683 research outputs found
Aviation spirit - past, present, and future
The volatile fuel of the high-speed internal combustion engine has, in the past, consisted almost exclusively of the lighter distillates from crude petroleum. Alternative and supplementary fuels are discussed such as: tetraline, dekalin, alcohol, cyclo-hexenes
Disordered proteins mitigate the temperature dependence of site-specific binding free energies
Biophysical characterization of protein-protein interactions involving disordered proteins is challenging. A common simplification is to measure the thermodynamics and kinetics of disordered site binding using peptides containing only the minimum residues necessary. We should not assume, however, that these few residues tell the whole story. Son of sevenless (Sos), a multidomain signaling protein from Drosophila melanogaster, is critical to the mitogen-activated protein kinase pathway, passing an external signal to Ras, which leads to cellular responses. The disordered 55 kDa C-terminal domain of Sos is an auto-inhibitor that blocks guanidine exchange factor activity. Activation requires another protein, Downstream of receptor kinase (Drk), which contains two Src homology 3 (SH3) domains. Here, we utilize nuclear magnetic resonance spectroscopy and isothermal titration calorimetry to quantify the thermodynamics and kinetics of the N-terminal SH3 domain binding to the strongest sites incorporated into the flanking disordered sequences. Comparing these results to those for isolated peptides provides information about how the larger domain affects binding. The affinities of sites on the disordered domain are like those of the peptides at low temperatures but less sensitive to temperature. Our results, combined with observations showing that IDPs become more compact with increasing temperature, suggest a mechanism for this effect
DISORDERED PROTEINS IN VITRO AND IN CELLS
One requirement for the survival and reproduction of living organisms is the ability to receive external stimuli and then respond appropriately. It is increasingly understood that intrinsically disordered proteins are key to many of these biological processes, providing a flexible foundation that allow cells to coordinate and tune signal transduction cascades. To understand how these proteins behave and function, researchers from diverse intellectual backgrounds have examined their biological functions, physical properties, and interactions with other species. My dissertation is an attempt to build on prior research and integrate knowledge of intrinsically disordered proteins within the field of macromolecular crowding—i.e., how the packing of many biological molecules inside of a single cell impact protein and protein-complex stability. I first discuss intrinsically disordered proteins and their properties and predict what types of disordered protein properties might be affected by macromolecular crowding. I then examine mitogen-activated protein kinase pathway signaling through the lens of Epidermal Growth Factor signaling to highlight some of the biological roles that disordered proteins perform. I quantify the binding between the C-terminal tail of Son of sevenless and its native SH3-binding domain partner and demonstrate that precise quantification is possible even when the disordered domain is extended. I then demonstrate an improved method for eukaryotic in-cell NMR for quantifying the effects of the cytoplasm on protein and protein-complexes in living cells. Finally, I provide comments regarding questions and experiments that I attempted thought my PhD training that will hopefully provide assistance for researchers who come after me. Overall, the perspectives and results in this document provide a roadmap for those who want to study disordered proteins in complex and crowded environments. Our understanding of disordered protein properties will continue to evolve, and I attempt to highlight relevant questions and areas researchers interested in developing macromolecular crowding theories must address and provide a foundation for the actual biological processes that underlie disordered protein function.Doctor of Philosoph
Magnetic circular dichroism of x-ray absorption spectroscopy at rare-earth L2,3 edges in RE2Fe14B compounds (RE = La, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu)
Magnetic circular dichroism (MCD) in the x-ray absorption spectroscopy (XAS)
at the L2,3 edges for almost entire series of rare-earth (RE) elements in
RE2Fe14B, is studied experimentally and theoretically. By a quantitative
comparison of the complicated MCD spectral shapes, we find that (i) the 4f-5d
intra-atomic exchange interaction not only induces the spin and orbital
polarization of the 5d states, which is vital for the MCD spectra of the
electric dipole transition from the 2p core states to the empty 5d conduction
band, but also it accompanies a contraction of the radial part of the 5d wave
function depending on its spin and orbital state, which results in the
enhancement of the 2p-5d dipole matrix element, (ii) there are cases where the
spin polarization of the 5d states due to the hybridization with the spin
polarized 3d states of surrounding irons plays important roles, and (iii) the
electric quadrupole transition from the 2p core states to the magnetic vale!
nce 4f states is appreciable at the pre-edge region of the dipole spectrum.
