Impact of Nanoscale Hindrances on the Relationship between Lipid Packing and Diffusion in Model Membranes

Abstract

Membrane models have allowed for precise study of the plasma membrane's biophysical properties, helping to unravel both structural and dynamic motifs within cell biology. Freestanding and supported bilayer systems are popular models to reconstitute membrane-related processes. Although it is wellknown that each have their advantages and limitations, comprehensive comparison of their biophysical properties is still lacking. Here, we compare the diffusion and lipid packing in giant unilamellar vesicles, planar and spherical supported membranes, and cell-derived giant plasma membrane vesicles. We apply florescence correlation spectroscopy (FCS), spectral imaging, and super-resolution stimulated emission depletion FCS to study the diffusivity, lipid packing, and nanoscale architecture of these membrane systems, respectively. Our data show that lipid packing and diffusivity is tightly correlated in freestanding bilayers. However, nanoscale interactions in the supported bilayers cause deviation from this correlation. These data are essential to develop accurate theoretical models of the plasma membrane and will serve as a guideline for suitable model selection in future studies to reconstitute biological processes.

Model membrane systems to reconstitute immune cell signaling

“…From yeast to mammals, sterols and acyl chain unsaturation are key factors of cellular membranes modulating membrane fluidity. As such, building synthetic LBs using phospholipids composed of fatty acids of varying lengths and saturation, as well as of varying sterol percentages, allows a fine tailoring of lipid packing and diffusion coefficients [12][13][14]. Beyond phospholipid composition, cholesterol concentration plays a dominant role in determining lipid packing and bilayer fluidity, with increasing concentrations leading to substantial packing and reduction in the diffusion coefficient of synthetic LBs [14].…”

“…An additional factor influencing fluidity is the presence of a support, which can be considered as a mimic of the cytoskeleton [19][20][21][22][23][24][25]. Even at equal phospholipid compositions, supports significantly influence lipid lateral mobility by imposing hindrances dependent among others on the substrate roughness, curvature, and nanoscale topography [14,[26][27][28][29].…”

“…Evidently, GUVs offer unique advantages regarding their 3D features and biophysical properties, positioning them between planar and bead SLBs [14]. However, though GUVs are an attractive model to study the cellular membrane, their soft exterior and fluidity also become their downfall; GUVs rupture in harsh experimental conditions such as extreme pH or high salt concentrations, or upon excessive washing [41].…”

“…Current methodologies are constantly being improved to mimic more closely the composition, asymmetry, and biophysical properties of cellular membranes. For instance, lipid matrixes comprising the neutral phosphocholine (PC) can be further tailored by varying the ratios of species differing in their acyl chain saturation; two [1,2-dioleoyl-sn-glycero-3-PC (DOPC)], one [1palmitoyl-2-oleoyl-sn-glycero-3-PC (POPC)], or no unsaturation [1,2-dipalmitoyl-sn-glycero-3-PC (DPPC)] lead to diffusion coefficients in the order DOPC > POPC ≫ DPPC [14]. Moreover, cholesterol concentration can be tuned to further control the fluidity of the cell membrane.…”

Lipoprotein particles interact with membranes and transfer their cargo without receptors

“…In SLBs, the manifestation of compositional changes in diffusion is largely masked by the support effect (25), thus the differences are very small. In contrary, free-standing membranes reflect the compositional changes better (25), thus, we also tested the diffusion of lipid analog in GUVs. In GUVs, diffusion coefficient of ASR-PE was 6.6±1.…”