Andrizhiyevskaya Elena G, Schwabe Tatjana M E, Germano Marta, D'Haene Sandrine, Kruip Jochen, van Grondelle Rienk, Dekker Jan P
Division of Physics and Astronomy, Institute of Molecular Biological Science, Faculty of Sciences, Vrije Universiteit, De Boelelaan 1081, 1081 HV, Amsterdam, The Netherlands.
Biochim Biophys Acta. 2002 Dec 2;1556(2-3):265-72. doi: 10.1016/s0005-2728(02)00371-7.
The cyanobacterium Synechococcus PCC 7942 grown under iron starvation assembles a supercomplex consisting of a trimeric Photosystem I (PSI) complex encircled by a ring of 18 CP43' or IsiA light-harvesting complexes [Nature 412 (2001) 745]. Here we present a spectroscopic characterization by temperature-dependent absorption and fluorescence spectroscopy, site-selective fluorescence spectroscopy at 5 K, and circular dichroism of isolated PSI-IsiA, PSI and IsiA complexes from this cyanobacterium grown under iron starvation. The results suggest that the IsiA ring increases the absorption cross-section of PSI by about 100%. Each IsiA subunit binds about 16-17 chlorophyll a (Chl a) molecules and serves as an efficient antenna for PSI. Each of the monomers of the trimeric PSI complex contains two red chlorophylls, which presumably give rise to one exciton-coupled dimer and at 5 K absorb and fluoresce at 703 and 713 nm, respectively. The spectral properties of these C-703 chlorophylls are not affected by the presence of the IsiA antenna ring. The spectroscopic properties of the purified IsiA complexes are similar to those of the related CP43 complex from plants, except that the characteristic narrow absorption band of CP43 at 682.5 nm is missing in IsiA.
在铁饥饿条件下生长的蓝藻聚球藻PCC 7942组装了一种超复合物，该超复合物由一个三聚体光系统I（PSI）复合物组成，周围环绕着18个CP43'或IsiA光捕获复合物组成的环[《自然》412 (2001) 745]。在此，我们通过温度依赖的吸收光谱和荧光光谱、5 K下的位点选择性荧光光谱以及对在铁饥饿条件下生长的这种蓝藻中分离出的PSI-IsiA、PSI和IsiA复合物的圆二色性进行了光谱表征。结果表明，IsiA环使PSI的吸收截面增加了约100%。每个IsiA亚基结合约16 - 17个叶绿素a（Chl a）分子，并作为PSI的有效天线。三聚体PSI复合物的每个单体包含两个红色叶绿素，推测这两个叶绿素形成一个激子耦合二聚体，在5 K下分别在703和713 nm处吸收和荧光发射。这些C-703叶绿素的光谱特性不受IsiA天线环存在的影响。纯化的IsiA复合物的光谱特性与植物中相关的CP43复合物相似，只是IsiA中缺少CP43在682.5 nm处的特征窄吸收带。
