9 research outputs found
Effect of Phospholipid Composition and Phase on Nanodisc Films at the SolidâLiquid Interface as Studied by Neutron Reflectivity
Nanodiscs are disc-like self-assembled
structures formed by phospholipids
and amphipatic proteins. The proteins wrap like a belt around the
hydrophobic part of the lipids, basically producing nanometer-sized
patches of lipid bilayers. The bilayer in the nanodisc constitutes
a native-like model of the cell membrane and can act as a nanometer-sized
container for functional single membrane proteins. In this study,
we present a general nanodisc-based system, intended for structural
and functional studies of membrane proteins. In this method, the nanodiscs
are aligned at a solid surface, providing the ability to determine
the average structure of the film along an axis perpendicular to the
interface as measured by neutron reflectivity. The nanodisc film was
optimized in terms of nanodisc coverage, reduced film roughness, and
stability for time-consuming studies. This was achieved by a systematic
variation of the lipid phase, charge, and length of lipid tails. Herein,
we show that, although all studied nanodiscs align with their lipid
bilayer parallel to the interface, gel-phase DMPC nanodiscs form the
most suitable film for future membrane protein studies since they
yield a dense irreversibly adsorbed film with low roughness and high
stability over time. This may be explained by the appropriate matching
between the thickness of the hydrophobic lipid core of gel phase DMPC
and the height of the belt protein. Moreover, once formed the gel-phase
DMPC nanodiscs film can be heated up to melt the lipid bilayer, thus
providing a more biologically friendly environment for membrane proteins
Effect of Functionalized Gold Nanoparticles on Floating Lipid Bilayers
The
development of novel nano-engineered materials poses important
questions regarding the impact of these new materials on living systems.
Possible adverse effects must be assessed in order to prevent risks
for health and the environment. On the other hand, a thorough understanding
of their interaction with biological systems might also result in
the creation of novel biomedical applications. We present a study
on the interaction of model lipid membranes with gold nanoparticles
(AuNP) of different surface modifications. Neutron reflectometry experiments
on zwitterionic lipid double bilayers were performed in the presence
of AuNP functionalized with cationic and anionic head groups. Structural
information was obtained that provided insight into the fate of the
AuNPs with regard to the integrity of the model cell membranes. The
AuNPs functionalized with cationic head groups penetrate into the
hydrophobic moiety of the lipid bilayers and cause membrane disruption
at an increased concentration. In contrast, the AuNPs functionalized
with anionic head groups do not enter but seem to impede the destruction
of the lipid bilayer at an alkaline pH. The information obtained might
influence the strategy for a better nanoparticle risk assessment based
on a surface charge evaluation and contribute to nano-safety considerations
during their design
Nanodisc films for membrane protein studies by neutron reflection : Effect of the protein scaffold choice
Nanodisc films are a promising approach to study the equilibrium conformation of membrane bound proteins in native-like environment. Here we compare nanodisc formation for NADPH-dependent cytochrome P450 oxidoreductase (POR) using two different scaffold proteins, MSP1D1 and MSP1E3D1. Despite the increased stability of POR loaded MSP1E3D1 based nanodiscs in comparison to MSP1D1 based nanodiscs, neutron reflection at the siliconâsolution interface showed that POR loaded MSP1E3D1 based nanodisc films had poor surface coverage. This was the case, even when incubation was carried out under conditions that typically gave high coverage for empty nanodiscs. The low surface coverage affects the embedded POR coverage in the nanodisc film and limits the structural information that can be extracted from membrane bound proteins within them. Thus, nanodisc reconstitution on the smaller scaffold proteins is necessary for structural studies of membrane bound proteins in nanodisc films
Additional file 1: of Immunoregulatory soluble CTLA-4 modifies effector T-cell responses in systemic lupus erythematosus
Full analysis of individual patient and donor peptide response datasets used to generate the summary data presented in Fig.ĂÂ 3. (DOCX 495 kb
Modulation of Dipalmitoylphosphatidylcholine Monolayers by Dimethyl Sulfoxide
The action of the penetration-enhancing
agent, dimethyl sulfoxide
(DMSO), on phospholipid monolayers was investigated at the airâwater
interface using a combination of experimental techniques and molecular
dynamics simulations. Brewster angle microscopy revealed that DPPC
monolayers remained laterally homogeneous at subphase concentrations
up to a mole fraction of 0.1 DMSO. Neutron reflectometry of the monolayers
in combination with isotopic substitution enabled the determination
of solvent profiles as a function of distance perpendicular to the
interface for the different DMSO subphase concentrations. These experimental
results were compared to those obtained from molecular dynamic (MD)
simulations of the corresponding monolayer systems. There was excellent
agreement found between the MD-derived reflectivity curves and the
measured data for all of the H/D contrast variations investigated.
The MD provide a detailed description of the distribution of water
and DMSO molecules around the phosphatidylcholine headgroup, and how
this distribution changes with increasing DMSO concentrations. Significantly,
the measurements and simulations that are reported here support the
hypothesis that DMSO acts by dehydrating the phosphatidylcholine headgroup,
and as such provide the first direct evidence that it does so primarily
by displacing water molecules bound to the choline group
The Relationship between Charge Density and Polyelectrolyte Brush Profile Using Simultaneous Neutron Reflectivity and In Situ Attenuated Total Internal Reflection FTIR
We
report on a novel experimental study of a pH-responsive polyelectrolyte
brush at the silicon/D<sub>2</sub>O interface. A polyÂ[2-(diethylamino)Âethyl
methacrylate] brush was grown on a large silicon crystal which acted
as both a substrate for a neutron reflectivity solid/liquid experiment
but also as an FTIR-ATR spectroscopy crystal. This arrangement has
allowed for both neutron reflectivities and FTIR spectroscopic information
to be measured in parallel. The chosen polybase brush shows strong
IR bands which can be assigned to the NâD<sup>+</sup> stretch,
D<sub>2</sub>O, and a carbonyl group. From such FTIR data, we are
able to closely monitor the degree of protonation along the polymer
chain as well as revealing information concerning the D<sub>2</sub>O concentration at the interface. The neutron reflectivity data allows
us to determine the physical brush profile normal to the solid/liquid
interface along with the corresponding degree of hydration. This combined
approach makes it possible to quantify the charge on a polymer brush
alongside the morphology adopted by the polymer chains
Is Osmotic Pressure Relevant in the Mechanical Confinement of a Polymer Brush?
