3,935 research outputs found
The Cell Wall Teichuronic Acid Synthetase (TUAS) Is an Enzyme Complex Located in the Cytoplasmic Membrane of Micrococcus luteus
The cell wall teichuronic acid (TUA) of Micrococcus luteus is a long-chain polysaccharide composed of disaccharide repeating units [-4-β-D-ManNAcAp-(1→6)α-D-Glcp−1-]n, which is covalently anchored to the peptidoglycan on the inner cell wall and extended to the outer surface of the cell envelope. An enzyme complex responsible for the TUA chain biosynthesis was purified and characterized. The 440kDa enzyme complex, named teichuronic acid synthetase (TUAS), is an octomer composed of two kinds of glycosyltransferases, Glucosyltransferase, and ManNAcA-transferase, which is capable of catalyzing the transfer of disaccharide glycosyl residues containing both glucose and the N-acetylmannosaminuronic acid residues. TUAS displays hydrophobic properties and is found primarily associated with the cytoplasmic membrane. The purified TUAS contains carotinoids and lipids. TUAS activity is diminished by phospholipase digestion. We propose that TUAS serves as a multitasking polysaccharide assembling station on the bacterial membrane.National Institute of Allergy and Infectious Diseases (Public Health Service Grants AI-08295); American Lung Association (RG-107-N
Pulsar Polar Cap Heating and Surface Thermal X-Ray Emission I. Curvature Radiation Pair Fronts
We investigate the effect of pulsar polar cap (PC) heating produced by
positrons returning from the upper pair formation front. Our calculations are
based on a self-consistent treatment of the pair dynamics and the effect of
electric field screening by the returning positrons. We calculate the resultant
X-ray luminosities, and discuss the dependence of the PC heating efficiencies
on pulsar parameters, such as characteristic spin-down age, spin period, and
surface magnetic field strength. In this study we concentrate on the regime
where the pairs are produced in a magnetic field by curvature photons emitted
by accelerating electrons. Our theoretical results are not in conflict with the
available observational X-ray data and suggest that the effect of PC heating
should significantly contribute to the thermal X-ray fluxes from middle-aged
and old pulsars. The implications for current and future X-ray observations of
pulsars are briefly outlined.Comment: 28 pages, 7 figures, accepted for publication in Ap
A probabilistic model to recover individual genomes from metagenomes
Shotgun metagenomics of microbial communities reveal information about strains of relevance for applications in medicine, biotechnology and ecology. Recovering their genomes is a crucial but very challenging step due to the complexity of the underlying biological system and technical factors. Microbial communities are heterogeneous, with oftentimes hundreds of present genomes deriving from different speci
The Cell Wall Teichuronic Acid Synthetase (TUAS) Is an Enzyme Complex Located in the Cytoplasmic Membrane of Micrococcus luteus
The cell wall teichuronic acid (TUA) of Micrococcus luteus is a long-chain polysaccharide
composed of disaccharide repeating units [-4-β-D-ManNAcAp-(1→6)α-D-Glcp−1-]n, which is covalently anchored to the peptidoglycan on the inner cell wall and extended to the outer surface of the cell envelope. An enzyme complex responsible for the TUA chain biosynthesis was purified and characterized. The 440 kDa enzyme complex, named teichuronic acid synthetase (TUAS), is an octomer composed of two kinds of glycosyltransferases, Glucosyltransferase, and ManNAcA-transferase, which is capable of catalyzing the transfer of disaccharide glycosyl residues containing both glucose and the N-acetylmannosaminuronic acid residues. TUAS displays hydrophobic properties and is found primarily associated with the cytoplasmic membrane. The purified TUAS contains carotinoids and lipids. TUAS activity is diminished by phospholipase digestion. We propose that TUAS serves as a multitasking polysaccharide assembling station on the bacterial membrane
The Cell Wall Teichuronic Acid Synthetase (TUAS) Is an Enzyme Complex Located in the Cytoplasmic Membrane of Micrococcus luteus
The cell wall teichuronic acid (TUA) of Micrococcus luteus is a long-chain polysaccharide
composed of disaccharide repeating units [-4-β-D-ManNAcAp-(1→6)α-D-Glcp−1-]n, which is covalently anchored to the peptidoglycan on the inner cell wall and extended to the outer surface of the cell envelope. An enzyme complex responsible for the TUA chain biosynthesis was purified and characterized. The 440 kDa enzyme complex, named teichuronic acid synthetase (TUAS), is an octomer composed of two kinds of glycosyltransferases, Glucosyltransferase, and ManNAcA-transferase, which is capable of catalyzing the transfer of disaccharide glycosyl residues containing both glucose and the N-acetylmannosaminuronic acid residues. TUAS displays hydrophobic properties and is found primarily associated with the cytoplasmic membrane. The purified TUAS contains carotinoids and lipids. TUAS activity is diminished by phospholipase digestion. We propose that TUAS serves as a multitasking polysaccharide assembling station on the bacterial membrane
Experimental estimation of entanglement at the quantum limit
Entanglement is the central resource of quantum information processing and
the precise characterization of entangled states is a crucial issue for the
development of quantum technologies. This leads to the necessity of a precise,
experimental feasible measure of entanglement. Nevertheless, such measurements
are limited both from experimental uncertainties and intrinsic quantum bounds.
