Resolving the effects of nanoscale membrane curvature on lipid mobility

TL;DR

This study uses advanced super-resolution microscopy techniques to investigate how nanoscale membrane curvature influences lipid mobility, revealing effects that are undetectable with traditional diffraction-limited methods.

Contribution

The paper demonstrates that super-resolution methods like PLM and SPT can resolve the effects of nanoscale membrane curvature on lipid behavior, surpassing limitations of conventional techniques.

Findings

FRAP and FCS show limited sensitivity to nanoscale curvature effects.

PLM and SPT successfully detect curvature-induced lipid mobility changes.

Nanoscale membrane buds affect lipid dynamics in ways detectable only with super-resolution microscopy.

Abstract

The biophysical consequences of nanoscale curvature have been challenging to resolve due to size-dependent membrane behavior and the experimental resolution limits imposed by optical diffraction. Recent advances in nanoengineering and super-resolution techniques have enabled new capabilities for creating and observing curvature. In particular, draping supported lipid bilayers over lithographically patterned substrates provides a model system for endocytic pits. The experiments and simulations presented below describe the possible detection of membrane curvature through fluorescence recovery after photobleaching (FRAP), fluorescence correlation spectroscopy (FCS), single particle tracking (SPT), and polarized localization microscopy (PLM). FRAP and FCS depend on diffraction-limited illumination and detection. In particular, a simulation of FRAP shows no effects on lipids diffusion due to a 50 nm diameter membrane bud at any stage in the budding process. Simulated FCS demonstrated small effects due to a 50 nm radius membrane bud that was amplified with curvature-dependent lipid mobility changes. However, PLM and SPT achieve sub-diffraction-limited resolution of membrane budding and lipid mobility through the identification of the single-lipid positions with <15 nm spatial and <20 ms temporal resolution. By mapping the single-lipid step lengths to locations on the membrane, the effects of curvature on lipid behavior have been resolved.