Two-Phase Contiguous Supported Lipid Bilayer Model for Membrane Rafts via Polymer Blotting and Stenciling

Kinetics of Ganglioside-Rich Supported Lipid Bilayer Formation with Tracer Vesicle Fluorescence Imaging

Gangliosides, forming a class of lipids complemented by sugar chains, influence the lateral distribution of membrane proteins or membrane-binding proteins, act as receptors for viruses and bacterial toxins, and mediate several types of cellular signaling. Gangliosides incorporated into supported lipid bilayers (SLBs) have been widely applied as a model system to examine these biological processes. In this work, we explored how ganglioside composition affects the kinetics of SLB formation using the vesicle rupturing method on a solid surface. We imaged the attachment of vesicles and the subsequent SLB formation using the time-lapse total internal reflection fluorescence microscopy technique. In the early phase, the ganglioside type and concentration influence the adsorption kinetics of vesicles and their residence/lifetime on the surface before rupturing. Our data confirm that a simultaneous rupturing of neighboring surface-adsorbed vesicles forms microscopic lipid patches on the surface and it is triggered by a critical coverage of the vesicles independent of their composition. In the SLB growth phase, lipid patches merge, forming a continuous SLB. The propagation of patch edges catalyzes the process and depends on the ganglioside type. Our pH-dependent experiments confirm that the polar/charged head groups of the gangliosides have a critical role in these steps and phases of SLB formation kinetics.

Multiplexed patterning of hybrid lipid membrane and protein arrays for cell signaling study

The supported lipid bilayer (SLB) is a powerful tool for studying dynamic cell-environment interactions and has been widely used for biosensing applications. Using a reusable microfluidic chip, we present here a strategy to fabricate highly multiplexed SLB and protein arrays for cell signaling research. This approach allows for the rapid patterning of hundreds of highly reproducible and size-tunable SLB arrays with distinct lipid composition and mobility. Using fluorescence microscopy and fluorescence correlation spectroscopy, the lipid mobility is found to play a central role for patterning this membrane assay. Adding protein rings as diffusion barriers extends the accessible mobility range and maintains long-term stability of the hybrid array. Subsequent protein functionalizations on the SLB could be conducted using standard conjugation methods. The utility of the hybrid array for cell signaling experiments is demonstrated by studying the immune NF-κB signaling, whose activity is triggered by the binding of the membrane receptor, toll-like-receptor 4 (TLR 4), to its ligand, lipopolysaccharide (LPS), that is functionalized on the SLB. The patterned array allows cells to adhere and spread on areas without LPS before migrating to interact with membrane-bound LPS to initiate NF-κB activation. Overall, the strategy offers an efficient route to rapidly generate easily controllable and multiplexed molecular arrays that can serve as versatile platforms for biosensing and cell signaling research.

Domain Sorting in Giant Unilamellar Vesicles Adsorbed on Glass

Giant unilamellar vesicles (GUVs) adsorb to a solid surface and rupture to form a planar bilayer patch. These bilayer patches are used to investigate the properties and functions of biological membranes. Therefore, it is crucial to understand the mechanisms of GUV adsorption. In this study, we investigate the adsorption of phase-separated GUVs on glass using fluorescence microscopy. GUVs containing liquid-ordered (L_o) and liquid-disordered (L_d) phases underwent domain sorting after adsorption. The L_d domain in the unbound region migrated to the highly curved region near the edge of the adsorbed region. Additionally, the L_o phase grew linearly along the edge of the adsorbed region, creating a thin ring-like domain. After the domain sorting event, the GUV ruptured to form a planar bilayer patch with circular-patterned domains in the initially adsorbed area. We found that domain sorting was promoted by increasing the extent of GUV deformation. These results suggest that both the L_d and L_o domains are reorganized for stabilizing the curved bilayer region in adsorbed GUVs.