Cystathionine-β-synthase (CBS) domains are found in proteins of all living organisms and have been proposed to play a role as energy sensors regulating protein activities through their adenosyl ligand binding capacity. In plants, members of the CBSX protein family carry a stand-alone pair of CBS domains. In Arabidopsis (Arabidopsis thaliana), CBSX1 and CBSX2 are targeted to plastids where they have been proposed to regulate thioredoxins (TRXs). TRXs are ubiquitous cysteine thiol oxido-reductases involved in the redox-based regulation of numerous enzymatic activities as well as in the regeneration of thiol-dependent peroxidases. In Arabidopsis, 10 TRX isoforms have been identified in plastids and divided into five sub-types. Here, we show that CBSX2 specifically inhibits the activities of m-type TRXs toward two chloroplast TRX-related targets. By testing activation of NADP-malate dehydrogenase and reduction of 2-Cys peroxiredoxin, we found that TRXm1/2 inhibition by CBSX2 was alleviated in the presence of AMP or ATP. We also determined, by pull-down assays, a direct interaction of CBSX2 with reduced TRXm1 and m2 that was abolished in the presence of adenosyl ligands. In addition, we report that, compared with wild-type plants, the Arabidopsis T-DNA double mutant cbsx1 cbsx2 exhibits growth and chlorophyll accumulation defects in cold conditions, suggesting a function of plastidial CBSX proteins in plant stress adaptation. Together, our results show an energy-sensing regulation of plastid TRX m activities by CBSX, possibly allowing a feedback regulation of ATP homeostasis via activation of cyclic electron flow in the chloroplast, to maintain a high energy level for optimal growth.

中文翻译：

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腺苷酸通过与 CBS 结构域蛋白的结合来调节拟南芥质体硫氧还蛋白活性。

胱硫醚-β-合酶 (CBS) 结构域存在于所有生物体的蛋白质中，并被认为通过其腺苷配体结合能力发挥能量传感器的作用，调节蛋白质活性。在植物中，CBSX 蛋白家族的成员携带一对独立的 CBS 结构域。在拟南芥 (Arabidopsis thaliana) 中，CBSX1 和 CBSX2 以质体为靶点，并被提议在质体中调节硫氧还蛋白 (TRX)。TRX 是普遍存在的半胱氨酸硫醇氧化还原酶，参与多种酶活性的氧化还原调节以及硫醇依赖性过氧化物酶的再生。在拟南芥中，质体中已鉴定出 10 种 TRX 亚型，并分为 5 个亚型。在这里，我们证明 CBSX2 特异性抑制 m 型 TRX 对两个叶绿体 TRX 相关靶标的活性。通过测试 NADP-苹果酸脱氢酶的激活和 2-Cys 过氧化还原酶的还原，我们发现 CBSX2 对 TRXm1/2 的抑制在 AMP 或 ATP 存在的情况下减轻。我们还通过下拉分析确定了 CBSX2 与减少的 TRXm1 和 m2 的直接相互作用，这种相互作用在腺苷配体存在时被消除。此外，我们报道，与野生型植物相比，拟南芥T-DNA双突变体cbsx1 cbsx2在寒冷条件下表现出生长和叶绿素积累缺陷，表明质体CBSX蛋白在植物逆境适应中的功能。总之，我们的结果表明 CBSX 对质体 TRX m 活性的能量感应调节，可能允许通过激活叶绿体中的循环电子流来反馈调节 ATP 稳态，以维持高能量水平以实现最佳生长。