Kaftan David, Brumfeld Vlad, Nevo Reinat, Scherz Avigdor, Reich Ziv
Department of Plant Sciences and Department of Biological Chemistry, Weizmann Institute of Science, Rehovot 76100, Israel.
EMBO J. 2002 Nov 15;21(22):6146-53. doi: 10.1093/emboj/cdf624.
Envelope-free chloroplasts were imaged in situ by contact and tapping mode scanning force microscopy at a lateral resolution of 3-5 nm and vertical resolution of approximately 0.3 nm. The images of the intact thylakoids revealed detailed structural features of their surface, including individual protein complexes over stroma, grana margin and grana-end membrane domains. Structural and immunogold-assisted assignment of two of these complexes, photosystem I (PS I) and ATP synthase, allowed direct determination of their surface density, which, for both, was found to be highest in grana margins. Surface rearrangements and pigment- protein complex redistribution associated with salt-induced membrane unstacking were followed on native, hydrated specimens. Unstacking was accompanied by a substantial increase in grana diameter and, eventually, led to their merging with the stroma lamellae. Concomitantly, PS IIalpha effective antenna size decreased by 21% and the mean size of membrane particles increased substantially, consistent with attachment of mobile light-harvesting complex II to PS I. The ability to image intact photosynthetic membranes at molecular resolution, as demonstrated here, opens up new vistas to investigate thylakoid structure and function.
通过接触模式和轻敲模式扫描力显微镜对无包膜叶绿体进行原位成像，横向分辨率为3 - 5纳米，纵向分辨率约为0.3纳米。完整类囊体的图像揭示了其表面的详细结构特征，包括基质、基粒边缘和基粒末端膜结构域上的单个蛋白质复合物。对其中两种复合物，即光系统I（PS I）和ATP合酶进行结构和免疫金辅助鉴定，可直接测定它们的表面密度，结果发现两者在基粒边缘的密度最高。在天然水合标本上观察了与盐诱导的膜解堆叠相关的表面重排和色素 - 蛋白质复合物再分布。解堆叠伴随着基粒直径的显著增加，并最终导致它们与基质类囊体融合。同时，PS IIα有效天线大小减小了21%，膜颗粒的平均大小大幅增加，这与移动性捕光复合物II附着到PS I上一致。如本文所示，以分子分辨率对完整光合膜进行成像的能力为研究类囊体结构和功能开辟了新的视野。
