Abstract
The presence of membrane tubules in living cells is essential to many biological processes. In cells, one mechanism to form nanosized lipid tubules is via molecular motor induced bilayer extraction. In this paper, we describe a simple experimental model to investigate the forces required for lipid tube formation using kinesin motors anchored to DOPC vesicles. Previous related studies have used molecular motors actively pulling on the membrane to extract a nanotube. Here, we invert the system geometry; molecular motors are used as static anchors linking DOPC vesicles to a two-dimensional microtubule network and an external flow is introduced to generate nanotubes facilitated by the drag force. We found that a drag force of ~7 pN was sufficient for tubule extraction for vesicles ranging from 1 to 2 um in radius. By our method, we found that the force generated by a single molecular motor was sufficient for membrane tubule extraction from a spherical lipid vesicle.
Highlights
The lipid membrane is a self-assembled system, which can take on various shapes by changing its composition, changing the concentration of specific lipids, or applying a force
By using filter paper to induce a flow, the anchored kinesins pulled out nanotubes from the moving giant unilamellar vesicles (GUVs)
A control experiment was done without kinesin, and as expected, all GUVs were washed away from the flow cell without binding to the microtubules
Summary
The lipid membrane is a self-assembled system, which can take on various shapes by changing its composition, changing the concentration of specific lipids, or applying a force. Lipids are amphipathic and self-assemble into a bilayer in the cell known as the plasma membrane. Lipid nanotubes are one of various shapes that help facilitate the organization of cellular processes. The smooth endoplasmic reticulum is an example of a lipid nanotube system that branches out from the rough endoplasmic reticulum and nuclear envelope. These membrane nanotubes are found to colocalize with fundamental biopolymers in cells known as microtubules; when the microtubules depolymerize, the lipid tubules retract (Terasaki et al, 1986). Recent studies demonstrated that a minimal system of microtubules and molecular motors were sufficient for tubule extraction (Roux et al, 2002)
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