Extremophiles : life under extreme conditions, Jan 16, 2015
Halobacterium salinarum is an extreme halophile archaeon with an absolute requirement for a multi... more Halobacterium salinarum is an extreme halophile archaeon with an absolute requirement for a multimolar salt environment. It accumulates molar concentrations of KCl in the cytosol to counterbalance the external osmotic pressure imposed by the molar NaCl. As a consequence, cytosolic proteins are permanently exposed to low water activity and highly ionic conditions. In non-adapted systems, such conditions would promote protein aggregation, precipitation, and denaturation. In contrast, in vitro studies showed that proteins from extreme halophilic cells are themselves obligate halophiles. In this paper, adaptation via dynamics to low-salt stress in H. salinarum cells was measured by neutron scattering experiments coupled with microbiological characterization. The molecular dynamic properties of a proteome represent a good indicator for environmental adaptation and the neutron/microbiology approach has been shown to be well tailored to characterize these modifications. In their natural se...
Physical chemistry chemical physics : PCCP, Jan 7, 2015
We used small-angle neutron scattering (SANS) to study the effects of high hydrostatic pressure o... more We used small-angle neutron scattering (SANS) to study the effects of high hydrostatic pressure on the structure of human acetylcholinesterase (hAChE). At atmospheric pressure, our SANS results obtained on D11 at ILL (Grenoble, France) give a radius of gyration close to that calculated for a mixture of monomers, dimers and tetramers of the enzyme, suggesting a good agreement between hAChE crystal structure and its conformation in solution. Applying high pressure to the sample we found a global compression of about 11% of the enzyme up to a pressure of 900 bar and then again an extension up to 2.1 kbar indicating unfolding of the tertiary structure due to a molten globule (MG) state. On the other hand, we studied the influence of pressure up to 6 kbar on the dynamics of this enzyme, on the backscattering spectrometer IN13 at ILL. For the first time, we used elastic incoherent neutron scattering (EINS) to probe the differences between hAChE in its folded state (N), its high-pressure i...
Journal of the Royal Society, Interface / the Royal Society, Jan 6, 2014
It is a long debated question whether catalytic activities of enzymes, which lie on the milliseco... more It is a long debated question whether catalytic activities of enzymes, which lie on the millisecond timescale, are possibly already reflected in variations in atomic thermal fluctuations on the pico- to nanosecond timescale. To shed light on this puzzle, the enzyme human acetylcholinesterase in its wild-type form and complexed with the inhibitor huperzine A were investigated by various neutron scattering techniques and molecular dynamics simulations. Previous results on elastic neutron scattering at various timescales and simulations suggest that dynamical processes are not affected on average by the presence of the ligand within the considered time ranges between 10 ps and 1 ns. In the work presented here, the focus was laid on quasi-elastic (QENS) and inelastic neutron scattering (INS). These techniques give access to different kinds of individual diffusive motions and to the density of states of collective motions at the sub-picoseconds timescale. Hence, they permit going beyond ...
The influence of high hydrostatic pressure on the internal sub-nanosecond dynamics of highly conc... more The influence of high hydrostatic pressure on the internal sub-nanosecond dynamics of highly concentrated lysozyme in aqueous solutions was studied by elastic incoherent neutron scattering (EINS) up to pressures of 4 kbar. We have found, with increasing pressure, a reduction in the dynamics of H atoms of folded lysozyme, suggesting a loss in protein mobility that follows a change in the local energy landscape upon the increase in packing density. Moreover, the amplitude of the protein fluctuations depends drastically on the protein concentration, and protein structural and interaction parameters as well as the dynamical properties are affected by pressure in a nonlinear way. A significant reduction of the mean squared displacement of H atoms occurs already at rather low pressures of a few hundred bars for lysozyme in bulk water solution. This trend is lifted at ∼2 kbar, which is probably due to a solvent-mediated effect. Conversely, for high protein concentrations (e.g., 160 mg mL(-1)), that is, under strong self-crowding conditions, as they are also encountered in the biological cell, strong restriction of the dynamics of protein motions takes place, reducing the mean squared displacement of H atoms by 60% and rendering its pressure dependence almost negligible. These results are also important for understanding the pressure stability of highly concentrated protein solutions in organisms thriving under hydrostatic pressure conditions such as in the deep sea, where pressures up to the kbar level are reached.
