Department of Biological Chemistry, College of Agriculture, Graduate School of Sciences and Technology for Innovation, Yamaguchi University, Yoshida, Yamaguchi, Japan.
Biosci Biotechnol Biochem. 2022 Apr 21;86(5):618-623. doi: 10.1093/bbb/zbac022.
In chloroplast stroma, dynamic pH change occurs in response to fluctuating light conditions. We investigated the pH-dependent electron transfer activity between ferredoxin-NADP+ reductase (FNR) and ferredoxin (Fd) isoproteins from maize leaves. By increasing pH (from 5.5 to 8.5), the electron transfer activity from FNR to photosynthetic-type Fd (Fd1) significantly increased while the activity to nonphotosynthetic type Fd (Fd3) decreased, which was mainly due to their differences in the pH dependency of Km for Fd. Mutation of His78 of Fd1 to Val, corresponding amino acid residue in Fd3, lost the pH dependency, indicating a regulatory role of the His78 in the interaction with FNR. We previously showed that the interaction between FNR and Fd was weakened by the allosteric binding of NADP(H) on FNR. His78Val Fd1 mutant largely suppressed this negative cooperativity. These results indicate the involvement of Fd1 His78 in pH dependency and negative cooperativity in the interaction with FNR.
在叶绿体基质中，动态 pH 值变化会响应波动的光照条件。我们研究了玉米叶片中来自铁氧还蛋白-NADP+还原酶（FNR）和铁氧还蛋白（Fd）同工型之间的 pH 依赖性电子转移活性。通过增加 pH 值（从 5.5 增加到 8.5），FNR 向光合型 Fd（Fd1）的电子转移活性显著增加，而向非光合型 Fd（Fd3）的活性降低，这主要是由于它们对 Fd 的 Km 值的 pH 依赖性不同。将 Fd1 的 His78 突变为 Fd3 中的相应氨基酸残基 Val，使其失去了 pH 依赖性，表明 His78 在与 FNR 的相互作用中起调节作用。我们之前曾表明，FNR 和 Fd 之间的相互作用会被 NADP(H) 在 FNR 上的变构结合所削弱。His78Val Fd1 突变体在很大程度上抑制了这种负协同作用。这些结果表明 Fd1 His78 参与了与 FNR 相互作用的 pH 值依赖性和负协同性。
