1,721,522 research outputs found
Biophysical studies of membrane protein structure and function
Full text linkMembrane proteins play a key role in numerous physiological processes such as transport, energy transduction in respiratory and photosynthetic systems, and signal transduction, and are of great pharmaceutical interest, comprising more than 60% of known drug targets. However, crystallisation of membrane proteins, and G protein-coupled receptors (GPCRs) in particular, still relies heavily on the use of protein engineering strategies, which have been shown to hamper protein activity. Here, a range of biophysical methods were used to study the structure and function of two membrane proteins, a prokaryotic peptide transporter, PepTSo and a GPCR, neurotensin receptor 1 (NTS1), using different membrane reconstitution methods to study the proteins in a native-like environment. Firstly, using the pulsed electron paramagnetic resonance (EPR) method of double electron-electron resonance (DEER) the conformation of PepTSo reconstituted into lipid bilayers was assessed and compared to previous structural data obtained from crystallography and modelling. The influence of the membrane potential and the presence of substrate on the conformational heterogeneity of this proton-coupled transporter were investigated. Secondly, NTS1 purification was optimized for biophysical study. Cysteine mutants were created and a labelling protocol was developed and optimized for fluorophore and nitroxide labelling studies. NTS1 was then studied by continuous-wave EPR, to assess the influence of ligand on local protein dynamics, and to assess the structure of a receptor segment known as helix 8, that was proposed to be an α-helix, but was only observed to be helical in one of the NTS1 crystallographic studies. Ensemble and single-molecule Förster resonance energy transfer (FRET), and DEER were combined to study the dimerisation behaviour of NTS1, showing novel dynamics of the interfacial associations. Finally, the signalling mechanism of NTS1 was also investigated using microscale thermophoresis (MST) to assess the affinity of the receptor for G protein in vitro in the absence of ligand, or in the presence of agonist or antagonist. MST measurements were performed in detergent and in nanodiscs of different lipid compositions, to assess the influence of the lipid environment on receptor function. In summary, this thesis demonstrates the potential of biophysical techniques to study various aspects of membrane protein structure and function in native-like lipid systems, complementing e.g. structural data obtained from crystallographic studies with functional data for membrane proteins in more native environments, as well as shedding light on protein dynamics. The work presented here provides novel insights into PepTSo transport, and in particular into NTS1 structure, signalling, and oligomerisation, opening up several avenues for future research
European lifelong guidance policies : progress report 2011-12 : a report on the work of the European Lifelong Guidance Policy Network 2011-12
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Career development and public policy
Full text linkThe rationale for policy interest in career development services, and the way in which this rationale is being strengthened by the current transformations in work and career, are discussed. The potential roles of public policy in relation to career development services are explored, along with ways in which such services can influence the policy-making process. A range of policy issues related to making career development services available to all throughout life are identified: these include the nature of such services, where they are to be located, and who is to pay for them. It is argued that there is a need for stronger structures and processes to bring together career development practitioners with policy- makers and other stakeholder interests in order to address tasks of common concern, at both national and international levels.Fil: Watts, Anthony G.. National Institute for Careers Education and Counselling, Reino Unido
The relationship between structure and seismogenic behaviour in subduction zones
