Nanodiscs are self-assembled $10 nm particles composed of lipid bilayer patches, stabilized by he... more Nanodiscs are self-assembled $10 nm particles composed of lipid bilayer patches, stabilized by helical amphipathic belt proteins. The size, monodispersity and well-defined structure make the nanodiscs a popular model for the biological cell membrane, especially for structural and functional studies of membrane proteins. The structures and properties of nanodiscs made of zwitterionic lipids are well known. However, the biological cell membrane is negatively charged and thus nanodiscs containing anionic lipids should provide a better mimic of the native environment for membrane proteins. Despite the broad potential of charged nanodiscs, a systematic study of the influence of charged lipids on the nanodisc structure and stability has not yet been accomplished. In this paper, binary systems of zwitterionic DMPC mixed with the anionic lipids DMPG or DMPA or with the cationic synthetic DMTAP are used to prepare negatively and positively charged nanodiscs, respectively. Size exclusion chromatography analysis shows that nanodiscs can be prepared with high yield at all compositions of DMPC and DMPG, while mixtures of DMPC with either DMPA or DMTAP impair nanodisc formation. The presence of DMPG improves the stability of the nanodisc, both thermally and over time upon storage at À20 C, as compared to pure DMPC nanodiscs. This stabilization is attributed to favourable electrostatic interactions between the anionic head of DMPG and cationic charges of the belt protein and internanodisc repulsion that prevents aggregation of nanodiscs. In contrast, even small fractions of DMPA result in a faster degradation at À20 C. These results suggest that the mixing of DMPC and DMPG provides nanodiscs that are better suited for studies of the function and structure of membrane proteins not only due to their inherent charge but also due to their improved thermal and storage stability compared to pure DMPC nanodiscs.
Page 1. 4866 J. Phys. Chem. 1995,99, 4866-4874 Interaction of ABA Block Copolymers with Ionic Sur... more Page 1. 4866 J. Phys. Chem. 1995,99, 4866-4874 Interaction of ABA Block Copolymers with Ionic Surfactants: Influence on Micellization and Gelation E. Hecht,? K. Mortensen: M. Gradzielski? and H. Hoffmann"" University of ...
... Previously, the crystal structures have been reported for X = PF Ô[1], AsFg[2], CJIO4, Re04[3... more ... Previously, the crystal structures have been reported for X = PF Ô[1], AsFg[2], CJIO4, Re04[3], BrÛ4, FS0 3 [4]and BF 4 [ 5 ] . This work présents the structures at room température for X = TaF5, NO3 and CF3SO3 as determined by X-ray dif-fraction. ...
Small-angle X-ray and neutron scattering have become increasingly popular owing to improvements i... more Small-angle X-ray and neutron scattering have become increasingly popular owing to improvements in instrumentation and developments in data analysis, sample handling and sample preparation. For some time, it has been suggested that a more systematic approach to the quantification of the information content in small-angle scattering data would allow for a more optimal experiment planning and a more reliable data analysis. In the present article, it is shown how ray-tracing techniques in combination with a statistically rigorous data analysis provide an appropriate platform for such a systematic quantification of the information content in scattering data. As examples of applications, it is shown how the exposure time at different instrumental settings or contrast situations can be optimally prioritized in an experiment. Also, the gain in information by combining small-angle X-ray and neutron scattering is assessed. While solution small-angle scattering data of proteins and protein–li...
SANS studies on the relaxation of an amorphous polymer melt is reported. Just after the uniaxial ... more SANS studies on the relaxation of an amorphous polymer melt is reported. Just after the uniaxial elongation the chains deform affinely. Shortly thereafter the SANS results give evidence of chain contraction. Some randomization is observed long before the reptation time is reached.
The critical tluctuations of a polymer blend (PVME/d-PS) were investigated by neutron small-angle... more The critical tluctuations of a polymer blend (PVME/d-PS) were investigated by neutron small-angle scattering. A mean-field behavior was observed, except in a region very close to the critical temperature where a transition to an Ising-type behavior occurs. The width of this ...
Calcium dodecyl sulfate (CDS) is insoluble both in water and in alcohols at room temperature. How... more Calcium dodecyl sulfate (CDS) is insoluble both in water and in alcohols at room temperature. However, it can be dissolved up to high concentrations in mixtures of water and ethanol, propanol, or butanol. No liquid-crystalline phases are formed with ethanol and propanol at 25°C but are observed with butanol at higher concentrations of CDS. With pentanol and hexanol, lamellar phases are observed, which can be swollen largely. Neutron scattering measurements of phases with a weight ratio CDS:hexanol) 1:1 show stiff lamellae in the concentration range of 1.5-25 wt % CDS. The repeat distance grows linearly with dilution. The effective thickness for the hydrocarbon part of the lamellae decreases to some extent at high CDS concentrations.
