9,571 research outputs found
Charlie May Simon materials
No full textThis collection contains materials relating to Arkansas author Charlie May Simon
Direct Observation of the Activation of MscL in Tethered Lipid Bilayers by an Antimicrobial Peptide
No full textData and Python code to support the manuscript "Direct Observation the Activation of MscL in Tethered Lipid Bilayers by an Antimicrobial Peptide". Abstract: Hypothesis Membrane proteins serve a wide range of vital roles in the functioning of living organisms. They account for approximately 20% to 30% of the genomes across bacterial, archaeal, and eukaryotic organisms. They are responsible for many cellular functions, such as signaling, ion and molecule transport, binding and catalytic reactions. Compared to other classes of proteins, determining membrane protein structures remains a challenge, in large part due to the difficulty in establishing experimental conditions that can preserve the correct conformation and function of the protein in isolation from its native environment. Many therapeutics target membrane proteins which are accessible on the surface of cells. Here we hypothesize that the observed efficacy of antimicrobial peptides (AMPs) that interact with bacterial membranes may in part be associated with their triggering of MscL (Mechansensitive Ion Channel of Large Conductance) gating. We further conjecture that the insertion of peptides into the membrane induces significant changes in membrane tension and/or curvature, leading to prolonged gating of the MscL channels.
Experiments We present realistic model membrane systems containing MscL. We investigated the ion channel in lipid vesicles and in a planar lipid bilayer. We developed a novel method for protein-lipid planar bilayer formation, avoiding the use of detergents. By using a polymeric tether our planar membrane mimetic was not constrained by the underlying solid substrate, making it sufficiently flexible to allow for increases in bilayer curvature and changes in membrane tension. We used quartz crystal microbalance with dissipation (QCM-D), and polarised neutron reflectivity (PNR) to show the formation of MscL containing phospholipid bilayers, tethered with a high density PEG layer onto gold substrates from vesicle rupture. The MscL containing vesicles were separately characterised with small angle neutron scattering (SANS).
Findings MscL was expressed into vesicles using cell free protein expression. Analysing these vesicles with small angle neutron scattering, the radius of gyration of the protein was determined to be between 26-29~\AA{}, consistent with the crystal structure of individual MscL channels. The MscL composition of the formed bilayer was 14\%v/v, close to the initial volume composition of the vesicles at ~13.6% and a protein protrusion extending ca. 46~\AA{} into the solvent was determined by PNR. Addition of 1.6 and 3.2 uM pexiganan resulted in a decrease in the protrusion of MscL (from ~46 to ~38~\AA{}). To our knowledge, these findings represent the first direct experimental evidence of a structural change in the C-terminus containing protrusion of MscL, triggered by an antimicrobial peptide. This adds to our understanding of antimicrobial peptide action in therapeutic treatments.Jupyter notebooks containing code to fit polarized neutron reflectivity data
Tether_bilayer_only_model-RefNX_volumes_final-Copy3.ipynb
MscL_1p6_PXG_model-RefNX_volumes_final.ipynb
MscL_3p2_PXG_model-RefNX_volumes_final.ipynb
SANS model fits and data
LysoPC
LysoPCmodel_1level_GP.csv
SANS_LysoPC_D2O.txt
MscLVesicle
MscLVesicle_2levelGPmodelfit.csv
SANS_MscLVesicle_D2O.txt
MscLVesicle post Lyso-PC
MscLVesicle_model_2level_GP.csv
SANS_MscLVesicle_LysoPC_D2O.txt
MscLVesicle post PXG
MscLvesicleafterPXG_model_2levelGP.csv
SANS_MscLVesicleafterPXG_D2O.txt
MscLVesicle(pre-PXG)
MscLVesicle_model_2level_GP.csv
SANS_MscLVesicle_D2O.txt
