548 research outputs found
TACKLING LOW INCOME AND DEPRIVATION: DEVELOPING EFFECTIVE POLICIES. RESEARCH SERIES NUMBER 1 JUNE 2008
This study examines options for the future development of the Irish welfare state, with a view to tackling low income and deprivation more effectively. It draws on existing national and cross-country evidence as well as providing new analyses to inform policy debate in this area. The impact of alternative policy choices is explored using SWITCH, the ESRI tax-benefit model
Generation of thiocillin variants by prepeptide gene replacement and in vivo processing by Bacillus cereus
(Figure Presented) The thiocillins are natural-product antibiotics derived from ribosomally encoded peptides that undergo extensive posttranslational modifications to yield the mature trithiazolylpyridine-containing macrocyclic compound. Poor pharmacokinetic properties have prevented the clinical use of these highly potent antibiotics. Through in vivo manipulation of the gene responsible for production of the thiocillin precursor peptide, we have generated 65 novel thiocillin variants, allowing us to explore structure-activity relationships involved in both precursor peptide maturation and antibiotic activity
Thiazolyl peptide antibiotic biosynthesis: A cascade of post-translational modifications on ribosomal nascent proteins
Antibiotics of the thiocillin, GE2270A, and thiostrepton class, which block steps in bacterial protein synthesis, contain a trithiazolyl (tetrahydro)pyridine core that provides the architectural constraints for high affinity binding to either the 50 S ribosomal subunit or elongation factor Tu. These mature antibiotic scaffolds arise from a cascade of post-translational modifications on 50-60-residue prepeptide precursors that trim away the N-terminal leader sequences (∼40 residues) while the C-terminal 14-18 residues are converted into the mature scaffold. In the producing microbes, the genes encoding the prepeptide open reading frames are flanked in biosynthetic clusters by genes encoding post-translational modification enzymes that carry out lantibiotic-type dehydrations of Ser and Thr residues to dehydroamino acid side chains, cyclodehydration and oxidation of cysteines to thiazoles, and condensation of two dehydroalanine residues en route to the (tetrahydro)pyridine core. The trithiazolyl pyridine framework thus arises from post-translational modification of the peptide backbone of three Cys and two Ser residues of the prepeptide
Genetic interception and structural characterization of thiopeptide cyclization precursors from bacillus cereus
The pyridine core of the thiocillins has long been postulated to arise from a late-stage tail-to-tail condensation of two dehydroalanines. Genetic disruption of tclM, a proposed "Diels-Alderase", allowed isolation of acyclic precursors to this pyridine ring. The isolated products possess the full cohort of post-translational modifications that are normally displayed by the thiocillins, including dehydrobutyrines, thiazoles, C-terminal decarboxylation, and the two previously unconfirmed dehydroalanines. Additionally, leader peptides have undergone extensive N-terminal degradation and the remaining leader peptide residues have been N-succinylated. These results identify TclM and its homologues in other thiazolyl peptide producing strains as the enzymes responsible for the trans-annular heteroannulation at core of this class of molecules
Manipulation of thiocillin variants by prepeptide gene replacement: Structure, conformation, and activity of heterocycle substitution mutants
Bacillus cereus ATCC 14579 converts the C-terminal 14 residues of a 52-mer prepeptide into a related set of eight variants of the thiocillin subclass of thiazolyl peptide antibiotics by a cascade of post-translational modifications that alter 13 of those 14 residues. We have introduced prepeptide gene variants into a knockout strain to conduct an alanine scan of all 14 progenitor residues, as well as a serine scan of the six cysteine residues that are converted to thiazoles in the mature natural product. No mature scaffolds were detected for the S1A and S10A mutants, consistent with their roles as the source of the pyridine core. In both the alanine and serine scans, only one substitution mutant failed to produce a mature scaffold: cysteine 11. Cysteine to serine mutants gave mixture of dehydrations, aromatizations, and unaltered alcohol side chains depending on position. Overall, substitutions that altered the trithiazolylpyridine core or reduced the conformational rigidity of the 26-membered macrocyclic loop led to loss of antibiotic activity. In total, 21 peptide mutants were cultured, from which production of 107 compounds was observed and 94 compounds, representing 17 structural mutants, were assayed for antibiotic activity. High-resolution NMR solution structures were determined for one mutant and one wild-type compound. These structures demonstrate that the tight conformational rigidity of the natural product is severely disrupted by loss of even a single heterocycle, perhaps accounting for the attendant loss of activity in such mutants
Generation of thiocillin ring size variants by prepeptide gene replacement and in vivo processing by Bacillus cereus
The thiocillins from Bacillus cereus ATCC 14579 are natural products from the broader class of thiazolyl peptides. Their biosynthesis proceeds via extensive post-translational modification of a ribosomally encoded precursor peptide. This post-translational tailoring involves a key step formal cycloaddition between two distal serine residues. In the wild-type structure, this cycloaddition forms a major macrocycle circumscribed by 26-atoms (shortest path). Results presented herein demonstrate the promiscuity of this last step by means of a set of "competition" experiments. Cyclization proceeds in many cases to provide altered ring sizes, giving access to several variant rings sizes that have not previously been observed in nature
A Backup Plan for Self-Protection: S-Methylation of Holomycin Biosynthetic Intermediates in Streptomyces clavuligerus
