  Learning from nature's amazing molecular machines, globular proteins, we
present a framework for the predictive design of nano-machines. We show that
the crucial ingredients for a chain molecule to behave as a machine are its
inherent anisotropy and the coupling between the local Frenet coordinate
reference frames of nearby monomers. We demonstrate that, even in the absence
of heterogeneity, protein-like behavior is obtained for a simple chain molecule
made up of just thirty hard spheres. This chain spontaneously switches between
two distinct geometries, a single helix and a dual helix, merely due to thermal
fluctuations.
