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Structural, dynamic and mechanical properties of POPC at low cholesterol concentration studied in pressure/temperature space.
Rappolt M, Vidal MF, Kriechbaum M, Steinhart M, Amenitsch H, Bernstorff S, Laggner P.
Institute of Biophysics and X-Ray Structure Research, Austrian Academy of Sciences, Schmiedlstrasse 6, 8042 Graz, Austria.
We have studied the structural, dynamic and mechanical properties of 1-palmitoyl-2-oleoyl- sn-glycero-3-phosphatidylcholine (POPC)/cholesterol binary mixtures by small-angle X-ray scattering. Our investigations were concentrated on the biologically most relevant pressure-temperature-cholesterol regime, i.e. the liquid crystalline phase and its phase boundary to the lamellar gel phase within a cholesterol concentration up to 25 mol%. From the dependence of the transition pressure we derived a value of 19 kJ/mol for the transition enthalpy Delta H(m) of POPC in excess water. With increasing cholesterol concentration, Delta H(m) drops to about 7 kJ/mol at 20 mol% cholesterol. Time-resolved pressure-scan (p-scan) and temperature-jump (T-jump) experiments reveal that at low cholesterol content (<5-8 mol%) the fluidity and also the bilayer compressibility increase remarkably. In contrast, at concentrations between 5 and 25 mol% cholesterol the bilayer becomes again more rigid and the lipid bilayer spacing increases about 2 A. Theses changes are attributed to the onset of phase separation between liquid disordered and liquid ordered phases. The fluid-fluid miscibility gap for this mono-unsaturated lecithin species is strongly enlarged compared with saturated lecithins.
PMID: 12582817 [PubMed - indexed for MEDLINE]
Solution structure of human and bovine beta(2)-glycoprotein I revealed by small-angle X-ray scattering.
Hammel M, Kriechbaum M, Gries A, Kostner GM, Laggner P, Prassl R.
Institute of Biophysics and X-ray Structure Research of the Austrian Academy of Sciences, Schmiedlstr. 6, A-8042 Graz, Austria.
beta(2)-Glycoprotein I (beta(2)GPI) is a highly glycosylated phospholipid-binding plasma protein comprised of four complement control protein (CCP) domains and a distinct fifth domain. The structural organisation of human and bovine beta(2)GPI in aqueous solution was studied by small-angle X-ray scattering (SAXS). Low-resolution models that match the SAXS experimental data best were independently constructed by three different ab initio 3D-reconstruction algorithms. Similar elongated S-shaped models with distinct side-arms, which were correlated to the position of the carbohydrate chains, were restored from all three algorithms. Due to an additional glycosylation site located on the CCP2 domain of bovine beta(2)GPI a small change in the characteristic SAXS parameters was observed, which coincided with results obtained from SDS-PAGE. In comparison to the human analogue the corresponding restored low-resolution models displayed a similar S-shape with less bending in the middle part. As the experimental SAXS curves fit poorly to the simulated scattering curves calculated from the crystallographic coordinates of human beta(2)GPI, the crystal structure was modified. First, additional carbohydrate residues missing from the crystal structure were modelled. Second, on the basis of the low-resolution models, the J-shaped crystal structure was rotated between CCP3 and CCP2 assuming the greatest interdomain flexibility between these domains. An S-shaped model with a tilt angle of approximately 60 degrees between CCP3 and CCP2 yielded the best fit to the experimental SAXS data. Since there is evidence that beta(2)GPI can adopt different conformations, which reveal distinct differences in autoantibody recognition, our data clearly point to a reorientation of the flexible domains, which may be an essential feature for binding of autoantibodies.
PMID: 12139935 [PubMed - indexed for MEDLINE]
SAXS investigation on aggregation phenomena in supercritical CO2.
Lo Celso F, Triolo A, Triolo F, Donato DI, Steinhart M, Kriechbaum M, Amenitsch H, Triolo R.
