterial infections remain a serious health concern, in particular causing life-threatening infections of hospitalized and immunocompromised patients. The situation is exacerbated by the rise in antibacterial drug resistance, and new treatments are urgently sought. In this endeavour, accurate structures of molecular targets can support early-stage drug discovery. Here, crystal structures, in three distinct forms, of recombinant Pseudomonas aeruginosaβ-ketoacyl-(acyl-carrier-protein) synthase II (FabF) are presented. This enzyme, which is involved in fatty-acid biosynthesis, has been validated by genetic and chemical means as an antibiotic target in Gram-positive bacteria and represents a potential target in Gram-negative bacteria. The structures of apo FabF, of a C164Q mutant in which the binding site is altered to resemble the substrate-bound state and of a complex with 3-(benzoylamino)-2-hydroxybenzoic acid are reported. This compound mimics aspects of a known natural product inhibitor, platensimycin, and surprisingly was observed binding outside the active site, interacting with a symmetry-related molecule. An unusual feature is a completely buried potassium-binding site that was identified in all three structures. Comparisons suggest that this may represent a conserved structural feature of FabF relevant to fold stability. The new structures provide templates for structure-based ligand design and, together with the protocols and reagents, may underpin a target-based drug-discovery project for urgently needed antibacterials. [ABSTRACT FROM AUTHOR]

In this study, we aimed to develop recombinant Saccharomyces cerevisiae with increased long-chain fatty acids by expressing essential genes involved in fatty acid synthesis elongation cycle. The relation of β-ketoacyl-ACP synthase II ( fabF) from S. cerevisiae YPH500 and 3-oxoacyl-[acyl-carrier-protein] reductase ( fabG), 3-hydroxyacyl-thioester dehydratase ( FabZ), enoyl-ACP reductase ( FabK), and acyl-ACP thioesterase ( EC.3.1.2.14) from Streptococcus pyogenes MGAS 10270 regarding fatty acid production was investigated. These genes were separately cloned, and the effects of respective genes on fatty acid production were analyzed. Compared with the wild type S. cerevisiae, fabF recombinant (SGJY01) showed about 1.8-fold enhanced fatty acid production. We also exhibited thermal regulation in the fatty acid composition of SGJY01 changed at lower temperatures. The fabF recombinant and wild-type were cultured at different temperatures (30, 20, and 10°C), resulting the unsaturated fatty acids (C16:1 and C18:1) increased up to 2.4-fold as compared to the wild-type. Of particular interest is that the proportion of unsaturated fatty acids was increased approximately 11.8% at 10°C compared to 30°C, although the proportion in the wild-type remained unchanged. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents a new method of fuzzy adaptive bacterial foraging (FABF) based congestion management (CM) for the first time by optimal rescheduling of active powers of generators selected based on the generator sensitivity to the congested line. In the proposed method, generators are selected based on their sensitivity to the congested line to utilize the generators efficiently and optimal rescheduling of the active powers of the participating generators was attempted by FABF. The FABF algorithm is tested on IEEE 30-bus system and Practical Indian 75-bus system and the results are compared with the Simple Bacterial Foraging (SBF) and Particle Swarm Optimization (PSO) algorithms for robustness and effectiveness of congestion management. It is observed from the results that FABF is effectively minimizing the cost of generation in comparison with SBF and PSO for optimal rescheduling of generators to relieve congestion in the transmission line. [Copyright &y& Elsevier]

Abstract: FabF elongation condensing enzyme is a critical factor in determining the spectrum of products produced by the FASII pathway. Its active site contains a critical cysteine-thiol residue, which is a plausible target for oxidation by H2O2. Streptococcus pneumoniae produces exceptionally high levels of H2O2, mainly through the conversion of pyruvate to acetyl-P via pyruvate oxidase (SpxB). We present evidence showing that endogenous H2O2 inhibits FabF activity by specifically oxidizing its active site cysteine-thiol residue. Thiol trapping methods revealed that one of the three FabF cysteines in the wild-type strain was oxidized, whereas in an spxB mutant, defective in H2O2 production, none of the cysteines was oxidized, indicating that the difference in FabF redox state originated from endogenous H2O2. In vitro exposure of the spxB mutant to various H2O2 concentrations further confirmed that only one cysteine residue was susceptible to oxidation. By blocking FabF active site cysteine with cerulenin we show that the oxidized cysteine was the catalytic one. Inhibition of FabF activity by either H2O2 or cerulenin resulted in altered membrane fatty acid composition. We conclude that FabF activity is inhibited by H2O2 produced by S. pneumoniae. [Copyright &y& Elsevier]

Abstract: Natural products continue to serve as one of the best sources for discovery of antibacterial agents as exemplified by the recent discoveries of platensimycin and platencin. Chemical modifications as well as discovery of congeners are the main sources for gaining knowledge of structure–activity relationship of natural products. Screening for congeners in the extracts of the fermentation broths of Streptomyces platensis led to the isolation of platencin A1, a hydroxy congener of platencin. The hydroxylation of the tricyclic enone moiety negatively affected the antibacterial activity and appears to be consistent with the hydrophobic binding pocket of the FabF. Isolation, structure, enzyme-bound structure and activity of platencin A1 and two other congeners have been described. [Copyright &y& Elsevier]

Abstract: Platensimycin (1) displays antibacterial activity due to its inhibition of the elongation condensing enzyme (FabF), a novel mode of action that could potentially lead to a breakthrough in developing a new generation of antibiotics. The medicinal chemistry efforts were focused on the modification of the enone moiety of platensimycin and several analogs showed significant activity against FabF and possess antibacterial activity. [Copyright &y& Elsevier]

A series of experiments with β-ketoacyl acyl carrier protein synthase II (FabF) from Streptococcus pneumonia (spFabF) were undertaken to evaluate the capability of surface-entropy reduction (SER) to manipulate protein crystallization. Previous work has shown that this protein crystallizes in two forms. The triclinic form contains four molecules in the asymmetric unit (a.u.) and diffracts to 2.1 Å resolution, while the more desirable primitive orthorhombic form contains one molecule in the a.u. and diffracts to 1.3 Å. The aim was to evaluate the effect of SER mutations that were specifically engineered to avoid perturbing the crystal-packing interfaces employed by the favorable primitive orthorhombic crystal form while potentially disrupting a surface of the protein employed by the less desirable triclinic crystal form. Two mutant proteins were engineered, each of which harbored five SER mutations. Extensive crystallization screening produced crystals of the two mutants, but only under conditions that differed from those used for the native protein. One of the mutant proteins yielded crystals that were of a new form (centered orthorhombic), despite the fact that the interfaces employed by the primitive orthorhombic form of the native protein were specifically unaltered. Structure determination at 1.75 Å resolution reveals that one of the mutations, E383A, appears to play a key role in disfavouring the less desirable triclinic crystal form and in generating a new surface for a packing interaction that stabilizes the new crystal form. [ABSTRACT FROM AUTHOR]

Whole-genome sequencing was used to examine a persistent Enterococcus faecium bacteremia that acquired heteroresistance to three antibiotics in response to prolonged multidrug therapy. A comparison of the complete genomes before and after each change revealed the emergence of known resistance determinants for vancomycin and linezolid and suggested that a novel mutation in fabF , encoding a fatty acid synthase, was responsible for daptomycin nonsusceptibility. Plasmid recombination contributed to the progressive loss of vancomycin resistance after withdrawal of the drug., (Copyright © 2018 Chacko et al.)