The structures of polymer brushes
under confinement were measured using a combination of neutron reflectivity
and a surface force type apparatus. The samples were either polyÂ(ethylene
oxide), PEO, used to investigate the effect of the grafting density
or polyÂ(acrylic acid), PAA, used to determine the effect of charge
on the structure of a polymer brushes under confinement. Without confinement
both PEO and PAA brushes are found to be highly swollen with water,
>50% v/v, with the expected parabolic brush structure. Compression
of the PEO brushes with as little as 0.5 bar of confinement is found
experimentally to reduce the brush to a polymer block of uniform density
that is significantly dehydrated, <12% v/v. Further subsequent
increases in the confinement pressure only marginally decrease the
hydration and thickness of the polymer block. The grafting density
of the brush does not significantly influence this behavior. PAA polymer
brushes with little (pH 3) or an intermediate level of charging (pH
5.5) are also found to be compressed into a single uniform density
polymer block with a confinement of 5 bar. However, with a high level
of charge (pH 9) the brush structure is believed to be partially retained
due to the repulsion between the internal charges. These experimental
results are compared against a theoretical model based on numerical
self-consistent field (nSCF) theory as well as to osmotic, SFA, and
AFM data. While the nSCF model correctly predicts the observed transition
from a brush to a block profile, experimentally it occurs at a pressure
2 orders of magnitude lower than the simulations would suggest. The
results acquired through simulation are consistent with available
osmotic pressure data; however, SFA and AFM measurements are consistent
with the neutron reflection experimental data presented here. This
significant disagreement between the two data sets indicates that
in a confined system the effective osmotic counter pressure to an
applied mechanical pressure is much less than the osmotic pressure
expected from the local polymer concentration
Nanoscale control of interfacial processes for latent fingerprint enhancement
Latent fingerprints on metal surfaces may be visualized by exploiting the insulating characteristics of the fingerprint deposit as a âmaskâ to direct electrodeposition of an electroactive polymer to the bare metal between the fingerprint ridges. This approach is complementary to most latent fingerprint enhancement methods, which involve physical or chemical interaction with the fingerprint residue. It has the advantages of sensitivity (a nanoscale residue can block electron transfer) and, using a suitable polymer, optimization of visual contrast. This study extends the concept in two significant respects. First, it explores the feasibility of combining observation based on optical absorption with observation based on fluorescence. Second, it extends the methodology to materials (here, polypyrrole) that may undergo post-deposition substitution chemistry, here binding of a fluorophore whose size and geometry preclude direct polymerization of the functionalised monomer. The scenario involves a lateral spatial image (the whole fingerprint, first level detail) at the centimetre scale, with identification features (minutiae, second level detail) at the 100â200 ÎŒm scale and finer features (third level detail) at the 10â50 ÎŒm scale. However, the strategy used requires vertical spatial control of the (electro)chemistry at the 10â100 nm scale. We show that this can be accomplished by polymerization of pyrrole functionalised with a good leaving group, ester-bound FMOC, which can be hydrolysed and eluted from the deposited polymer to generate solvent âvoidsâ. Overall the âvoidâ volume and the resulting effect on polymer dynamics facilitate entry and amide bonding of Dylight 649 NHS ester, a large fluorophore. FTIR spectra demonstrate the spatially integrated compositional changes. Both the hydrolysis and fluorophore functionalization were followed using neutron reflectivity to determine vertical spatial composition variations, which control image development in the lateral direction
Interactions of PAMAM Dendrimers with Negatively Charged Model Biomembranes
We have investigated the interactions
between cationic polyÂ(amidoamine)
(PAMAM) dendrimers of generation 4 (G4), a potential gene transfection
vector, with net-anionic model biomembranes composed of different
ratios of zwitterionic phosphocholine (PC) and anionic phospho-l-serine (PS) phospholipids. Two types of model membranes were
used: solid-supported bilayers, prepared with lipids carrying palmitoyl-oleoyl
(PO) and diphytanoyl (DPh) acyl chains, and free-standing bilayers,
formed at the interface between two aqueous droplets in oil (droplet
interface bilayers, DIBs) using the DPh-based lipids. G4 dendrimers
were found to translocate through POPC:POPS bilayers deposited on
silica surfaces. The charge density of the bilayer affects translocation,
which is reduced when the ionic strength increases. This shows that
the dendrimerâbilayer interactions are largely controlled by
their electrostatic attraction. The structure of the solid-supported
bilayers remains intact upon translocation of the dendrimer. However,
the amount of lipids in the bilayer decreases and dendrimer/lipid
aggregates are formed in bulk solution, which can be deposited on
the interfacial layers upon dilution of the system with dendrimer-free
solvent. Electrophysiology measurements on DIBs confirm that G4 dendrimers
cross the lipid membranes containing PS, which then become more permeable
to ions. The obtained results have implications for PAMAM dendrimers
as delivery vehicles to cells