307 research outputs found
Extracellular adherence protein (Eap) from Staphylococcus aureus does not function as a superantigen
AbstractExtracellular adherence protein (Eap) from Staphylococcus aureus has been reported to have strong anti-inflammatory properties, which make Eap a potential anti-inflammatory agent. However, Eap has also been demonstrated to trigger T-cell activation and to share structural homology with superantigens. In this study, we focused on whether Eap fulfilled the definition criteria for a superantigen. We demonstrate that T-cell activation by Eap is dependent on both major histocompatibility complex class II and intercellular adhesion molecule type 1, that cellular processing is required for Eap to elicit T-cell proliferation, and that the kinetics of proliferation resemble the profile of a conventional antigen and not that of a superantigen
Ovine clone ST1464:A predominant genotype of Staphylococcus aureus subsp. anaerobius isolated from sheep in Sudan
Ovine clone ST1464:A predominant genotype of Staphylococcus aureus subsp. anaerobius isolated from sheep in Sudan
Binding of Brucella protein, Bp26, to select extracellular matrix molecules
Background: Brucella is a facultative intracellular pathogen responsible for zoonotic disease brucellosis. Little is known about the molecular basis of Brucella adherence to host cells. In the present study, the possible role of Bp26 protein as an adhesin was explored. The ability of Brucella protein Bp26 to bind to extracellular matrix (ECM) proteins was determined by enzyme-linked immunosorbent assay (ELISA) and biolayer interferometry (BLI).
Results: ELISA experiments showed that Bp26 bound in a dose-dependent manner to both immobilized type I collagen and vitronectin. Bp26 bound weakly to soluble fibronectin but did not bind to immobilized fibronectin. No binding to laminin was detected. Biolayer interferometry showed high binding affinity of Bp26 to immobilized type I collagen and no binding to fibronectin or laminin. Mapping of Bp26 antigenic epitopes by biotinylated overlapping peptides spanning the entire sequence of Bp26 using anti Bp26 mouse serum led to the identification of five linear epitopes. Collagen and vitronectin bound to peptides from several regions of Bp26, with many of the binding sites for the ligands overlapping.
The strongest binding for anti-Bp26 mouse serum, collagen and vitronectin was to the peptides at the C-terminus of Bp26. Fibronectin did not bind to any of the peptides, although it bound to the whole Bp26 protein.
Conclusions: Our results highlight the possible role of Bp26 protein in the adhesion process of Brucella to host cells through ECM components. This study revealed that Bp26 binds to both immobilized and soluble type I collagen and vitronectin. It also binds to soluble but not immobilized fibronectin. However, Bp26 does not bind to laminin.
These are novel findings that offer insight into understanding the interplay between Brucella and host target cells, which may aid in future identification of a new target for diagnosis and/or vaccine development and prevention of brucellosis
ALMA and VLA Observations of EX Lupi in its Quiescent State
Extreme outbursts in young stars may be a common stage of pre-main-sequence
stellar evolution. These outbursts, caused by enhanced accretion and
accompanied by increased luminosity, can also strongly impact the evolution of
the circumstellar environment. We present ALMA and VLA observations of EX Lupi,
a prototypical outburst system, at 100 GHz, 45 GHz, and 15 GHz. We use these
data, along with archival ALMA 232 GHz data, to fit radiative transfer models
to EX Lupi's circumstellar disk in its quiescent state following the extreme
outburst in 2008. The best fit models show a compact disk with a characteristic
dust radius of 45 au and a total mass of 0.01 M. Our modeling
suggests grain growth to sizes of at least 3 mm in the disk, possibly spurred
by the recent outburst, and an ice line that has migrated inward to
au post-outburst. At 15 GHz, we detected significant emission over the expected
thermal disk emission which we attribute primarily to stellar (gyro)synchrotron
and free-free disk emission. Altogether, these results highlight what may be a
common impact of outbursts on the circumstellar dust.Comment: Accepted to ApJ, 15 pages, 8 figure
Saving Super-Earths:Interplay between Pebble Accretion and Type I Migration
Overcoming type I migration and preventing low-mass planets from spiralling into the central star is a long-studied topic. It is well known that outward migration is possible in viscously heated disks relatively close to the central star because the entropy gradient can be sufficiently steep for the positive corotation torque to overcome the negative Lindblad torque. Yet efficiently trapping planets in this region remains elusive. Here we study disk conditions that yield outward migration for low-mass planets under specific planet migration prescriptions. In a steady-state disk model with a constant α-viscosity, outward migration is only possible when the negative temperature gradient exceeds ∼0.87. We derive an implicit relation for the highest mass at which outward migration is possible as a function of viscosity and disk scale height. We apply these criteria, using a simple power-law disk model, to planets that have reached their pebble isolation mass after an episode of rapid accretion. It is possible to trap planets with the pebble isolation mass farther than the inner edge of the disk provided that α crit 0.004 for disks older than 1 Myr. In very young disks, the high temperature causes the planets to grow to masses exceeding the maximum for outward migration. As the disk evolves, these more massive planets often reach the central star, generally only toward the end of the disk lifetime. Saving super-Earths is therefore a delicate interplay between disk viscosity, the opacity profile, and the temperature gradient in the viscously heated inner disk
GLOBAL SIMULATIONS OF PROTOPLANETARY DISKS WITH OHMIC RESISTIVITY AND AMBIPOLAR DIFFUSION
Protoplanetary disks are believed to accrete onto their central T Tauri star
because of magnetic stresses. Recently published shearing box simulations
indicate that Ohmic resistivity, ambipolar diffusion and the Hall effect all
play important roles in disk evolution. In the presence of a vertical magnetic
field, the disk remains laminar between 1-5au, and a magnetocentrifugal disk
wind forms that provides an important mechanism for removing angular momentum.
