Thermodynamic uncertainty relation in helicases: Experiments and simulations

Abstract

Helicases are molecular motors that translocate on DNA in non-equilibrium conditions and use the energy from ATP hydrolysis to unwind DNA. Here we carry out magnetic tweezers experiments to study the unwinding and translocation activities of the gp41 replicative helicase in a DNA hairpin under the effect of a mechanical force. We analyze the experimental results to compute the mean helicase rate and the diffusion coefficient in different experimental conditions (forces and ATP concentration). These quantities are related to the thermodynamic uncertainty factor Q [1], which can be used as a measure of the irreversibility of a given enzymatic process. We find that the Q factor decreases with the applied force and has a non-monotonic behaviour with the ATP concentration. The results are compared with simulations of a simple model based on a biased random walk to describe the helicase motion on DNA