CHARACTERIZATION OF HtsA, THE FERRIC-STAPHYLOFERRIN A-BINDING PROTEIN IN STAPHYLOCOCCUS AUREUS

The frequent human pathogen Staphylococcus aureus requires a sufficient source of iron to proliferate and, thus, to sustain an infection of a mammalian host. However, the free iron concentration in the host is insufficient for bacterial growth without use of specialized uptake mechanisms. To overcome this, S. aureus utilizes multiple systems to scavenge host iron. One such strategy that S. aureus employs is the use of siderophores: secreted, small-molecular-weight, high-affinity iron chelators. S. aureus synthesizes and secretes two anionic a-hydroxycarboxylate siderophores, staphyloferrin A (SA) and staphyloferrin B (SB). Fe-SA and Fe-SB complexes are transported into the cell through the highly specific ABC-type transporters HtsABC and SirABC, respectively. The crystal structures of HtsA, the SA receptor, have been solved for both SA bound and unbound forms. Structural data indicate that HtsA has a unique positively charged binding pocket and many charged residues form contacts with the anionic siderophore including R86, R104, R126, K203, H209, and Y239. Their contribution to productive binding and transport is currently unknown. To investigate the role of each residue found to interact with SA, site-directed mutagenesis was used to substitute each interacting residue with either alanine or an amino acid with more conserved properties. Fluorescence titrations of SA, produced and purified in vitro, with wild-type (WT) or mutant rHtsA were used to determine the effect that each substitution had on the binding affinity of HtsA for SA. Growth curves and disk- diffusion assays were completed on strains expressing mutated or WT HtsA to determine the biological significance of each mutation under SA-dependant growth conditions. These studies have confirmed significant roles in SA binding and transport for HtsA residues R104, R126, and H209, strengthening the conclusions drawn from the HtsA crystal structure and providing new insight into the mechanism of SA-dependant iron uptake in S. aureus

Motivation as a predictor of outcomes in school-based humanistic counselling

Recent years have seen a growth in the provision of counselling within UK secondary schools, and research indicates that it is associated with significant reductions in psychological distress. However, little is known about the moderators and mediators of positive therapeutic benefit. In the field of adult mental health, motivation has been found to be one of the strongest predictors of therapeutic outcomes, and it was hypothesised that this may also be a predictor of outcomes for young people in school-based counselling services. To assess the relationship between young people’s motivation for counselling and its effectiveness within a secondary school setting. Eighty-one young people (12 - 17 years old) who attended school-based humanistic counselling services in Scotland. Clients completed a measure of motivation for counselling at the commencement of their therapeutic work and a measure of psychological wellbeing at the commencement and termination of counselling. Motivation for counselling was not found to be significantly related to outcomes. The results indicate that the association between motivation and outcomes may be weaker in young people as compared with adults. However, a number of design factors may also account for the non-significant findings: insufficient participants, marginal reliability of the motivation measure and social desirability effects

Birth asphyxia - Presenting the case for' A stitch in time'

Objectives. To. review the current birth asphyxia and subsequent cerebral palsy (CP) rates at a teaching hospital in a developing country, and to place these rates within the context of the current caesarean section (CS) rate. To determine the number of cases of birth asphyxia that are preventable.Design. Retrospective, descriptiv.e study.Setting. Neonatal nursery and intensive care unit, Johannesburg Hospital.Methods. Maternal and mionatal records were reviewed for 48 babies weighing less than 1 800 g born between 1 January and 31 December 1997 with birth asphyxia. Outcome after discharge was determined from the neonatal follow-up notes until 31 March 1998.Results. Mortality in the group of birth-asphyxiated babies was 12.5%. The birth asphyxia rate was 6/1 000 live births, and the CP rate in the study group was 1.15/1 000 live births. The CS rate for the group was 29%, with an overall CS rate at the hospital of 20.5%. In 22 cases (46%) the cause of birth asphyxia was considered to have been preventable.Conclusion. The cr rate is considerably higher than that quoted for developed  countries, and a significant number of cases of birth asphyxia in the study were  preventable. In the face of the high birth asphyxia and cr rates, the CS rate appears to be inappropriately Iow. The CS rate should be audited in the context of the birth asphyxia and cr rates

Study of the dependence of 198Au half-life on source geometry

We report the results of an experiment to determine whether the half-life of \Au{198} depends on the shape of the source. This study was motivated by recent suggestions that nuclear decay rates may be affected by solar activity, perhaps arising from solar neutrinos. If this were the case then the $\beta$-decay rates, or half-lives, of a thin foil sample and a spherical sample of gold of the same mass and activity could be different. We find for \Au{198}, $(T_{1/2})_{\rm foil}/(T_{1/2})_{\rm sphere} = 0.999 \pm 0.002$, where $T_{1/2}$ is the mean half-life. The maximum neutrino flux at the sample in our experiments was several times greater than the flux of solar neutrinos at the surface of the Earth. We show that this increase in flux leads to a significant improvement in the limits that can be inferred on a possible solar contribution to nuclear decays.Comment: 5 pages, 1 figur

