Interplay between lipid lateral diffusion, dye concentration and membrane permeability unveiled by a combined spectroscopic and computational study of a model lipid bilayer

Abstract

Lipid lateral diffusion in membrane bilayers is a fundamental process exploited by cells to enable complex protein structural and dynamic reorganizations. For its importance, lipid mobility in both cellular and model bilayers has been extensively investigated in recent years, especially through the application of time-resolved, fluorescence-based, optical microscopy techniques. However, one caveat of fluorescence techniques is the need to use dye-labeled variants of the lipid of interest, thus potentially perturbing the structural and dynamic properties of the native species. Generally, the effect of the dye/tracer molecule is implicitly assumed to be negligible. Nevertheless, in view of the widespread use of optically modified lipids for studying lipid bilayer dynamics, it is highly desirable to well assess this point. Here, fluorescence correlation spectroscopy (FCS) and molecular dynamics (MD) simulations have been combined together to uncover subtle structural and dynamic effects in DOPC planar membranes enriched with a standard Rhodamine-labeled lipid. Our findings support a non-neutral role of the dye-labeled lipids in diffusion experiments, quantitatively estimating a decrease in lipid mobility of up to 20% with respect to the unlabeled species. Moreover, results highlight the existing interplay between dye concentration, lipid lateral diffusion and membrane permeability, thus suggesting possible implications for future optical microscopy studies of biophysical processes occurring at the membrane level.

Ultrafast energy transfer between lipid-linked chromophores and plant light-harvesting complex II

“…The resulting trajectories were analysed in order to reveal the motion of the protein, lipids and TR. The calculated diffusion constant for the non-tagged lipid was found to be 8.4 μm 2 s −1 (see ESI, † 2.22), in good agreement with previously published calculations 74 and within the experimentally reported range of 5–14 μm 2 s −1 . 75 The TR-tagged lipid tail exhibited slower diffusion (4.5 μm 2 s −1 ), reflecting the hydrodynamic drag of the TR.…”

Water at charged interfaces

“…We should also keep in mind that most surfaces are not only spatially heterogeneous but also highly dynamic (temporally heterogeneous), a property that considerably complicates their molecular-level description. The spatial heterogeneity is nicely exemplified in biomembranes, which exhibit a soft surface with charge-bearing constituents that are laterally mobile 87 : a time-dependent, non-uniform charge distribution 88 . Another example is the charged silica-water interface, for which the macroscopic wetting angle results from the subtle interplay between nanometre-scale hydrophobic and hydrophilic (potentially charged) patches on the surface 89 .…”

Surfactant-free production of biomimetic artificial cells using PDMS-based microfluidics

“…Furthermore, the diffusion coefficient observed in these measurements are in agreement with previous literature values. [31,34]…”