Nanoroughness Strongly Impacts Lipid Mobility in Supported Membranes

Abstract

In vivo lipid membranes interact with rough supramolecular structures such as protein clusters and fibrils. How these features whose size ranges from a few nanometers to a few tens of nanometers impact lipid and protein mobility is still being investigated. Here, we study supported phospholipid bilayers, a unique biomimetic model, deposited on etched surfaces bearing nanometric corrugations. The surface roughness and mean curvature are carefully characterized by AFM imaging using ultrasharp tips. Neutron specular reflectivity supplements this surface characterization and indicates that the bilayers follow the large-scale corrugations of the substrate. We measure the lateral mobility of lipids in both the fluid and gel phases by fluorescence recovery after patterned photobleaching. Although the mobility is independent of the roughness in the gel phase, it exhibits a 5-fold decrease in the fluid phase when the roughness increases from 0.2 to 10 nm. These results are interpreted with a two-phase model allowing for a strong decrease in the lipid mobility in highly curved or defect-induced gel-like nanoscale regions. This suggests a strong link between membrane curvature and fluidity, which is a key property for various cell functions such as signaling and adhesion.

Impact of nanoscale hindrances on the relationship between lipid packing and diffusion in model membranes

“…There is already substantial evidence of a support's influence on bilayer diffusion [25][26][27][28] . To further assess the influence of support on other pivotal biophysical parameters and the relationships between them, we have selected four models that broadly represent the spectrum of designs extensively utilised.…”

“…Lipid ordering was comparable between GUVs, SLBs, and BSLBs of equal composition -at least at the microscopic scale, suggesting a more direct influence of support on diffusion. Indeed, the drag imparted by a lipid support is widely appreciated 18,27 . However, our application of STED-FCS adds a spatial-temporal framework for these interactions and suggests repeated, but brief interactions between support and constituting lipids.…”

“…4A) with which nanoscale dynamics can be addressed 17,38 . In this regard, STED can glean assessment of bilayer dynamics in the context of surface architecture, an appreciated consideration in supported model design 27 . For instance, unwanted aggregates or surface defects could hinder diffusion of the fluorescent species as they travel through the observation spot and thus yield slow diffusion that is independent of the microscopic viscosity or lipid packing of the sample.…”

Nanoscale Substrate Roughness Hinders Domain Formation in Supported Lipid Bilayers

“…Increased roughness has been shown to reduce diffusion up to 5-fold on etched glass and silicon surfaces (Rq=0.1-3 nm) 47 and silicon zerogels (Rq=0.71 nm) 48…”

Nanometer-Scale Resolution Achieved with Nonradiative Excitation

“…Then, dynamical aspects of cell adhesion and migration can be studied as the acquisition time is typically few hundreds ms. NEFM is also relevant to study th interaction and diusion of supported lipid bilayers on nanoroughness surfaces. 42 Finally, this method is also well suited to study biological samples as it was previously demonstrated. 19 We believe that our technic can be used to probe the dynamic of focal adhesions and also localize precisely cell integrins involved in the focal adhesion plaques.…”