Noninvasive Neutron Scattering Measurements Reveal Slower Cholesterol Transport in Model Lipid Membranes

Garg, Sumit; Porcar, Lionel; Woodka, Andrea; Butler, Paul; Perez-Salas, Ursula

doi:10.1016/j.bpj.2011.06.014

Cited by 71 publications

(81 citation statements)

References 39 publications

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“…The lipids in each bilayer leaflet are known to spontaneously exchange 92 in a process called 'flip-flop', reducing any imposed asymmetry as a function of time. This 'flip-flop' rate is a feature of the state of the lipids themselves, as well as their acyl chain length, the presence of ions in the buffer and/or supporting interfaces [93][94][95][96][97] .…”

Section: Supported Lipid Bilayersmentioning

confidence: 99%

Lateral organization, bilayer asymmetry, and inter-leaflet coupling of biological membranes

Nickels

Smith

Cheng

2015

Chemistry and Physics of Lipids

108

115

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Understanding of cell membrane organization has evolved significantly from the classic fluid mosaic model. It is now recognized that biological membranes are highly organized structures, with differences in lipid compositions between inner and outer leaflets and in lateral structures within the bilayer plane, known as lipid rafts. These organizing principles are important for protein localization and function as well as cellular signaling. However, the mechanisms and biophysical basis of lipid raft formation, structure, dynamics and function are not clearly understood. One key question, which we focus on in this review, is how lateral organization and leaflet compositional asymmetry are coupled. Detailed information elucidating this question has been sparse because of the small size and transient nature of rafts and the experimental challenges in constructing asymmetric bilayers. Resolving this mystery will require advances in both experimentation and modeling. We discuss here the preparation of model systems along with experimental and computational approaches that have been applied in efforts to address this key question in membrane biology. We seek to place recent and future advances in experimental and computational techniques in context, providing insight into in-plane and transverse organization of biological membranes.

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Section: Supported Lipid Bilayersmentioning

confidence: 99%

Lateral organization, bilayer asymmetry, and inter-leaflet coupling of biological membranes

Nickels

Smith

Cheng

2015

Chemistry and Physics of Lipids

108

115

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“…Thus, cholesterol and SipB mediate the preferential targeting of mitotic cells by Salmonella. Interestingly, Salmonella invades cycling but not quiescent stem cells in a SipB-and (Garg et al, 2011), we also used a fluorescent ester of polyethylene glycol-cholesterol (fPEG-cholesterol; Fig. 3D-F), which partitions in cholesterol-rich domains.…”

Section: Surface Cholesterol Mediates Targeting Of Mitotic Cells By Smentioning

confidence: 99%

Preferential invasion of mitotic cells by Salmonella reveals that cell surface cholesterol is maximal during metaphase

Santos

Meinecke

Fessler

et al. 2013

Journal of Cell Science

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SummaryCell surface-exposed cholesterol is crucial for cell attachment and invasion of many viruses and bacteria, including the bacterium Salmonella, which causes typhoid fever and gastroenteritis. Using flow cytometry and 3D confocal fluorescence microscopy, we found that mitotic cells, although representing only 1-4% of an exponentially growing population, were much more efficiently targeted for invasion by Salmonella. This targeting was not dependent on the spherical shape of mitotic cells, but was instead SipB and cholesterol dependent. Thus, we measured the levels of plasma membrane and cell surface cholesterol throughout the cell cycle using, respectively, brief staining with filipin and a fluorescent ester of polyethylene glycol-cholesterol that cannot flip through the plasma membrane, and found that both were maximal during mitosis. This increase was due not only to the rise in global cell cholesterol levels along the cell cycle but also to a transient loss in cholesterol asymmetry at the plasma membrane during mitosis. We measured that cholesterol, but not phosphatidylserine, changed from a ,20:80 outer:inner leaflet repartition during interphase to ,50:50 during metaphase, suggesting this was specific to cholesterol and not due to a broad change of lipid asymmetry during metaphase. This explains the increase in outer surface levels that make dividing cells more susceptible to Salmonella invasion and perhaps to other viruses and bacteria entering cells in a cholesterol-dependent manner. The change in cholesterol partitioning also favoured the recruitment of activated ERM (Ezrin, Radixin, Moesin) proteins at the plasma membrane and thus supported mitotic cell rounding.

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“…At SDD 13 m, focusing lenses were employed to increase the average neutron wavelength and access lower scattering vectors: wavelengths were λ = 6 Å without lenses and λ = 8 Å with lenses, with wavelength resolution Δλ/λ = 11–15%. For a dilute solution (such as our 10 mg mL −1 PEO–PPO–PEO solutions) particles are approximately noninteracting, and the scattering intensity I(Q) can be calculated using Equation

I (Q) = n V^{2} {(ρ_{normalparticle} - ρ_{normalsolvent})}^{2} P (Q)

where n is the particle number density, V is particle volume, P ( Q ) is a shape‐dependent particle form factor, and ρ is the particle or solvent scattering length density (SLD) . We calculated that the average SLD of PEO–PPO–PEO is 0.5 × 10 −6 Å −2 using scattering lengths from the NCNR SLD calculator and Equation

ρ = \frac{\sum b_{i}}{v_{normalm}}

where b i is the neutron scattering cross section of atom i in the molecule of interest and v m is the molecular volume.…”

Section: Methodsmentioning

confidence: 99%

Porous Vesicles with Extrusion‐Tunable Permeability and Pore Size from Mixed Solutions of PEO–PPO–PEO Triblock Copolymers

Schantz

Ren

Pachalla

et al. 2018

Macro Chemistry & Physics

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Block copolymer (BC) vesicles in aqueous solution can encapsulate hydrophilic molecules or nanoparticles for drug and gene delivery, enhanced imaging, microreactors, or sensors. Inexpensive, biocompatible poly(ethylene oxide)–poly(propylene oxide)–poly(ethylene oxide) (PEO–PPO–PEO) triblock copolymers (TBCs) would be ideal for these applications if they could form concentrated vesicle solutions to encapsulate such molecules with high efficiency. It is shown that solutions of two PEO–PPO–PEO TBCs (EO5–PO68–EO5 and EO100–PO65–EO100) form vesicles, that the vesicle membranes are permeable to low‐molecular weight (MW) solutes, and that extrusion reduces the membrane permeability and MW cutoff. Osmotic permeabilities before and after extrusion are ≈1000 and ≈10 µm s−1, respectively, while the MW cutoffs for solute rejection are ≈1000 and ≈400 g mol−1. Therefore, it is hypothesized that the vesicles contain pores, and that extrusion reduces the pores' size and the membrane's porosity. These selectively permeable vesicles can function as microreactors or sensors encapsulating large solutes without the need to add channel molecules or proteins.

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Noninvasive Neutron Scattering Measurements Reveal Slower Cholesterol Transport in Model Lipid Membranes

Cited by 71 publications

References 39 publications

Lateral organization, bilayer asymmetry, and inter-leaflet coupling of biological membranes

Lateral organization, bilayer asymmetry, and inter-leaflet coupling of biological membranes

Preferential invasion of mitotic cells by Salmonella reveals that cell surface cholesterol is maximal during metaphase

Porous Vesicles with Extrusion‐Tunable Permeability and Pore Size from Mixed Solutions of PEO–PPO–PEO Triblock Copolymers

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