Topological Connection between Vesicles and Nanotubes in Single-Molecule Lipid Membranes Driven by Head–Tail Interactions

Abstract

Lipid nanotube–vesicle networks are important channels for intercellular communication and transport of matter. Experimentally observed in neighboring mammalian cells but also reproduced in model membrane systems, a broad consensus exists on their formation and stability. Lipid membranes must be composed of at least two molecular components, each stabilizing low (generally a phospholipid) and high curvatures. Strong anisotropy or enhanced conical shape of the second amphiphile is crucial for the formation of nanotunnels. Anisotropic driving forces generally favor nanotube protrusions from vesicles. In this work, we report the unique case of topologically connected nanotubes–vesicles obtained in the absence of directional forces, in single-molecule membranes, composed of an anisotropic bolaform glucolipid, above its melting temperature, T m. Cryo-TEM and fluorescence confocal microscopy show the interconnection between vesicles and nanotubes in a single-phase region, between 60 and 90 °C under diluted conditions. Solid-state NMR demonstrates that the glucolipid can assume two distinct configurations, head–head and head–tail. These arrangements, seemingly of comparable energy above the T m, could explain the existence and stability of the topologically connected vesicles and nanotubes, which are generally not observed for classical single-molecule phospholipid-based membranes above their T m.

Self-Assembly of Rhamnolipid Bioamphiphiles: Understanding the Structure–Property Relationship Using Small-Angle X-ray Scattering

“…Conformational changes in glycolipids are not unusual. They were reported for alkylaldonamides, − with a critical impact on the self-assembly, but also more recently by us on bolaform di-sophorolipids and glucolipids . In the case of RLs, the amount of experimental data is limited, but a body of work, generated by numerical modeling, − ,,, agrees on the importance and impact of rhamnose headgroup conformation and C10C10 chain tilting on the self-assembly properties.…”

“…They were reported for alkylaldonamides, 76−78 with a critical impact on the self-assembly, but also more recently by us on bolaform di-sophorolipids 79 and glucolipids. 80 In the case of RLs, the amount of experimental data is limited, but a body of work, generated by numerical modeling, [26][27][28]67,68,81 agrees on the importance and impact of rhamnose headgroup conformation and C10C10 chain tilting on the self-assembly properties. Simulation data, which were generated for systems both at air− water interface 67,68,81 and in bulk water, 26−28 are sometimes contradicting, depending on the dilution regime, 67,68 and for this reason they must be considered with caution.…”