Biomedical subjects

Manfred Kriechbaum

Publications and source records attributed to Manfred Kriechbaum.

6 recordsLinked to original sources

PubMed2006

Electric and structural studies of hormone interaction with chloroplast envelope membranes isolated from vegetative and generative rape.

The electric and structural properties of envelope membranes of chloroplasts obtained from vegetative and generative plants of rape and the effect of hormone (IAA, GA(3) and zearalenone) treatment were determined by zeta potential and small-angle X-ray scattering (SAXS) methods. Chloroplasts were isolated from leaves cut off from the vegetative (before cooling) and generative apical parts of plants. The lipid composition of chloroplast envelope membranes were analyzed by chromatographic techniques. Envelopes from generative plants contained higher levels of digalactosyldiacylglycerol (DGDG) and smaller amounts of phospholipids (PLs) in comparison to those obtained from vegetative ones. Moreover, envelopes of generative plants were characterized by higher fractions of unsaturated fatty acids. The zeta potential changes caused by hormone treatment were higher for chloroplasts isolated from vegetative plants in comparison to chloroplasts isolated from generative ones. An especially strong effect was observed for chloroplasts treated with IAA. The thickness of bilayers of untreated chloroplasts from vegetative plants were larger by 0.4 nm when comparing to the thickness of layers obtained from generative ones. The effect of hormones (GA(3) and zearalenone) was detected only for vegetative chloroplasts. Both applied methods indicated differences in the properties of untreated and hormone-treated chloroplasts obtained from vegetative and generative plants.

Brassica napus↗

PubMed2005

Structure of bacterial extracellular polymeric substances at different pH values as determined by SAXS.

Extracellular polymeric substances (EPS) play an important role in cell aggregation, cell adhesion, and biofilm formation, and protect cells from a hostile environment. The EPS was isolated by trichloroacetic acid/ethanol extraction from broth culture of a marine bacterium isolate. The EPS was composed of glucose and galactose as determined by HPLC and TLC; the protein content was on average 15 +/- 5% of EPS dry mass. The solution structure of EPS at different values of pH was revealed by small-angle x-ray scattering. Scattering curves of EPS solutions (0.4%, w/v) consistently showed two nearly linear log-log regions with slopes a and b in the q-ranges from 0.06 nm(-1) to 0.26 nm(-1), and from 0.27 nm(-1) to 0.88 nm(-1), respectively. Slope a was sensitive to pH changes whereas slope b was not. The observed sensitivity to pH was not a consequence of ionic strength variation with pH, as checked by salt addition. The pH variation causes major rearrangements of EPS structure mainly at length scales above 24 nm. To get a better understanding of the pH effect on EPS structure, the original model proposed by Geissler was refined into a mathematical model that enabled fitting of the experimental scattering curves in the pH range from 0.7 to 11.0. The model describes EPS structure as a network of randomly coiled polymeric chains with denser domains of polymeric chains. The results obtained from the model indicate that dense domains increase in average size from 19 nm at pH 11.0 to 52 nm at pH 0.7. The average distance between the polysaccharide chains at pH 0.7 was 2.3 nm, which indicates a compact EPS structure. Swelling was found to be at a maximum around pH = 8.8, where the average distance between the chains was 4.8 nm.

Biopolymers↗

PubMed2005

Effect of indole-3-acetic acid on surface properties of the wheat plastid lipids.

Surface parameters of polar lipids extracted from winter wheat plastids were investigated by the Langmuir and X-ray differentiation scattering methods. Highly purified plastids were isolated from non-embryogenic (NE) and embryogenic (E) calli initiated from inflorescences. NE plastids contained more monogalactosyldiacylglycerol (MGDG) and digalactosyldiacylglycerol (DGDG) and less phospholipids (PL) fraction than E plastids. Moreover, in E calli, unsaturated fatty acids were detected in a higher proportion than in NE for both MGDG and DGDG. No significant differences in fatty acids saturation of PL between NE and E objects were detected. Aqueous surface monolayers were prepared from separate lipids and from mixtures of glycolipids and PL. In the case of MGDG, isotherms showed specific shoulders, contrary to continuous isotherms obtained for other investigated lipids. On the base of pi-A isotherms, the surface parameters: limiting area (A(lim)) and collapse pressure (pi(coll)) were calculated. Indole-3-acetic acid (IAA) increased the A(lim) of all separated lipids about 4-10 angstrom2/mol. However, for NE lipid mixture, the effect of IAA was much smaller (about 2 angstroms2/mol) than for other objects (usually about 5 angstroms2/mol). X-ray experiments for liposomes, obtained from mixtures of glycolipids and PL of NE and E plastids, showed continuous scattering curves with maxima characteristic for lipid bilayer membranes. Calculations of distance distribution functions indicated that bilayer thickness was 41 and 38 angstroms for NE and E, respectively. IAA influence on membrane structures was detected especially in E liposomes and increased the distance between head groups by about 2 angstroms. It is suggested that changes occur during embryogenesis in specific structure of plastid membranes determined also the formation of domains, similar to that suggested for plasmalemma (Plant Sci. 165 (2003) 265). IAA treatment influenced the membrane structure, especially E plastids increasing distances between polar groups.

Cells, Cultured↗

PubMed2004

Phospholipid mesophases at solid interfaces: in-situ X-ray diffraction and spin-label studies.

In this work, we report on recent investigations, both on the global and on the local molecular architecture of supported phospholipid model membranes. A brief theoretical introduction explains how global structural information on supramolecular lipid ensembles can be retrieved from surface X-ray diffraction measurements as well as how spin-label electron paramagnetic resonance spectroscopy (EPR) provides complementary information on the local environment of probe molecules. The combination of especially designed X-ray cells with the technique of small- and wide-angle X-ray surface scattering makes it possible to explore various fields of lipid research and its applications. Examples for different physico-chemical conditions are presented: (i) in situ chemistry under excess of water conditions demonstrating how solid-supported lipid films sense salinity, (ii) the 3D electron density reconstruction of a vesicle-fusion intermediate under controlled humidity, and (iii) complementary temperature and pressure effects on oriented phospholipid samples. Further, special attention has been given to the influence of different film preparation techniques with respect to quality and the defect structure manifestation. To resolve the proportions and local properties of defects in a hydrated lipid-deposited surface, spin-label EPR was applied. The results from 9.6 GHz EPR as well as from 1.2 GHz EPR suggest the alignment to be in the range between 30% and 80%. In addition, slow time-dependent EPR measurements point to nano-structural rearrangements due to water flow and reduction of alignment quality.

Cell Membrane↗

PubMed2002

Structural, dynamic and mechanical properties of POPC at low cholesterol concentration studied in pressure/temperature space.

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.

Cholesterol↗

PubMed2002

Solution structure of human and bovine beta(2)-glycoprotein I revealed by small-angle X-ray scattering.

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.

Algorithms↗