Especially, our results evidence that it is important to include the
enhancement effect of the dipole matrix element in the correct interpretation
of the MCD spectra at the RE L2,3 edges.Comment: 9 pages, 5 figures, 1 table, REVTe
Improving Male Partner Involvement in HIV-Positive Women's Care Through Behavioral Change Interventions in Malawi (WeMen Study): A Prospective, Controlled Before-and-After Study
Several strategies and interventions have been implemented to improve male partner involvement (MI) in Sub-Saharan Africa, but evidence on successful interventions is scarce. This controlled before-and-after intervention study aims to evaluate the impact of three interventions on male partners' involvement in HIV+ women's care in Malawi. We piloted these three interventions: the organization of a special day for men, the deployment of male champions in communities to increase awareness on MI, and the delivery of an incentive (food package) for couples attending the facility. We observed a significant increase in the number of women accompanied by their partners (from 48.5 to 81.4%) and the number of women feeling safe at home (from 63.5 to 95.2%) after the special day intervention. This outcome increased after the deployment of male champions in communities (from 44.0 to 75.0%). No significant improvement was observed in the site where we delivered the incentive to couples. Our findings showed that the special day for men and the use of male champions might effectively increase the male involvement in the health of their female partners
Band-theoretical prediction of magnetic anisotropy in uranium monochalcogenides
Magnetic anisotropy of uranium monochalcogenides, US, USe and UTe, is studied
by means of fully-relativistic spin-polarized band structure calculations
within the local spin-density approximation. It is found that the size of the
magnetic anisotropy is fairly large (about 10 meV/unit formula), which is
comparable with experiment. This strong anisotropy is discussed in view of a
pseudo-gap formation, of which crucial ingredients are the exchange splitting
of U 5f states and their hybridization with chalcogen p states (f-p
hybridization). An anomalous trend in the anisotropy is found in the series
(US>>USe<UTe) and interpreted in terms of competition between localization of
the U 5f states and the f-p hybridization. It is the spin-orbit interaction on
the chalcogen p states that plays an essential role in enlarging the strength
of the f-p hybridization in UTe, leading to an anomalous systematic trend in
the magnetic anisotropy.Comment: 4 pages, 5 figure
Estrogen-Receptor Expression and Function in Thymocytes in Relation to Gender and Age
The expression of estrogen receptor (ER) in thymocytes was studied in young, middle-aged, and
old (2, 12, and 24 months, respectively) female and male C57BL/6J mice. Western immunoblots
prepared from the thymocytes of females of all age groups showed the presence of a 67-kD
protein band, which has been associated with the apparent MW of denatured ER. Flow cytometry
analysis o,f cells stained with a monoclonal anti-ER antibody (clone 13H2) disclosed ER
expression in both females and males of all age groups. In vivo treatment with estradiol (E2) led
to an increase in the specific activity of thymic creatine kinase (CK) in the female mice, whereas
the male thymocytes responded with an increase in CK activity only on treatment with
dihydrotestosterone (DHT). The data show no differences in ER expression between male and
females, but the receptor appears not to be functional in males. Interestingly, when estradiol was
applied to co-cultures of lymphoid-depleted fetal thymus (FT) explants and bone-marrow cells,
or thymocytes, from young and old females, it resulted in increased cellularity of cultures
containing cells of the young, and not those of the old. The proportion of CD4/CD8 phenotypes
of the developing cells in these cultures was not affected by E2 treatment. These observations
provide a new insight into ER expression and function in T-cell development in relation to
gender and age
Observation of magnetic circular dichroism in Fe L_{2,3} x-ray-fluorescence spectra
We report experiments demonstrating circular dichroism in the x-ray-fluorescence spectra of magnetic systems, as predicted by a recent theory. The data, on the L_{2,3} edges of ferromagnetic iron, are compared with fully relativistic local spin density functional calculations, and the relationship between the dichroic spectra and the spin-resolved local density of occupied states is discussed
On-site correlation in valence and core states of ferromagnetic nickel
We present a method which allows to include narrow-band correlation effects
into the description of both valence and core states and we apply it to the
prototypical case of nickel. The results of an ab-initio band calculation are
used as input mean-field eigenstates for the calculation of self-energy
corrections and spectral functions according to a three-body scattering
solution of a multi-orbital Hubbard hamiltonian. The calculated quasi-particle
spectra show a remarkable agreement with photoemission data in terms of band
width, exchange splitting, satellite energy position of valence states, spin
polarization of both the main line and the satellite of the 3p core level.Comment: 14 pages, 10 PostScript figures, RevTeX, submitted to PR
Direct observation of electron doping in La0.7Ce0.3MnO3 using x-ray absorption spectroscopy
We report on a X-ray absorption spectroscopic (XAS) study on a thin film of
La0.7Ce0.3MnO3, a manganite which was previously only speculated to be an
electron doped system. The measurements clearly show that the cerium is in the
Ce(IV) valence state and that the manganese is present in a mixture of Mn2+ and
Mn3+ valence states. These data unambiguously demonstrate that La0.7Ce0.3MnO3
is an electron doped colossal magnetoresistive manganite, a finding that may
open up new opportunities both for device applications as well as for further
basic research towards a better modelling of the colossal magnetoresistance
phenomenon in these materials.Comment: 4 pages, 3 figures, revised versio
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