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Frederick Heberle

Drew Marquardt, Frederick A Heberle, Denise V Greathouse, Roger E Koeppe, Robert F Standaert, Brad J Van Oosten, Thad A Harroun, Jacob J Kinnun, Justin A Williams, Stephen R Wassall, John Katsaras
Cholesterol is an essential biomolecule of animal cell membranes, and an important precursor for the biosynthesis of certain hormones and vitamins. It is also thought to play a key role in cell signaling processes associated with functional plasma membrane microdomains (domains enriched in cholesterol), commonly referred to as rafts. In all of these diverse biological phenomena, the transverse location of cholesterol in the membrane is almost certainly an important structural feature. Using a combination of neutron scattering and solid-state (2)H NMR, we have determined the location and orientation of cholesterol in phosphatidylcholine (PC) model membranes having fatty acids of different lengths and degrees of unsaturation...
November 1, 2016: Soft Matter
Yan Xia, Kamil Charubin, Drew Marquardt, Frederick A Heberle, John Katsaras, Jianhui Tian, Xiaolin Cheng, Ying Liu, Mu-Ping Nieh
Molecular transfer between nanoparticles has been considered to have important implications regarding nanoparticle stability. Recently, the interparticle spontaneous lipid transfer rate constant for discoidal bicelles was found to be very different from spherical, unilamellar vesicles (ULVs). Here, we investigate the mechanism responsible for this discrepancy. Analysis of the data indicates that lipid transfer is entropically favorable, but enthalpically unfavorable with an activation energy that is independent of bicelle size and long- to short-chain lipid molar ratio...
September 27, 2016: Langmuir: the ACS Journal of Surfaces and Colloids
Frederick A Heberle, Drew Marquardt, Milka Doktorova, Barbara Geier, Robert F Standaert, Peter Heftberger, Benjamin Kollmitzer, Jonathan D Nickels, Robert A Dick, Gerald W Feigenson, John Katsaras, Erwin London, Georg Pabst
Cell membranes possess a complex three-dimensional architecture, including nonrandom lipid lateral organization within the plane of a bilayer leaflet, and compositional asymmetry between the two leaflets. As a result, delineating the membrane structure-function relationship has been a highly challenging task. Even in simplified model systems, the interactions between bilayer leaflets are poorly understood, due in part to the difficulty of preparing asymmetric model membranes that are free from the effects of residual organic solvent or osmotic stress...
May 24, 2016: Langmuir: the ACS Journal of Surfaces and Colloids
Yan Xia, Ming Li, Kamil Charubin, Ying Liu, Frederick A Heberle, John Katsaras, Benxin Jing, Yingxi Zhu, Mu-Ping Nieh
We report on studies of lipid transfer rates between different morphology nanoparticles and lipids with different length acyl chains. The lipid transfer rate of dimyristoylphosphatidylcholine (di-C14, DMPC) in discoidal "bicelles" (0.156 h(-1)) is 2 orders of magnitude greater than that of DMPC vesicles (ULVs) (1.1 × 10(-3) h(-1)). For both bicellar and ULV morphologies, increasing the acyl chain length by two carbons [going from di-C14 DMPC to di-C16, dipalmitoylphosphatidylcholine (DPPC)] causes lipid transfer rates to decrease by more than 2 orders of magnitude...
December 1, 2015: Langmuir: the ACS Journal of Surfaces and Colloids
Norbert Kučerka, Brad van Oosten, Jianjun Pan, Frederick A Heberle, Thad A Harroun, John Katsaras
Following our previous efforts in determining the structures of commonly used PC, PG, and PS bilayers, we continue our studies of fully hydrated, fluid phase PE bilayers. The newly designed parsing scheme for PE bilayers was based on extensive MD simulations, and is utilized in the SDP analysis of both X-ray and neutron (contrast varied) scattering measurements. Obtained experimental scattering form factors are directly compared to our simulation results, and can serve as a benchmark for future developed force fields...
February 5, 2015: Journal of Physical Chemistry. B
Jianjun Pan, Drew Marquardt, Frederick A Heberle, Norbert Kučerka, John Katsaras
We recently published two papers detailing the structures of fluid phase phosphatidylglycerol (PG) lipid bilayers (Kučerka et al., 2012 J. Phys. Chem. B 116: 232-239; Pan et al., 2012 Biochim. Biophys. Acta Biomembr. 1818: 2135-2148), which were determined using the scattering density profile model. This hybrid experimental/computational technique utilizes molecular dynamics simulations to parse a lipid bilayer into components whose volume probabilities follow simple analytical functional forms. Given the appropriate scattering densities, these volume probabilities are then translated into neutron scattering length density (NSLD) and electron density (ED) profiles, which are used to jointly refine experimentally obtained small angle neutron and X-ray scattering data...
