Thermal Stress of Supported Lipid Bilayer Induces Formation and Collapse of Uniform Radius Tubules

Abstract

Lipid bilayer morphologies and the transitions between them are important to many cellular processes. Supported lipid bilayer (SLB) provides a model system in which to quantitatively investigate transitions from planar to tubular and tubular to spherical morphologies. Following a small increase in temperature (∼5-10°C) flexible filaments extrude from a fluid SLB. Individual filaments can reach hundreds of microns in length before spontaneously collapsing into discs. We demonstrate that the filaments are tubular by decreasing the external buffer concentration, which causes them to swell, first into resolvable tubules with capped ends and then into giant vesicles. At high ionic strength, the sub-resolution tubules are adsorbed to the SLB, enabling the measurement of their radius to within ±5 nm using conventional fluorescence microscopy. The radius depends on the lipid tail composition and varies <10% along the tubule length. Under tension, tubules are even more uniform, having no measurable variation in radius.