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My research interests lie in the general area of the physical
biochemistry of naturally occurring and synthetic bioactive lipids with
respect to their behavior in model membranes.
I am particularly interested in continuing my investigations into
the structure-function relationships of sterols and lysolipids (and
LPS), and how chemical modifications alter their interactions between
other lipids and proteins. Familiarity
with a number of biophysical techniques, including calorimetry
(isothermal titration and differential scanning), spectroscopy (UV-vis,
fluorescence), photoaffinity labeling, and Langmuir monolayers allows me
to bring to bear a powerful arsenal of investigatory tools on many
unanswered questions in the field of lipidomics.
An abbreviated discussion follows.
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Oxysterols:
Reverse cholesterol efflux is significantly inhibited in the presence
of keto-cholesterol
(1)
, a product of oxidative stress. This oxysterol is also less
efficient in promoting a lipid-ordered domain compared to cholesterol,
a phase widely believed to be required for the formation of lipid
“rafts”
(2, 3)
. Other oxidized sterol compounds produced under conditions of
stress are shown to cause apoptosis through Ca2+ release
(4)
and are found in red blood sickle cells
(5)
. Using the monolayer technique, as well as a simple turbidity
assay, one can detect the formation of lipid-ordered domains. I
plan to continue my study into the hypothesis that the
cytotoxicity of these sterols is due, in part, to their inability to
simulate native cholesterol in membranes. Using commercially
available oxygenated sterols and other membrane lipids (e.g.,
phosphatidylcholine, sphingomyelin), as well as synthetic lipid
analogs available from the many collaborations that I have
established, and a small amount of standard reagents (buffers, etc.),
these issues can be investigated. |
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Plot of OD (600 nm) remaining after
treatment of sterol-ESPM MLVs with Triton
X-100. Cholesterol, ■, solid line; 6-ketocholesterol,
●, dashed line; 7-ketocholesterol, ▲, dotted line;
19-hydroxycholesterol, ▼, dash-dotted line;
24-ketocholesterol, ◄,
dashed-dotted-dotted line; 25-ketocholesterol, ►, short
dashed line.
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Area/composition
curves showing sterol-induced condensation of POPC monolayers at three surface
pressures.
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Lysophosphatidic
acid (LPA) and lipopolysaccharide(LPS) : The structurally simplest
of the glycerophospholipids, LPA is produced in many cell types via de
novo synthesis or through the deacylation of phosphatidic acid.
This lipid exhibits growth factor properties and displays a
wide array of cellular functions, mainly via interactions through
high-affinity binding to G-protein-coupled receptors
(6)
. Recent studies suggest
that LPA binds with high affinity to the lipid-binding domain of the
actin-severing protein gelsolin
(7)
. I am interested in
examining the structural requirements and further characterizing the
thermodynamics of these interactions using a short (19-mer) sequence
of gelsolin. This sequence
is known to be the binding domain of the well-established gelsolin
regulating lipid, phosphatidylinositol-4,5-bisphosphate
(8, 9)
. Interestingly, it has
also been shown that LPS binds the same sequence with even higher
affinity
(7, 10)
, and I would continue these studies. |
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LPA |
LPS |
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Titration isotherm of binding of LPS with P2 in
sodium phosphate buffer, pH 7.4. |
Recent publications
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Li, Z., Mintzer, E., and Bittman R., "First synthesis of free
cholesterol-BODIPY conjugates", J. Org. Chem. 71, 1718-1721
(2006) |
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Mintzer, E., Sargsyan, H., and Bittman, R., "Lysophosphatidic acid
and lipopolysaccharide bind to the PIP2-binding domain of gelsolin",
Biochim. Biophys. Acta 1758, 85-89 (2006) |
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Li, Z., Mintzer, E., and Bittman, R., "The critical micelle
concentrations of lysophosphatidic acid and sphingosylphosphorylcholine",
Chem. Phys. Lipids 130, 197-201 (2004) |
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Mintzer, E., Waarts, B.L., Wilschut, J., and Bittman, R., "Behavior
of a photoactivatable analog of cholesterol, 6-photocholesterol, in model
membranes", FEBS Lett. 510, 181-184 (2002)
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(1) Gaus,
K., Dean, R. T., Kritharides, L., and Jessup, W. (2001) Inhibition of
cholesterol efflux by 7-ketocholesterol: comparison between cells, plasma
membrane vesicles, and liposomes as cholesterol donors. Biochemistry 40,
13002-13014.
(2)
Theunissen, J. J., Jackson, R. L., Kempen, H. J., and Demel, R. A.
(1986) Membrane properties of oxysterols. Interfacial orientation, influence
on membrane permeability and redistribution between membranes. Biochim.
Biophys. Acta 860, 66-74.
(3)
Wang, J., Megha, and London, E. (2004) Relationship between
sterol/steroid structure and participation in ordered lipid domains (lipid
rafts): implications for lipid raft structure and function. Biochemistry
43, 1010-1018.
(4)
Berthier, A., Lemaire-Ewing, S., Prunet, C., Monier, S., Athias, A.,
Bessede, G., Pais de Barros, J. P., Laubriet, A., Gambert, P., Lizard, G., and
Neel, D. (2004) Involvement of a calcium-dependent dephosphorylation of BAD
associated with the localization of Trpc-1 within lipid rafts in
7-ketocholesterol-induced THP-1 cell apoptosis. Cell
Death Differ. 11, 897-905.
(5)
Kucuk, O., Lis, L. J., Dey, T., Mata, R., Westerman, M. P., Yachnin,
S., Szostek, R., Tracy, D., Kauffman, J. W., and Gage, D. A. (1992) The
effects of cholesterol oxidation products in sickle and normal red blood cell
membranes. Biochim. Biophys. Acta 1103,
296-302.
(6)
Goetzl, E. J., and An, S. (1998) Diversity of cellular receptors and
functions for the lysophospholipid growth factors lysophosphatidic acid and
sphingosine 1-phosphate. FASEB J. 12,
1589-1598.
(7)
Mintzer, E. A., Sargsyan, H., and Bittman, R. (2006) Lysophosphatidic
acid and lipopolysaccharide bind to the PIP2-binding domain of gelsolin. Biochim.
Biophys. Acta 1758, 85-89.
(8)
Janmey, P. A. (1994) Phosphoinositides and calcium as regulators of
cellular actin assembly and disassembly. Annu.
Rev. Physiol. 56, 169-191.
(9)
Janmey, P. A., Stossel, T. P., and Allen, P. G. (1998) Deconstructing
gelsolin: identifying sites that mimic or alter binding to actin and
phosphoinositides. Chem. Biol. 5, R81-R85.
(10) Bucki,
R., Georges, P. C., Espinassous, Q., Funaki, M., Pastore, J. J., Chaby, R.,
and Janmey, P. A. (2005) Inactivation of endotoxin by human plasma gelsolin. Biochemistry
44, 9590-9597.
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