41 research outputs found
Dynamics of hydration water in deuterated purple membranes explored by neutron scattering
The function and dynamics of proteins depend on their direct environment, and much evidence has pointed to a strong coupling between water and protein motions. Recently however, neutron scattering measurements on deuterated and natural-abundance purple membrane (PM), hydrated in H2O and D2O, respectively, revealed that membrane and water motions on the nsâps time scale are not directly coupled below 260Â K (Wood et al. in Proc Natl Acad Sci USA 104:18049â18054, 2007). In the initial study, samples with a high level of hydration were measured. Here, we have measured the dynamics of PM and water separately, at a low-hydration level corresponding to the first layer of hydration water only. As in the case of the higher hydration samples previously studied, the dynamics of PM and water display different temperature dependencies, with a transition in the hydration water at 200Â K not triggering a transition in the membrane at the same temperature. Furthermore, neutron diffraction experiments were carried out to monitor the lamellar spacing of a flash-cooled deuterated PM stack hydrated in H2O as a function of temperature. At 200Â K, a sudden decrease in lamellar spacing indicated the onset of long-range translational water diffusion in the second hydration layer as has already been observed on flash-cooled natural-abundance PM stacks hydrated in D2O (Weik et al. in J Mol Biol 275:632â634, 2005), excluding thus a notable isotope effect. Our results reinforce the notion that membrane-protein dynamics may be less strongly coupled to hydration water motions than the dynamics of soluble proteins
Caseload midwifery as organisational change:the interplay between professional and organisational projects in Denmark
BACKGROUND: The large obstetric units typical of industrialised countries have come under criticism for fragmented and depersonalised care and heavy bureaucracy. Interest in midwife-led continuity models of care is growing, but knowledge about the accompanying processes of organisational change is scarce. This study focuses on midwivesâ role in introducing and developing caseload midwifery. Sociological studies of midwifery and organisational studies of professional groups were used to capture the strong interests of midwives in caseload midwifery and their key role together with management in negotiating organisational change. METHODS: We studied three hospitals in Denmark as arenas for negotiating the introduction and development of caseload midwifery and the processes, interests and resources involved. A qualitative multi-case design was used and the selection of hospitals aimed at maximising variance. Ten individual and 14 group interviews were conducted in spring 2013. Staff were represented by caseload midwives, ward midwives, obstetricians and health visitors, management by chief midwives and their deputies. Participants were recruited to maximise the diversity of experience. The data analysis adopted a thematic approach, using within- and across-case analysis. RESULTS: The analysis revealed a highly interdependent interplay between organisational and professional projects in the change processes involved in the introduction and development of caseload midwifery. This was reflected in three ways: first, in the key role of negotiations in all phases; second, in midwivesâ and managementâs engagement in both types of projects (as evident from their interests and resources); and third in a high capacity for resolving tensions between the two projects. The ward midwivesâ role as a third party in organisational change further complicated the process. CONCLUSIONS: For managers tasked with the introduction and development of caseload midwifery, our study underscores the importance of understanding the complexity of the underlying change processes and of activating midwivesâ and managersâ interests and resources in addressing the challenges. Further studies of female-dominated professions such as midwifery should offer good opportunities for detailed analysis of the deep-seated interdependence of professional and organisational projects and for identifying the key dimensions of this interdependence
Structure and Dynamics of Biological Systems: Integration of Neutron Scattering with Computer Simulation
The combination of molecular dynamics simulation and neutron scattering techniques has emerged as a highly synergistic approach to elucidate the atomistic details of the structure, dynamics and functions of biological systems. Simulation models can be tested by calculating neutron scattering structure factors and comparing the results directly with experiments. If the scattering profiles agree the simulations can be used to provide a detailed decomposition and interpretation of the experiments, and if not, the models can be rationally adjusted. Comparison with neutron experiment can be made at the level of the scattering functions or, less directly, of structural and dynamical quantities derived from them. Here, we examine the combination of simulation and experiment in the interpretation of SANS and inelastic scattering experiments on the structure and dynamics of proteins and other biopolymers
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Temperature dependence of protein dynamics simulated with three different water models
The effect of variation of the water model on the temperature dependence of protein and hydration water dynamics is examined by performing molecular dynamics simulations of myoglobin with the TIP3P, TIP4P, and TIP5P water models and the CHARMM protein force field at temperatures between 20 and 300 K. The atomic mean-square displacements, solvent reorientational relaxation times, pair angular correlations between surface water molecules, and time-averaged structures of the protein are all found to be similar, and the protein dynamical transition is described almost indistinguishably for the three water potentials. The results provide evidence that for some purposes changing the water model in protein simulations without a loss of accuracy may be possible
Proton channel hydration and dynamics of a bacteriorhodopsin triple mutant with an M-state-like conformation
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Structural properties of a peptide derived from H+-V-ATPase subunit a
The 3D structure of a peptide derived from the putative transmembrane segment 7 (TM7) of subunit a from H+-V-ATPase from Saccharomyces cerevisiae has been determined by solution state NMR in SDS. A stable helix is formed from L736 up to and including Q745, the lumenal half of the putative TM7. The helical region extends well beyond A738, as was previously suggested based on NMR studies of a similar peptide in DMSO. The pKa of both histidine residues that are important for proton transport was measured in water and in SDS. The differences that are found demonstrate that the histidine residues interact with the SDS polar heads. In detergent, circular dichroism data indicate that the secondary structure of the peptide depends on the pH and the type of detergent used. Using solid-state NMR, it is shown that the peptide is immobile in phospholipid bilayers, which means that it is probably not a single transmembrane helix in these samples. The environment is important for the structure of TM7, so in subunit a it is probably held in place by the other transmembrane helices of this subuni
Appl. Phys. A-Mater. Sci. Process.
Local atomic motions in bacteriorhodopsin (BR), the membrane protein in purple membranes (PMs) of Halobacterium salinarum, were studied by incoherent neutron scattering. The analysed sample consisted of fully deuterated purple membranes with BR- containing H-retinal, H-tryptophan, and H-methionine. These labelled groups are present in the retinal binding pocket and the extracellular part of BR. By using incoherent neutron scattering on two different backscattering instruments at the Institut Laue-Langevin, we. determined the mean-square displacements of small- and large-amplitude motions as a function of temperature for labelled as well as completely hydrogenated PM samples at different hydration states. We showed that the dynamics of the labelled part is more rigid, and influenced by temperature and hydration in a different way, than the membrane globally