  Motivated by the mechanics of dynamin-mediated membrane tube fission we
analyse the stability of fluid membrane tubes subjected to shear flow in
azimuthal direction. We find a novel helical instability driven by the membrane
shear flow which results in a non-equilibrium steady state for the tube
fluctuations. This instability has its onset at shear rates that may be
physiologically accessible under the action of dynamin and could also be probed
using in-vitro experiments on membrane nanotubes, e.g. using magnetic tweezers.
We discuss how such an instability may play a role in the mechanism for
dynamin-mediated membrane tube fission.
