  The membrane tubulation induced by banana-shaped protein rods is investigated
by using coarse-grained meshless membrane simulations. It is found that the
tubulation is promoted by laterally isotropic membrane inclusions that generate
the same sign of spontaneous curvature as the adsorbed protein rods. The
inclusions are concentrated in the tubules and reduce the bending energy of the
tip of the tubules. On the other hand, the inclusions with an opposite
curvature suppress the tubulation by percolated-network formation at a high
protein-rod density while they induce a spherical membrane bud at a low rod
density. When equal amounts of the two types of inclusions (with positive and
negative curvatures) are added, their effects cancel each other for the first
short period but later the tubulation is slowly accelerated. A positive surface
tension suppresses the tubulation. Out results suggest that the cooperation of
scaffolding of BAR (Bin/Amphiphysin/Rvs) domains and isotropic membrane
inclusions is important for the tubulation.