No full textThe largest earthquakes on Earth take place on the megathrusts of subduction zones, but the slip behavior of megathrusts is variable. This thesis considers why by conducting local, regional and global studies of the interrelationships between the structure and seismogenic behavior of subduction zones. New marine geophysical data collected from the collision zone between the Louisville Ridge seamount chain with the Tonga-Kermadec trench constrain overthrusting and subducting plate structure. Mo'unga seamount is identified beneath the outer-forearc, which calibrates the association of residual bathymetric anomalies and subducting relief, implies an E-W geometry for the subducted ridge and suggests the 200 km wide Louisville seismic gap is modulated by the sediment filled flexural moat. Spectral averaging is then applied along the Tonga-Kermadec margin and along strike variations in overthrusting plate structure are verified by wide-angle seismic transects. The remnant Tonga-Ridge occupies the inner fore-arc and residual free-air gravity anomalies constrain its latitudinal extent (north of 30.5°S), width (110±20 km) and strike (~005° south of 25°S). Plate tectonic reconstructions suggest the Lau Ridge is unmodified by subduction related erosion, <200 km of the Tonga Ridge has been eroded, and neither ridge ever occupied the southern Kermadec arc. Crustal thickness variations are thus inherited, reflecting the Cenozoic tectonic evolution of the Tonga-Kermadec-Hikurangi margin. Spectral averaging is finally applied to all subduction zones on Earth. Part one develops a global catalogue of subducting relief, which is compared with seismological and geodetic inferences of fault-slip behavior. Most seamounts are aseismic, relatively undeformed and observations are not consistent with mechanical models proposing full-decapitation. Aseismic ridges are also associated with megathrust complexity, but are of a larger wavelength and contrasting mode of isostatic compensation. Part two shows almost all intra-margin along-strike transitions in seismogenic behavior are related to pre-existing crustal structure. A paired forearc anomaly is interpreted consisting of a trench-parallel ridge landward of the deep-sea-terrace basin. The ridge crest correlates with the down-dip limit of coseismic slip and strong interplate coupling, the up- dip limit of tremor epicentres, and is interpreted as defining the boundary between the velocity-weakening and seismogenic portion of the subduction interface and the down-dip frictional transition zone. Paired anomalies may be attributed to unrecovered interseismic elastic strain, the preferential subduction erosion of the outer-forearc and/or underplating beneath the inner forearc
Desarrollo vocacional y política pública
Full text linkEl trabajo analiza la base para el interés político en los servicios de desarrollo vocacional, y la manera en la cual esta base está siendo fortalecida por las actuales transformaciones en el trabajo y en el desarrollo vocacional. Se exploran los papeles potenciales de la política pública en los servicios de desarrollo vocacional así como las formas en las que dichos servicios pueden influenciar el proceso de la creación de políticas. Se identifican una gama de temas de política relacionados con los servicios de desarrollo vocacional disponibles para todos a lo largo de toda la vida: estos incluyen la naturaleza de ese tipo de servicios, dónde deben situarse, y quién debe pagar por ellos. Se sostiene que existe la necesidad de estructuras y procesos más fuertes a fin de reunir a quienes hacen del desarrollo vocacional su profesión habitual y a quienes hacen las políticas y a otros grupos interesados para estudiar tareas de interés común, tanto en el nivel nacional como en el internacional.Fil: Watts, Anthony G.. National Institute for Careers Education and Counselling, Reino Unido
A comparative study of the Parnaíba, Michigan and Congo cratonic basins
No full textWe used compilations of geological and geophysical data to compare the structure, subsidence history and evolution of the Parnaíba, Michigan and Congo cratonic basins. These basins consist of 3–6 km of Paleozoic to Recent sediments and are located on thick (>150 km) lithosphere, far from plate boundaries. Sediment-corrected Bouguer gravity anomalies show that the basins are associated with a central high of up to 40–60 mGal. The high could reflect crustal thinning, but seismic refraction data suggest that the Moho is either at a similar depth or deeper beneath the basins than beneath their flanks. The seismic reflection profiles show no evidence of extensional structures in the underlying basement. We propose that the central high reflects an extensive igneous intrusion, which, on solidification, loaded the crust and lithosphere, causing a surface flexure into which sediments accumulated. Viscoelastic plate modelling of the backstripped well data shows that a subsurface load can explain the tectonic subsidence of the basins as well as some details of their internal stratigraphy, including offlap. Offlap, a ubiquitous feature of cratonic basins, can therefore be explained by tectonics in the form of flexure and does not require other controlling factors such as long-term sea-level changes
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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