Structural changes of the RecA filament upon binding of cofactors have been investigated by small... more Structural changes of the RecA filament upon binding of cofactors have been investigated by small-angle neutron scattering. Both ATP and ADP increased the helical pitch of the RecA homopolymer, which is observed to be 7 nm in the absence of any cofactor. The binding of ATP altered the pitch to 9 nm, whereas the binding of ADP only produced a pitch of 8.2 nm. The pitch determined for the RecA complex with the ATP analog adenosine 5'-[gamma-thio]triphosphate was similar to that found with ATP. Thus, at least three, somewhat different. RecA helical filamentous structures may form in solution. The binding of DNA to RecA did not alter the pitch significantly, indicating that the cofactor binding is the determining factor for the size of the helical pitch of the RecA filament. We also found that elongation of the helical pitch is a necessary, but not a sufficient condition, for the coprotease activity of RecA. The presence of acetate or glutamate ions is also required. The pitch of the ADP.RecA filament is in agreement with that found in the crystal structure. This correlation indicates that this structure corresponds to that of the ADP.RecA filament in solution, although this is not the species active in recombination.
Solid State Communications, Vol. 33, pp. 11191125. Pergamon Press Ltd. 1980. Printed in Great Bri... more Solid State Communications, Vol. 33, pp. 11191125. Pergamon Press Ltd. 1980. Printed in Great Britain. THEPROPERTIESOF FIVEHIGHLYCONDUCTINGSALTS: (TMTSF)2X,X= PF,AsF, SbF, BF AND N0, DERIVED FROM TETRAMETHYLTETRASELENAFULVALENE ...
The growth of humic acids, prepared by a gentle method from two different kinds of soils (I and I... more The growth of humic acids, prepared by a gentle method from two different kinds of soils (I and II), has been studied using small-angle neutron scattering at an acidity corresponding to pH 5.0 and 0.10 M ionic strength (NaCl). Humic acids aggregate either to large clusters with a fractal dimension of 2.3 and an average diameter of 1720 A (I) or to clusters with an average diameter of 700 A (II). After storage for 2 days at 4 degrees C, the latter aggregates (II) formed a gel. In a step toward gelation, we observed cluster-cluster interaction from the neutron-scattering data in the form of a correlation peak. These differences in size can be explained by assuming that the smaller particles (II) are trapped into a nonequilibrium state characterized by the temperature-solvent condition. The importance of a humic acid gel network for the conservation of water and nutrients in the environment is discussed.
Nanodiscs are self-assembled $10 nm particles composed of lipid bilayer patches, stabilized by he... more Nanodiscs are self-assembled $10 nm particles composed of lipid bilayer patches, stabilized by helical amphipathic belt proteins. The size, monodispersity and well-defined structure make the nanodiscs a popular model for the biological cell membrane, especially for structural and functional studies of membrane proteins. The structures and properties of nanodiscs made of zwitterionic lipids are well known. However, the biological cell membrane is negatively charged and thus nanodiscs containing anionic lipids should provide a better mimic of the native environment for membrane proteins. Despite the broad potential of charged nanodiscs, a systematic study of the influence of charged lipids on the nanodisc structure and stability has not yet been accomplished. In this paper, binary systems of zwitterionic DMPC mixed with the anionic lipids DMPG or DMPA or with the cationic synthetic DMTAP are used to prepare negatively and positively charged nanodiscs, respectively. Size exclusion chromatography analysis shows that nanodiscs can be prepared with high yield at all compositions of DMPC and DMPG, while mixtures of DMPC with either DMPA or DMTAP impair nanodisc formation. The presence of DMPG improves the stability of the nanodisc, both thermally and over time upon storage at À20 C, as compared to pure DMPC nanodiscs. This stabilization is attributed to favourable electrostatic interactions between the anionic head of DMPG and cationic charges of the belt protein and internanodisc repulsion that prevents aggregation of nanodiscs. In contrast, even small fractions of DMPA result in a faster degradation at À20 C. These results suggest that the mixing of DMPC and DMPG provides nanodiscs that are better suited for studies of the function and structure of membrane proteins not only due to their inherent charge but also due to their improved thermal and storage stability compared to pure DMPC nanodiscs.
Page 1. 4866 J. Phys. Chem. 1995,99, 4866-4874 Interaction of ABA Block Copolymers with Ionic Sur... more Page 1. 4866 J. Phys. Chem. 1995,99, 4866-4874 Interaction of ABA Block Copolymers with Ionic Surfactants: Influence on Micellization and Gelation E. Hecht,? K. Mortensen: M. Gradzielski? and H. Hoffmann"" University of ...
... Previously, the crystal structures have been reported for X = PF Ô[1], AsFg[2], CJIO4, Re04[3... more ... Previously, the crystal structures have been reported for X = PF Ô[1], AsFg[2], CJIO4, Re04[3], BrÛ4, FS0 3 [4]and BF 4 [ 5 ] . This work présents the structures at room température for X = TaF5, NO3 and CF3SO3 as determined by X-ray dif-fraction. ...
