Institut de Biologie Physico-Chimique, UMR 7141 CNRS-UPMC, 13 rue P et M Curie, Paris 75005, France.
Molecular Biotechnology and Systems Biology, University of Kaiserslautern, Kaiserlautern 67663, Germany.
Mol Plant. 2016 Apr 4;9(4):558-68. doi: 10.1016/j.molp.2015.12.017. Epub 2016 Jan 6.
While photosynthetic linear electron flow produces both ATP and NADPH, cyclic electron flow (CEF) around photosystem I (PSI) and cytochrome b6f generates only ATP. CEF is thus essential to balance the supply of ATP and NADPH for carbon fixation; however, it remains unclear how the system tunes the relative levels of linear and cyclic flow. Here, we show that PETO, a transmembrane thylakoid phosphoprotein specific of green algae, contributes to the stimulation of CEF when cells are placed in anoxia. In oxic conditions, PETO co-fractionates with other thylakoid proteins involved in CEF (ANR1, PGRL1, FNR). In PETO-knockdown strains, interactions between these CEF proteins are affected. Anoxia triggers a reorganization of the membrane, so that a subpopulation of PSI and cytochrome b6f now co-fractionates with the CEF effectors in sucrose gradients. The absence of PETO impairs this reorganization. Affinity purification identifies ANR1 as a major interactant of PETO. ANR1 contains two ANR domains, which are also found in the N-terminal region of NdhS, the ferredoxin-binding subunit of the plant ferredoxin-plastoquinone oxidoreductase (NDH). We propose that the ANR domain was co-opted by two unrelated CEF systems (PGR and NDH), possibly as a sensor of the redox state of the membrane.
虽然光合线性电子流既产生 ATP 又产生 NADPH，但光系统 I（PSI）和细胞色素 b6f 周围的循环电子流（CEF）仅产生 ATP。因此，CEF 对于平衡碳固定所需的 ATP 和 NADPH 的供应至关重要；然而，该系统如何调节线性和循环流的相对水平仍不清楚。在这里，我们表明，跨膜类囊体磷蛋白 PETO 是绿藻特有的，当细胞处于缺氧状态时，它有助于刺激 CEF。在好氧条件下，PETO 与其他参与 CEF 的类囊体蛋白（ANR1、PGRL1、FNR）共分馏。在 PETO 敲低菌株中，这些 CEF 蛋白之间的相互作用受到影响。缺氧会引发膜的重新排列，使得一部分 PSI 和细胞色素 b6f 现在与蔗糖梯度中的 CEF 效应物共分馏。PETO 的缺失会损害这种重组。亲和纯化鉴定出 ANR1 是 PETO 的主要相互作用蛋白。ANR1 包含两个 ANR 结构域，这些结构域也存在于植物铁氧还蛋白-质体醌氧化还原酶（NDH）的铁氧还蛋白结合亚基 NdhS 的 N 端区域中。我们提出，ANR 结构域被两个不相关的 CEF 系统（PGR 和 NDH）共同选择，可能作为膜氧化还原状态的传感器。
