Single Lipid Molecule Dynamics on Supported Lipid Bilayers with Membrane Curvature

Abstract

The plasma membrane is a highly compartmentalized, dynamic material and this organization is essential for a wide variety of cellular processes. Nanoscale domains allow proteins to organize for cell signaling, endo- and exocytosis, and other essential processes. Even in the absence of proteins, lipids have the ability to organize into domains as a result of a variety of chemical and physical interactions. One feature of membranes that affects lipid domain formation is membrane curvature. To directly test the role of curvature in lipid sorting, we measured the accumulation of two similar lipids, 1,2-Dihexadecanoyl-sn-glycero-3-phosphoethanolamine (DHPE) and hexadecanoic acid (HDA), using a supported lipid bilayer that was assembled over a nanopatterned surface to obtain regions of membrane curvature. Both lipids studied contain 16 carbon, saturated tails and a head group tag for fluorescence microscopy measurements. The accumulation of lipids at curvatures ranging from 28 nm to 55 nm radii was measured and fluorescein labeled DHPE accumulated more than fluorescein labeled HDA at regions of membrane curvature. We then tested whether single biotinylated DHPE molecules sense curvature using single particle tracking methods. Similar to groups of fluorescein labeled DHPE accumulating at curvature, the dynamics of single molecules of biotinylated DHPE was also affected by membrane curvature and highly confined motion was observed.

Nanoscale Membrane Budding Induced by CTxB and Detected via Polarized Localization Microscopy

“…In comparing the diffusion coefficient measured by SPT to that measured by FRAP or fluorescence correlation spectroscopy, it is critical to consider the differences in sensitivity to detecting mobile versus immobile diffusers, length-and timescale-dependent processes, and subpopulations of diffusers (33,34). The SPT results presented here are consistent with prior SPT results and, as expected, report a slower diffusion rate than FRAP or fluorescence correlation spectroscopy measurements (43,45). If the effective membrane viscosity changes upon membrane bending, then the diffusion of the DiI molecules in both leaflets could be affected, regardless of the supporting substrate or local CTxB concentrations.…”

Biomimetic Models to Investigate Membrane Biophysics Affecting Lipid–Protein Interaction

“…The combination of membrane models and single-molecule fluorescence microscopy became an exciting research area to investigate binding and diffusion events of individual molecules (Weiss, 1999;Michalet et al, 2003;Mashaghi and van Oijen, 2014;Cheney et al, 2017). Novel optics and cameras with high signal to noise ratio made single molecule detection possible under low molecule concentrations (Gell et al, 2006).…”

Topography design in model membranes: Where biology meets physics

“…Interestingly, over a specific threshold (∼0.8 µm -1 ), curvature appears to regulate the spatial organization of lipid phases including cholesterol 75 , and also the segregation of lipids such 10 ! as hexadecanoic acid 76 and cardiolipin 77 . Importantly, local membrane curvature also controls the segregation of curvature-sensing proteins 78 (Figure 2B).…”