Enzymes are animated by a hierarchy of motions occurring on time scales that span more than 15 or... more Enzymes are animated by a hierarchy of motions occurring on time scales that span more than 15 orders of magnitude from femtoseconds (10(-15) s) to several minutes. As a consequence, an enzyme is characterized by a large number of conformations, so-called conformational substates that interconvert via molecular motions. The energy landscapes of these macromolecules are very complex, and many conformations are separated by only small energy barriers. Movements at this level are fast thermal atomic motions occurring on a time scale between 10(-7) and 10(-12) s, which are experimentally accessible by incoherent neutron scattering techniques. They correspond to local fluctuations within the molecule and are believed to act as coupling links for larger, conformational changes. Several questions related to this hierarchy of motions are a matter of very active research: which of the motions are involved in the biological functions of the macromolecule and are motions of different energy (and thus time) scale correlated? How does the distribution of motions change when an enzyme is inhibited? We report here on investigations of the enzyme human acetylcholinesterase, unliganded and in complex with the noncovalent inhibitor Huperzine A, by incoherent neutron scattering. Different time scales are explored to shed light on the interplay of enzyme activity, dynamics, and inhibition. Surprisingly the average molecular dynamics do not seem to be altered by the presence of the inhibitor used in this study within the considered time scales. The activation energy for the free and the inhibited form of the enzyme is moreover found to be almost identical despite changes of interactions inside the gorge, which leads to the active site of the enzyme.
Myelin is an insulating, multi-lamellar membrane structure wrapped around selected nerve axons. I... more Myelin is an insulating, multi-lamellar membrane structure wrapped around selected nerve axons. Increasing the speed of nerve impulses, it is crucial for the proper functioning of the vertebrate nervous system. Human neurodegenerative diseases, such as multiple sclerosis, are linked to damage to the myelin sheath through demyelination. Myelin exhibits a well defined subset of myelin-specific proteins, whose influence on membrane dynamics, i.e., myelin flexibility and stability, has not yet been explored in detail. In a first paper [W. Knoll, J. Peters, P. Kursula, Y. Gerelli, J. Ollivier, B. Demé, M. Telling, E. Kemner, and F. Natali, Soft Matter 10, 519 (2014)] we were able to spotlight, through neutron scattering experiments, the role of peripheral nervous system myelin proteins on membrane stability at room temperature. In particular, the myelin basic protein and peripheral myelin protein 2 were found to synergistically influence the membrane structure while keeping almost unchanged the membrane mobility. Further insight is provided by this work, in which we particularly address the investigation of the membrane flexibility in the low temperature regime. We evidence a different behavior suggesting that the proton dynamics is reduced by the addition of the myelin basic protein accompanied by negligible membrane structural changes. Moreover, we address the importance of correct sample preparation and characterization for the success of the experiment and for the reliability of the obtained results.
ABSTRACT Fixation is a key element for many clinical researches requiring long exposure time and ... more ABSTRACT Fixation is a key element for many clinical researches requiring long exposure time and resting of the tissue to avoid experimental artifacts; condition which is not easy achieved during in-vivo experiments. Several ex-vivo, e.g. post-mortem, fixation processes are commonly used, from chemical fixation to cryo-preserving methods, both having advantages and drawbacks and eventually affecting structural and dynamical properties of water within the tissue. In this paper we make use of neutron scattering technique to compare the dynamical properties of ex-vivo sections of cerebral bovine hemisphere preserved using formalin fixation and cryo-protection. Neutron scattering is a unique technique able to monitor water diffusion at atomic scale. Results suggest reduction of global water dynamics induced by the formalin fixation protocol at room temperature.
Myelin is a multilamellar membrane which, wrapping the nerve axons, increases the efficiency of n... more Myelin is a multilamellar membrane which, wrapping the nerve axons, increases the efficiency of nervous signal transmission. Indeed, the molecular components of the myelin sheath interact tightly with each other and molecules on the axonal surface to drive myelination, to keep both myelin and the axon intact, and to transduce signals from myelin to the axon and vice versa. Myelin is strongly affected in human demyelinating diseases in both the central and peripheral nervous system (CNS and PNS, respectively). Despite the presence of a well-defined set of myelin-specific proteins, little is known about the structure and the dynamics of these proteins, their interactions with the membrane and their influence on myelin stability. We present here the first neutron scattering results on the dynamics of the myelin sheath in PNS and of the interaction between its constituents. Specifically, the human P2 protein is shown to stabilize the lipid membrane upon binding to it.