Searches for solar-influenced radioactive decay anomalies using Spacecraft RTGs

Experiments showing a seasonal variation of the nuclear decay rates of a number of different nuclei, and decay anomalies apparently related to solar flares and solar rotation, have suggested that the Sun may somehow be influencing nuclear decay processes. Recently, Cooper searched for such an effect in $^{238}$Pu nuclei contained in the radioisotope thermoelectric generators (RTGs) on board the Cassini spacecraft. In this paper we modify and extend Cooper's analysis to obtain constraints on anomalous decays of $^{238}$Pu over a wider range of models, but these limits cannot be applied to other nuclei if the anomaly is composition-dependent. We also show that it may require very high sensitivity for terrestrial experiments to discriminate among some models if such a decay anomaly exists, motivating the consideration of future spacecraft experiments which would require less precision.Comment: 8 pages, 4 figures (to appear in Astroparticle Physics

MSbar quark distribution and dipole scattering matrix elements at high energy

We discuss the operator relation that connects the renormalized quark distribution in the MSbar scheme with the Wilson-line correlator representing dipole scattering in the s-channel picture

Discovery of functionally selective C5aR2 ligands: novel modulators of C5a signalling.

The complement cascade is comprised of a highly sophisticated network of innate immune proteins that are activated in response to invading pathogens or tissue injury. The complement activation peptide, C5a, binds two seven transmembrane receptors, namely the C5a receptor 1 (C5aR1) and C5a receptor 2 (C5aR2, or C5L2). C5aR2 is a non-G-protein-signalling receptor whose biological role remains controversial. Some of this controversy arises owing to the lack of selective ligands for C5aR2. In this study, a library of 61 peptides based on the C-terminus of C5a was assayed for the ability to selectively modulate C5aR2 function. Two ligands (P32 and P59) were identified as functionally selective C5aR2 ligands, exhibiting selective recruitment of β-arrestin 2 via C5aR2, partial inhibition of C5a-induced ERK1/2 activation and lipopolysaccharide-stimulated interleukin-6 release from human monocyte-derived macrophages. Importantly, neither ligand could induce ERK1/2 activation or inhibit C5a-induced ERK1/2 activation via C5aR1 directly. Finally, P32 inhibited C5a-mediated neutrophil mobilisation in wild-type, but not C5aR2(-/-) mice. These functionally selective ligands for C5aR2 are novel tools that can selectively modulate C5a activity in vitro and in vivo, and thus will be valuable tools to interrogate C5aR2 function.Immunology and Cell Biology advance online publication, 17 May 2016; doi:10.1038/icb.2016.43

The freeze-out mechanism and phase-space density in ultrarelativistic heavy-ion collisions

We explore the consequences of a freeze-out criterion for heavy-ion collisions, based on pion escape probabilities from the hot and dense but rapidly expanding collision region. The influence of the expansion and the scattering rate on the escape probability is studied. The temperature dependence of this scattering rate favors a low freeze-out temperature of ~100 MeV. In general, our results support freeze-out along finite four-volumes rather than sharp three-dimensional hypersurfaces, with high-pt particles decoupling earlier from smaller volumes. We compare our approach to the proposed universal freeze-out criteria using the pion phase-space density and its mean free path.Comment: 8 pages, 2 figures, although conclusions are unchanged, the paper has been re-written and the title has been changed for the sake of better presentatio

Bottom-Up and Top-Down Processes in Emotion Generation: Common and Distinct Neural Mechanisms

Emotions are generally thought to arise through the interaction of bottom-up and top-down processes. However, prior work has not delineated their relative contributions. In a sample of 20 females, we used functional magnetic resonance imaging to compare the neural correlates of negative emotions generated by the bottom-up perception of aversive images and by the top-down interpretation of neutral images as aversive. We found that (a) both types of responses activated the amygdala, although bottom-up responses did so more strongly; (b) bottom-up responses activated systems for attending to and encoding perceptual and affective stimulus properties, whereas top-down responses activated prefrontal regions that represent high-level cognitive interpretations; and (c) self-reported affect correlated with activity in the amygdala during bottom-up responding and with activity in the medial prefrontal cortex during top-down responding. These findings provide a neural foundation for emotion theories that posit multiple kinds of appraisal processes and help to clarify mechanisms underlying clinically relevant forms of emotion dysregulation.National Institutes of Health (U.S.) (Grant MH58147)National Institutes of Health (U.S.) (Grant MH076137