The role of kinetic asymmetry and power strokes in an information ratchet

Biomolecular machines are driven by information ratchet mechanisms, where kinetic asymmetry in the machine's chemomechanical cycle of fuel-to-waste catalysis induces net directional dynamics. A large-scale energetically downhill conformational change, termed a "power stroke,"has often been erroneously implicated as a mechanistic driving feature in such machines. We investigated the roles of kinetic asymmetry and power strokes in a series of rotaxane-based information ratchets and found that kinetic asymmetry alone determines ratchet directionality such that all ratchets use the same amount of fuel to reach the same normalized steady state. However, power strokes can nonetheless influence ratchet performance, such as how fast the steady state is reached. Moreover, nonequilibrium thermodynamic analysis revealed that power strokes alter the amount and form (information [Shannon entropy] versus intercomponent binding energy) of the free energy stored by ratchets. These findings have implications for both the understanding of biological ratchets and the design principles for artificial nonequilibrium (supra)molecular machines.