Institute for Protein Research, Osaka University, Suita, Osaka, Japan.
Department of Biological Sciences, Graduate School of Science, Osaka University, Suita, Osaka, Japan.
Protein Sci. 2020 Dec;29(12):2538-2545. doi: 10.1002/pro.3964. Epub 2020 Oct 16.
Photosynthetic electron transport occurs on the thylakoid membrane of chloroplasts. Ferredoxin (Fd), the final acceptor in the electron transport chain, distributes electrons to several Fd-dependent enzymes including Fd-thioredoxin reductase (FTR). A cascade from Fd to FTR further reduces Thioredoxin (Trx), which tunes the activity of target metabolic enzymes eventually in a light-dependent manner. We previously reported that 10 Trx isoforms in Arabidopsis thaliana can be clustered into three classes based on the kinetics of the FTR-dependent reduction (high-, middle-, and low-efficiency classes). In this study, we determined the X-ray structure of three electron transfer complexes of FTR and Trx isoform, Trx-y1, Trx-f2, and Trx-m2, as representative examples of each class. Superposition of the FTR structure with/without Trx showed no main chain structural changes upon complex formation. There was no significant conformational change for single and complexed Trx-m structures. Nonetheless, the interface of FTR:Trx complexes displayed significant variation. Comparative analysis of the three structures showed two types of intermolecular interactions; (i) common interactions shared by all three complexes and (ii) isoform-specific interactions, which might be important for fine-tuning FTR:Trx activity. Differential electrostatic potentials of Trx isoforms may be key to isoform-specific interactions.
光合作用电子传递发生在叶绿体的类囊体膜上。铁氧还蛋白（Fd）是电子传递链中的最终受体，它将电子分配给几种依赖 Fd 的酶，包括 Fd-硫氧还蛋白还原酶（FTR）。Fd 到 FTR 的级联反应进一步还原硫氧还蛋白（Trx），从而以光依赖的方式调节靶代谢酶的活性。我们之前报道过，拟南芥中的 10 种 Trx 同工型可以根据 FTR 依赖性还原的动力学（高效、中效和低效类）分为三类。在这项研究中，我们确定了 FTR 和 Trx 同工型 Trx-y1、Trx-f2 和 Trx-m2 的三种电子传递复合物的 X 射线结构，它们分别是每种类别中的代表。FTR 结构与 Trx 形成复合物前后的叠加显示，复合物形成时主链结构没有明显变化。单体和复合物 Trx-m 结构也没有明显的构象变化。然而，FTR:Trx 复合物的界面显示出显著的变化。对这三种结构的比较分析表明，存在两种类型的分子间相互作用；（i）所有三种复合物共有的相互作用和（ii）同工型特异性相互作用，这可能对精细调节 FTR:Trx 活性很重要。Trx 同工型的差异静电势可能是同工型特异性相互作用的关键。
