Energy and information flows in strongly coupled rotary motors

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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 FoF1-ATP synthase and study the energy and information flows through the machine. We find that the output power of a work-to-work converter 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. We observe several characteristics that similarly show up at intermediate coupling strength, near the coupling strength that maximizes output power: a maximum in power transmitted from Fo to F1, a maximum in information flow, and equal subsystem entropy production rates. These observations are unified in a bound on the machine’s input and output power, which accounts for the energy and information passed between subsystems. We conclude that intermediate-strength coupling is a realistic option for biological systems passing on energy and information to downstream processes