Small-angle X-ray and neutron scattering have become increasingly popular owing to improvements i... more Small-angle X-ray and neutron scattering have become increasingly popular owing to improvements in instrumentation and developments in data analysis, sample handling and sample preparation. For some time, it has been suggested that a more systematic approach to the quantification of the information content in small-angle scattering data would allow for a more optimal experiment planning and a more reliable data analysis. In the present article, it is shown how ray-tracing techniques in combination with a statistically rigorous data analysis provide an appropriate platform for such a systematic quantification of the information content in scattering data. As examples of applications, it is shown how the exposure time at different instrumental settings or contrast situations can be optimally prioritized in an experiment. Also, the gain in information by combining small-angle X-ray and neutron scattering is assessed. While solution small-angle scattering data of proteins and protein–li...
SANS studies on the relaxation of an amorphous polymer melt is reported. Just after the uniaxial ... more SANS studies on the relaxation of an amorphous polymer melt is reported. Just after the uniaxial elongation the chains deform affinely. Shortly thereafter the SANS results give evidence of chain contraction. Some randomization is observed long before the reptation time is reached.
The critical tluctuations of a polymer blend (PVME/d-PS) were investigated by neutron small-angle... more The critical tluctuations of a polymer blend (PVME/d-PS) were investigated by neutron small-angle scattering. A mean-field behavior was observed, except in a region very close to the critical temperature where a transition to an Ising-type behavior occurs. The width of this ...
Calcium dodecyl sulfate (CDS) is insoluble both in water and in alcohols at room temperature. How... more Calcium dodecyl sulfate (CDS) is insoluble both in water and in alcohols at room temperature. However, it can be dissolved up to high concentrations in mixtures of water and ethanol, propanol, or butanol. No liquid-crystalline phases are formed with ethanol and propanol at 25°C but are observed with butanol at higher concentrations of CDS. With pentanol and hexanol, lamellar phases are observed, which can be swollen largely. Neutron scattering measurements of phases with a weight ratio CDS:hexanol) 1:1 show stiff lamellae in the concentration range of 1.5-25 wt % CDS. The repeat distance grows linearly with dilution. The effective thickness for the hydrocarbon part of the lamellae decreases to some extent at high CDS concentrations.
Structural changes of the RecA filament upon binding of cofactors have been investigated by small... more Structural changes of the RecA filament upon binding of cofactors have been investigated by small-angle neutron scattering. Both ATP and ADP increased the helical pitch of the RecA homopolymer, which is observed to be 7 nm in the absence of any cofactor. The binding of ATP altered the pitch to 9 nm, whereas the binding of ADP only produced a pitch of 8.2 nm. The pitch determined for the RecA complex with the ATP analog adenosine 5'-[gamma-thio]triphosphate was similar to that found with ATP. Thus, at least three, somewhat different. RecA helical filamentous structures may form in solution. The binding of DNA to RecA did not alter the pitch significantly, indicating that the cofactor binding is the determining factor for the size of the helical pitch of the RecA filament. We also found that elongation of the helical pitch is a necessary, but not a sufficient condition, for the coprotease activity of RecA. The presence of acetate or glutamate ions is also required. The pitch of the ADP.RecA filament is in agreement with that found in the crystal structure. This correlation indicates that this structure corresponds to that of the ADP.RecA filament in solution, although this is not the species active in recombination.
Solid State Communications, Vol. 33, pp. 11191125. Pergamon Press Ltd. 1980. Printed in Great Bri... more Solid State Communications, Vol. 33, pp. 11191125. Pergamon Press Ltd. 1980. Printed in Great Britain. THEPROPERTIESOF FIVEHIGHLYCONDUCTINGSALTS: (TMTSF)2X,X= PF,AsF, SbF, BF AND N0, DERIVED FROM TETRAMETHYLTETRASELENAFULVALENE ...
The growth of humic acids, prepared by a gentle method from two different kinds of soils (I and I... more The growth of humic acids, prepared by a gentle method from two different kinds of soils (I and II), has been studied using small-angle neutron scattering at an acidity corresponding to pH 5.0 and 0.10 M ionic strength (NaCl). Humic acids aggregate either to large clusters with a fractal dimension of 2.3 and an average diameter of 1720 A (I) or to clusters with an average diameter of 700 A (II). After storage for 2 days at 4 degrees C, the latter aggregates (II) formed a gel. In a step toward gelation, we observed cluster-cluster interaction from the neutron-scattering data in the form of a correlation peak. These differences in size can be explained by assuming that the smaller particles (II) are trapped into a nonequilibrium state characterized by the temperature-solvent condition. The importance of a humic acid gel network for the conservation of water and nutrients in the environment is discussed.
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