Biomedical subjects

B Angerstein

Publications and source records attributed to B Angerstein.

4 recordsLinked to original sources

PubMed2004

Probing membrane protein orientation and structure using fast magic-angle-spinning solid-state NMR.

One and two-dimensional solid-state NMR experiments are discussed that permit probing local structure and overall molecular conformation of membrane-embedded polypeptides under Magic Angle Spinning. The functional dependence of a series of anisotropic recoupling schemes is analyzed using theoretical and numerical methods. These studies lead to the construction of a set of polarization dephasing or transfer units that probe local backbone conformation and overall molecular orientation within the same NMR experiment. Experimental results are shown for a randomly oriented peptide and for two model membrane-peptides reconstituted into lipid bilayers and oriented on polymer films according to a method proposed by Bechinger et al.

Anisotropy↗

PubMed2000

Spin-label electron spin resonance studies on the mode of anchoring and vertical location of the N-acyl chain in N-acylphosphatidylethanolamines.

Electron spin resonance (ESR) studies have been performed on N-myristoyl dimyristoylphosphatidylethanolamine (N-14-DMPE) membranes using both phosphatidylcholines spin-labeled at different positions in the sn-2 acyl chain and N-acyl phosphatidylethanolamines spin-labeled in the N-acyl chain to characterize the location and mobility of the N-acyl chain in the lipid membranes. Comparison of the positional dependences of the spectral data for the two series of spin-labeled lipids suggests that the N-acyl chain is positioned at approximately the same level as the sn-2 chain of the phosphatidylcholine spin-label. Further, similar conclusions are reached when the ESR spectra of the N-acyl PE spin-labels in dimyristoylphosphatidylcholine (DMPC) or dimyristoylphosphatidylethanolamine (DMPE) host matrixes are compared with those of phosphatidylcholine spin-labels in these two lipids. Finally, the chain ordering effect of cholesterol has also been found to be similar for the N-acyl PE spin-label and PC spin-labels, when the host matrix is either DMPC and cholesterol or N-14-DMPE and cholesterol at a 6:4 mole ratio. In both cases, the gel-to-liquid crystalline phase transition is completely abolished but cholesterol perturbs the gel-phase mobility of N-14-DMPE more readily than that of DMPC. These results demonstrate that the long N-acyl chains are anchored firmly in the hydrophobic interior of the membrane, in an orientation that is parallel to that of the O-acyl chains, and are located at nearly the same vertical position as that of the sn-2 acyl chains in the lipid bilayer. There is a high degree of dynamic compatibility between the N-acyl chains and the O-acyl chains of the lipid bilayer core, although bilayers of N-acyl phosphatidylethanolamines possess a more hydrophobic interior than phosphatidylcholine bilayers. These results provide a structural basis for rationalizing the biological properties of NAPEs.

Cholesterol↗

PubMed1999

Binding of peripheral proteins to mixed lipid membranes: effect of lipid demixing upon binding.

Binding isotherms have been determined for the association of horse heart cytochrome c with dioleoyl phosphatidylglycerol (DOPG)/dioleoyl phosphatidylcholine (DOPC) bilayer membranes over a range of lipid compositions and ionic strengths. In the absence of protein, the DOPG and DOPC lipids mix nearly ideally. The binding isotherms have been analyzed using double layer theory to account for the electrostatics, either the Van der Waals or scaled particle theory equation of state to describe the protein surface distribution, and a statistical thermodynamic formulation consistent with the mass-action law to describe the lipid distribution. Basic parameters governing the electrostatics and intrinsic binding are established from the binding to membranes composed of anionic lipid (DOPG) alone. Both the Van der Waals and scaled particle equations of state can describe the effects of protein distribution on the DOPG binding isotherms equally well, but with different values of the maximum binding stoichiometry (13 lipids/protein for Van der Waals and 8 lipids/protein for scaled particle theory). With these parameters set, it is then possible to derive the association constant, Kr, of DOPG relative to DOPC for surface association with bound cytochrome c by using the binding isotherms obtained with the mixed lipid membranes. A value of Kr (DOPG:DOPC) = 3.3-4.8, depending on the lipid stoichiometry, is determined that consistently describes the binding at different lipid compositions and different ionic strengths. Using the value of Kr obtained it is possible to derive the average in-plane lipid distribution and the enhancement in protein binding induced by lipid redistribution using the statistical thermodynamic theory.

Animals↗

PubMed1994

Differential scanning calorimetry of thermotropic phase transitions in vitaminylated lipids: aqueous dispersions of N-biotinyl phosphatidylethanolamines.

The thermotropic phase behavior of a homologous series of saturated diacyl phosphatidylethanolamines in which the headgroup is N-derivatized with biotin has been investigated by differential scanning calorimetry. In 1 M NaCl, derivatives with acyl chainlengths from C(12:0) to C(20:0) all exhibit sharp chain-melting phase transitions, which are reversible with a hysteresis of 1.5 degrees or less, except for the C(12:0) lipid which has a transition temperature below 0 degree C. The transition enthalpy and the transition entropy depend approximately linearly on the lipid chainlength, with incremental values per CH2 group that are very similar to those obtained for the corresponding underivatized phosphatidylethanolamines in aqueous dispersion. The chainlength-independent contribution to the transition enthalpy is significantly smaller than that for the underivatized phosphatidylethanolamines, and that for the transition entropy is much smaller; the latter suggesting that the N-biotinylated phosphatidylethanolamine headgroups are differently hydrated from those of the underivatized lipids. The gel-to-fluid phase transition temperatures of the N-biotinylated lipids are lower than those of the parent phosphatidylethanolamines, and their chainlength dependence conforms well with that predicted by assuming that the transition enthalpy and entropy are linearly dependent on chainlength. Although the chain-melting phase behavior is generally similar to that of the parent phosphatidylethanolamines, the gel phases (and the fluid phases in the case of chainlengths C(12:0) to C(16:0)) have a different lyotropic structure in the two cases, and this is reflected in the chainlength-independent contributions to the thermodynamic parameters. In the absence of salt, the thermotropic phase behavior of aqueous dispersions of the N-biotinyl phosphatidylethanolamines is considerably more complex. The transition temperatures are consistently lower than those in 1 M NaCI, but the transitions are broader, contain multiple peaks and exhibit a much larger hysteresis between heating and cooling scans. Additionally, the lipids with shorterchainlengths exhibit metastability in the absence of salt, converting from a micellar solution to a lamellar gel phase only after incubation at low temperature with freeze-thaw cycling.

Biotin↗