Biomedical subjects

J Struppe

Publications and source records attributed to J Struppe.

3 recordsLinked to original sources

PubMed2000

Acidic phospholipid bicelles: a versatile model membrane system.

With the aim of establishing acidic bicellar solutions as a useful membrane model system, we have used deuterium NMR spectroscopy to investigate the properties of dimyristoyl/dihexanoylphosphatidylcholine (DMPC/DHPC) bicelles containing 25% (w/w in H(2)O) of either dimyristoylphosphatidylserine (DMPS) or dimyristoylphosphatidylglycerol (DMPG). The addition of the acidic lipid component to this lyotropic liquid crystalline system reduces its range of stability because of poor miscibility of the two dimyristoylated phospholipids. Compared to the neutral bicelles, which are stable at pH 4 to pH 7, acidic bicelles are stable only from pH 5.5 to pH 7. Solid-state deuterium NMR analysis of d(54)-DMPC showed similar ordering in neutral and acidic bicelles. Fully deuterated DMPS or DMPG is ordered in a way similar to that of DMPC. Study of the binding of the myristoylated N-terminal 14-residue peptide mu-GSSKSKPKDPSQRR from pp60(nu-src) to both neutral and acidic bicelles shows the utility of these novel membrane mimetics.

Amino Acid Sequence↗

PubMed1998

2H NMR studies of a myristoylated peptide in neutral and acidic phospholipid bicelles.

Deuterium NMR spectra of Myr-d27-GNAAAAKKGSEQES (Cat14), the N-terminal 14-residue peptide from the catalytic subunit of cAMP-dependent protein kinase A (PKA), illustrate how magnetically aligned neutral and acidic phospholipid bicelles can be used to characterize the ordering and mode of binding of peptides to membranes. Since Cat14 is electrically neutral, the major interaction responsible for binding is the insertion of the myristoyl group into the hydrophobic core of the bilayer. The inclusion of 25% phosphatidylserine or phosphatidylglycerol into phosphatidylcholine bicelles results in a moderate increase in the ordering of the peptide relative to the bicelle normal, presumably because of favorable electrostatic interactions between the phospholipid headgroups and the two lysines in positions 7 and 8. Successful preparation of acidic bicelles was achieved by careful adjustment of lipid composition, pH and ionic strength.

Deuterium↗

PubMed1998

Dilute bicellar solutions for structural NMR work.

Deuterium NMR spectroscopy has been employed to characterize the concentration dependence of orientational order in DMPC/DHPC bicellar solutions with molar ratios q = [DMPC]/[DHPC] = 3.3, 2.7, and 2.3. The stability of a discotic nematic phase can, in general, be predicted from a simple Onsager picture involving the size and concentration of the mesogenic unit, but for the bicellar solutions this model is not adequate. Specifically, macroscopic alignment is observed at total lipid concentrations well below that, 1-10% (w/w) predicted by Onsager's model. Thus the discotic nematic phase is stable to approximately 3-5% (w/w) for q = 3.3-2.3, and the bicellar order is highest just before phase separation occurs at the minimum total phospholipid concentration. This implies the presence of a DHPCbic -->/<-- DHPCsol equilibrium in establishing bicellar size, thereby extending the range of concentrations for which alignment occurs. Bicellar morphology has been verified for a wide range of concentrations, temperatures, and q-values, but as viscosity measurements demonstrate, major morphological changes take place as the temperature is reduced below 30 degreesC.

Algorithms↗