ABSTRACT The majority of the biosphere is a high pressure environment. Around 70% of the marine b... more ABSTRACT The majority of the biosphere is a high pressure environment. Around 70% of the marine biosphere lies at depths below 1000 m, i.e. at pressures of 100 bars or higher. To survive in these environments, deep-biosphere organisms have adapted to life at high pressure. In vitro studies showed that the activity of certain proteins originating from deep-sea organisms is less affected by high pres-sure than that of enzymes from surface organisms [1–3]. However, the genetic and structural bases for this increased pressure resistance are still unknown. Elastic incoherent neutron scattering studies, which provide access to information about molecular dynamics, constitute a very promising approach to decipher the struc-tural adaptation in proteins living under high pressure. This approach has been used in the past to investigate the adaptation of biological systems to temperature and salinity and proved to be essential and complementary to structural studies. Here first investigations of high pressure effects on cell dynamics are presented using Thermococcales as models.
Analysis of Quasi-elastic Neutron Scattering (QENS) data of complex systems such as biological or... more Analysis of Quasi-elastic Neutron Scattering (QENS) data of complex systems such as biological or soft matter samples in a comprehensive and explicit way often requires great efforts. Most popular software only allows to fit spectra originating from one single instrument and does not permit to extract parameters from a model that is fitted simultaneously to data taken at different instrumental resolutions. We present here a new program, mQfit (multiple QENS dataset fitting), that enables to fit QENS data taken at different spectrometers (with typical resolutions between 0.01 and 0.1 meV) and momentum transfer ranges. This allows drastically reducing the number of fitting parameters. The routine is implemented with a user friendly Graphical User's Interface (GUI), and freely available. As an example, we will present results obtained on E. coli bacterial pellets, and compare them to values published in the literature. This is an Open Access article distributed under the terms of the Creative Commons Attribution License 4.0, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Nuclear Instruments & Methods in Physics Research Section a-Accelerators Spectrometers Detectors and Associated Equipment, 2004
Recent developments of the VITESS Monte Carlo software package for simulation of neutron scatteri... more Recent developments of the VITESS Monte Carlo software package for simulation of neutron scattering instruments allow for the computation of neutronic systems of very complex geometry. For example, the module 'supermirror ensemble' simulates a number of supermirror plane sections in any geometry, including spin dependent reflectivity and absorption. This module was intensively used in the optimisation of the bi-spectral extraction system for the new guide hall of BENSC at HMI. It was also used for simulations of beam splitter polarizing cavities at BENSC. Another example is the module 'Fermi chopper' which simulates real three-dimensional slit packages with no analytic approximations. It will also be shown that this latter module has been very successfully bench-marked with HET/ISIS experimental data and is consistent with analytic theory. Finally, we will present a sophisticated Monte Carlo simulation study of a time-focused pulsed source crystal analyzer spectrometer prototype, which is planned to be realized in a test at IPNS. A short account will be given of this example illustrating the high performance of the VITESS simulation package. r
In this work we investigate, by means of elastic neutron scattering, the pressure dependence of m... more In this work we investigate, by means of elastic neutron scattering, the pressure dependence of mean square displacements (MSD) of hydrogen atoms of deeply cooled water confined in the pores of a three-dimensional disordered SiO2 xerogel; experiments have been performed at 250 and 210 K from atmospheric pressure to 1200 bar. The "pressure anomaly" of supercooled water (i.e., a mean square displacement increase with increasing pressure) is observed in our sample at both temperatures; however, contrary to previous simulation results and to the experimental trend observed in bulk water, the pressure effect is smaller at lower (210 K) than at higher (250 K) temperature. Elastic neutron scattering results are complemented by differential scanning calorimetry data that put in evidence, besides the glass transition at about 170 K, a first-order-like endothermic transition occurring at about 230 K that, in view of the neutron scattering results, can be attributed to a liquid-liquid crossover. Our results give experimental evidence for the presence, in deeply cooled confined water, of a crossover occurring at about 230 K (at ambient pressure) from a liquid phase predominant at 210 K to another liquid phase predominant at 250 K; therefore, they are fully consistent with the liquid-liquid transition hypothesis.
