Whiles-Lillig, Jennifer
http://hdl.handle.net/10211.1/1506
2024-03-29T12:18:44ZStructural Evaluation of Phospholipid Bicelles for Solution-State Studies of Membrane-Associated Biomolecules
http://hdl.handle.net/10211.3/124842
Structural Evaluation of Phospholipid Bicelles for Solution-State Studies of Membrane-Associated Biomolecules
Glover, Kerney J.; Whiles-Lillig, Jennifer; Wu, Guohua; Yu, Nan-jun; Deems, Raymond; Struppe, Jochem O.; Stark, Ruth E.; Komives, Elizabeth A.; Vold, Regitze R.
Several complementary physical techniques have been used to characterize the aggregate structures formed
in solutions containing dimyristoylphosphatidylcholine (DMPC)/dihexanoylphosphatidylcholine (DHPC) at ratios of ≤ 0.5 and
to establish their morphology and lipid organization as that of bicelles. ^31P NMR studies showed that the DMPC and DHPC
components were highly segregated over a wide range of DMPC/DHPC ratios (q = 0.05–0.5) and temperatures (15°C and
37°C). Only at phospholipid concentrations below 130 mM did the bicelles appear to undergo a change in morphology. These
results were corroborated by fluorescence data, which demonstrated the inverse dependence of bicelle size on phospholipid
concentration as well as a distinctive change in phospholipid arrangement at low concentrations. In addition, dynamic light
scattering and electron microscopy studies supported the hypothesis that the bicellar phospholipid aggregates are disk shaped.
The radius of the planar domain of the disk was found to be directly proportional to the ratio of DMPC/DHPC and
inversely proportional to the total phospholipid concentration when the DMPC/DHPC ratio was held constant at 0.5. Taken
together, these results suggest that bicelles with low q retain the morphology and bilayer organization typical of their
liquid-crystalline counterparts, making them useful membrane mimetics.
Published by Cell Press on behalf of The Biophysical Society. Copyright of The Biophysical Society. The definitive version of this article is available at: http://www.sciencedirect.com/science/article/pii/S000634950175864X
2001-10-01T00:00:00ZOrientation and Effects of Mastoparan X on Phospholipid Bicelles
http://hdl.handle.net/10211.3/124828
Orientation and Effects of Mastoparan X on Phospholipid Bicelles
Whiles-Lillig, Jennifer; Brasseur, Robert; Glover, Kerney J.; Melacini, Giuseppe; Komives, Elizabeth A.; Vold, Regitze R.
Mastoparan X (MPX: INWKGIAAMAKKLL-NH2) belongs to a family of ionophoric peptides found in wasp
venom. Upon binding to the membrane, MPX increases the cell’s permeability to cations leading to a disruption in the
electrolyte balance and cell lysis. This process is thought to occur either through a membrane-thinning mechanism, where the
peptide resides on the membrane surface thereby disrupting lipid packing, or through formation of an oligomeric pore. To
address this issue, we have used both high-resolution and solid-state 2H NMR techniques to study the structure and
orientation of MPX when associated with bicelles. NOESY and chemical shift analysis showed that in bicelles, MPX formed
a well-structured amphipathic -helix. In zwitterionic bicelles, the helical axis was found to rest generally perpendicular to the
membrane normal, which could be consistent with the “carpet” mechanism for lytic activity. In anionic bicelles, on the other
hand, the helical axis was generally parallel to the membrane normal, which is more consistent with the pore model for lytic
activity. In addition, MPX caused significant disruption in lipid packing of the negatively charged phospholipids. Taken
together, these results show that MPX associates differently with zwitterionic membranes, where it rests parallel to the
surface, compared with negatively charged membranes, where it penetrates longitudinally.
Published by Cell Press on behalf of The Biophysical Society. Copyright of The Biophysical Society. The definitive version of this article is available at: http://www.sciencedirect.com/science/article/pii/S0006349501760134
2001-01-01T00:00:00ZAcidic Phospholipid Bicelles: A Versatile Model Membrane System
http://hdl.handle.net/10211.3/124661
Acidic Phospholipid Bicelles: A Versatile Model Membrane System
Struppe, Jochem; Whiles-Lillig, Jennifer; Vold, R.R.
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 H2O) 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 d54-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 -GSSKSKPKDPSQRR from pp60 -src to both neutral
and acidic bicelles shows the utility of these novel membrane mimetics.
Published by Cell Press on behalf of The Biophysical Society. Copyright of The Biophysical Society. The definitive version of this article is available at: http://www.sciencedirect.com/science/article/pii/S000634950076591X
2000-01-01T00:00:00ZOrientation and Helical Conformation of a Tissue-specific Hunter-killer Peptide in Micelles
http://hdl.handle.net/10211.1/1511
Orientation and Helical Conformation of a Tissue-specific Hunter-killer Peptide in Micelles
Plesniak, Leigh A.; Parducho, Jonathan I.; Ziebart, Angie; Geierstanger, Bernhard H; Whiles-Lillig, Jennifer; Melacini, Guiseppe; Jennings, Patricia A.
Hunter-killer peptides are chimeric synthetic peptides that selectively target specific cell types for an apoptotic death. These peptides, which are models for potential therapeutics, contain a homing sequence for receptor-mediated interactions and a pro-apoptotic sequence. Homing domains have been designed to target angiogenic tumor cells, prostate cells, arthritic tissue and, most recently, adipose tissue. After a receptor-mediated internalization, the apoptotic sequence, which contains D-enantiomer amino acids, initiates apoptosis through mitochondrial membrane disruption. We have begun structure and functional studies on a peptide (HKP1) that specifically targets angiogenic tumor cells for apoptosis. As a model for mitochondrial membrane disruption, we have examined peptide-induced leakage of a calcein fluorophore from large unilamellar vesicles. These experiments demonstrate more potent leakage activity by HKP1 than the peptide lacking the homing domain. Circular dichroism and 2D homonuclear NMR experiments demonstrate that this tumor-specific HKP adopts a left-handed amphipathic helix in association with dodecylphosphorylcholine micelles in a parallel orientation to the lipid–water interface with the homing domain remaining exposed to solvent. The amphipathic helix of the apoptotic domain orients with nonpolar leucine and alanine residues inserting most deeply into the lipid environment.
Published by and copyright by The Protein Society.
2004-01-01T00:00:00Z