Electron Microscopy Group, Groningen Biomolecular Sciences & Biotechnology Institute, University of Groningen, 9747 AG, Groningen, The Netherlands.
Department of Biophysics, Centre of the Region Haná for Biotechnological and Agricultural Research, Faculty of Science, Palacký University, 78371 Olomouc, Czech Republic.
Biochim Biophys Acta Bioenerg. 2017 Jan;1858(1):12-20. doi: 10.1016/j.bbabio.2016.10.006. Epub 2016 Oct 15.
Photosystem I (PSI) is a pigment-protein complex required for the light-dependent reactions of photosynthesis and participates in light-harvesting and redox-driven chloroplast metabolism. Assembly of PSI into supercomplexes with light harvesting complex (LHC) II, cytochrome bf (Cytbf) or NAD(P)H dehydrogenase complex (NDH) has been proposed as a means for regulating photosynthesis. However, structural details about the binding positions in plant PSI are lacking. We analyzed large data sets of electron microscopy single particle projections of supercomplexes obtained from the stroma membrane of Arabidopsis thaliana. By single particle analysis, we established the binding position of Cytbf at the antenna side of PSI. The rectangular-shaped Cytbf dimer binds at the side where Lhca1 is located. The complex binds with its short side rather than its long side to PSI, which may explain why these supercomplexes are difficult to purify and easily disrupted. Refined analysis of the interaction between PSI and the NDH complex indicates that in total up to 6 copies of PSI can arrange with one NDH complex. Most PSI-NDH supercomplexes appeared to have 1-3 PSI copies associated. Finally, the PSI-LHCII supercomplex was found to bind an additional LHCII trimer at two positions on the LHCI side in Arabidopsis. The organization of PSI, either in a complex with NDH or with Cytbf, may improve regulation of electron transport by the control of binding partners and distances in small domains.
光系统 I (PSI) 是光合作用光依赖反应所必需的色素-蛋白复合物，参与光捕获和氧化还原驱动的叶绿体代谢。PSI 与光收集复合物 (LHC) II、细胞色素 bf (Cytbf) 或 NAD(P)H 脱氢酶复合物 (NDH) 组装成超复合物，被认为是调节光合作用的一种手段。然而，关于植物 PSI 结合位置的结构细节尚不清楚。我们分析了来自拟南芥基质膜的超复合物电子显微镜单颗粒投影的大型数据集。通过单颗粒分析，我们确定了 Cytbf 在 PSI 天线侧的结合位置。矩形 Cytbf 二聚体结合在 Lhca1 所在的位置。复合物以其短边而不是长边与 PSI 结合，这可能解释了为什么这些超复合物难以纯化且容易被破坏。对 PSI 与 NDH 复合物相互作用的精细分析表明，总共多达 6 个 PSI 副本可以与一个 NDH 复合物排列。大多数 PSI-NDH 超复合物似乎有 1-3 个 PSI 副本与之相关。最后，在拟南芥中发现 PSI-LHCII 超复合物在 LHCI 侧的两个位置结合额外的 LHCII 三聚体。PSI 与 NDH 或 Cytbf 的结合，可能通过控制结合伙伴和小域内的距离来改善电子传递的调节。
