A model for non-equilibrium fluctuations of intracellular filaments

Microtubules are highly dynamic biopolymer filaments involved in a wide variety of biological processes like cell division and intracellular transport. These filaments are semi-flexible polymers, i.e. their bending energy is comparable to the thermal energy. Even though they form a rather stiff and highly cross-linked structural network, it has been shown that they typically exhibit significant bends on all length scales in the living cell.

Measurements of thermally driven microtubule fluctuations under laboratory conditions reveal a persistence length, which is several orders of magnitude larger than observed in living cells. Several studies investigated the interactions of motor proteins and mircotubules. Experiments and in vivo observations have shown microtubules to exhibit buckling instabilities induced by molecular motors, which compress the filament longitudinally. However, direct transversal motor activity on microtubules cannot be ruled out.

I will present a toy model for transversal deformations of a microtubule due to active processes. Simulations of motor proteins deforming a microtubule against a background network mimic the microtubule's behaviour under rapid step-like force fluctuations. The analysis of these fluctuations reveal interesting aspects of the apparent persistence length, motor cooperation as well as global filament displacement, which can be interpreted as a fractional random walk.