Diffusion is the primary mechanism for movement of lipids and proteins in the lateral direction o... more Diffusion is the primary mechanism for movement of lipids and proteins in the lateral direction of a biological membrane. In this paper we have used quasi-elastic neutron scattering to examine the diffusion process of lipid molecules in fluid DMPC membranes. We found that the motion over length scales greater than the lipid diameter could be characterized as a continuous diffusion process, with a diffusion coefficient of D ¼ 64 Â 10 À12 m 2 /s. The continuous diffusion model has been successfully used in the past to describe the motion of lipid over long length scales. However, the focus of this measurement was to determine how the character of the molecular motion changes on length scales shorter than the nearest neighbour distance. At very short length scales (<2.37 A), we see first experimental evidence for a short-range flow-like ballistic motion.
The myelin sheath is a tightly packed, multilayered membrane structure wrapped around selected ne... more The myelin sheath is a tightly packed, multilayered membrane structure wrapped around selected nerve axons in the central and the peripheral nervous system. Because of its electrical insulation of the axons, which allows fast, saltatory nerve impulse conduction, myelin is crucial for the proper functioning of the vertebrate nervous system. A subset of myelin-specific proteins is well-defined, but their influence on membrane dynamics, i.e. myelin stability, has not yet been explored in detail. We investigated the structure and the dynamics of reconstituted myelin membranes on a pico- to nanosecond timescale, influenced by myelin basic protein (MBP) and myelin protein 2 (P2), using neutron diffraction and quasi-elastic neutron scattering. A model for the scattering function describing molecular lipid motions is suggested. Although dynamical properties are not affected significantly by MBP and P2 proteins, they act in a highly synergistic manner influencing the membrane structure.
The effects of high hydrostatic pressure on the structure and dynamics of model membrane systems ... more The effects of high hydrostatic pressure on the structure and dynamics of model membrane systems were investigated using neutron scattering. Diffraction experiments show shifts of the pre- and main-phase transitions of multilamellar vesicles of 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) to higher temperatures with increased pressure which are close to results observed previously by other techniques, namely (10.4 ± 1.0) K kbar(-1) and (20.0 ± 0.5) K kbar(-1) for the two transitions. Backscattering spectroscopy reveals that the mean square displacements in the liquid phase are about 10% smaller at 300 bar and about 20% smaller at 600 bar compared to atmospheric pressure, whereas in the gel phase below the main phase transition the mean square displacements show a smaller difference in the dynamics of the three pressure values within the studied pressure range.
In 1998, a prototype of a time-of-flight (TOF) powder diffractometer was built at KFKI in Budapes... more In 1998, a prototype of a time-of-flight (TOF) powder diffractometer was built at KFKI in Budapest in collaboration with the Hahn-Meitner-Institut (HMI) in Berlin. At a reactor source the neutron pulses are produced by a chopper system, which allows for shorter pulses than those ...
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2006
This work is part of a series of papers [H.N. Bordallo, G. Zsigmond, J.D.M. Champion, Physica B 3... more This work is part of a series of papers [H.N. Bordallo, G. Zsigmond, J.D.M. Champion, Physica B 350 (2004) e717; J. Peters, Nucl. Instr. and Meth. A 540 (2005) 419] about benchmarking studies related to Fermi choppers (FC) used for pulse shaping of neutron scattering instruments. Here, we discuss the comparison of simulated and analytical results to experimental data of
Apolipoprotein B100 (apoB100)-containing plasma lipoproteins (LDL and VLDL) supply tissues and ce... more Apolipoprotein B100 (apoB100)-containing plasma lipoproteins (LDL and VLDL) supply tissues and cells with cholesterol and fat. During lipolytic conversion from VLDL to LDL the size and chemical composition of the particles change, but the apoB100 molecule remains bound to the lipids and regulates the receptor mediated uptake. The molecular physical parameters which control lipoprotein remodeling and enable particle stabilization by apoB100 are largely unknown. Here, we have compared the molecular dynamics and elasticities of VLDL and LDL derived by elastic neutron scattering temperature scans. We have determined thermal motions, dynamical transitions, and molecular fluctuations, which reflect the temperature-dependent motional coupling between lipid and protein. Our results revealed that lipoprotein particles are extremely soft and flexible. We found substantial differences in the molecular resiliences of lipoproteins, especially at higher temperatures. These discrepancies not only can be explained in terms of lipid composition and mobility but also suggest that apoB100 displays different dynamics dependent on the lipoprotein it is bound to. Hence, we suppose that the inherent conformational flexibility of apoB100 permits particle stabilization upon lipid exchange, whereas the dynamic coupling between protein and lipids might be a key determinant for lipoprotein conversion and atherogenicity.
