Department of Biochemistry and Molecular Biology, The George S. Wise Faculty of Life Sciences, Tel Aviv University, Tel Aviv 69978, Israel.
Department of Biochemistry and Molecular Biology, The George S. Wise Faculty of Life Sciences, Tel Aviv University, Tel Aviv 69978, Israel.
Biochim Biophys Acta Bioenerg. 2018 Sep;1859(9):645-654. doi: 10.1016/j.bbabio.2018.02.002. Epub 2018 Feb 4.
The ability of photosynthetic organisms to use the sun's light as a sole source of energy sustains life on our planet. Photosystems I (PSI) and II (PSII) are large, multi-subunit, pigment-protein complexes that enable photosynthesis, but this intriguing process remains to be explained fully. Currently, crystal structures of these complexes are available for thermophilic prokaryotic cyanobacteria. The mega-Dalton trimeric PSI complex from thermophilic cyanobacterium, Thermosynechococcus elongatus, was solved at 2.5 Å resolution with X-ray crystallography. That structure revealed the positions of 12 protein subunits (PsaA-F, PsaI-M, and PsaX) and 127 cofactors. Although mesophilic organisms perform most of the world's photosynthesis, no well-resolved trimeric structure of a mesophilic organism exists. Our research model for a mesophilic cyanobacterium was Synechocystis sp. PCC6803. This study aimed to obtain well-resolved crystal structures of [1] a monomeric PSI with all subunits, [2] a trimeric PSI with a reduced number of subunits, and [3] the full, trimeric wild-type PSI complex. We only partially succeeded with the first two structures, but we successfully produced the trimeric PSI structure at 2.5 Å resolution. This structure was comparable to that of the thermophilic species, but we provided more detail. The PSI trimeric supercomplex consisted of 33 protein subunits, 72 carotenoids, 285 chlorophyll a molecules, 51 lipids, 9 iron-sulfur clusters, 6 plastoquinones, 6 putative calcium ions, and over 870 water molecules. This study showed that the structure of the PSI in Synechocystis sp. PCC6803 differed from previously described PSI structures. These findings have broadened our understanding of PSI structure.
光合作用生物利用阳光作为唯一的能量来源的能力维持了我们星球上的生命。光系统 I（PSI）和 II（PSII）是大型的多亚基、色素-蛋白复合物，使光合作用成为可能，但这个有趣的过程仍有待充分解释。目前，这些复合物的晶体结构可用于嗜热原核蓝藻。来自嗜热蓝藻 Thermosynechococcus elongatus 的 mega-Dalton 三聚 PSI 复合物通过 X 射线晶体学以 2.5Å 分辨率解决。该结构揭示了 12 种蛋白质亚基（PsaA-F、PsaI-M 和 PsaX）和 127 种辅因子的位置。尽管嗜中温生物进行了世界上大部分的光合作用，但不存在中温生物的良好分辨率三聚体结构。我们研究的中温蓝藻模型是 Synechocystis sp. PCC6803。本研究旨在获得[1]具有所有亚基的单体 PSI 的良好分辨率晶体结构，[2]具有减少亚基数的三聚 PSI 的晶体结构，以及[3]完整的三聚野生型 PSI 复合物的晶体结构。我们在前两种结构上只取得了部分成功，但我们成功地以 2.5Å 分辨率生产了三聚 PSI 结构。该结构与嗜热物种相似，但提供了更多细节。PSI 三聚体超复合物由 33 种蛋白质亚基、72 种类胡萝卜素、285 个叶绿素 a 分子、51 个脂质、9 个铁-硫簇、6 个质体醌、6 个拟议的钙离子和超过 870 个水分子组成。本研究表明，Synechocystis sp. PCC6803 的 PSI 结构与先前描述的 PSI 结构不同。这些发现拓宽了我们对 PSI 结构的理解。
