Structural basis of redox modulation on chloroplast ATP synthase

Jay-How Yang,Dewight Williams,Eaazhisai Kandiah,Petra Fromme,Po-Lin Chiu

doi:10.1038/s42003-020-01221-8

Abstract

In higher plants, chloroplast ATP synthase has a unique redox switch on its γ subunit that modulates enzyme activity to limit ATP hydrolysis at night. To understand the molecular details of the redox modulation, we used single-particle cryo-EM to determine the structures of spinach chloroplast ATP synthase in both reduced and oxidized states. The disulfide linkage of the oxidized γ subunit introduces a torsional constraint to stabilize the two β hairpin structures. Once reduced, free cysteines alleviate this constraint, resulting in a concerted motion of the enzyme complex and a smooth transition between rotary states to facilitate the ATP synthesis. We added an uncompetitive inhibitor, tentoxin, in the reduced sample to limit the flexibility of the enzyme and obtained high-resolution details. Our cryo-EM structures provide mechanistic insight into the redox modulation of the energy regulation activity of chloroplast ATP synthase.

Highlights

In higher plants, chloroplast ATP synthase has a unique redox switch on its γ subunit that modulates enzyme activity to limit ATP hydrolysis at night
In vitro biochemical assays and mutagenesis have shown that the redox state modulates the CF1FO activities[4,5,6,8,17], and cryogenic microscopy (cryo-electron microscopy (EM)) imaging of the CF1FO in an autoinhibited and oxidized state has shown a unique disulfide linkage in the γ subunit[18], which stabilizes the local structure of the two β hairpin motifs of the γ subunit
It has been shown that the reduced form of the plant CF1FO is more active in producing ATP molecules than the oxidized form, and the rate of the ATP synthesis of the reduced form is much faster than that of the oxidized form[4]

Summary

Introduction

Chloroplast ATP synthase has a unique redox switch on its γ subunit that modulates enzyme activity to limit ATP hydrolysis at night. To understand the molecular details of the redox modulation, we used single-particle cryo-EM to determine the structures of spinach chloroplast ATP synthase in both reduced and oxidized states. In the thylakoid membrane, the photosynthetic electron transport chain, consisting of photosystem II, cytochrome b6f complex, and photosystem I, performs a light-induced charge separation, which energizes the membrane and creates an electrochemical gradient[9] This gradient activates the CF1FO, which releases a tightly bound ATP and enters an active but still oxidized state, synthesizing ATP molecules at a slower rate[10,11,12]. To understand the molecular mechanism of the redox modulation of CF1FO, a more complete structural view is required in order to provide a fundamental framework of energy regulation in plants

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Conclusion