Extremophiles : life under extreme conditions, Jan 16, 2015
Halobacterium salinarum is an extreme halophile archaeon with an absolute requirement for a multi... more Halobacterium salinarum is an extreme halophile archaeon with an absolute requirement for a multimolar salt environment. It accumulates molar concentrations of KCl in the cytosol to counterbalance the external osmotic pressure imposed by the molar NaCl. As a consequence, cytosolic proteins are permanently exposed to low water activity and highly ionic conditions. In non-adapted systems, such conditions would promote protein aggregation, precipitation, and denaturation. In contrast, in vitro studies showed that proteins from extreme halophilic cells are themselves obligate halophiles. In this paper, adaptation via dynamics to low-salt stress in H. salinarum cells was measured by neutron scattering experiments coupled with microbiological characterization. The molecular dynamic properties of a proteome represent a good indicator for environmental adaptation and the neutron/microbiology approach has been shown to be well tailored to characterize these modifications. In their natural se...
Physical chemistry chemical physics : PCCP, Jan 7, 2015
We used small-angle neutron scattering (SANS) to study the effects of high hydrostatic pressure o... more We used small-angle neutron scattering (SANS) to study the effects of high hydrostatic pressure on the structure of human acetylcholinesterase (hAChE). At atmospheric pressure, our SANS results obtained on D11 at ILL (Grenoble, France) give a radius of gyration close to that calculated for a mixture of monomers, dimers and tetramers of the enzyme, suggesting a good agreement between hAChE crystal structure and its conformation in solution. Applying high pressure to the sample we found a global compression of about 11% of the enzyme up to a pressure of 900 bar and then again an extension up to 2.1 kbar indicating unfolding of the tertiary structure due to a molten globule (MG) state. On the other hand, we studied the influence of pressure up to 6 kbar on the dynamics of this enzyme, on the backscattering spectrometer IN13 at ILL. For the first time, we used elastic incoherent neutron scattering (EINS) to probe the differences between hAChE in its folded state (N), its high-pressure i...
Journal of the Royal Society, Interface / the Royal Society, Jan 6, 2014
It is a long debated question whether catalytic activities of enzymes, which lie on the milliseco... more It is a long debated question whether catalytic activities of enzymes, which lie on the millisecond timescale, are possibly already reflected in variations in atomic thermal fluctuations on the pico- to nanosecond timescale. To shed light on this puzzle, the enzyme human acetylcholinesterase in its wild-type form and complexed with the inhibitor huperzine A were investigated by various neutron scattering techniques and molecular dynamics simulations. Previous results on elastic neutron scattering at various timescales and simulations suggest that dynamical processes are not affected on average by the presence of the ligand within the considered time ranges between 10 ps and 1 ns. In the work presented here, the focus was laid on quasi-elastic (QENS) and inelastic neutron scattering (INS). These techniques give access to different kinds of individual diffusive motions and to the density of states of collective motions at the sub-picoseconds timescale. Hence, they permit going beyond ...
The influence of high hydrostatic pressure on the internal sub-nanosecond dynamics of highly conc... more The influence of high hydrostatic pressure on the internal sub-nanosecond dynamics of highly concentrated lysozyme in aqueous solutions was studied by elastic incoherent neutron scattering (EINS) up to pressures of 4 kbar. We have found, with increasing pressure, a reduction in the dynamics of H atoms of folded lysozyme, suggesting a loss in protein mobility that follows a change in the local energy landscape upon the increase in packing density. Moreover, the amplitude of the protein fluctuations depends drastically on the protein concentration, and protein structural and interaction parameters as well as the dynamical properties are affected by pressure in a nonlinear way. A significant reduction of the mean squared displacement of H atoms occurs already at rather low pressures of a few hundred bars for lysozyme in bulk water solution. This trend is lifted at ∼2 kbar, which is probably due to a solvent-mediated effect. Conversely, for high protein concentrations (e.g., 160 mg mL(-1)), that is, under strong self-crowding conditions, as they are also encountered in the biological cell, strong restriction of the dynamics of protein motions takes place, reducing the mean squared displacement of H atoms by 60% and rendering its pressure dependence almost negligible. These results are also important for understanding the pressure stability of highly concentrated protein solutions in organisms thriving under hydrostatic pressure conditions such as in the deep sea, where pressures up to the kbar level are reached.