Dipartimento di Chimica-Fisica, Universita di Palermo, viale delle Scienze Parco d'Orleans II, 90128 Palermo, Italy.
Synchrotron Small-Angle X-Ray scattering (SAXS) measurements on aggregate formation of a Polyvinyl acetate- b-Perfluoro octyl acrylate (PVAc- b-PFOA) block copolymer in supercritical CO(2) are here reported. Experiments were carried out for a series of different thermodynamic conditions, changing the solvent density by profiling both the pressure at constant temperature and the temperature at constant pressure. This block copolymer and in general fluorocarbon-hydrocarbon di-blocks form aggregates depending on the value of CO(2) density. A sharp transition between monomers dissolved as random coils and micelles characterized by a solvophilic shell and a solvophobic core occurs when the CO(2) density reaches a critical value. Results of critical micellization density (CMD) derived from pressure and temperature ramps experiment along with the comparison with previous SANS results are here reported to give additional experimental support to the solvent density-driven aggregation process.
PMID: 15010952 [PubMed]
Studies of the structure and organization of cationic lipid bilayer membranes: calorimetric, spectroscopic, and x-ray diffraction studies of linear saturated P-O-ethyl phosphatidylcholines.
Lewis RN, Winter I, Kriechbaum M, Lohner K, McElhaney RN.
Department of Biochemistry, University of Alberta, Edmonton, Alberta T6G 2H7, Canada.
Differential scanning calorimetry, x-ray diffraction, and infrared and (31)P-nuclear magnetic resonance ((31)P-NMR) spectroscopy were used to examine the thermotropic phase behavior and organization of cationic model membranes composed of the P-O-ethyl esters of a homologous series of n-saturated 1,2-diacyl phosphatidylcholines (Et-PCs). Differential scanning calorimetry studies indicate that on heating, these lipids exhibit single highly energetic and cooperative endothermic transitions whose temperatures and enthalpies are higher than those of the corresponding phosphatidylcholines (PCs). Upon cooling, these Et-PCs exhibit two exothermic transitions at temperatures slightly below the single endotherm observed upon heating. These cooling exotherms have both been assigned to transitions between the liquid-crystalline and gel phases of these lipids by x-ray diffraction. The x-ray diffraction data also show that unlike the parent PCs, the chain-melting phase transition of these Et-PCs involves a direct transformation of a chain-interdigitated gel phase to the lamellar liquid-crystalline phase for the homologous series of n > or = 14. Our (31)P-NMR spectroscopic studies indicate that the rates of phosphate headgroup reorientation in both gel and liquid-crystalline phases of these lipids are comparable to those of the corresponding PC bilayers. However, the shape of the (31)P-NMR spectra observed in the interdigitated gel phase indicates that phosphate headgroup reorientation is subject to constraints that are not encountered in the non-interdigitated gel phases of parent PCs. The infrared spectroscopic data indicate that the Et-PCs adopt a very compact form of hydrocarbon chain packing in the interdigitated gel phase and that the polar/apolar interfacial regions of these bilayers are less hydrated than those of corresponding PC bilayers in both the gel and liquid-crystalline phases. Our results indicate that esterification of PC phosphate headgroups results in many alterations of bilayer physical properties aside from the endowment of a positively charged surface. This fact should be considered in assessing the interactions of these compounds with naturally occurring lipids and with other biological materials.
PMID: 11222294 [PubMed - indexed for MEDLINE]
X-ray studies on the interaction of the antimicrobial peptide gramicidin S with microbial lipid extracts: evidence for cubic phase formation.
Staudegger E, Prenner EJ, Kriechbaum M, Degovics G, Lewis RN, McElhaney RN, Lohner K.
Institut fur Biophysik und Rontgenstrukturforschung, Osterreichische Akademie der Wissenschaften, Steyrergasse 171VI, A-8010 Graz, Austria.
