Effects of Symmetry on the Performance of Coupled Rotary Molecular Motors

Synopsis

As engineering advances toward the nanoscale, understanding design principles for molecular motors becomes increasingly valuable. Many molecular motors consist of coupled components transducing one free-energy source into another. Here, we study the performance of coupled rotary molecular motors with different rotational symmetries under two coupling types (spring-like and gear-like) and two driving-force schemes (constant and scaling with the number of subunits), motivated by ATP synthase and the bacterial flagellar motor (BFM). We numerically simulate the Fokker-Planck equation describing the system, focusing on output power. Under spring-like coupling with scaling driving, excessively strong driving of the upstream motor can reduce downstream output power—a counterintuitive phenomenon we termed disruption—effectively disconnecting the motors. Disruption can also occur under gear-like coupling with constant driving. Understanding disruption helps avoid energy waste. Furthermore, under gear-like coupling with constant driving, output power maximizes near symmetry match, opening avenues for BFM studies. These findings could inform synthetic nanomotor design and structure-based drug development.