Department of Biophysical Chemistry, Groningen Biomolecular Sciences and Biotechnology Institute, University of Groningen, The Netherlands.
Biochem J. 2011 Feb 1;433(3):477-85. doi: 10.1042/BJ20101538.
The outer antenna of higher-plant PSI (Photosystem I) is composed of four complexes [Lhc (light-harvesting complex) a1-Lhca4] belonging to the light-harvesting protein family. Difficulties in their purification have so far prevented the determination of their properties and most of the knowledge about Lhcas has been obtained from the study of the in vitro reconstituted antennas. In the present study we were able to purify the native complexes, showing that Lhca2/3 and Lhca1/4 form two functional heterodimers. Both dimers show red-fluorescence emission with maxima around 730 nm, as in the intact PSI complex. This indicates that the dimers are in their native state and that LHCI-680, which was previously assumed to be part of the PSI antenna, does not represent the native state of the system. The data show that the light-harvesting properties of the two dimers are functionally identical, concerning absorption, long-wavelength emission and fluorescence quantum yield, whereas they differ in their high-light response. Implications of the present study for the understanding of the energy transfer process in PSI are discussed. Finally, the comparison of the properties of the native dimers with those of the reconstituted complexes demonstrates that all of the major properties of the Lhcas are reproduced in the in vitro systems.
高等植物 PSI（光系统 I）的外部天线由属于捕光蛋白家族的四个复合物 [Lhc（光捕获复合物）a1-Lhca4] 组成。由于其纯化困难，迄今为止，它们的性质仍未确定，并且大多数关于 Lhcas 的知识都是通过体外重建天线的研究获得的。在本研究中，我们能够纯化天然复合物，表明 Lhca2/3 和 Lhca1/4 形成两个功能异二聚体。这两个二聚体均显示出 730nm 左右的红色荧光发射，与完整的 PSI 复合物相同。这表明二聚体处于天然状态，并且先前假定为 PSI 天线一部分的 LHCI-680 不代表该系统的天然状态。数据表明，两个二聚体的光捕获特性在功能上是相同的，涉及吸收、长波长发射和荧光量子产率，而它们在高光响应方面存在差异。本研究对理解 PSI 中的能量转移过程具有重要意义。最后，将天然二聚体的性质与重建复合物的性质进行比较，证明了体外系统中再现了 Lhcas 的所有主要性质。
