Böttcher B, Gräber P, Boekema E J
BIOSON Research Institute, University of Groningen, Netherlands.
Biochim Biophys Acta. 1992 May 20;1100(2):125-36. doi: 10.1016/0005-2728(92)90073-b.
The structure of the Photosystem I (PS I) complex from the thermophilic cyanobacterium Synechococcus sp. has been investigated by electron microscopy and image analysis of two-dimensional crystals. Crystals were obtained from isolated PS I by removal of detergents with Bio-Beads. After negative staining, either single layers or two superimposed layers with a rotational different orientation were observed. The layers have a rectangular unit cell of 16.0 x 15.0 nm, which contains two PS I monomers. The monomers are arranged alternating up and down in each layer. For double-layer crystals, the images of the two layers could be separately processed by a combination of Fourier-peak-filtering and correlation averaging. Features in the two-dimensional plane can be seen with a resolution up to 1.5-1.8 nm. A model for the PS I structure was obtained by combining three-dimensional reconstructions from three tilt-series. The model shows an asymmetric PS I complex. On one side (presumably the stromal side) there is a 3 nm high ridge. This is most likely comprised of the psaC, psaD and psaE subunits. The other side (presumably the lumenal side) is rather flat, but in the center there is a 3 nm deep indentation, which possibly separates partly the two large subunits psaA and psaB.
通过电子显微镜和二维晶体图像分析，对嗜热蓝细菌聚球藻属（Synechococcus sp.）的光系统I（PS I）复合物结构进行了研究。通过用Bio-Beads去除去污剂，从分离的PS I中获得晶体。负染后，观察到单层或具有旋转不同取向的两个叠加层。这些层具有16.0×15.0 nm的矩形晶胞，其中包含两个PS I单体。单体在每层中上下交替排列。对于双层晶体，两层的图像可以通过傅里叶峰滤波和相关平均相结合的方法分别处理。二维平面中的特征分辨率可达1.5 - 1.8 nm。通过结合来自三个倾斜系列的三维重建获得了PS I结构模型。该模型显示了一个不对称的PS I复合物。在一侧（可能是基质侧）有一个3 nm高的脊。这很可能由psaC、psaD和psaE亚基组成。另一侧（可能是腔侧）相当平坦，但在中心有一个3 nm深的凹陷，这可能部分地将两个大亚基psaA和psaB分开。
