Rojdestvenski Igor, Ivanov Alexander G, Cottam M G, Borodich Andrei, Huner Norman P A, Oquist Gunnar
Department of Plant Physiology, Umeå University, Umeå S-90 187, Sweden.
Biophys J. 2002 Apr;82(4):1719-30. doi: 10.1016/S0006-3495(02)75524-0.
The distribution of the two photosystems, PSI and PSII, in grana and stroma lamellae of the chloroplast membranes is not uniform. PSII are mainly concentrated in grana and PSI in stroma thylakoids. The dynamics and factors controlling the spatial segregation of PSI and PSII are generally not well understood, and here we address the segregation of photosystems in thylakoid membranes by means of a molecular dynamics method. The lateral segregation of photosystems was studied assuming a model comprising a two-dimensional (in-plane), two-component, many-body system with periodic boundary conditions and competing interactions between the photosystems in the thylakoid membrane. PSI and PSII are represented by particles with different values of negative charge. The pair interactions between particles include a screened Coulomb repulsive part and an exponentially decaying attractive part. The modeling results suggest a complicated phase behavior of the system, including quasi-crystalline phase of randomly distributed complexes of PSII and PSI at low ionic screening, well defined clustered state of segregated complexes at high screening, and in addition, an intermediate agglomerate phase where the photosystems tend to aggregate together without segregation. The calculations demonstrated that the ordering of photosystems within the membrane was the result of interplay between electrostatic and lipid-mediated interactions. At some values of the model parameters the segregation can be represented visually as well as by analyzing the correlation functions of the configuration.
叶绿体膜的基粒和基质类囊体中光系统I（PSI）和光系统II（PSII）的分布并不均匀。PSII主要集中在基粒中，而PSI则主要分布在基质类囊体中。目前，人们对控制PSI和PSII空间分离的动力学及相关因素普遍了解不足。在此，我们借助分子动力学方法来研究类囊体膜中光系统的分离情况。我们假设一个包含二维（平面内）、两组分、多体系统的模型，该模型具有周期性边界条件且类囊体膜中的光系统之间存在竞争相互作用，以此来研究光系统的横向分离。PSI和PSII由带有不同负电荷值的粒子表示。粒子之间的成对相互作用包括屏蔽库仑排斥部分和指数衰减吸引部分。建模结果表明该系统具有复杂的相行为，包括在低离子屏蔽下PSII和PSI随机分布复合物的准晶相、在高屏蔽下分离复合物的明确聚集态，此外，还存在一个中间团聚相，其中光系统倾向于聚集在一起而不发生分离。计算结果表明，膜内光系统的有序排列是静电相互作用和脂质介导相互作用共同作用的结果。在某些模型参数值下，分离情况既可以通过可视化表示，也可以通过分析构型的相关函数来体现。
