Polymer-Cushioned Bilayers. II. An Investigation of Interaction Forces and Fusion Using the Surface Forces Apparatus

Wong, Joyce Y.; Park, Chad K.; Seitz, Markus; Israelachvili, Jacob N.

doi:10.1016/s0006-3495(99)76993-6

Cited by 115 publications

(140 citation statements)

References 50 publications

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“…Such a preserved "dynamic behavior" is in good agreement with the recently observed "self-healing" of two polyethylenimine-supported DMPC bilayers after their hemifusion in the surface forces apparatus. 17 In summary, this AFM study provides evidence of tethered lipid bilayer formation by vesicle adsorption onto lipopolymer monolayers. Polymer hydration has been found earlier to be an important factor governing this process.…”

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confidence: 69%

Formation of Tethered Supported Bilayers by Vesicle Fusion onto Lipopolymer Monolayers Promoted by Osmotic Stress

et al. 2000

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Lipid bilayer systems have been used extensively to study the structure and function of biomembranes including molecular recognition, permeation, adhesion, and fusion. 1-5 Further interest arises from their potential use as biosensors.6 , 7 While classical black lipid bilayer membranes are highly suitable as such model systems, they suffer from their limited long-term stability. 1 Additionally, to apply the broad range of surface sensitive experimental techniques developed in recent years for the characterization of ultrathin films, it is often necessary to immobilize lipid bilayers on solid supports. However, lateral fluidity of the lipid membrane is governed by the physical and chemical properties of the solid substrate. Thus, bilayer membranes prepared by the Langmuir-Blodgett (LB) technique or by vesicle fusion directly onto solid substrates are often polycrystalline or amorphous, and lateral lipid mobility within the membrane is restricted. While on hydrophilic oxidized silicon or glass a water layer (~1 nm thick) is formed which allows for free diffusion of phospholipid molecules (but not membrane-spanning proteins) within the bilayer,8 -10 on most other metals and metal oxides, lipid mobility is strongly suppressed.11 , 12 To preserve the membrane's natural properties, one promising approach is to rest it on a water-swellable (hydrophilic) polymer or polyelectrolyte cushion which can act as a deformable and mobile substrate6 , 13 , 14 like the cytoskeletal support in living cells. Such softly supported lipid bilayers can, in principle, exist in an entirely fluid state, nearly undisturbed by the presence of the supporting polymer gel which provides an aqueous compartment between the solid substrate and the membrane. In our recent work, we have studied DMPC bilayers on a highly branched cationic polymer (polyethylenimine, PEI). Important structural information about these polymer-supported bilayer systems formed by various preparation methods was provided by neutron scattering experiments.15 , 16 Furthermore, measuring the intermembrane interaction forces using the surface forces apparatus (SFA) technique has shown the effect of fluidity on membrane functionality.17These physisorbed, polymer-supported bilayers are only the first step in the approach of creating artificial biomembranes that more closely resemble living cells. To provide more biologically relevant architectures, molecular assemblies of increased complexity and longterm stability have been tested, including a partial chemical fixation of the membrane's lipids to the underlying polymeric substrate. 7,14,18,19 However, the construction of such "asymmetric" tethered supported membranes is not always straightforward, and each particular NIH Public Access Author ManuscriptLangmuir. Author manuscript; available in PMC 2010 October 13. NIH-PA Author ManuscriptNIH-PA Author Manuscript NIH-PA Author Manuscript system needs to be optimized. The most versatile approach appears to be vesicle fusion onto polymer-supported lipid monolayers previously prep...

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confidence: 69%

Formation of Tethered Supported Bilayers by Vesicle Fusion onto Lipopolymer Monolayers Promoted by Osmotic Stress

et al. 2000

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“…18 This allowed us to study the interaction forces, adhesion, and fusion of lipid bilayers in a more natural state employing the surface forces apparatus (SFA). 19 We found that the presence of the soft polymer cushion significantly alters the interaction between two bilayers, both the long-range force and the fusion pressure, when compared to solid-or rigidly supported systems. Thus, above the main transition temperature of DMPC bilayers (T m ≈ 24 °C), the activation pressure for hemifusion of softly supported bilayers is considerably smaller than for rigidly supported bilayers (i.e., directly supported on mica).…”

Section: Introductionmentioning

confidence: 82%

“…Below T m (in the gel state), very high pressures were needed for hemifusion and the healing process became very slow. 19 In our earlier work, we focused on the effects of the polymer layer on the short-range interaction potential, but we also measured a long-range repulsive force that could not be explained by a purely electrostatic interaction. Furthermore, in structural investigations of our PEI-supported membrane system by neutron reflectivity, we were able to show a significant swelling of the polyelectrolyte cushion separating the lipid membrane from the substrate (quartz).…”

Section: Introductionmentioning

confidence: 99%

Long-Range Interaction Forces between Polymer-Supported Lipid Bilayer Membranes

et al. 2001

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Much of the short-range forces and structures of softly supported DMPC bilayers has been described previously. However, one interesting feature of the measured force-distance profile that remained unexplained is the presence of a long-range exponentially decaying repulsive force that is not observed between rigidly supported bilayers on solid mica substrate surfaces. This observation is discussed in detail here based on recent static and dynamic surface force experiments. The repulsive forces in the intermediate distance regime (mica-mica separations from 15 to 40 nm) are shown to be due not to an electrostatic force between the bilayers but to compression (deswelling) of the underlying soft polyelectrolyte layer, which may be thought of as a model cytoskeleton. The experimental data can be fit by simple theoretical models of polymer interactions from which the elastic properties of the polymer layer can be deduced.

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“…This happens when their surfaces are dehydrated beyond a critical point, tipping the energetic balance in favor of radically curved nonbilayer structures (such as inverted hexagonal phases, rhombohedral phases) 71, 72. An analogous abrupt transition is also observed when two bilayers are directly pressured together in the surfaces forces apparatus 73. Following on this pioneering work, detailed measurements suggest that the transition pressure is in the range of 200–500 atm (one atm is the typical pressure of the atmosphere at sea level) for lipid compositions bracketing the inner leaflets of the SV and PM (see Appendix 1 for details) 48, 49.…”

Section: Quantitative Considerationsmentioning

confidence: 99%

Hypothesis – buttressed rings assemble, clamp, and release SNAREpins for synaptic transmission

et al. 2017

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Neural networks are optimized to detect temporal coincidence on the millisecond timescale. Here, we offer a synthetic hypothesis based on recent structural insights into SNAREs and the C2 domain proteins to explain how synaptic transmission can keep this pace. We suggest that an outer ring of up to six curved Munc13 ‘MUN’ domains transiently anchored to the plasma membrane via its flanking domains surrounds a stable inner ring comprised of synaptotagmin C2 domains to serve as a work‐bench on which SNAREpins are templated. This ‘buttressed‐ring hypothesis’ affords straightforward answers to many principal and long‐standing questions concerning how SNAREpins can be assembled, clamped, and then released synchronously with an action potential.

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Polymer-Cushioned Bilayers. II. An Investigation of Interaction Forces and Fusion Using the Surface Forces Apparatus

Cited by 115 publications

References 50 publications

Formation of Tethered Supported Bilayers by Vesicle Fusion onto Lipopolymer Monolayers Promoted by Osmotic Stress

Formation of Tethered Supported Bilayers by Vesicle Fusion onto Lipopolymer Monolayers Promoted by Osmotic Stress

Long-Range Interaction Forces between Polymer-Supported Lipid Bilayer Membranes

Hypothesis – buttressed rings assemble, clamp, and release SNAREpins for synaptic transmission

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