Institute of Plant Biology and Biotechnology, University of Münster, 48143 Münster, Germany.
School of Plant Sciences and Food Security, The George S. Wise Faculty of Life Sciences, Tel Aviv University, Tel Aviv 6997801, Israel.
Plant Physiol. 2023 Oct 26;193(3):2122-2140. doi: 10.1093/plphys/kiad426.
Calredoxin (CRX) is a calcium (Ca2+)-dependent thioredoxin (TRX) in the chloroplast of Chlamydomonas (Chlamydomonas reinhardtii) with a largely unclear physiological role. We elucidated the CRX functionality by performing in-depth quantitative proteomics of wild-type cells compared with a crx insertional mutant (IMcrx), two CRISPR/Cas9 KO mutants, and CRX rescues. These analyses revealed that the chloroplast NADPH-dependent TRX reductase (NTRC) is co-regulated with CRX. Electron transfer measurements revealed that CRX inhibits NADPH-dependent reduction of oxidized chloroplast 2-Cys peroxiredoxin (PRX1) via NTRC and that the function of the NADPH-NTRC complex is under strict control of CRX. Via non-reducing SDS-PAGE assays and mass spectrometry, our data also demonstrated that PRX1 is more oxidized under high light (HL) conditions in the absence of CRX. The redox tuning of PRX1 and control of the NADPH-NTRC complex via CRX interconnect redox control with active photosynthetic electron transport and metabolism, as well as Ca2+ signaling. In this way, an economic use of NADPH for PRX1 reduction is ensured. The finding that the absence of CRX under HL conditions severely inhibited light-driven CO2 fixation underpins the importance of CRX for redox tuning, as well as for efficient photosynthesis.
钙依赖型硫氧还蛋白（Calredoxin，CRX）是衣藻（Chlamydomonas reinhardtii）叶绿体中的一种硫氧还蛋白，其生理功能尚不清楚。我们通过对野生型细胞与 crx 插入突变体（IMcrx）、两个 CRISPR/Cas9 KO 突变体和 CRX 挽救体进行深入的定量蛋白质组学比较，阐明了 CRX 的功能。这些分析表明，叶绿体 NADPH 依赖的硫氧还蛋白还原酶（NADPH-TRX 还原酶）与 CRX 共同调节。电子转移测量表明，CRX 通过 NTRC 抑制 NADPH 依赖的氧化型叶绿体 2-Cys 过氧化物酶（PRX1）的还原，并且 NADPH-NTRC 复合物的功能受到 CRX 的严格控制。通过非还原 SDS-PAGE 测定和质谱分析，我们的数据还表明，在没有 CRX 的情况下，高光（HL）条件下 PRX1 更容易氧化。PRX1 的氧化还原调谐以及通过 CRX 对 NADPH-NTRC 复合物的控制，将活性光合作用电子传递和代谢以及 Ca2+信号与氧化还原控制联系起来。通过这种方式，可以确保 NADPH 用于 PRX1 还原的经济利用。在 HL 条件下缺乏 CRX 严重抑制了光驱动的 CO2 固定，这表明 CRX 对于氧化还原调谐以及高效光合作用非常重要。