November 2014: Biochimica et Biophysica Acta
Jianjun Pan, Xiaolin Cheng, Luca Monticelli, Frederick A Heberle, Norbert Kučerka, D Peter Tieleman, John Katsaras
Phosphatidylserine (PS) lipids play essential roles in biological processes, including enzyme activation and apoptosis. We report on the molecular structure and atomic scale interactions of a fluid bilayer composed of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphatidylserine (POPS). A scattering density profile model, aided by molecular dynamics (MD) simulations, was developed to jointly refine different contrast small-angle neutron and X-ray scattering data, which yielded a lipid area of 62.7 Å(2) at 25 °C. MD simulations with POPS lipid area constrained at different values were also performed using all-atom and aliphatic united-atom models...
June 7, 2014: Soft Matter
Peter Heftberger, Benjamin Kollmitzer, Frederick A Heberle, Jianjun Pan, Michael Rappolt, Heinz Amenitsch, Norbert Kučerka, John Katsaras, Georg Pabst
The highly successful scattering density profile (SDP) model, used to jointly analyze small-angle X-ray and neutron scattering data from unilamellar vesicles, has been adapted for use with data from fully hydrated, liquid crystalline multilamellar vesicles (MLVs). Using a genetic algorithm, this new method is capable of providing high-resolution structural information, as well as determining bilayer elastic bending fluctuations from standalone X-ray data. Structural parameters such as bilayer thickness and area per lipid were determined for a series of saturated and unsaturated lipids, as well as binary mixtures with cholesterol...
February 1, 2014: Journal of Applied Crystallography
Frederick A Heberle, Milka Doktorova, Shih Lin Goh, Robert F Standaert, John Katsaras, Gerald W Feigenson
Nanometer-scale domains in cholesterol-rich model membranes emulate lipid rafts in cell plasma membranes (PMs). The physicochemical mechanisms that maintain a finite, small domain size are, however, not well understood. A special role has been postulated for chain-asymmetric or hybrid lipids having a saturated sn-1 chain and an unsaturated sn-2 chain. Hybrid lipids generate nanodomains in some model membranes and are also abundant in the PM. It was proposed that they align in a preferred orientation at the boundary of ordered and disordered phases, lowering the interfacial energy and thus reducing domain size...
October 9, 2013: Journal of the American Chemical Society
Tatyana M Konyakhina, Jing Wu, James D Mastroianni, Frederick A Heberle, Gerald W Feigenson
We report the first 4-component phase diagram for the lipid bilayer mixture, DSPC/DOPC/POPC/chol (distearoylphosphatidylcholine/dioleoylphosphatidylcholine/1-palmitoyl, 2-oleoylphosphatidylcholine/cholesterol). This phase diagram, which has macroscopic Ld+Lo phase domains, clearly shows that all phase boundaries determined for the 3-component mixture containing DOPC transition smoothly into the boundaries for the 3-component mixture containing POPC, which has nanoscopic phase domains of Ld+Lo. Our studies start from two published ternary phase diagrams, and show how these can be combined into a quaternary phase diagram by study of a few hundred samples of intermediate compositions...
September 2013: Biochimica et Biophysica Acta
David G Ackerman, Frederick A Heberle, Gerald W Feigenson
The properties of lipid bilayer nanometer-scale domains could be crucial for understanding cell membranes. Fluorescent probes are often used to study bilayers, yet their effects on host lipids are not well understood. We used molecular dynamics simulations to investigate perturbations in a fluid DPPC bilayer upon incorporation of three indocarbocyanine probes: DiI-C18:0, DiI-C18:2, or DiI-C12:0. We find a 10-12% decrease in chain order for DPPC in the solvation shell nearest the probe but smaller effects in subsequent shells, indicating that the probes significantly alter only their local environment...
May 2, 2013: Journal of Physical Chemistry. B
Jianjun Pan, Frederick A Heberle, Robin S Petruzielo, John Katsaras
The cell plasma membrane is a complex system, which is thought to be capable of exhibiting non-random lateral organization. Studies of live cells and model membranes have yielded mechanisms responsible for the formation, growth, and maintenance of nanoscopic heterogeneities, although the existence and mechanisms that give rise to these heterogeneities remain controversial. Small-angle neutron scattering (SANS) is a tool ideally suited to interrogate lateral heterogeneity in model membranes, primarily due to its unique spatial resolution (i...
May 2013: Chemistry and Physics of Lipids
Frederick A Heberle, Robin S Petruzielo, Jianjun Pan, Paul Drazba, Norbert Kučerka, Robert F Standaert, Gerald W Feigenson, John Katsaras
The observation of lateral phase separation in lipid bilayers has received considerable attention, especially in connection to lipid raft phenomena in cells. It is widely accepted that rafts play a central role in cellular processes, notably signal transduction. While micrometer-sized domains are observed with some model membrane mixtures, rafts much smaller than 100 nm-beyond the reach of optical microscopy-are now thought to exist, both in vitro and in vivo. We have used small-angle neutron scattering, a probe free technique, to measure the size of nanoscopic membrane domains in unilamellar vesicles with unprecedented accuracy...
