Dynamic modulation of transthylakoid electric potential by chloroplast ATP synthases

Abstract

The light-induced transthylakoid membrane potential (ΔΨ_m) can function as a driving force to help catalyzing the formation of ATP molecules, proving a tight connection between ΔΨ_m and the ATP synthase. Naturally, a question can be raised on the effects of altered functioning of ATP synthases on regulating ΔΨ_m, which is attractive in the area of photosynthetic research. Lots of findings, when making efforts of solving this difficulty, can offer an in-depth understanding into the mechanism behind. However, the functional network on modulating ΔΨ_m is highly interdependent. It is difficult to comprehend the consequences of altered activity of ATP synthases on adjusting ΔΨ_m because parameters that have influences on ΔΨ_m would themselves be affected by ΔΨ_m. In this work, a computer model was applied to check the kinetic changes in polarization/depolarization across the thylakoid membrane (TM) regulated by the modified action of ATP synthases. The computing data revealed that under the extreme condition by numerically “switching off” the action of the ATP synthase, the complete inactivation of ATP synthase would markedly impede proton translocation at the cytb₆f complex. Concurrently, the KEA3 (CLCe) porter, actively pumping protons into the stroma, further contributes to achieving a sustained low level of ΔΨ_m. Besides, the quantitative consequences on every particular component of ΔΨ_m adjusted by the modified functioning of ATP synthases were also explored. By employing the model, we bring evidence from the theoretical perspective that the ATP synthase is a key factor in forming a transmembrane proton loop thereby maintaining a propriate steady-state ΔΨ_m to meet variable environmental conditions.