Nanomechanics of lipid nanotubes
Résumé
Lipid nanotubes serve in intra and extracellular transport processes, for instance by generating vesicles in endocytosis
[1]. While these processes crucially involve the ill-understood local mechanics of the nanotube [2], existing
micromanipulation assays (optical tweezers, micropipette) only give access to its global, averaged mechanical
properties. Moreover, micromanipulation assays can analyze only one tube at a time.
Here we develop a new platform to study nanotube local mechanics using atomic force microscopy (AFM) [3]. On a
single coverslip we generate millions of substrate-bound nanotubes, out of which dozens can be imaged by AFM in a
single experiment. AFM provides not only the fine morphology of the nanotube, but also a map of the local rigidity with
spatial resolution in the order of nanometers (Figure 1).
A full theoretical description of the AFM tip-membrane interaction allows us to accurately relate AFM measurements of
the nanotubes’ heights, widths, and rigidities to the membrane bending rigidity and tension, thus demonstrating our
assay as an accurate probe of nanotube mechanics. We find that the range of membrane tensions as measured by our
assay cover well the ranges of membrane tensions that have been measured within cells.
Finally, we mimic in vivo actin polymerization on nanotubes, and use AFM to assess the induced changes in nanotube
physical properties. Our assay thus provides access to high-throughput nanomechanical mapping of bare and proteincoated
lipid nanotubes, and thus may help unraveling the local mechanics of membrane-protein interactions, including
membrane remodeling in nanotube scission and vesicle formation.