Fluctuating-friction molecular motors

We show that the correlated stochastic fluctuation of the friction coefficient can,give rise to long-range directional motion of a particle performing a Brownian random walk in the constant landscape of a periodic potential energy. The occurrence of this motion requires the presence of two additional independent bodies interacting with the particle via friction and via the energy potential, respectively, which can move relative to one another. Such a three-body system generalizes the classical Brownian ratchet mechanism, which requires only two interacting bodies. In particular, we describe a simple two-level model of a fluctuating-friction molecular motor that can be solved analytically. In our previous work (Kreuzer M, Marrucci L and Paparo D 2000 J. Nonlinear Opt. Phys. Mater. 9 157) this model was applied, for the first time, in an effort to understand the fundamental mechanism of the photoinduced reorientation of dye-doped liquid crystals. Applications of the same idea to other fields such as molecular biology and nanotechnology can be envisioned. As an example, in this paper we work out a model of the actin-myosin system based on the fluctuating-friction mechanism.