We have investigated the effect of the interaction of the antimicrobial peptide gramicidin S (GS) on the thermotropic phase behavior of model lipid bilayer membranes generated from the total membrane lipids of Acholeplasma laidlawii B and Escherichia coli. The A. laidlawii B membrane lipids consist primarily of neutral glycolipids and anionic phospholipids, while the E. coli inner membrane lipids consist exclusively of zwitterionic and anionic phospholipids. We show that the addition of GS at a lipid-to-peptide molar ratio of 25 strongly promotes the formation of bicontinuous inverted cubic phases in both of these lipid model membranes, predominantly of space group Pn3m. In addition, the presence of GS causes a thinning of the liquid-crystalline bilayer and a reduction in the lattice spacing of the inverted cubic phase which can form in the GS-free membrane lipid extracts at sufficiently high temperatures. This latter finding implies that GS potentiates the formation of an inverted cubic phase by increasing the negative curvature stress in the host lipid bilayer. This effect may be an important aspect of the permeabilization and eventual disruption of the lipid bilayer phase of biological membranes, which appears to be the mechanism by which GS kills bacterial cells and lysis erythrocytes.
PMID: 11018666 [PubMed - indexed for MEDLINE]
New evidence for gel-liquid crystalline phase coexistence in the ripple phase of phosphatidylcholines.
Rappolt M, Pabst G, Rapp G, Kriechbaum M, Amenitsch H, Krenn C, Bernstorff S, Laggner P.
Institute of Biophysics and X-ray Structure Research, Austrian Academy of Sciences, Graz. firstname.lastname@example.org
Experimental evidence supporting the hypothesis of gel-liquid crystalline phase coexistence in the stable ripple phase of diacylphosphatidylcholines has been obtained from time-resolved X-ray small- (SAXS) and wide-angle diffraction (WAXS) in the millisecond to second time domain. The pretransition of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) exhibits a thin lamellar liquid crystalline intermediate phase (designated Lalpha) if driven far away from equilibrium by an infrared temperature jump (T-jump) technique. The findings can be described by a two-step model. (1) Instantaneously with the T-jump, an anomalously thin lamellar liquid crystalline intermediate phase (d = 5.6-5.8 nm) forms, coexisting with the original gel-phase Lbeta'. Within the first seconds, the lamellar repeat distance of the intermediate increases to a value of about 6.7 nm. A closer examination of these kinetics reveals two relaxation components: a fast process, proceeding within tenths of a second, and a slow process, on the time scale of a few seconds. (2) Finally, both the liquid crystalline and the gel-phase relax into the stable ripple phase Pbeta'. The total process time of the transition is nearly independent of the addition of NaCl, but varies strongly with the chain length of the lecithin species.
PMID: 10877021 [PubMed - indexed for MEDLINE]
Effect of staphylococcal delta-lysin on the thermotropic phase behavior and vesicle morphology of dimyristoylphosphatidylcholine lipid bilayer model membranes. Differential scanning calorimetric, 31P nuclear magnetic resonance and Fourier transform infrared spectroscopic, and X-ray diffraction studies.
Lohner K, Staudegger E, Prenner EJ, Lewis RN, Kriechbaum M, Degovics G, McElhaney RN.
