Structural characterization of an elevated lipid bilayer obtained by stepwise functionalization of a self-assembled alkenyl silane film

Daniel, Christian; Sohn, Karen E.; Mates, Thomas E.; Krämer, Edward J.; Rädler, Joachim O.; Sackmann, E.; Nickel, Bert; Andruzzi, Luisa

doi:10.1116/1.2790852

Cited by 24 publications

(37 citation statements)

References 47 publications

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“…One may thus expect a similar architecture also on the solid surface, with a PEG layer between the Al oxide surface and the lipid monolayer. However, also intermixed phases of PEG and lipids (25), as well as the escape of PEG from the space between oxide surface and lipid layer (26), have been reported. In the present work, SWXF puts us in the position to accurately localize P atoms and thus directly discriminate between different scenarios.…”

Section: Resultsmentioning

confidence: 99%

Atom-scale depth localization of biologically important chemical elements in molecular layers

Schneck

Scoppola

Drnec

et al. 2016

Proc. Natl. Acad. Sci. U.S.A.

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In nature, biomolecules are often organized as functional thin layers in interfacial architectures, the most prominent examples being biological membranes. Biomolecular layers play also important roles in context with biotechnological surfaces, for instance, when they are the result of adsorption processes. For the understanding of many biological or biotechnologically relevant phenomena, detailed structural insight into the involved biomolecular layers is required. Here, we use standing-wave X-ray fluorescence (SWXF) to localize chemical elements in solid-supported lipid and protein layers with near-Ångstrom precision. The technique complements traditional specular reflectometry experiments that merely yield the layers' global density profiles. While earlier work mostly focused on relatively heavy elements, typically metal ions, we show that it is also possible to determine the position of the comparatively light elements S and P, which are found in the most abundant classes of biomolecules and are therefore particularly important. With that, we overcome the need of artificial heavy atom labels, the main obstacle to a broader application of high-resolution SWXF in the fields of biology and soft matter. This work may thus constitute the basis for the label-free, element-specific structural investigation of complex biomolecular layers and biological surfaces.surfaces | interfaces | lipid membranes | protein adsorption | X-ray scattering N anometric biomolecular layers in interfacial geometries are key components of biological matter. Biological membranes, for example, are 2D molecular structures composed mainly of lipids and proteins in an aqueous environment (1, 2). Interfacial biomolecular layers are also important from a biotechnological perspective, where surfaces are often designed to selectively promote or prevent the adsorption of bio(macro)molecules from solution (3). To investigate the diverse behavior of biomolecules at interfaces, well-defined planar model systems of biological and biotechnologically relevant interfaces have been established (4, 5). Processes involving biomolecules at interfaces are typically accompanied by a spatial reorganization of molecules, changes in molecular conformations, or the adsorption of molecules in a chemically heterogeneous environment (6). Structural insight on the nanometer scale is therefore of paramount importance.X-ray and neutron scattering are uniquely suited for the structural investigation of biomolecular systems. Specular reflectometry reveals matter density profiles perpendicular to a planar interface. However, it is generally difficult to elucidate molecular conformations and elemental distributions from such "global" density profiles. In contrast, standing-wave X-ray fluorescence (SWXF) allows determining element-specific density profiles across an interface. The SWXF technique is based on the elementcharacteristic fluorescence induced by a standing X-ray wave. The latter is formed by interference of the incident and reflected waves and its shape depends o...

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Section: Resultsmentioning

confidence: 99%

Atom-scale depth localization of biologically important chemical elements in molecular layers

Schneck

Scoppola

Drnec

et al. 2016

Proc. Natl. Acad. Sci. U.S.A.

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“…Within the second approach, the layer thickness was chosen to match the resolution of the experimental data. The resolution in a reflectometry experiment can be estimated by (π/q max ) (25). Here q max represents the maximum q value achieved before the reflectivity signal decreases below the background signal.…”

Section: Methodsmentioning

confidence: 99%

Arrangement of Annexin A2 tetramer and its impact on the structure and diffusivity of supported lipid bilayers

Fritz

Windschiegl

et al. 2010

Soft Matter

Self Cite

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Annexins are a family of proteins that bind to anionic phospholipid membranes in a Ca 2+ -dependent manner. Annexin A2 forms heterotetramers (Anx A2t) with the S100A10 (p11) protein dimer. The tetramer is capable of bridging phospholipid membranes and it has been suggested to play a role in Ca 2+ -dependent exocytosis and cell-cell adhesion of metastatic cells. Here, we employ x-ray reflectivity measurements to resolve the conformation of Anx A2t upon Ca 2+ -dependent binding to single supported lipid bilayers (SLBs) composed of different mixtures of anionic (POPS) and neutral (POPC) phospholipids. Based on our results we propose that Anx A2t binds in a side-byside configuration, i.e., both Anx A2 monomers bind to the bilayer with the p11 dimer positioned on top. Furthermore, we observe a strong decrease of lipid mobility upon binding of Anx A2t to SLBs with varying POPS content. X-ray reflectivity measurements indicate that binding of Anx A2t also increases the density of the SLB. Interestingly, in the protein-facing leaflet of the SLB the lipid density is higher than in the substrate-facing leaflet. This asymmetric densification of the lipid bilayer by Anx A2t and Ca 2+ might have important implications for the biochemical mechanism of Anx A2t-induced endo-and exocytosis.

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“…However, due to their simple geometry and proximity to the surface they offer an excellent model system for studying the self-assembly of lipid membranes and to probe membrane physicochemical properties by a wide range of techniques [105,109,111,113,[129][130][131]. Further, decoupling of the membrane from the surface by forming a tethered supported lipid bilayer (Figure 4c), first demonstrated by Vogel and coworkers [132], has been achieved primarily by forming a supported lipid bilayer onto a hydrophobic anchor layer separated from the surface by a short hydrophilic polymer spacer [59,111,[133][134][135][136][137][138][139][140][141][142][143][144], typically oligo(ethylene glycol) with a lipid anchor [111,132,[134][135][136][137]145,146]. The additional space of a few nanometers allows for integration of small transmembrane proteins without undesired surface interaction, but the reservoir is still too restricted to monitor continuous ion transport and the preparation can be difficult for solvent-free membranes [145].…”

Section: Supported Lipid Membrane Platformsmentioning

confidence: 99%

Nanoscale Biosensors and Biochips

Leifert

Glatz

Bailey

et al. 2009

Annual Review of Nano Research

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Structural characterization of an elevated lipid bilayer obtained by stepwise functionalization of a self-assembled alkenyl silane film

Cited by 24 publications

References 47 publications

Atom-scale depth localization of biologically important chemical elements in molecular layers

Atom-scale depth localization of biologically important chemical elements in molecular layers

Arrangement of Annexin A2 tetramer and its impact on the structure and diffusivity of supported lipid bilayers

Nanoscale Biosensors and Biochips

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