Biosynthesis of the dithiolopyrrolone antibiotic holomycin in Streptomyces clavuligerus involves the closure of a pair of enethiols to a cyclic disulfide. We have shown that the dithiol oxidase HlmI is responsible for the disulfide formation and this enzyme also plays a role in self-protection. In the present study, we examine how S. clavuligerus deals with the proposed toxic dithiol intermediates when hlmI is deleted. We used differential NMR spectroscopy and mass spectrometry to profile the metabolomes of hlmI deletion mutants along with the wild-type strain and a holomycin-overproducing strain. A number of metabolites unique to ΔhlmI strains were identified. In these metabolites the enethiols have been incapacitated by a combination of mono- and di-S-methylation. We also observed an intriguing dimeric thioether adduct in low quantities in the wild-type strain and at much higher levels in the ΔhlmI strains. The structures of these novel metabolites highlight the reactivity of the dihydrodithiolopyrrolone scaffold. Furthermore, bioassays suggest that modification of the enethiol warhead by S-alkylation provides a host strategy for detoxification, one that is shared amongst multiple species producing such bioactive disulfide natural products
Multi-drug resistant Escherichia coli in diarrhoeagenic foals: Pulsotyping, phylotyping, serotyping, antibiotic resistance and virulence profiling
Extraintestinal pathogenic E. coli (ExPEC) possess the ability to cause extraintestinal infections such as urinary tract infections, neonatal meningitis and sepsis. While information is readily available describing pathogenic E. coli populations in food-producing animals, studies in companion/sports animals such as horses are limited. In addition, many antimicrobial agents used in the treatment of equine infections are also utilised in human medicine, potentially contributing to the spread of antibiotic resistance determinants among pathogenic strains. The aim of this study was to phenotypically and genotypically characterise the multidrug resistance and virulence associated with 83 equine E. coli isolates recovered from foals with diarrhoeal disease. Serotyping was performed by both PCR and sequencing. Antibiotic resistance was assessed by disc diffusion. Phylogenetic groups, virulence genes, antibiotic resistance genes and integrons were determined by PCR. Thirty-nine (46%) of the isolates were classified as ExPEC and hence considered to be potentially pathogenic to humans and animals. Identified serogroups O1, O19a, O40, O101 and O153 are among previously reported human clinical ExPEC isolates. Over a quarter of the E. coli were assigned to pathogenic phylogroups B2 (6%) and D (23%). Class 1 and class 2 integrons were detected in 85% of E. coli, revealing their potential to transfer MDR to other pathogenic and non-pathogenic bacteria. With 65% of potentially pathogenic isolates harbouring one or more TEM, SHV and CTX-M-2 group β-lactamases, in addition to the high levels of resistance to fluoroquinolones observed, our findings signal the need for increased attention to companion/sport animal reservoirs as public health threats
Distinct cell wall architectures in seed endosperms in representatives of the brassicaceae and solanaceae
In some species, a crucial role has been demonstrated for the seed endosperm during germination. The endosperm has been shown to integrate environmental cues with hormonal networks that underpin dormancy and seed germination, a process that involves the action of cell wall remodeling enzymes (CWREs). Here, we examine the cell wall architectures of the endosperms of two related Brassicaceae, Arabidopsis (Arabidopsis thaliana) and the close relative Lepidium (Lepidium sativum), and that of the Solanaceous species, tobacco (Nicotiana tabacum). The Brassicaceae species have a similar cell wall architecture that is rich in pectic homogalacturonan, arabinan, and xyloglucan. Distinctive features of the tobacco endosperm that are absent in the Brassicaceae representatives are major tissue asymmetries in cell wall structural components that reflect the future site of radicle emergence and abundant heteromannan. Cell wall architecture of the micropylar endosperm of tobacco seeds has structural components similar to those seen in Arabidopsis and Lepidium endosperms. In situ and biomechanical analyses were used to study changes in endosperms during seed germination and suggest a role for mannan degradation in tobacco. In the case of the Brassicaceae representatives, the structurally homogeneous cell walls of the endosperm can be acted on by spatially regulated CWRE expression. Genetic manipulations of cell wall components present in the Arabidopsis seed endosperm demonstrate the impact of cell wall architectural changes on germination kinetics
Low- and high-mass components of the photon distribution functions
The structure of the general solution of the inhomogeneous evolution
equations allows the separation of a photon structure function into
perturbative (``anomalous") and non-perturbative contributions. The former part
is fully calculable, and can be identified with the high-mass contributions to
the dispersion integral in the photon mass. Properly normalized ``state"
distributions can be defined, where the \gamma\to\qqbar splitting probability
is factored out. These state distributions are shown to be useful in the
description of the hadronic event properties, and necessary for a proper
eikonalization of jet cross sections. Convenient parametrizations are provided
both for the state and for the full anomalous parton distributions. The
non-perturbative parts of the parton distribution functions of the photon are
identified with the low-mass contributions to the dispersion integral. Their
normalizations, as well as the value of the scale at which the
perturbative parts vanish, are fixed by approximating the low-mass
contributions by a discrete, finite sum of vector mesons. The shapes of these
hadronic distributions are fitted to the available data on .
Parametrizations are provided for GeV and GeV, both in the
DIS and the factorization schemes. The full
parametrizations are extended towards virtual photons. Finally, the often-used
``FKP-plus-TPC/" solution for is commented upon.Comment: 33 pages, Latex, 6 Z-compressed and uuencoded figure
- …