Institut fur Biophysik und Rontgenstrukturforschung, Osterreichische Akademie der Wissenschaften, Steyrergasse 17/VI, A-8010 Graz, Austria. email@example.com
We investigated the effects of various concentrations of staphylococcal delta-lysin on the thermotropic phase behavior of large multilamellar dimyristoylphosphatidylcholine (DMPC) vesicles by differential scanning calorimetry (DSC), 31P nuclear magnetic resonance (NMR) and Fourier transform infrared (FTIR) spectroscopy, and X-ray diffraction. The DSC studies revealed that at all concentrations, the addition of delta-lysin progressively decreases the enthalpy of the pretransition of DMPC bilayers without significantly affecting its temperature or cooperativity. Similarly, the addition of smaller quantities of peptide has little effect on the temperature of the main phase transition of DMPC bilayers but does reduce the cooperativity and enthalpy of this transition somewhat. However, at higher peptide concentrations, a second phase transition with a slightly increased temperature and a markedly reduced cooperativity and enthalpy is also induced, and this latter phase transition resolves itself into two components at the highest peptide concentrations that are tested. Moreover, our 31P NMR spectroscopic studies reveal that at relatively low delta-lysin concentrations, essentially all of the phospholipid molecules produce spectra characteristic of the lamellar phase, whereas at the higher peptide concentrations, an increasing proportion exhibit an isotropic signal. Also, at the highest delta-lysin concentrations that are studied, the isotropic component of the 31P NMR spectrum also resolves itself into two components. At the highest peptide concentration that was tested, we are also able to effect a macroscopic separation of our sample into two fractions by centrifugation, a pellet containing relatively smaller amounts of delta-lysin and a supernatant containing larger amounts of peptide relative to the amount of lipid present. We are also able to show that the more cooperative phase transition detected calorimetrically, and the lamellar phase 31P NMR signal, arise from the pelleted material, while the less cooperative phase transition and the isotropic 31P NMR signal arise from the supernatant. In addition, we demonstrate by X-ray diffraction that the pelleted material corresponds to delta-lysin-containing large multilamellar vesicles and the supernatant to a mixture of delta-lysin-containing small unilamellar vesicles and discoidal particles. We also show by FTIR spectroscopy that delta-lysin exists predominantly in the alpha-helical conformation in aqueous solution or when interacting with DMPC, and that a large fraction of the peptide bonds undergo H-D exchange in D(2)O. However, upon interaction with DMPC, the fraction of exchangeable amide protons decreases. We also demonstrate by this technique that both of the phase transitions detected by DSC correspond to phospholipid hydrocarbon chain-melting phase transitions. Finally, we show by several techniques that the absolute concentrations of delta-lysin and the thermal history, as well as the lipid:peptide ratio, can affect the thermotropic phase behavior and morphology of peptide-lipid aggregates.
PMID: 10600113 [PubMed - indexed for MEDLINE]
Microphase separation in low density lipoproteins. Evidence for a fluid triglyceride core below the lipid melting transition.
Pregetter M, Prassl R, Schuster B, Kriechbaum M, Nigon F, Chapman J, Laggner P.
Institut fur Biophysik und Rontgenstrukturforschung, Osterreichische Akademie der Wissenschaften, A-8010 Graz, Austria.
The structural organization of the neutral lipid core in human low density lipoproteins (LDL) was investigated in physicochemically defined, distinct human LDL subspecies in the density range of 1. 0244-1.0435 g/ml by evaluation of the core lipid transition temperature, chemical composition, and the behavior of spin-labeled core lipids. Calorimetric studies were performed on more than 60 LDL preparations, and the transition temperature, which varied between 19 and 32 degreesC, was correlated to the chemical composition and revealed a discontinuity at a critical cholesteryl ester to triglyceride ratio of approximately 7:1. For electron spin resonance studies, several LDL preparations were probed with spin-labeled cholesteryl esters and triglycerides, respectively. In LDL with a high triglyceride content, both labels exhibited similar mobility behavior. In contrast, in LDL with only small concentrations of triglycerides, the behavior of labeled cholesteryl esters and labeled triglycerides differed distinctly. The cholesteryl esters were strongly immobilized below the transition temperature, whereas the triglycerides remained fluid throughout the measured temperatures. These results suggest that the critical cholesteryl ester to triglyceride mass ratio of 7:1 corresponds to two concentric compartments with a radial ratio of 2:1, where the liquid triglycerides occupy the core, and the cholesteryl esters form the frozen shell. At higher triglyceride contents, the triglyceride molecules insert into the cholesteryl ester shell and depress the peak transition temperature of the LDL core, whereas at lower triglyceride contents, excess cholesteryl esters are dissolved in the core.
PMID: 9880504 [PubMed - indexed for MEDLINE]
Structural changes of creatine kinase upon substrate binding.
