Atomic force microscopy (AFM) study of thick lamellar stacks of phospholipid bilayers

We report an Atomic Force Microscopy (AFM) study on thick multi lamellar stacks of approx. 10 mum thickness (about 1500 stacked membranes) of DMPC (1,2-dimyristoyl-sn-glycero-3-phoshatidylcholine) deposited on silicon wafers. These thick stacks could be stabilized for measurements under excess water or solution. From force curves we determine the compressional modulus B and the rupture force F_r of the bilayers in the gel (ripple), the fluid phase and in the range of critical swelling close to the main transition. AFM allows to measure the compressional modulus of stacked membrane systems and values for B compare well to values reported in the literature. We observe pronounced ripples on the top layer in the Pbeta' (ripple) phase and find an increasing ripple period Lambda_r when approaching the temperature of the main phase transition into the fluid Lalpha phase at about 24 C. Metastable ripples with 2Lambda_r are observed. Lambda_r also increases with increasing osmotic pressure, i.e., for different concentrations of polyethylene glycol (PEG)

Collective Molecular Dynamics in Proteins and Membranes

The understanding of dynamics and functioning of biological membranes and in particular of membrane embedded proteins is one of the most fundamental problems and challenges in modern biology and biophysics. In particular the impact of membrane composition and properties and of structure and dynamics of the surrounding hydration water on protein function is an upcoming hot topic, which can be addressed by modern experimental and computational techniques. Correlated molecular motions might play a crucial role for the understanding of, for instance, transport processes and elastic properties, and might be relevant for protein function. Experimentally that involves determining dispersion relations for the different molecular components, i.e., the length scale dependent excitation frequencies and relaxation rates. Only very few experimental techniques can access dynamical properties in biological materials on the nanometer scale, and resolve dynamics of lipid molecules, hydration water molecules and proteins and the interaction between them. In this context, inelastic neutron scattering turned out to be a very powerful tool to study dynamics and interactions in biomolecular materials up to relevant nanosecond time scales and down to the nanometer length scale. We review and discuss inelastic neutron scattering experiments to study membrane elasticity and protein-protein interactions of membrane embedded proteins

Motional Coherence in Fluid Phospholipid Membranes

URL:http://link.aps.org/doi/10.1103/PhysRevLett.101.248106 DOI:10.1103/PhysRevLett.101.248106We report a high energy-resolution neutron backscattering study, combined with in situ diffraction, to investigate slow molecular motions on nanosecond time scales in the fluid phase of phospholipid bilayers of 1,2-dimyristoyl-sn-glycero-3-phoshatidylcholine. A cooperative structural relaxation process was observed. From the in-plane scattering vector dependence of the relaxation rates in hydrogenated and deuterated samples, combined with results from a 0.1  μs long all-atom molecular dynamics simulation, it is concluded that correlated dynamics in lipid membranes occurs over several lipid distances, spanning a time interval from pico- to nanoseconds.We acknowledge financial support from the DFG through Project No. SA 772/8-2

Studies of Lipid Bilayer Structure and Dynamics

The biological membrane is one of the fundamental components in nature, however it is still not well understood. The variety of lipids and other macromolecules found in the membrane makes it very difficult to discern its properties in vivo. Lipid bilayers form the backbone of biological membranes and provide an ideal model system with which to study membrane function and properties. Here we present the results of studies of lipid bilayer structure and dynamics with neutron and x-ray scattering techniques. In particular, the diffusion of single solid supported bilayers and the collective dynamics of lipid-ethanol systems were studied. The first observations of single bilayer diffusion with quasi-elastic neutron scattering are presented. Single solid supported bilayers of 1,2-dimyristoyl-sn-glycero-3-phosphatidylcholine (DMPC) were prepared and examined with a backscattering spectrometer. Diffusion constants were found to be consistent with multilamellar systems. Single solid ! supported bilayer diffusion was also found to exhibit a continuous character with enhanced diffusion at the nearest neighbour distance. Investigations of the effects of ethanol on collective lipid tail dynamics are also presented. Highly oriented multilamellar solid supported DMPC bilayers were prepared and immersed in a 5% ethanol/water solution. Inelastic neutron scattering experiments and all atom molecular dynamics simulations reveal the presence of a new low-energy dynamic mode in the lipid tails of DMPC-ethanol systems. This mode exhibits little dispersion and appears in addition to the high energy acoustic mode associated with lipid tail fluctuations in pure lipid systems, which is also observed. Both modes demonstrate in-plane and perpendicular character which may be related to the transport of small molecules through the membrane core. Additional x-ray diffraction studies of DMPC-ethanol systems hydrated from the vapour phase demonstrate that lipid tail fluctuations in DMPC-ethanol systems exhibit lengthscales equal or less than the thickness of the bilayer.Master of Science (MSc

Neutron Scattering

This book brings suitable data concerning theory and experiments of neutron interactions with different materials. Since the neutron discovery by Chadwick in 1932, researchers of the entire world begin to make studies about it. It is well known that neutron have no charge, and their electric dipole moment is either zero or too small to measure, but theories and experiments show that neutron has spin (presence of magnetic moment), and polarization neutron scattering is plausible. The reader can obtain remarks about inelastic scattering cross sections for neutron; polarized neutron reflectivity; scattering methods; neutron reflectometry tool to probe the chemical structures; neutron scattering for amino acid crystals; and small-angle neutron scattering nanoemulsion heat transfer fluids in this book

La dynamique des systèmes biologiques en fonction de l’hydratation, de la température et de la pression étudiée pardiffusion neutronique

