Division of Molecular Biosciences, Imperial College London, South Kensington Campus, London, UK.
Philos Trans R Soc Lond B Biol Sci. 2012 Dec 19;367(1608):3444-54. doi: 10.1098/rstb.2012.0066.
Photosystem II (PSII) mutants are useful experimental tools to trap potential intermediates involved in the assembly of the oxygen-evolving PSII complex. Here, we focus on the subunit composition of the RC47 assembly complex that accumulates in a psbC null mutant of the cyanobacterium Synechocystis sp. PCC 6803 unable to make the CP43 apopolypeptide. By using native gel electrophoresis, we showed that RC47 is heterogeneous and mainly found as a monomer of 220 kDa. RC47 complexes co-purify with small Cab-like proteins (ScpC and/or ScpD) and with Psb28 and its homologue Psb28-2. Analysis of isolated His-tagged RC47 indicated the presence of D1, D2, the CP47 apopolypeptide, plus nine of the 13 low-molecular-mass (LMM) subunits found in the PSII holoenzyme, including PsbL, PsbM and PsbT, which lie at the interface between the two momomers in the dimeric holoenzyme. Not detected were the LMM subunits (PsbK, PsbZ, Psb30 and PsbJ) located in the vicinity of CP43 in the holoenzyme. The photochemical activity of isolated RC47-His complexes, including the rate of reduction of P680(+), was similar to that of PSII complexes lacking the Mn(4)CaO(5) cluster. The implications of our results for the assembly and repair of PSII in vivo are discussed.
光系统 II（PSII）突变体是一种有用的实验工具，可以捕获参与氧释放 PSII 复合物组装的潜在中间体。在这里，我们重点研究了在不能产生 CP43 脱辅基蛋白的蓝藻集胞藻 PCC 6803 的 psbC 缺失突变体中积累的 RC47 组装复合物的亚基组成。通过使用天然凝胶电泳，我们表明 RC47 是异质的，主要以 220 kDa 的单体形式存在。RC47 复合物与小 Cab 样蛋白（ScpC 和/或 ScpD）以及 Psb28 和其同源物 Psb28-2 共同纯化。对分离的 His 标记的 RC47 的分析表明存在 D1、D2、CP47 脱辅基蛋白，以及在 PSII 全酶中发现的 13 个低分子量（LMM）亚基中的九个，包括位于二聚体全酶两个单体之间界面的 PsbL、PsbM 和 PsbT。未检测到 LMM 亚基（PsbK、PsbZ、Psb30 和 PsbJ）位于全酶中 CP43 附近。分离的 RC47-His 复合物的光化学活性，包括 P680(+)的还原速率，与缺乏 Mn(4)CaO(5)簇的 PSII 复合物相似。我们的结果对体内 PSII 组装和修复的影响进行了讨论。
