Wednesday 10 July 2013, Sidlaw Room, 14:30-16:30
Membranes
Thermal fluctuation and elasticity of lipid membranes interacting with transmembrane proteins
S-M Choi1, J-H Lee1, C Do1, S-H Kang1, M-J Lee1, A Faraone2, S R Kline2 and P A Pincus3
1
KAIST, South Korea, 2NIST Center for Neutron Research, USA, 3University of California, USA
Cell membrane, a barrier to maintain cytoplasmic materials inside the cell, consists of lipid bilayer and a plethora of
membrane proteins. Various cellular processes, such as mass and signal transfer between cells and their
environments, cell fission and fusion, are governed by the interplay between proteins and lipid membranes, and
subsequent membrane-mediated protein-protein interactions. These interactions often cause morphological
changes of membrane and determine the collective activities of membrane proteins.While there have been many
theoretical and computational simulation works for the membrane-protein and membrane-mediated protein-protein
interactions, experimental investigations remains still challenging and, especially, it is not fully understood how the
membrane elastic properties are affected by the interactions.In this talk, recent neutron spin echo investigations on
the thermal fluctuation and elasticity of large unilamellar lipid vesicles (DOPC, DMPC and DLPC) interacting with
transmembrane proteins (melittins and gramicidins) [1,2] will be presented, from which the membrane-mediated
protein-protein interactions will be discussed.
[1]
[2]
J.-H. Lee, S.-M. Choi, C. Doe, A. Faraone, P.A. Pincus, and S.R. Kline, Phys. Rev. Lett., 105, 038101
(2010)
J.-H. Lee, S.-M. Choi et al (in preparation)
Confined soft matter: Measuring the structure of lipid bilayers under confinement using neutron reflection
L Mears1, W de Vos2, R Barker3, S Prescott1, T Cosgrove1, S Abbott1 and R Richardson1
1
University of Bristol, UK, 2University of Twente, Netherlands, 3Institut Laue Langevin, France
Supported lipid bilayers provide an excellent model system for cell membranes. The mechanical and structural
properties of lipid bilayers are very important to their behaviour and interactions with similar membranes, proteins
or other small molecules. When membranes are pushed against each other these soft systems are forced to interact
as they are confined. We have recently developed a novel sample environment which applies a confining pressure
to the sample during neutron reflection experiments [1, 2]. Here, we will discuss reflectivity data from confined lipid
bilayer stacks. Phosphatidylcholine lipids with a range of tail lengths were investigated and consistently showed that
water could be excluded from between the bilayers under a low confining pressure of 1 bar. DMPC showed a
significant decrease in its inter layer spacing under confinement. Using kinetic data, we have tracked this
dehydration and re-ordering of the bilayers in DMPC as the system equilibrates into a different, confined state.
Interestingly for the lipid, DPPC, a temperature dependent increase in the inter layer spacing was observed, this
indicates a confinement induced phase transition.
[1]
[2]
W. M. de Vos et al.. Measuring the structure of thin soft matter films under confinement: A surface-force
type apparatus for neutron reflection , based on a flexible membrane approach, Rev. Sci. Instrum., 2012,
83, 113903.
W. M. de Vos et al., Nonuniform Hydration and Odd–Even Effects in Polyelectrolyte Multilayers under a
Confining Pressure, Macromolecules, 2013, 46 (3), 1027.
ICNS 2013 International Conference on Neutron Scattering
Binding mechanisms of cell-penetrating peptides on lipid mono- and bilayers revealed using neutron and x-ray
reflection
K Shin1, D Lee2, M W Kim3, B Akgun4, S Saitja4, K Y Lee5 and M James6
1
Sogang University, Korea, 2Soongsil University, Korea, 3KAIST, Korea, 4NIST, USA, 5University of Chicago, USA,
Australian Synchrotron, Australia
6
Cell-penetrating peptides (CPPs) are short peptides that can traverse cell membranes efficiently. Although many
results on the cellular uptake of CPP-carrying cargos have been reported, the molecular mechanisms of membrane
binding and translocation are still controversial and unclear.Among CPPs, the transcription-activating-factor (TAT)derived peptide (TDP), which has 11 key amino acid residues with mostly lysines and arginines from the humanimmunodeficiency-virus (HIV-1) TAT protein, is the most widely studied CPP. We will present results from X-ray and
neutron reflectivity measurement on systems composed of a 1,2-dipalmitoyl-sn-glycero-3-phosphocholine
membranes (e.g. bilayer [1] and monolayer [2]) and Tat peptides which were obtained to investigate the
mechanism of membrane translocation at the solid-water interface for the bilayer and the receptor-aided adsorption
at air-water interface for the monolayer. We monitored the structural changes caused by binding with Tat peptides
while systemically varying the temperature, membrane compositions, and the concentration of Tat peptides. Our
results reveal the detailed molecular structures of the stepwise interactions that appear during the translocation of
the Tat peptides across the lipid bilayers, and the receptor aided binding phenomena of the Tat peptide on heparininserted lipid monolayer.
[1]
[2]
D. Choi, J.H. Moon, H. Kim, B.J. Sung, M.W. Kim, G. Tae, S.K. Satija, B. Akgun, C.-J. Yu, H.W. Lee, D.R.
Lee, J.M. Henderson, J.W. Kwong, K.L. Lam,K.Y.C. Lee, and K. Shin, Soft Matter, 8, 8294 (2012).