Neutron reflectivity datafiles used in the Jupyter notebooks
IvsQ_26838_26839_26840_IvsQ_26838_1_IvsQ_26839_1_IvsQ_26840_1.dat.txt
IvsQ_26841_26842_26843_IvsQ_26841_1_IvsQ_26842_1_IvsQ_26843_1.dat.txt
IvsQ_26841_26842_26843_IvsQ_26841_2_IvsQ_26842_2_IvsQ_26843_2.dat.txt
IvsQ_26844_26845_26846_IvsQ_26844_1_IvsQ_26845_1_IvsQ_26846_1.dat.txt
IvsQ_26844_26845_26846_IvsQ_26844_2_IvsQ_26845_2_IvsQ_26846_2.dat.txt
POLLREFfinalIvsQ_26838_26839_26840_IvsQ_26838_1_IvsQ_26839_1_IvsQ_26840_1.dat
POLLREFfinalIvsQ_26838_26839_26840_IvsQ_26838_2_IvsQ_26839_2_IvsQ_26840_2.dat
POLLREFfinalIvsQ_26854_26855_26856_IvsQ_26854_1_IvsQ_26855_1_IvsQ_26856_1.dat.txt
POLLREFfinalIvsQ_26854_26855_26856_IvsQ_26854_2_IvsQ_26855_2_IvsQ_26856_2.dat.txt
POLLREFfinalIvsQ_26860_26861_26862_IvsQ_26860_1_IvsQ_26861_1_IvsQ_26862_1.dat.txt
POLLREFfinalIvsQ_26860_26861_26862_IvsQ_26860_2_IvsQ_26861_2_IvsQ_26862_2.dat.txt
POLLREFfinalIvsQ_26863_26864_26865_IvsQ_26863_1_IvsQ_26864_1_IvsQ_26865_1.dat.txt
POLLREFfinalIvsQ_26863_26864_26865_IvsQ_26863_2_IvsQ_26864_2_IvsQ_26865_2.dat.txt
POLLREFfinalIvsQ_26875_26876_26877_IvsQ_26875_1_IvsQ_26876_1_IvsQ_26877_1.dat.txt
POLLREFfinalIvsQ_26875_26876_26877_IvsQ_26875_2_IvsQ_26876_2_IvsQ_26877_2.dat.txt
POLLREFfinalIvsQ_26878_26879_26880_IvsQ_26878_1_IvsQ_26879_1_IvsQ_26880_1.dat.txt
POLLREFfinalIvsQ_26878_26879_26880_IvsQ_26878_2_IvsQ_26879_2_IvsQ_26880_2.dat.txt
POLLREFfinalIvsQ_26881_26882_26883_IvsQ_26881_1_IvsQ_26882_1_IvsQ_26883_1.dat.txt
POLLREFfinalIvsQ_26881_26882_26883_IvsQ_26881_2_IvsQ_26882_2_IvsQ_26883_2.dat.tx
Diffusion-limited evaporation of polymer solutions
No full textIn many processes in nature and industry, water evaporates from polymer
solutions. When the evaporation is fast, a polymer layer can form at the water-air interface resulting in a diffusive mass transfer resistance inside the solution, in a process termed diffusion-limited evaporation (DLE). DLE has been observed in solutions containing lipids or microgels, that often have a specific structural complexity. To understand the generality of the physical mechanisms in DLE, it is highly relevant to study DLE of polymer solutions.
In this thesis, we study the evaporation of water from solutions containing
structurally simple polymers, with the aim of improving the fundamental
understanding of DLE. We first present experimental data, where a polymerwater solution evaporates unidirectionally from rectangular capillaries. The evaporation rate settles according to the predicted diffusive scaling m˙ (t) ∼ t−1/2, but surprisingly does not settle with m˙ (t) → 0 at late times, which would be expected at thermodynamic equilibrium with the environment. The steady state evaporation dynamics in our experiments is explained as resulting from the buildup of a tensile stress in a glassy polymer layer at the interface, resulting from the compression by the evaporation flux, that offsets the water activity at the interface ai from thermodynamic equilibrium with the environment. We furthermore show how DLE can result in evaporation from polymer solutions that is insensitive to the ambient humidity, which sets the driving force for
evaporation. Importantly, we find that for certain polymers evaporation is also humidity-insensitive at early times, without becoming diffusion-limited. This effect is caused by the rapid adsorption of polymers at the solution-air interface, with the interfacial polymer layer setting the early-times evaporation rate.
In the second part of this thesis we show DLE from polyelectrolyte solutions, that is similar to the neutral polymer at late times as a result of increased counterion condensation at high polyelectrolyte concentrations. The polymers we tested also approach a similar non-zero steady state evaporation rate m˙ (t), which suggests similar contributions from the mixing energy and mechanical response to the evaporative driving force.
