Aspinwall Caroline L, Duncan James, Bibby Thomas, Mullineaux Conrad W, Barber James
Department of Biology, University College London, Darwin Building, Gower Street, London WC1E 6BT, UK.
FEBS Lett. 2004 Sep 10;574(1-3):126-30. doi: 10.1016/j.febslet.2004.08.016.
A mutant of Synechocystis PCC 6803 lacking the PsaL subunit of photosystem I (PSI) has been grown in iron-deficient media to induce the expression of the isiA gene, which encodes the chlorophyll a-binding protein CP43'. The purpose of this was to establish whether or not the formation of an 18-mer CP43'-PSI supercomplex reported for wild type Synechocystis cells [Nature 412 (2001) 743-745] was dependent on the trimeric conformation of the cyanobacterial PSI reaction centre. Structural characterisation by electron microscopy and single particle image analysis has revealed that the PsaL-mutant does not form trimers of PSI. However, despite this, CP43' was found to associate with the PSI monomer. The PSI monomer bound six or seven copies of CP43' along one edge of the PSI monomer and can be compared with one segment of the trimeric 18-mer CP43'-PSI supercomplex. We therefore conclude that the trimeric nature of cyanobacterial PSI is not required for the assembly of the CP43' antenna system under iron-deficient conditions.
一种缺乏光系统I（PSI）的PsaL亚基的集胞藻PCC 6803突变体已在缺铁培养基中培养，以诱导isiA基因的表达，该基因编码叶绿素a结合蛋白CP43'。这样做的目的是确定野生型集胞藻细胞中报道的18聚体CP43'-PSI超复合物的形成是否依赖于蓝藻PSI反应中心的三聚体构象。通过电子显微镜和单颗粒图像分析进行的结构表征表明，PsaL突变体不会形成PSI三聚体。然而，尽管如此，仍发现CP43'与PSI单体相关联。PSI单体沿着PSI单体的一条边缘结合了六个或七个CP43'拷贝，并且可以与三聚体18聚体CP43'-PSI超复合物的一个片段进行比较。因此，我们得出结论，在缺铁条件下，蓝藻PSI的三聚体性质对于CP43'天线系统的组装不是必需的。
