Disentangling chloroplast ATP synthase regulation by proton motive force and thiol modulation in Arabidopsis leaves

Abstract

The chloroplast ATP synthase (CF1Fo) contains a specific feature to the green lineage: a γ-subunit redox domain that contains a cysteine couple which interacts with the torque-transmitting βDELSEED-loop. This thiol modulation equips CF1Fo with an important environmental fine-tuning mechanism. In vitro, disulfide formation in the γ-redox domain slows down the activity of the CF1Fo at low transmembrane electrochemical proton gradient (Δμ~H+), which agrees with its proposed role as chock based on recently solved structure. The γ-dithiol formation at the onset of light is crucial to maximize photosynthetic efficiency since it lowers the Δμ~H+ activation level for ATP synthesis in vitro. Here, we validate these findings in vivo by utilizing absorption spectroscopy in Arabidopsis thaliana. To do so, we monitored the Δμ~H+ present in darkness and identified its mitochondrial sources. By following the fate and components of light-induced extra Δμ~H+, we estimated the ATP lifetime that lasted up to tens of minutes after long illuminations. Based on the relationship between Δμ~H+ and CF1Fo activity, we conclude that the dithiol configuration in vivo facilitates photosynthesis by driving the same ATP synthesis rate at a significative lower Δμ~H+ than in the γ-disulfide state. The presented in vivo findings are an additional proof of the importance of CF1Fo thiol modulation, reconciling biochemical in vitro studies and structural insights.