Belozersky Institute of Physico-Chemical Biology, Lomonosov Moscow State University, 119992 Moscow, Russia.
Emanuel Institute of Biochemical Physics, Russian Academy of Sciences, 119334 Moscow, Russia.
Int J Mol Sci. 2023 Oct 11;24(20):15060. doi: 10.3390/ijms242015060.
PsbS is one of the key photoprotective proteins, ensuring the tolerance of the photosynthetic apparatus (PSA) of a plant to abrupt changes in irradiance. Being a component of photosystem II, it provides the formation of quenching centers for excited states of chlorophyll in the photosynthetic antenna with an excess of light energy. The signal for "turning on" the photoprotective function of the protein is an excessive decrease in pH in the thylakoid lumen occurring when all the absorbed light energy (stored in the form of transmembrane proton potential) cannot be used for carbon assimilation. Hence, lumen-exposed protonatable amino acid residues that could serve as pH sensors are the essential components of PsbS-dependent photoprotection, and their pK values are necessary to describe it. Previously, calculations of the lumen-exposed protonatable residue pK values in PsbS from spinach were described in the literature. However, it has recently become clear that PsbS, although typical of higher plants and charophytes, can also provide photoprotection in green algae. Namely, the stress-induced expression of PsbS was recently shown for two green microalgae species: and . Therefore, we determined the amino acid sequence and modeled the three-dimensional structure of the PsbS from , as well as calculated the pK values of its lumen-exposed protonatable residues. Despite significant differences in amino acid sequence, proteins from and have similar three-dimensional structures. Along with the other differences, one of the two pH-sensing glutamates in PsbS from (namely, Glu-173) has no analogue in protein. Moreover, there are only four glutamate residues in the lumenal region of the protein, while there are eight glutamates in . However, our calculations show that, despite the relative deficiency in protonatable residues, at least two residues of PsbS can be considered probable pH sensors: Glu-87 and Lys-196.
PsbS 是一种关键的光保护蛋白，可确保植物光系统（PSA）对辐照度的突然变化具有耐受性。它作为光系统 II 的组成部分，为光合作用天线中过量光能的叶绿素激发态形成淬灭中心。该蛋白的光保护功能的“开启”信号是当所有吸收的光能（以跨膜质子势的形式储存）不能用于碳同化时，类囊体腔中 pH 的过度下降。因此，作为 pH 传感器的腔暴露质子化氨基酸残基是 PsbS 依赖性光保护的基本组成部分，其 pK 值对于描述光保护是必要的。以前，文献中描述了菠菜 PsbS 腔暴露质子化残基 pK 值的计算。然而，最近清楚的是，虽然 PsbS 是高等植物和轮藻的典型代表，但它也可以为绿藻提供光保护。即，最近表明，在两种绿藻中，应激诱导表达 PsbS：和。因此，我们确定了 的 PsbS 的氨基酸序列并对其进行了三维结构建模，还计算了其腔暴露质子化残基的 pK 值。尽管氨基酸序列存在显著差异，但来自和的蛋白质具有相似的三维结构。除了其他差异之外，来自的 PsbS 中的两个 pH 感应谷氨酸之一（即 Glu-173）在 蛋白中没有类似物。此外，在 的腔内部区域仅有四个谷氨酸残基，而 蛋白中有八个谷氨酸。然而，我们的计算表明，尽管质子化残基相对缺乏，但至少有两个 蛋白的 PsbS 残基可以被认为是可能的 pH 传感器：Glu-87 和 Lys-196。
