Fotiadis D, Müller D J, Tsiotis G, Hasler L, Tittmann P, Mini T, Jenö P, Gross H, Engel A
M. E. Müller Institute for Microscopy, Division of Biochemistry Biozentrum, University of Basel, Switzerland.
J Mol Biol. 1998;283(1):83-94. doi: 10.1006/jmbi.1998.2097.
Two-dimensional (2D) crystals of the photosystem I (PSI) reaction center from Synechococcus sp. OD24 were analyzed by electron and atomic force microscopy. Surface relief reconstructions from electron micrographs of freeze-dried unidirectionally shadowed samples and topographs recorded with the atomic force microscope (AFM) provided a precise definition of the lumenal and stromal PSI surfaces. The lumenal surface was composed of four protrusions that surrounded an indentation. One of the protrusions, the PsaF subunit, was often missing. Removal of the extrinsic proteins with the AFM stylus exposed the stromal side of the PSI core, whose surface structure could then be imaged at a resolution better than 1.4 nm. This interfacial surface between core and extrinsic subunits, had a pseudo-2-fold symmetry and protrusions that correlated with the surface helices e and e' or were at the sites of putative alpha-helix-connecting loops estimated from the 4 A map of the complex. The molecular dissection achieved with the AFM, opens new possibilities to unveil the interfaces between subunits of supramolecular assemblies.
对来自聚球藻属菌株OD24的光系统I（PSI）反应中心的二维（2D）晶体进行了电子显微镜和原子力显微镜分析。通过对冻干单向阴影样品的电子显微照片进行表面起伏重建以及用原子力显微镜（AFM）记录的形貌图，精确界定了腔面和基质面的PSI表面。腔面由围绕一个凹陷的四个突起组成。其中一个突起，即PsaF亚基，常常缺失。用AFM探针去除外在蛋白后，暴露出PSI核心的基质侧，其表面结构随后可以在优于1.4纳米的分辨率下成像。核心亚基和外在亚基之间的这个界面表面具有准二重对称性，且其突起与表面螺旋e和e'相关，或者位于根据该复合物的4埃图谱估计的假定α螺旋连接环的位置。用AFM实现的分子剖析为揭示超分子组装体亚基之间的界面开辟了新的可能性。