Questions remain, however, about the establishment of a true physical wind
solution in the shearing box simulations because of the symmetries inherent in
the local approximation. We present global MHD simulations of protoplanetary
disks that include Ohmic resistivity and ambipolar diffusion, where the
time-dependent gas-phase electron and ion fractions are computed under FUV and
X-ray ionization with a simplified recombination chemistry. Our results show
that the disk remains laminar, and that a physical wind solution arises
naturally in global disk models. The wind is sufficiently efficient to explain
the observed accretion rates. Furthermore, the ionization fraction at
intermediate disk heights is large enough for magneto-rotational channel modes
to grow and subsequently develop into belts of horizontal field. Depending on
the ionization fraction, these can remain quasi-global, or break-up into
discrete islands of coherent field polarity. The disk models we present here
show a dramatic departure from our earlier models including Ohmic resistivity
only. It will be important to examine how the Hall effect modifies the
evolution, and to explore the influence this has on the observational
appearance of such systems, and on planet formation and migration.Comment: 18 pages, 12 figures, accepted for publication in Ap
A live cell assay of GPCR coupling allows identification of optogenetic tools for controlling Go and Gi signaling
Efferent Control of the Electrical and Mechanical Properties of Hair Cells in the Bullfrog's Sacculus
Background: Hair cells in the auditory, vestibular, and lateral-line systems respond to mechanical stimulation and transmit information to afferent nerve fibers. The sensitivity of mechanoelectrical transduction is modulated by the efferent pathway, whose activity usually reduces the responsiveness of hair cells. The basis of this effect remains unknown. Methodology and Principal Findings: We employed immunocytological, electrophysiological, and micromechanical approaches to characterize the anatomy of efferent innervation and the effect of efferent activity on the electrical and mechanical properties of hair cells in the bullfrog’s sacculus. We found that efferent fibers form extensive synaptic terminals on all macular and extramacular hair cells. Macular hair cells expressing the Ca 2+-buffering protein calretinin contain half as many synaptic ribbons and are innervated by twice as many efferent terminals as calretinin-negative hair cells. Efferent activity elicits inhibitory postsynaptic potentials in hair cells and thus inhibits their electrical resonance. In hair cells that exhibit spiking activity, efferent stimulation suppresses the generation of action potentials. Finally, efferent activity triggers a displacement of the hair bundle’s resting position. Conclusions and Significance: The hair cells of the bullfrog’s sacculus receive a rich efferent innervation with the heaviest projection to calretinin-containing cells. Stimulation of efferent axons desensitizes the hair cells and suppresses their spiking activity. Although efferent activation influences mechanoelectrical transduction, the mechanical effects on hair bundles ar
Functional Changes in the Snail Statocyst System Elicited by Microgravity
BACKGROUND: The mollusk statocyst is a mechanosensing organ detecting the animal's orientation with respect to gravity. This system has clear similarities to its vertebrate counterparts: a weight-lending mass, an epithelial layer containing small supporting cells and the large sensory hair cells, and an output eliciting compensatory body reflexes to perturbations. METHODOLOGY/PRINCIPAL FINDINGS: In terrestrial gastropod snail we studied the impact of 16- (Foton M-2) and 12-day (Foton M-3) exposure to microgravity in unmanned orbital missions on: (i) the whole animal behavior (Helix lucorum L.), (ii) the statoreceptor responses to tilt in an isolated neural preparation (Helix lucorum L.), and (iii) the differential expression of the Helix pedal peptide (HPep) and the tetrapeptide FMRFamide genes in neural structures (Helix aspersa L.). Experiments were performed 13-42 hours after return to Earth. Latency of body re-orientation to sudden 90° head-down pitch was significantly reduced in postflight snails indicating an enhanced negative gravitaxis response. Statoreceptor responses to tilt in postflight snails were independent of motion direction, in contrast to a directional preference observed in control animals. Positive relation between tilt velocity and firing rate was observed in both control and postflight snails, but the response magnitude was significantly larger in postflight snails indicating an enhanced sensitivity to acceleration. A significant increase in mRNA expression of the gene encoding HPep, a peptide linked to ciliary beating, in statoreceptors was observed in postflight snails; no differential expression of the gene encoding FMRFamide, a possible neurotransmission modulator, was observed. CONCLUSIONS/SIGNIFICANCE: Upregulation of statocyst function in snails following microgravity exposure parallels that observed in vertebrates suggesting fundamental principles underlie gravi-sensing and the organism's ability to adapt to gravity changes. This simple animal model offers the possibility to describe general subcellular mechanisms of nervous system's response to conditions on Earth and in space
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