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The present report assesses the capability of a soluble glycosyltransferase to modify glycolipids organized in two synthetic membrane systems that are attractive models to mimic cell membranes: giant unilamellar vesicles (GUVs) and supported lipid bilayers (SLBs). The objective was to synthesize the Gb3 antigen (Galα1,4Galβ1,4Glcβ-Cer), a cancer biomarker, at the surface of these membrane models. A soluble form of LgtC that adds a galactose residue from UDP-Gal to lactose-containing acceptors was selected. Although less efficient than with lactose, the ability of LgtC to utilize lactosyl–ceramide as an acceptor was demonstrated on GUVs and SLBs. The reaction was monitored using the B-subunit of Shiga toxin as Gb3-binding lectin. Quartz crystal microbalance with dissipation analysis showed that transient binding of LgtC at the membrane surface was sufficient for a productive conversion of LacCer to Gb3. Molecular dynamics simulations provided structural elements to help rationalize experimental data. [ABSTRACT FROM AUTHOR]

We describe a method that combines colloidal probe atomicforcemicroscopy (AFM) and reflection interference contrast microscopy (RICM)to characterize the mechanical properties of thin and solvated polymerfilms. When analyzing polymer films, a fundamental problem in colloidalprobe AFM experiments is to determine the distance at closest approachbetween the probe and the substrate on which the film is deposited.By combining AFM and RICM in situ, forces and absolute distances canbe measured simultaneously. Using the combined setup, we quantifythe compressive mechanics of films of the polysaccharide hyaluronanthat is end-grafted to a supported lipid bilayer. The experimentaldata, and comparison with polymer theory, show that hyaluronan films are well-describedas elastic, very soft and highly solvated polymer brushes. The dataon these well-defined films should be a useful reference for the investigationof the more complex hyaluronan-rich coats that surround many livingcells. [ABSTRACT FROM AUTHOR]

The current interest in reconstituting biological membranes on solid supports aims at linking the biological world, with its elaborate molecular architectures, properties, and functions, to the field of surface science, with its advanced technologies and sophisticated surface-sensitive analytical methods. Success in this enterprise would not only improve our understanding and description of basic cellular functions but also help developing biotechnological tools, biomedical devices, or biofunctional materials. To achieve this goal, reliable methods need to be developed for controlling the formation of solid-supported lipid membranes and the deposition, incorporation, and addressing of biological entities, from molecules to cells.This review focuses on a versatile approach that combines the formation of solid-supported lipid bilayers (SLBs) by deposition of lipid vesicles with the adsorption of proteins and formation of ordered protein layers via specific interaction with ligands incorporated in the SLBs. This approach provides access to basic aspects of membrane biophysics, membrane-protein interactions, and molecular ordering in two dimensions. It may also constitute a strategy for the design of biofunctional surfaces at the nanoscale. [Copyright &y& Elsevier]

The article presents a method of creating hyaluronan films that are well-defined in their molecular attachment to the substrate, a supported lipid bilayer (SLB). According to the authors, the subjection to a solid support makes the model coats available to characterization with a range of surface-sensitive techniques. They examine the films' thickness, grafting density, permeability and mechanical properties.

Decoratinglipid bilayers with oligonucleotides has great potentialfor both fundamental studies and applications, taking advantage ofthe membrane properties and the specific Watson–Crick basepairing. Here, we systematically studied the binding of DNA oligonucleotideswith the frequently used hydrophobic anchors cholesterol, stearyl,and distearyl to supported lipid bilayers made of dioleoylphosphatidylcholine(DOPC) by quartz crystal microbalance with dissipation monitoringand spectroscopic ellipsometry (SE). All three anchors were foundto incorporate well into DOPC lipid membranes, yet only the distearyl-basedanchor remained stable in the bilayer when it was rinsed. The unstableanchoring of the cholesterol- and stearyl-based oligonucleotides can,however, be stabilized by hybridization of the oligonucleotides tocomplementary DNA modified with a second hydrophobic anchor of thesame type. In all cases, the incorporation into the lipid bilayerwas found to be limited by mass transport, although micelle formationlikely reduced the effective concentration of available oligonucleotidesin some samples, leading to substantial differences in binding rates.Using a viscoelastic model to determine the thickness of the DNA layerand elucidating the surface coverage by SE, we found that at equalbulk concentrations double-stranded DNA constructs attached to thelipid bilayer establish a layer that is thicker than that of single-strandedoligonucleotides, whereas the DNA surface densities are similar. Shorteningthe length of the oligonucleotides, on the other hand, does alterboth the thickness and surface density of the DNA layer. This indicatesthat at the bulk oligonucleotide concentrations employed in our experiments,the packing of the oligonucleotides is not affected by the anchortype, but rather by the length of the DNA. The results are usefulfor material and biomedical applications that require efficient linkingof oligonucleotides to lipid membranes. [ABSTRACT FROM AUTHOR]

Abstract: A challenge to mimicking nature''s “bottom up” approach to generate tissue is the coordination of cellular self-assembly and emergent phenotype. Here we create a biosynthetic platform to mimic native cell–cell interactions and to drive emergent tissue behavior by human multipotent cells from the periosteal niche, i.e. PDCs, whose regenerative capacity is equal or greater to those from the bone marrow niche. Western blots showed that human PDCs express proteins for both N-cadherin, a hallmark of mesenchymal condensation, as well as for ZO-1, a tight junction membrane protein conferring epithelial barrier membrane properties. Hence, we functionalized a solid supported lipid bilayer (SLB) membrane with recombinant N-cadherin and investigated the short term phenotype of PDCs seeded on unfunctionalized and N-cadherin functionalized SLBs compared to that of PDCs seeded on glass coverslips. After 24 h, SLB functionalization promoted aggregation of PDCs seeded at high density (35,000 cells/cm2), with no significant concomitant changes in transcription of N-cadherin (CDH2) as measured by rtPCR. In contrast, cells seeded on unfunctionalized SLBs remained non-adherent but showed a significant upregulation in transcription of N-cadherin. Furthermore, culture of PDCs at high density on N-cadherin functionalized SLBs was negatively correlated with expression of ZO-1, while culture on unfunctionalized SLBs was positively correlated with the expression of the tight junction membrane protein. High density seeding on N-cadherin functionalized and unfunctionalized SLBs places PDCs in distinct cellular contexts and relates to emergent behavior typical for mesenchymal condensation. These studies demonstrate a biosynthetic in vitro cell culture platform to elucidate and guide emergent tissue architectures by PDCs. [Copyright &y& Elsevier]