Abstract
While the field of ATP synthase research has a long history filled with landmark discoveries, recent structural works provide us with important insights into the mechanisms that links the proton movement with the rotation of the Fo motor. Here, we propose a mechanism of unidirectional rotation of the Fo complex, which is in agreement with these new structural insights as well as our more general ΔΨ-driving hypothesis of membrane proteins: A proton path in the rotor-stator interface is formed dynamically in concert with the rotation of the Fo rotor. The trajectory of the proton viewed in the reference system of the rotor (R-path) must lag behind that of the stator (S-path). The proton moves from a higher energy site to a lower site following both trajectories simultaneously. The two trajectories meet each other at the transient proton-binding site, resulting in a relative rotation between the rotor and stator. The kinetic energy of protons gained from ΔΨ is transferred to the c-ring as the protons are captured sequentially by the binding sites along the proton path, thus driving the unidirectional rotation of the c-ring. Our ΔΨ-driving hypothesis on Fo motor is an attempt to unveil the robust mechanism of energy conversion in the highly conserved, ubiquitously expressed rotary ATP synthases.
Highlights
VANTAGE POINTSHow does transmembrane electrochemical potential drive the rotation of Fo motor in an ATP synthase?
Boyer PD (1993) The binding change mechanism for ATP synthase– some probabilities and possibilities
In contrast to the earlier rigid-rotor model, we argue that the driving substance, e.g. protons, must stay in the rotorstator interface where its free energy is converted into the kinetic energy of the rotor
Summary
How does transmembrane electrochemical potential drive the rotation of Fo motor in an ATP synthase?. In this article, based on theoretical considerations and in light of recent structural insights, Zhang and colleagues propose that the Fo rotation is driven by a noise-resistant thermodynamic process which converts the electrostatic free energy of the cations moving in the rotor-stator interface into the rotational kinetic energy In this hypothesis, the shape difference between the interface-located trajectories in the rotator- and statorreference systems ensures the unidirectional rotation of the Fo motor. The central idea of this hypothesis is that the interaction of charged groups in a membrane protein with ΔΨ can provide a major driving force for the functional cycle of the corresponding membrane protein This hypothesis has been used to explain the energy coupling mechanisms of PMF-driven major facilitator superfamily (MFS) transporters (Zhang et al, 2015a), of proton transfer-mediated GPCR activation
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