Terentyev Vasily V, Trubitsina Liubov I, Khoroshaeva Tatyana P, Trubitsin Ivan V
Institute of Basic Biological Problems, Pushchino Scientific Center for Biological Research, Russian Academy of Sciences, Pushchino, Moscow Region, 142290, Russia.
G. K. Skryabin Institute of Biochemistry and Physiology of Microorganisms, Pushchino Scientific Center for Biological Research, Russian Academy of Sciences, Pushchino, Moscow Region, 142290, Russia.
Biochemistry (Mosc). 2025 Jul;90(7):860-872. doi: 10.1134/S0006297925601133.
Photosystem II (PSII) is one of the most vulnerable components of photosynthetic apparatus of the thylakoid membrane to the action of inhibitory factors. The donor side of PSII exhibits high sensitivity to photoinhibition and thermal inactivation, which leads to the loss of O-evolving function of the water-oxidizing complex (WOC). The data obtained in this study demonstrated increased stability of WOC activity in the PSII membrane preparations from the wild-type (WT) compared to the PSII preparations from the mutant, which lack α-carbonic anhydrase (CA) CAH3, under conditions of moderate photoinhibition and thermal inactivation. This effect was completely eliminated by adding a CA inhibitor to the PSII preparations from WT. At the same time, addition of active recombinant CAH3 (rCAH3) protein to the preparations from restored increased resistance of PSII to these factors. Under the same conditions of photoinhibition and thermal inactivation, the PSII preparations from demonstrated very low loss of O-evolving activity, regardless of the presence or absence of carbonic anhydrase α-CA4, which is similar to CAH3. More pronounced suppression of the O-evolving activity in the PSII from mutants lacking CA4 was observed only when they were incubated at elevated temperature, indicating the possibility of more significant conformational changes in the WOC proteins of PSII. Despite the clear binding of the rCAH3 to PSII membrane preparations from , the enzyme had little effect on the WOC activity in these preparations, suggesting absence of functional interaction between the rCAH3 and PSII from . The obtained results indicate different mechanisms of involvement of CAH3 and CA4, both of which are assumed to exist in close association with PSII in live systems, in the PSII functioning.
光系统II（PSII）是类囊体膜光合装置中对抑制因子作用最敏感的组件之一。PSII的供体侧对光抑制和热失活表现出高度敏感性，这导致水氧化复合物（WOC）的放氧功能丧失。本研究获得的数据表明，在中度光抑制和热失活条件下，与缺乏α-碳酸酐酶（CA）CAH3的突变体的PSII制剂相比，野生型（WT）的PSII膜制剂中WOC活性的稳定性有所提高。向WT的PSII制剂中添加CA抑制剂可完全消除这种效应。同时，向突变体的制剂中添加活性重组CAH3（rCAH3）蛋白可恢复PSII对这些因素的抗性增强。在相同的光抑制和热失活条件下，无论是否存在与CAH3类似的碳酸酐酶α-CA4，突变体的PSII制剂的放氧活性损失都非常低。仅当缺乏CA4的突变体在高温下孵育时，才观察到其PSII中放氧活性受到更明显的抑制，这表明PSII的WOC蛋白可能发生更显著的构象变化。尽管rCAH3与突变体的PSII膜制剂有明显结合，但该酶对这些制剂中的WOC活性影响很小，这表明rCAH3与突变体的PSII之间不存在功能相互作用。所得结果表明，CAH3和CA4参与PSII功能的机制不同，在活体系统中，二者均被认为与PSII紧密结合。
