Membrane Nanotubes: Computational Modeling of Actin-Membrane Interactions

Membrane nanotubes are tubular membrane structures that contain actin and connect cells over long distances. Cells may use membrane nanotubes to communicate over long distances, and viruses can exploit membrane nanotubes to propagate from one cell to another. Disrupting the actin cytoskeleton abrogates membrane nanotubes, making them an interesting model system for studying membrane-cytoskeleton interactions. In this talk, we study membrane nanotubes using a theoretical framework based on continuum models. We employ analytical theory and Monte Carlo computer simulation methods to explore properties of semiflexible polymers – representing bundles of actin – confined within fluid membrane tubes. We investigate the effects of membrane bending rigidity, polymer length, and polymer persistence length. Interestingly, for an empty tube at low bending rigidity, we observe a peak in the specific heat of the membrane. Characterizing the membrane shapes sampled in simulations indicate that this peak is associated with a transition from a crumpled membrane to a locally flat membrane. Further, we find the presence of a polymer within the membrane suppresses membrane shape fluctuations, and that the peak in the specific heat of the membrane is suppressed by the polymer in a manner that depends on the length and persistence length of the polymer. Bundles of actin filaments can significantly deform the surrounding membrane and may stabilize membrane nanotubes by suppressing membrane shape fluctuations.