Energy and information flows in strongly coupled rotary machines

Synopsis

Living systems at the molecular scale are composed of many coupled components with interactions varying in nature and strength. They operate far from equilibrium and are subject to strong fluctuations. These conditions pose significant challenges to efficient, precise, and rapid free energy transduction, yet nature has evolved numerous molecular machines that do just this. We present a model of strongly coupled stochastic rotary motors inspired by F_oF₁-ATP synthase and study the energy and information flows through the machine. We find that the output power of this microscopic engine consisting of two coupled subsystems in the presence of energy barriers can be maximized at intermediate-strength coupling rather than at tight coupling. This phenomenon is backed up by a simple theory that predicts the power maximizing coupling strength and agrees well with numerical results. Furthermore, we find that the sum of energy and information flows through the system places a bound on the in- and output power, and this bound is equally loose at maximum output power. In other words, the subsystems are equally dissipative at maximal output power. These findings provide insight into the design principles governing transduction of free energy through microscopic biological machines.