Lipid-microtubule nanotube. Complexed nanotube consisting of a microtubule (~26 nm in diameter) made of tubulin protein subunits (red-blue-yellow-green spheres) coated by a cationic lipid bilayer (headgroups in green and white, hydrocarbon tails in yellow). A third layer of tubulin oligomers actually wraps up the bilayer in the plane perpendicular to the nanotube axis. The arrangement is deduced from x-ray data and transmission electron microscopy images. Reproduced from reference  with permission. Copyright 2007 by the Biophysical Society.