Mozzo Milena, Mantelli Manuela, Passarini Francesca, Caffarri Stefano, Croce Roberta, Bassi Roberto
Department of Biophysical Chemistry, Groningen Biomolecular Sciences and Biotechnology Institute, University of Groningen, Nijenborgh 4, 9747 AG Groningen, The Netherlands.
Biochim Biophys Acta. 2010 Feb;1797(2):212-21. doi: 10.1016/j.bbabio.2009.10.005. Epub 2009 Oct 21.
The outer antenna system of Chlamydomonas reinhardtii Photosystem I is composed of nine gene products, but due to difficulty in purification their individual properties are not known. In this work, the functional properties of the nine Lhca antennas of Chlamydomonas, have been investigated upon expression of the apoproteins in bacteria and refolding in vitro of the pigment-protein complexes. It is shown that all Lhca complexes have a red-shifted fluorescence emission as compared to the antenna complexes of Photosystem II, similar to Lhca from higher plants, but less red-shifted. Three complexes, namely Lhca2, Lhca4 and Lhca9, exhibit emission maxima above 707 nm and all carry an asparagine as ligand for Chl 603. The comparison of the protein sequences and the biochemical/spectroscopic properties of the refolded Chlamydomonas complexes with those of the well-characterized Arabidopsis thaliana Lhcas shows that all the Chlamydomonas complexes have a chromophore organization similar to that of A. thaliana antennas, particularly to Lhca2, despite low sequence identity. All the major biochemical and spectroscopic properties of the Lhca complexes have been conserved through the evolution, including those involved in "red forms" absorption. It has been proposed that in Chlamydomonas PSI antenna size and polypeptide composition can be modulated in vivo depending on growth conditions, at variance as compared to higher plants. Thus, the different properties of the individual Lhca complexes can be functional to adapt the architecture of the PSI-LHCI supercomplex to different environmental conditions.
莱茵衣藻光系统I的外周天线系统由9种基因产物组成，但由于纯化困难，其各自的特性尚不清楚。在这项工作中，通过在细菌中表达脱辅基蛋白并在体外对色素-蛋白复合物进行重折叠，研究了衣藻9种Lhca天线的功能特性。结果表明，与光系统II的天线复合物相比，所有Lhca复合物的荧光发射都发生了红移，类似于高等植物的Lhca，但红移程度较小。三种复合物，即Lhca2、Lhca4和Lhca9，在707nm以上呈现发射最大值，并且都含有一个天冬酰胺作为叶绿素603的配体。将重折叠的衣藻复合物的蛋白质序列与已充分表征的拟南芥Lhcas的蛋白质序列以及生化/光谱特性进行比较，结果表明，尽管序列同一性较低，但所有衣藻复合物都具有与拟南芥天线，特别是与Lhca2相似的发色团组织。Lhca复合物的所有主要生化和光谱特性在进化过程中都得以保留，包括那些与“红色形式”吸收有关的特性。有人提出，与高等植物不同，在衣藻中，光系统I天线的大小和多肽组成可以在体内根据生长条件进行调节。因此，各个Lhca复合物的不同特性可能有助于使光系统I-LHCI超复合物的结构适应不同的环境条件。