Incoherent elastic and quasi-elastic neutron scattering were used to measure membrane and protein dynamics in the nano- to picosecond time and Ångstrom length scale.The hydration dependent dynamics of DMPC model membranes was studied using elastic and quasi-elastic neutron scattering. The elastic experiments showed a clear shift of the temperature of the main phase transition to higher temperatures with decreasing hydration level.The performed quasi-elastic measurements demonstrated nicely the influence, hydration has on the diffusive motions of the head lipid groups. Different models are necessary to fit the Q-dependence of the elastic incoherent structure factor and show therefore the reduced mobility as a result of reduced water content.In addition to temperature, pressure as a second thermodynamical variable was used to explore dynamics of DMPC membranes. The ordering introduced by applying pressure has similar effect to decreased hydration, therefore both approaches are complementary. Covering three orders of magnitude in observation time, the dynamics of native AChE and its complexed counterpart in presence of Huperzin A was investigated in the range from 1 ns to 100 ps. The mean square displacements obtained from the elastic data allowed the determination of activation energies and gave evidence that a hierarchyof motions contributes to the enzymatic activity. Diffusion constants and residence times were extracted from the quasi-elastic broadening.La diffusion incohérente élastique et quasi-élastique de neutrons a été utilisée pour mesurer la dynamique de membranes et de protéines à l’échelle de la pico- à la nanoseconde et de la longueur de l’Ångstrom.La dynamique de membranes modèles DMPC, en fonction de l’hydratation a été étudiée par diffusion neutronique. Les expériences élastiques ont, clairement montré un décalage de la température de transition de phase principale vers une température plus haute pour une diminution du niveau d’hydratation.Les mesures quasi-élastiques effectuées ont montré l’influence de l’hydratation sur les mouvements diffusifs des têtes lipidiques. Différents modèles ont été nécessaires pour affiner les dépendances en Q des facteurs de structure élastiques incohérents et montrent donc la mobilité réduite due à l’hydratation inférieure.En plus de la température, la pression comme deuxième variable thermodynamique a été utilisée pour étudier la dynamique des membranes DMPC. L’ordre induit par l’application d’une pression a un effet similaire à une hydratation diminuée, donc les deux approches sont complémentaires.Couvrant trois ordres de grandeur, la dynamique d’AChE libre ou complexée avec de l’Huperzine A a été étudiée dans le domaine allant de 1 ns à 100 ps. Les déplacements carrés moyens obtenues à partir des données élastiques ont permis la détermination des énergies d’activation et prouvent que toute une hiérarchie de mouvements contribue a l’activité enzymatique. Les constantes de diffusion et les temps de corrélation ont été extraits de l’élargissement quasi-élastique

La dynamique des systèmes biologiques en fonction de l’hydratation, de la température et de la pression étudiée pardiffusion neutronique

Incoherent elastic and quasi-elastic neutron scattering were used to measure membrane and protein dynamics in the nano- to picosecond time and Ångstrom length scale.The hydration dependent dynamics of DMPC model membranes was studied using elastic and quasi-elastic neutron scattering. The elastic experiments showed a clear shift of the temperature of the main phase transition to higher temperatures with decreasing hydration level.The performed quasi-elastic measurements demonstrated nicely the influence, hydration has on the diffusive motions of the head lipid groups. Different models are necessary to fit the Q-dependence of the elastic incoherent structure factor and show therefore the reduced mobility as a result of reduced water content.In addition to temperature, pressure as a second thermodynamical variable was used to explore dynamics of DMPC membranes. The ordering introduced by applying pressure has similar effect to decreased hydration, therefore both approaches are complementary. Covering three orders of magnitude in observation time, the dynamics of native AChE and its complexed counterpart in presence of Huperzin A was investigated in the range from 1 ns to 100 ps. The mean square displacements obtained from the elastic data allowed the determination of activation energies and gave evidence that a hierarchyof motions contributes to the enzymatic activity. Diffusion constants and residence times were extracted from the quasi-elastic broadening.La diffusion incohérente élastique et quasi-élastique de neutrons a été utilisée pour mesurer la dynamique de membranes et de protéines à l’échelle de la pico- à la nanoseconde et de la longueur de l’Ångstrom.La dynamique de membranes modèles DMPC, en fonction de l’hydratation a été étudiée par diffusion neutronique. Les expériences élastiques ont, clairement montré un décalage de la température de transition de phase principale vers une température plus haute pour une diminution du niveau d’hydratation.Les mesures quasi-élastiques effectuées ont montré l’influence de l’hydratation sur les mouvements diffusifs des têtes lipidiques. Différents modèles ont été nécessaires pour affiner les dépendances en Q des facteurs de structure élastiques incohérents et montrent donc la mobilité réduite due à l’hydratation inférieure.En plus de la température, la pression comme deuxième variable thermodynamique a été utilisée pour étudier la dynamique des membranes DMPC. L’ordre induit par l’application d’une pression a un effet similaire à une hydratation diminuée, donc les deux approches sont complémentaires.Couvrant trois ordres de grandeur, la dynamique d’AChE libre ou complexée avec de l’Huperzine A a été étudiée dans le domaine allant de 1 ns à 100 ps. Les déplacements carrés moyens obtenues à partir des données élastiques ont permis la détermination des énergies d’activation et prouvent que toute une hiérarchie de mouvements contribue a l’activité enzymatique. Les constantes de diffusion et les temps de corrélation ont été extraits de l’élargissement quasi-élastique