Here we present an experiment where the amount of entanglement of a family of
two-qubit mixed photon states is estimated with the ultimate precision allowed
by quantum mechanics.Comment: 4 pages, 3 figure
The prevalence and distribution of the amyloidogenic transthyretin (TTR) V122I allele in Africa
Transthyretin (TTR) pV142I (rs76992529-A) is one of the 113 variants in the human TTR gene associated with systemic amyloidosis. It results from a G to A transition at a CG dinucleotide in the codon for amino acid 122 of the mature protein (TTR V122I). The allele frequency is 0.0173 in African Americans
Pulsar Polar Cap Heating and Surface Thermal X-Ray Emission II. Inverse Compton Radiation Pair Fronts
We investigate the production of electron-positron pairs by inverse Compton
scattered (ICS) photons above a pulsar polar cap (PC) and surface heating by
returning positrons. This paper is a continuation of our self-consistent
treatment of acceleration, pair dynamics and electric field screening above
pulsar PCs. We calculate the altitude of the inverse Compton pair formation
fronts, the flux of returning positrons and present the heating efficiencies
and X-ray luminosities. We revise pulsar death lines implying cessation of pair
formation, and present them in surface magnetic field-period space. We find
that virtually all known radio pulsars are capable of producing pairs by
resonant and non-resonant ICS photons radiated by particles accelerated above
the PC in a pure star-centered dipole field, so that our ICS pair death line
coincides with empirical radio pulsar death. Our calculations show that ICS
pairs are able to screen the accelerating electric field only for high neutron
star surface temperatures and magnetic fields. We argue that such screening at
ICS pair fronts occurs locally, slowing but not turning off acceleration of
particles until screening can occur at a curvature radiation (CR) pair front at
higher altitude. In the case where no screening occurs above the PC surface, we
anticipate that the pulsar gamma-ray luminosity will be a substantial fraction
of its spin-down luminosity. The X-ray luminosity resulting from PC heating by
ICS pair fronts is significantly lower than the PC heating luminosity from CR
pair fronts, which dominates for most pulsars. PC heating from ICS pair fronts
is highest in millisecond pulsars, which cannot produce CR pairs, and may
account for observed thermal X-ray components in the spectra of these old
pulsars.Comment: 29 pages, 10 figures, accepted for publication in Ap
Visualisation of variable binding pockets on protein surfaces by probabilistic analysis of related structure sets
Background: Protein structures provide a valuable resource for rational drug design. For a protein with no known ligand, computational tools can predict surface pockets that are of suitable size and shape to accommodate a complementary small-molecule drug. However, pocket prediction against single static structures may miss features of pockets that arise from proteins’ dynamic behaviour. In particular, ligand-binding conformations can be observed as transiently populated states of the apo protein, so it is possible to gain insight into ligand-bound forms by considering conformational variation in apo proteins. This variation can be explored by considering sets of related structures: computationally generated conformers, solution NMR ensembles, multiple crystal structures, homologues or homology models. It is non-trivial to compare pockets, either from different programs or across sets of structures. For a single structure, difficulties arise in defining particular pocket’s boundaries. For a set of conformationally distinct structures the challenge is how to make reasonable comparisons between them given that a perfect structural alignment is not possible.
Results: We have developed a computational method, Provar, that provides a consistent representation of
predicted binding pockets across sets of related protein structures. The outputs are probabilities that each atom or
residue of the protein borders a predicted pocket. These probabilities can be readily visualised on a protein using
existing molecular graphics software. We show how Provar simplifies comparison of the outputs of different pocket
prediction algorithms, of pockets across multiple simulated conformations and between homologous structures.
We demonstrate the benefits of use of multiple structures for protein-ligand and protein-protein interface analysis
on a set of complexes and consider three case studies in detail:
i) analysis of a kinase superfamily highlights the
conserved occurrence of surface pockets at the active and regulatory sites
ii) a simulated ensemble of unliganded
Bcl2 structures reveals extensions of a known ligand-binding pocket not apparent in the apo crystal structure;
iii) visualisations of interleukin-2 and its homologues highlight conserved pockets at the known receptor interfaces
and regions whose conformation is known to change on inhibitor binding.
Conclusions: Through post-processing of the output of a variety of pocket prediction software, Provar provides a
flexible approach to the analysis and visualization of the persistence or variability of pockets in sets of related
protein structures
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