Enzymes are animated by a hierarchy of motions occurring on time scales that span more than 15 or... more Enzymes are animated by a hierarchy of motions occurring on time scales that span more than 15 orders of magnitude from femtoseconds (10(-15) s) to several minutes. As a consequence, an enzyme is characterized by a large number of conformations, so-called conformational substates that interconvert via molecular motions. The energy landscapes of these macromolecules are very complex, and many conformations are separated by only small energy barriers. Movements at this level are fast thermal atomic motions occurring on a time scale between 10(-7) and 10(-12) s, which are experimentally accessible by incoherent neutron scattering techniques. They correspond to local fluctuations within the molecule and are believed to act as coupling links for larger, conformational changes. Several questions related to this hierarchy of motions are a matter of very active research: which of the motions are involved in the biological functions of the macromolecule and are motions of different energy (and thus time) scale correlated? How does the distribution of motions change when an enzyme is inhibited? We report here on investigations of the enzyme human acetylcholinesterase, unliganded and in complex with the noncovalent inhibitor Huperzine A, by incoherent neutron scattering. Different time scales are explored to shed light on the interplay of enzyme activity, dynamics, and inhibition. Surprisingly the average molecular dynamics do not seem to be altered by the presence of the inhibitor used in this study within the considered time scales. The activation energy for the free and the inhibited form of the enzyme is moreover found to be almost identical despite changes of interactions inside the gorge, which leads to the active site of the enzyme.
Myelin is an insulating, multi-lamellar membrane structure wrapped around selected nerve axons. I... more Myelin is an insulating, multi-lamellar membrane structure wrapped around selected nerve axons. Increasing the speed of nerve impulses, it is crucial for the proper functioning of the vertebrate nervous system. Human neurodegenerative diseases, such as multiple sclerosis, are linked to damage to the myelin sheath through demyelination. Myelin exhibits a well defined subset of myelin-specific proteins, whose influence on membrane dynamics, i.e., myelin flexibility and stability, has not yet been explored in detail. In a first paper [W. Knoll, J. Peters, P. Kursula, Y. Gerelli, J. Ollivier, B. Demé, M. Telling, E. Kemner, and F. Natali, Soft Matter 10, 519 (2014)] we were able to spotlight, through neutron scattering experiments, the role of peripheral nervous system myelin proteins on membrane stability at room temperature. In particular, the myelin basic protein and peripheral myelin protein 2 were found to synergistically influence the membrane structure while keeping almost unchanged the membrane mobility. Further insight is provided by this work, in which we particularly address the investigation of the membrane flexibility in the low temperature regime. We evidence a different behavior suggesting that the proton dynamics is reduced by the addition of the myelin basic protein accompanied by negligible membrane structural changes. Moreover, we address the importance of correct sample preparation and characterization for the success of the experiment and for the reliability of the obtained results.
ABSTRACT Fixation is a key element for many clinical researches requiring long exposure time and ... more ABSTRACT Fixation is a key element for many clinical researches requiring long exposure time and resting of the tissue to avoid experimental artifacts; condition which is not easy achieved during in-vivo experiments. Several ex-vivo, e.g. post-mortem, fixation processes are commonly used, from chemical fixation to cryo-preserving methods, both having advantages and drawbacks and eventually affecting structural and dynamical properties of water within the tissue. In this paper we make use of neutron scattering technique to compare the dynamical properties of ex-vivo sections of cerebral bovine hemisphere preserved using formalin fixation and cryo-protection. Neutron scattering is a unique technique able to monitor water diffusion at atomic scale. Results suggest reduction of global water dynamics induced by the formalin fixation protocol at room temperature.
Myelin is a multilamellar membrane which, wrapping the nerve axons, increases the efficiency of n... more Myelin is a multilamellar membrane which, wrapping the nerve axons, increases the efficiency of nervous signal transmission. Indeed, the molecular components of the myelin sheath interact tightly with each other and molecules on the axonal surface to drive myelination, to keep both myelin and the axon intact, and to transduce signals from myelin to the axon and vice versa. Myelin is strongly affected in human demyelinating diseases in both the central and peripheral nervous system (CNS and PNS, respectively). Despite the presence of a well-defined set of myelin-specific proteins, little is known about the structure and the dynamics of these proteins, their interactions with the membrane and their influence on myelin stability. We present here the first neutron scattering results on the dynamics of the myelin sheath in PNS and of the interaction between its constituents. Specifically, the human P2 protein is shown to stabilize the lipid membrane upon binding to it.