May 8, 2013: Journal of the American Chemical Society
Robin S Petruzielo, Frederick A Heberle, Paul Drazba, John Katsaras, Gerald W Feigenson
Membrane raft size measurements are crucial to understanding the stability and functionality of rafts in cells. The challenge of accurately measuring raft size is evidenced by the disparate reports of domain sizes, which range from nanometers to microns for the ternary model membrane system sphingomyelin (SM)/1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC)/cholesterol (Chol). Using Förster resonance energy transfer (FRET) and differential scanning calorimetry (DSC), we established phase diagrams for porcine brain SM (bSM)/dioleoyl-sn-glycero-3-phosphocholine (DOPC)/Chol and bSM/POPC/Chol at 15 and 25°C...
April 2013: Biochimica et Biophysica Acta
Jianjun Pan, Xiaolin Cheng, Frederick A Heberle, Barmak Mostofian, Norbert Kučerka, Paul Drazba, John Katsaras
Cholesterol and ether lipids are ubiquitous in mammalian cell membranes, and their interactions are crucial in ether lipid mediated cholesterol trafficking. We report on cholesterol's molecular interactions with ether lipids as determined using a combination of small-angle neutron and X-ray scattering, and all-atom molecular dynamics (MD) simulations. A scattering density profile model for an ether lipid bilayer was developed using MD simulations, which was then used to simultaneously fit the different experimental scattering data...
December 27, 2012: Journal of Physical Chemistry. B
Frederick A Heberle, Jianjun Pan, Robert F Standaert, Paul Drazba, Norbert Kučerka, John Katsaras
Some of our recent work has resulted in the detailed structures of fully hydrated, fluid phase phosphatidylcholine (PC) and phosphatidylglycerol (PG) bilayers. These structures were obtained from the joint refinement of small-angle neutron and X-ray data using the scattering density profile (SDP) models developed by Kučerka et al. (Biophys J 95:2356-2367, 2008; J Phys Chem B 116:232-239, 2012). In this review, we first discuss models for the standalone analysis of neutron or X-ray scattering data from bilayers, and assess the strengths and weaknesses inherent to these models...
October 2012: European Biophysics Journal: EBJ
Jianjun Pan, Frederick A Heberle, Stephanie Tristram-Nagle, Michelle Szymanski, Mary Koepfinger, John Katsaras, Norbert Kučerka
We have determined the molecular structures of commonly used phosphatidylglycerols (PGs) in the commonly accepted biologically relevant fluid phase. This was done by simultaneously analyzing small angle neutron and X-ray scattering data, with the constraint of measured lipid volumes. We report the temperature dependence of bilayer parameters obtained using the one-dimensional scattering density profile model - which was derived from molecular dynamics simulations - including the area per lipid, the overall bilayer thickness, as well as other intrabilayer parameters (e...
September 2012: Biochimica et Biophysica Acta
Frederick A Heberle, Gerald W Feigenson
Cell membranes show complex behavior, in part because of the large number of different components that interact with each other in different ways. One aspect of this complex behavior is lateral organization of components on a range of spatial scales. We found that lipid-only mixtures can model the range of size scales, from approximately 2 nm up to microns. Furthermore, the size of compositional heterogeneities can be controlled entirely by lipid composition for mixtures such as 1,2-distearoyl-sn-glycero-3-phosphocholine (DSPC)/1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC)/1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC)/cholesterol or sphingomyelin (SM)/DOPC/POPC/cholesterol...
April 2011: Cold Spring Harbor Perspectives in Biology
Frederick A Heberle, Jing Wu, Shih Lin Goh, Robin S Petruzielo, Gerald W Feigenson
Phase diagrams of ternary lipid mixtures containing cholesterol have provided valuable insight into cell membrane behaviors, especially by describing regions of coexisting liquid-disordered (Ld) and liquid-ordered (Lo) phases. Fluorescence microscopy imaging of giant unilamellar vesicles has greatly assisted the determination of phase behavior in these systems. However, the requirement for optically resolved Ld + Lo domains can lead to the incorrect inference that in lipid-only mixtures, Ld + Lo domain coexistence generally shows macroscopic domains...
November 17, 2010: Biophysical Journal
Thalia T Mills, Stephanie Tristram-Nagle, Frederick A Heberle, Nelson F Morales, Jiang Zhao, Jing Wu, Gilman E S Toombes, John F Nagle, Gerald W Feigenson
Wide angle x-ray scattering (WAXS) from oriented lipid multilayers is used to examine liquid-ordered (Lo)/liquid-disordered (Ld) phase coexistence in the system 1,2-dioleoyl-sn-glycero-3-phosphocholine/1,2-dipalmitoyl-sn-glycero-3-phosphocholine/cholesterol (DOPC/DPPC/Chol), which is a model for the outer leaflet of the animal cell plasma membrane. Using the method of analysis developed in the accompanying work, we find that two orientational distributions are necessary to fit the WAXS data at lower temperatures, whereas only one distribution is needed at temperatures higher than the miscibility transition temperature, T(mix) = 25-35 degrees C (for 1:1 DOPC/DPPC with 15%, 20%, 25%, and 30% Chol)...
July 2008: Biophysical Journal
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