Forstner M, Kriechbaum M, Laggner P, Wallimann T.
Institute of Cell Biology, Swiss Federal Institute of Technology Zurich, CH-8093 Zurich, Switzerland. firstname.lastname@example.org
Small-angle x-ray scattering was used to investigate structural changes upon binding of individual substrates or a transition state analog complex (TSAC; Mg-ADP, creatine, and KNO3) to creatine kinase (CK) isoenzymes (dimeric muscle-type (M)-CK and octameric mitochondrial (Mi)-CK) and monomeric arginine kinase (AK). Considerable changes in the shape and the size of the molecules occurred upon binding of Mg-nucleotide or TSAC. The radius of gyration of Mi-CK was reduced from 55.6 A (free enzyme) to 48.9 A (enzyme plus Mg-ATP) and to 48.2 A (enzyme plus TSAC). M-CK showed similar changes from 28.0 A (free enzyme) to 25.6 A (enzyme plus Mg-ATP) and to 25.5 A (enzyme plus TSAC). Creatine alone did not lead to significant changes in the radii of gyration, nor did free ATP or ADP. AK also showed a change of the radius of gyration from 21.5 A (free enzyme) to 19.7 A (enzyme plus Mg-ATP), whereas with arginine alone only a minor change could be observed. The primary change in structure as seen with monomeric AK seems to be a Mg-nucleotide-induced domain movement relative to each other, whereas the effect of substrate may be of local order only. In CK, however, additional movements have to be involved.
PMID: 9675202 [PubMed - indexed for MEDLINE]
Mutation of cis-proline 207 in mitochondrial creatine kinase to alanine leads to increased acid stability.
Forstner M, Muller A, Rognan D, Kriechbaum M, Wallimann T.
Institute of Cell Biology, Zurich, Switzerland.
We show that the mutation of an uncharged residue far from the active site to another uncharged residue can have effects on the active site without disturbing the overall structure of the protein. Cis-proline 207 of mitochondrial creatine kinase was mutated to alanine. The mutant showed a decrease in the pH-optimum for ATP synthesis by 1.5 units while the maximum relative activity was lowered to 53% of the wild-type enzyme. In the direction of ATP consumption, the pH optimum was lowered by 1.3 units and the maximum relative activity was 49% of the wild-type enzyme. The enzyme kinetic parameters Km and Kd for the substrates did not change dramatically, indicating a largely unperturbed active site. Small-angle X-ray scattering was used to investigate the structural change concomitant with the mutation, yielding a scattering profile only slightly different from that of the wild-type enzyme. Neither the radius of gyration nor the molecular mass showed any significant differences, leading to the conclusion that quarternary organization and fold of the mutant and the wild-type enzymes were similar. Theoretical analysis suggests the most probable primary source of structural change to be a transition of residue 207 peptide bond torsional angle co from the cis to the trans configuration.
PMID: 9740374 [PubMed - indexed for MEDLINE]
First performance assessment of the small-angle X-ray scattering beamline at ELETTRA.
Amenitsch H, Rappolt M, Kriechbaum M, Mio H, Laggner P, Bernstorff S.
Institute of Biophysics and X-ray Structure Research, Austrian Academy of Sciences, Steyrergasse 17, A-8010 Graz, Austria.
The double-focusing high-flux wiggler beamline dedicated to small-angle X-ray scattering (SAXS) and wide-angle X-ray scattering (WAXS) at ELETTRA has gone into user operation recently. It has been designed specifically for time-resolved studies of non-crystalline and fibrous materials in the submillisecond time scale, and has been optimized for small-angle scattering measurements. An overview of the beamline status and of some representative results, highlighting the performance of the SAXS beamline, are given.
PMID: 15263560 [PubMed - in process]
Trapping of short-lived intermediates in phospholipid phase transitions: the L* alpha phase.
Laggner P, Amenitsch H, Kriechbaum M, Pabst G, Rappolt M.