ABSTRACT The majority of the biosphere is a high pressure environment. Around 70% of the marine b... more ABSTRACT The majority of the biosphere is a high pressure environment. Around 70% of the marine biosphere lies at depths below 1000 m, i.e. at pressures of 100 bars or higher. To survive in these environments, deep-biosphere organisms have adapted to life at high pressure. In vitro studies showed that the activity of certain proteins originating from deep-sea organisms is less affected by high pres-sure than that of enzymes from surface organisms [1–3]. However, the genetic and structural bases for this increased pressure resistance are still unknown. Elastic incoherent neutron scattering studies, which provide access to information about molecular dynamics, constitute a very promising approach to decipher the struc-tural adaptation in proteins living under high pressure. This approach has been used in the past to investigate the adaptation of biological systems to temperature and salinity and proved to be essential and complementary to structural studies. Here first investigations of high pressure effects on cell dynamics are presented using Thermococcales as models.
Analysis of Quasi-elastic Neutron Scattering (QENS) data of complex systems such as biological or... more Analysis of Quasi-elastic Neutron Scattering (QENS) data of complex systems such as biological or soft matter samples in a comprehensive and explicit way often requires great efforts. Most popular software only allows to fit spectra originating from one single instrument and does not permit to extract parameters from a model that is fitted simultaneously to data taken at different instrumental resolutions. We present here a new program, mQfit (multiple QENS dataset fitting), that enables to fit QENS data taken at different spectrometers (with typical resolutions between 0.01 and 0.1 meV) and momentum transfer ranges. This allows drastically reducing the number of fitting parameters. The routine is implemented with a user friendly Graphical User's Interface (GUI), and freely available. As an example, we will present results obtained on E. coli bacterial pellets, and compare them to values published in the literature. This is an Open Access article distributed under the terms of the Creative Commons Attribution License 4.0, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Nuclear Instruments & Methods in Physics Research Section a-Accelerators Spectrometers Detectors and Associated Equipment, 2004
Recent developments of the VITESS Monte Carlo software package for simulation of neutron scatteri... more Recent developments of the VITESS Monte Carlo software package for simulation of neutron scattering instruments allow for the computation of neutronic systems of very complex geometry. For example, the module 'supermirror ensemble' simulates a number of supermirror plane sections in any geometry, including spin dependent reflectivity and absorption. This module was intensively used in the optimisation of the bi-spectral extraction system for the new guide hall of BENSC at HMI. It was also used for simulations of beam splitter polarizing cavities at BENSC. Another example is the module 'Fermi chopper' which simulates real three-dimensional slit packages with no analytic approximations. It will also be shown that this latter module has been very successfully bench-marked with HET/ISIS experimental data and is consistent with analytic theory. Finally, we will present a sophisticated Monte Carlo simulation study of a time-focused pulsed source crystal analyzer spectrometer prototype, which is planned to be realized in a test at IPNS. A short account will be given of this example illustrating the high performance of the VITESS simulation package. r
In this work we investigate, by means of elastic neutron scattering, the pressure dependence of m... more In this work we investigate, by means of elastic neutron scattering, the pressure dependence of mean square displacements (MSD) of hydrogen atoms of deeply cooled water confined in the pores of a three-dimensional disordered SiO2 xerogel; experiments have been performed at 250 and 210 K from atmospheric pressure to 1200 bar. The &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;quot;pressure anomaly&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;quot; of supercooled water (i.e., a mean square displacement increase with increasing pressure) is observed in our sample at both temperatures; however, contrary to previous simulation results and to the experimental trend observed in bulk water, the pressure effect is smaller at lower (210 K) than at higher (250 K) temperature. Elastic neutron scattering results are complemented by differential scanning calorimetry data that put in evidence, besides the glass transition at about 170 K, a first-order-like endothermic transition occurring at about 230 K that, in view of the neutron scattering results, can be attributed to a liquid-liquid crossover. Our results give experimental evidence for the presence, in deeply cooled confined water, of a crossover occurring at about 230 K (at ambient pressure) from a liquid phase predominant at 210 K to another liquid phase predominant at 250 K; therefore, they are fully consistent with the liquid-liquid transition hypothesis.