The final part of this thesis presents a phase field model which allows us to
establish the ubiquitous nature of DLE, independent of polymer properties. For a one-dimensional geometry, results from the model clearly show how DLE with m˙ (t) ∼ t−1/2 occupies a large region in the evaporation phase space, which also includes pure solvent-like (m˙ (t) ∼ const.) and arrested (m˙ (t) ∼ 0) evaporative regions. Finally, we show how the model can be extended to more complicated systems, like droplets or materials with heterogeneous internal structuring, which is important to translating our results to many practical applications
Simon Nyakot
No full textabstract: Simon Nyakot left his village when he was six years old.
“Lost Boys Found” is an ongoing, interdisciplinary project that is collecting, recording and archiving the oral histories of the Lost Boys/Girls of Sudan. The collection is a work-in-progress, seeking to record the oral history of as many Lost Boys/Girls as are willing, and will be used in a future book.Age: 27Region: LakeThis picture and bio was donated to the Lost Boys Found project from The Arizona Lost Boys Cente
Cahiers Saint-Simon
No full texthttps://www.persee.fr/renderCollectionCover/simon.pngThe Société Saint-Simon was founded in 1972 in order to promote studies about the Duke of Saint-Simon (1675-1755), namely about the work, life, and thinking of the Mémoires’s author. Each year it issues a Cahier Saint-Simon. It contains the Acts of the annual Journée d’étude in Versailles, but also Notes and Documents, News of the Society and Book reviews.Fondée en 1972, la Société Saint-Simon a pour but de développer les études concernant l'oeuvre, la personne et la pensée du duc de Saint-Simon (1675-1755), l’auteur des Mémoires. Chaque année, paraît un numéro de Cahiers Saint-Simon contenant les actes de la journée annuelle de Versailles, ainsi que des Mélanges, des Notes et Documents et une Chronique bibliographique détaillée
Cahiers Saint-Simon
No full texthttps://www.persee.fr/renderCollectionCover/simon.pngThe Société Saint-Simon was founded in 1972 in order to promote studies about the Duke of Saint-Simon (1675-1755), namely about the work, life, and thinking of the Mémoires’s author. Each year it issues a Cahier Saint-Simon. It contains the Acts of the annual Journée d’étude in Versailles, but also Notes and Documents, News of the Society and Book reviews.Fondée en 1972, la Société Saint-Simon a pour but de développer les études concernant l'oeuvre, la personne et la pensée du duc de Saint-Simon (1675-1755), l’auteur des Mémoires. Chaque année, paraît un numéro de Cahiers Saint-Simon contenant les actes de la journée annuelle de Versailles, ainsi que des Mélanges, des Notes et Documents et une Chronique bibliographique détaillée
Simon Weir - The Sydney Surrealist
No full textExhibition catalogue of "Simon Weir - The Sydney Surrealist", Exhibition at Disorder Gallery, Darlinghurst NSW, Australia, in April 2024. The catalogue contains images of exhibited works and statements by the artist Simon Weir, the gallery Director Elliott Cole, and author and journalist Margie Smithurst
Knights, knaves or pawns? Human behaviour and social policy.
No full textThere are two fundamental changes currently under way in the welfare state. These are the development of quasi-markets in welfare provision, and the supplementation of ‘fiscal’ welfare by ‘legal’ welfare: policies that rely on redistributing income through regulation and other legal devices, instead of through the tax and social security system. This article argues that these changes are in part the result of a fundamental shift in policy-makers’ beliefs concerning human motivation and behaviour. People who finance, operate and use the welfare stateare no longer assumed to be either public spirited altruists (knights) or passive recipients of state largesse (pawns); instead they are all considered to be in one way or another self-interested (knaves). However, since neither the ‘new’ nor the ‘old’ set of assumptions are based on evidence, policies based on the new set are as likely to fail as those based on the old. What is needed are ‘robust’ policies that are not dependent on any simple view of human behaviour.
Joan Simon Correspondence
No full textEntries include a typed biographical letter from Simon in New York, explaining her relationship to Maine for the purposes of presentation to the Maine Author Collection
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