Institute of Biophysics and X-ray Structure Research, Austrian Academy of Sciences, Graz, Austria.
Time-resolved small-angle X-ray diffraction of liquid-crystalline phospholipid-water systems under temperature or pressure jump conditions has demonstrated the existence of an ordered, intermediate L alpha phase, with a sub-second lifetime, designated as the L* alpha-phase. The lamellar repeat spacing is, universally, 0.3 nm smaller than that of the parent phase, irrespective of the lipid composition and of the jump conditions, provided that the jump leads to a net volume expansion of the phase. The presence of salts, most notably LiCl, leads to a prolongation of the lifetime. The results suggest a non-monotonic potential function for the interbilayer water thickness.
PMID: 10822598 [PubMed - indexed for MEDLINE]
Pressure induced hydration dynamics of membranes.
Osterberg F, Kriechbaum M, Polcyn A, Skita V V, Tate MW, So PT, Gruner SM, Erramilli S.
PMID: 10056030 [PubMed - as supplied by publisher]
Phospholipid phase transitions: kinetics and structural mechanisms.
Laggner P, Kriechbaum M.
Institut fur Rontgenfeinstrukturforschung, Austrian Academy of Sciences, Graz.
A brief review is given on the principles and methods used to investigate structural phase transitions in phospholipid supramolecular structures. The conceptual differences of approaches close to and far from equilibrium are addressed, and the consequences in terms of the limits of interpretation for different types of methods, in particular referring to jump-relaxation and steady-state techniques, are surveyed. With the emphasis on connecting dynamic and structural information, the results obtained so far from different techniques are reviewed, and the open questions addressed. The more recent advances by millisecond time-resolved X-ray diffraction with synchrotron radiation and their main results obtained for transitions triggered by IR-laser temperature jumps are summarized. As a major novel aspect in the field, the necessity of considering martensitic, diffusionless transformation mechanisms and the occurrence of intermediate structures is highlighted.
PMID: 2054900 [PubMed - indexed for MEDLINE]
A small-angle X-ray scattering study on pre-irradiated malate synthase. The influence of formate, superoxide dismutase, and catalase on the X-ray induced aggregation of the enzyme.
Zipper P, Wilfing R, Kriechbaum M, Durchschlag H.
The sulfhydryl enzyme malate synthase from baker's yeast was X-irradiated with 6 kGy in air-saturated aqueous solution (enzyme concentration: congruent to 10 mg/ml; volume: 120 microliters), in the absence or presence of the specific scavengers formate, superoxide dismutase, and catalase. After X-irradiation, a small aliquot of the irradiated solutions was tested for enzymic activity while the main portion was investigated by means of small-angle X-ray scattering. Additionally, an unirradiated sample without additives was investigated as a reference. Experiments yielded the following results: X-irradiation in the absence of the mentioned scavengers caused considerable aggregation, fragmentation, and inactivation of the enzyme. The dose Dt37 for total (= repairable + non-repairable) inactivation resulted as 4.4 kGy. The mean radius of gyration was found to be about 13 nm. The mean degree of aggregation was obtained as 5.7, without correction for fragmentation. An estimation based on the thickness factor revealed that about 19% of material might be strongly fragmented. When this amount of fragments was accordingly taken into account, a value of 7.1 was obtained as an upper limit for the mean degree of aggregation. The observed retention of the thickness factor and the finding of two different cross-section factors are in full accord with the two-dimensional aggregation model established previously (Zipper and Durchschlag, Radiat. Environ. Biophys. 18, 99-121 (1980)). The presence of catalytic amounts of superoxide dismutase and/or catalase, in the absence of formate, during X-irradiation reduced both aggregation and inactivation significantly. The presence of formate (10 or 100 mM) during X-irradiation led to a strong decrease of aggregation and inactivation.(ABSTRACT TRUNCATED AT 250 WORDS)
PMID: 4024705 [PubMed - indexed for MEDLINE]