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蓝细菌类囊体膜的超分子结构:藻胆体与光系统如何连接?

Supramolecular architecture of cyanobacterial thylakoid membranes: How is the phycobilisome connected with the photosystems?

机构信息

Institute of Botany, University of Münster, Schlossgarten 3, D-48149, Münster, Germany.

出版信息

Photosynth Res. 1996 Aug;49(2):103-18. doi: 10.1007/BF00117661.

Abstract

Cyanobacteria, as the most simple organisms to perform oxygenic photosynthesis differ from higher plants especially with respect to the thylakoid membrane structure and the antenna system used to capture light energy. Cyanobacterial antenna systems, the phycobilisomes (PBS), have been shown to be associated with Photosystem 2 (PS 2) at the cytoplasmic side, forming a PS 2-PBS-supercomplex, the structure of which is not well understood. Based on structural data of PBS and PS 2, a model for such a supercomplex is presented. Its key features are the PS 2 dimer as prerequisite for formation of the supercomplex and the antiparallel orientation of PBS-cores and the two PS 2 monomers which form the 'contact area' within the supercomplex. Possible consequences for the formation of 'superstructures' (PS 2-PBS rows) within the thylakoid membrane under so-called 'state 1' conditions are discussed. As there are also indications for specific functional connections of PBS with Photosystem 1 (PS 1) under so-called 'state 2' conditions, we show a model which reconciles the need for a structural interaction between PBS and PS 1 with the difference in structural symmetry (2-fold rotational symmetry of PBS-cores, 3-fold rotational symmetry of trimeric PS 1). Finally, the process of dynamic coupling and uncoupling of PBS to PS 1 and PS 2, based on the presented models, shows analogies to mechanisms for the regulation of photosynthetic electron flow in higher plants-despite the very different organization of their thylakoid membranes in comparison to cyanobacteria.

摘要

蓝藻作为进行放氧光合作用的最原始的生物,与高等植物在类囊体膜结构和天线系统用于捕获光能方面有很大的不同。蓝藻天线系统——藻胆体(PBS),已被证明与细胞质侧的光系统 2(PS 2)相关联,形成 PS 2-PBS-超复合物,其结构尚不清楚。基于 PBS 和 PS 2 的结构数据,提出了这样一个超复合物的模型。其关键特征是 PS 2 二聚体是形成超复合物的前提,以及 PBS 核心和形成超复合物“接触区”的两个 PS 2 单体的反平行取向。在所谓的“状态 1”条件下,讨论了类囊体膜中 PBS 形成“超结构”(PS 2-PBS 行)的可能后果。由于在所谓的“状态 2”条件下,也有 PBS 与光系统 1(PS 1)之间存在特定功能连接的迹象,我们展示了一个模型,该模型协调了 PBS 与 PS 1 之间的结构相互作用的必要性与结构对称性的差异(PBS 核心的 2 重旋转对称性,三聚 PS 1 的 3 重旋转对称性)。最后,基于所提出的模型,展示了 PBS 与 PS 1 和 PS 2 的动态偶联和去偶联过程,与高等植物光合电子流调控机制有相似之处——尽管与蓝藻相比,它们的类囊体膜的组织非常不同。

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