Department of Biology, Washington University, St. Louis, MO 63130, USA.
Biochemistry. 2011 Jan 25;50(3):329-39. doi: 10.1021/bi101077e. Epub 2010 Dec 22.
Sll1252 was identified as a novel protein in photosystem II complexes from Synechocystis sp. PCC 6803. To investigate the function of Sll1252, the corresponding gene, sll1252, was deleted in Synechocystis 6803. Despite the homology of Sll1252 to YlmH, which functions in the cell division machinery in Streptococcus, the growth rate and cell morphology of the mutant were not affected in normal growth medium. Instead, it seems that cells lacking this polypeptide have increased sensitivity to Cl(-) depletion. The growth and oxygen evolving activity of the mutant cells was highly suppressed compared with those of wild-type cells when Cl(-) and/or Ca(2+) was depleted from the medium. Recovery of photosystem II from photoinhibition was suppressed in the mutant. Despite the defects in photosystem II, in the light, the acceptor side of photosystem II was more reduced and the donor side of photosystem I was more oxidized compared with wild-type cells, suggesting that functional impairments were also present in cytochrome b(6)/f complexes. The amounts of cytochrome c(550) and cytochrome f were smaller in the mutant in the Ca(2+)- and Cl(-)-depleted medium. Furthermore, the amount of IsiA protein was increased in the mutant, especially in the Cl(-)-depleted medium, indicating that the mutant cells perceive environmental stress to be greater than it is. The amount of accompanying cytochrome c(550) in purified photosystem II complexes was also smaller in the mutant. Overall, the Sll1252 protein appears to be closely related to redox sensing of the plastoquinone pool to balance the photosynthetic electron flow and the ability to cope with global environmental stresses.
Sll1252 被鉴定为集光复合体 II 中的一种新型蛋白，来源于集胞藻 PCC 6803。为了研究 Sll1252 的功能，我们在集胞藻 6803 中敲除了相应的基因 sll1252。尽管 Sll1252 与 YlmH 同源，后者在链球菌的细胞分裂机制中发挥作用，但突变体的生长速度和细胞形态在正常生长培养基中并未受到影响。相反，似乎缺乏这种多肽的细胞对 Cl(-)耗尽更为敏感。与野生型细胞相比，当培养基中耗尽 Cl(-)和/或 Ca(2+)时，突变体细胞的生长和氧释放活性受到高度抑制。突变体的光系统 II 从光抑制中的恢复受到抑制。尽管光系统 II 存在缺陷，但在光照下，与野生型细胞相比，光系统 II 的受体侧更为还原，光系统 I 的供体侧更为氧化，这表明细胞色素 b(6)/f 复合物也存在功能障碍。在 Ca(2+)和 Cl(-)耗尽的培养基中，突变体中的细胞色素 c(550)和细胞色素 f 含量较小。此外，在突变体中，IsiA 蛋白的含量增加，尤其是在 Cl(-)耗尽的培养基中，这表明突变体细胞感知到的环境应激比实际情况更大。在纯化的光系统 II 复合物中，伴随的细胞色素 c(550)的含量也较小。总的来说，Sll1252 蛋白似乎与质醌库的氧化还原感应密切相关，以平衡光合电子流和应对全球环境压力的能力。