Diffusion is the primary mechanism for movement of lipids and proteins in the lateral direction o... more Diffusion is the primary mechanism for movement of lipids and proteins in the lateral direction of a biological membrane. In this paper we have used quasi-elastic neutron scattering to examine the diffusion process of lipid molecules in fluid DMPC membranes. We found that the motion over length scales greater than the lipid diameter could be characterized as a continuous diffusion process, with a diffusion coefficient of D ¼ 64 Â 10 À12 m 2 /s. The continuous diffusion model has been successfully used in the past to describe the motion of lipid over long length scales. However, the focus of this measurement was to determine how the character of the molecular motion changes on length scales shorter than the nearest neighbour distance. At very short length scales (<2.37 A), we see first experimental evidence for a short-range flow-like ballistic motion.
The myelin sheath is a tightly packed, multilayered membrane structure wrapped around selected ne... more The myelin sheath is a tightly packed, multilayered membrane structure wrapped around selected nerve axons in the central and the peripheral nervous system. Because of its electrical insulation of the axons, which allows fast, saltatory nerve impulse conduction, myelin is crucial for the proper functioning of the vertebrate nervous system. A subset of myelin-specific proteins is well-defined, but their influence on membrane dynamics, i.e. myelin stability, has not yet been explored in detail. We investigated the structure and the dynamics of reconstituted myelin membranes on a pico- to nanosecond timescale, influenced by myelin basic protein (MBP) and myelin protein 2 (P2), using neutron diffraction and quasi-elastic neutron scattering. A model for the scattering function describing molecular lipid motions is suggested. Although dynamical properties are not affected significantly by MBP and P2 proteins, they act in a highly synergistic manner influencing the membrane structure.
The effects of high hydrostatic pressure on the structure and dynamics of model membrane systems ... more The effects of high hydrostatic pressure on the structure and dynamics of model membrane systems were investigated using neutron scattering. Diffraction experiments show shifts of the pre- and main-phase transitions of multilamellar vesicles of 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) to higher temperatures with increased pressure which are close to results observed previously by other techniques, namely (10.4 ± 1.0) K kbar(-1) and (20.0 ± 0.5) K kbar(-1) for the two transitions. Backscattering spectroscopy reveals that the mean square displacements in the liquid phase are about 10% smaller at 300 bar and about 20% smaller at 600 bar compared to atmospheric pressure, whereas in the gel phase below the main phase transition the mean square displacements show a smaller difference in the dynamics of the three pressure values within the studied pressure range.
In 1998, a prototype of a time-of-flight (TOF) powder diffractometer was built at KFKI in Budapes... more In 1998, a prototype of a time-of-flight (TOF) powder diffractometer was built at KFKI in Budapest in collaboration with the Hahn-Meitner-Institut (HMI) in Berlin. At a reactor source the neutron pulses are produced by a chopper system, which allows for shorter pulses than those ...
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2006
This work is part of a series of papers [H.N. Bordallo, G. Zsigmond, J.D.M. Champion, Physica B 3... more This work is part of a series of papers [H.N. Bordallo, G. Zsigmond, J.D.M. Champion, Physica B 350 (2004) e717; J. Peters, Nucl. Instr. and Meth. A 540 (2005) 419] about benchmarking studies related to Fermi choppers (FC) used for pulse shaping of neutron scattering instruments. Here, we discuss the comparison of simulated and analytical results to experimental data of
Apolipoprotein B100 (apoB100)-containing plasma lipoproteins (LDL and VLDL) supply tissues and ce... more Apolipoprotein B100 (apoB100)-containing plasma lipoproteins (LDL and VLDL) supply tissues and cells with cholesterol and fat. During lipolytic conversion from VLDL to LDL the size and chemical composition of the particles change, but the apoB100 molecule remains bound to the lipids and regulates the receptor mediated uptake. The molecular physical parameters which control lipoprotein remodeling and enable particle stabilization by apoB100 are largely unknown. Here, we have compared the molecular dynamics and elasticities of VLDL and LDL derived by elastic neutron scattering temperature scans. We have determined thermal motions, dynamical transitions, and molecular fluctuations, which reflect the temperature-dependent motional coupling between lipid and protein. Our results revealed that lipoprotein particles are extremely soft and flexible. We found substantial differences in the molecular resiliences of lipoproteins, especially at higher temperatures. These discrepancies not only can be explained in terms of lipid composition and mobility but also suggest that apoB100 displays different dynamics dependent on the lipoprotein it is bound to. Hence, we suppose that the inherent conformational flexibility of apoB100 permits particle stabilization upon lipid exchange, whereas the dynamic coupling between protein and lipids might be a key determinant for lipoprotein conversion and atherogenicity.
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Papers by Judith Peters