D. Hong, K. Shin, M. James, G. Tae, Soft Matter, 8, 8616 (2012).
Bilayer undulation dynamics in unilamellar phospholipid vesicles: Effect of temperature, cholesterol and trehalose
B A Brüning1, S Prévost2, R Stehle2, R Steitz2, P Falus3, B Farago3 and T Hellweg4
1
Universität Erlangen-Nürnberg, Germany, 2Helmholtz Zentrum Berlin, Germany, 3Institut Laue Langevin,
France, 4Universität Bielefeld, Germany
We report a combined dynamic light scattering (DLS) and neutron spin-echo (NSE) study on lipid vesicles
composed of 1,2-dimyristoyl-snglycero-3-phosphatidylcholine (DMPC), respectively under the influence of
temperature and the membrane additives cholesterol and trehalose. Mechanical properties of a model membrane
and thus the corresponding bilayer undulation dynamics can be specifically tuned by changing its lipid headgroup
or acyl chain properties through temperature or composition. A structural characterization of the respective model
systems at varied phase state was performed to investigate lipid vesicle size and polydispersity. We have performed
dynamic light scattering on the lipid (mixtures) to investigate changes in vesicle size and mass diffusion. We study
bilayer undulation and bulk diffusion dynamics using neutron spin-echo spectroscopy, on two distinct time scales,
namely around 25 ns and 100 ns. Finally, we calculate the respective bilayer bending rigidities for all types of lipid
vesicles. We find, that on the local length scale changes at the lipid headgroup influence the bilayer undulation
dynamics and bilayer bending rigidity less than at the lipid acyl chain: We observe a bilayer softening around the
main phase transition temperature Tm of the single lipid model system, and a bilayer stiffening the more cholesterol
is added, whereas the insertion of trehalose hardly changes the bilayer undulations and membrane rigidity [1]. We
explain our findings on the basis of a free volume available to lipid molecules in the membrane plane, which
encounters the most pronounced changes in the acyl chain regime.
[1]
B. Brüning, S. Prévost, R. Stehle, R. Steitz, P. Falus, T. Hellweg, submitted.
ICNS 2013 International Conference on Neutron Scattering
Scaling of RO-Membranes in desalination of wastewater and the effect of organic matter on calcium mineralization
explored by SANS
D Schwahn1, V Pipich2 and Y Dahdal3
1
TU Munich, Germany, 2Forschungszentrum Jülich GmbH, Germany, 3Ben Gurion University, Israel
Reclaimed municipal wastewater is considered today as an important source for maintaining adequate fresh water
supply. Major limitations of using membrane-based desalination techniques are biofouling and calcium phosphate
scaling. It has been shown that the formation of biofilms and scaling, especially that caused by calcium phosphates
on reverse osmosis (RO) membranes limit desalination efficiency of secondary wastewater effluents. The formation
of biofilm and scaling is the topic of our research. In particular we are interested in the effect of components
representing the biofilm on calcium phosphate mineralization at a molecular level using SANS technique. To this
end we are studying the formation of calcium minerals in a model solution simulating secondary waste water
effluents (SSE) after adding the biopolymers as single molecules or as grafted at gold nanoparticles. The latter
experiment should simulate mineralization at surfaces such as membranes. SANS is a promising tool in this field as
was demonstrated on similar studies in the related field of biomineralization [1,2]. We will present data showing the
process of mineralization in SSE solutions stimulated by the proteins BSA and lysozyme using stopped-flow
technique in combination with classical SANS as well as with focusing USANS techniques.
[1]
[2]
V. Pipich, M. Balz, S.E. Wolf, W. Tremel, and D. Schwahn, J. Am. Chem. Soc. (JACS) 130, 2008, 68796892
A. Heiss, V. Pipich, W. Jahnen-Dechent, and D. Schwahn, Biophysical Journal 99 (2010) 3986-3995
Interaction of trehalose with membranes by neutron diffraction
G Bryant1, B Kent2, T Hunt1, T Hauß3, T Lenné4 and C J Garvey2
1
RMIT University, Australia, 2Bragg Institute, ANSTO, Australia, 3Helmholtz-Zentrum Berlin für Materialien und Energie
GmbH, Germany, 4Australian National University, Australia
Small solute molecules, particularly di- and mono-saccharides, are associated with cryoprotective effects, and in
model systems the concentration of sugars between bilayers is correlated with changes in lipid phase transition
temperatures during dehydration. One explanation for this effect is that the presence of sugars leads to increased
bilayer separation at a particular dehydration level, due to osmotic and volumetric effects. An alternate mechanism
posits that the effect is due to specific short range interactions between lipid head groups and specific sugars. The
two mechanisms of cryoprotection imply quite different concentration profiles of sugar molecules between bilayers.
Using Fourier methods to reconstruct the scattering length density profile of the unit cell from neutron diffraction
measurements carried out at the Membrane Diffractometer V1 (Helmholtz Zentrum, Berlin) we show clearly that the
profile of trehalose between the bilayer implies no specific interaction between phospholipid and trehalose.
ICNS 2013 International Conference on Neutron Scattering