Antonkine Mikhail L, Jordan Patrick, Fromme Petra, Krauss Norbert, Golbeck John H, Stehlik Dietmar
Institut für Experimentalphysik, Freie Universität Berlin, Arnimallee 14, D-14195 Berlin, Germany.
J Mol Biol. 2003 Mar 28;327(3):671-97. doi: 10.1016/s0022-2836(03)00145-1.
The X-ray structure of Photosystem I (PS I) from Synechococcus elongatus was recently solved at 2.5A resolution (PDB entry 1JB0). It provides a structural model for the stromal subunits PsaC, PsaD and PsaE, which comprise the "stromal ridge" of PS I. In a separate set of studies the three-dimensional solution structures of the unbound, recombinant PsaC (PDB entry 1K0T) and PsaE (PDB entries 1PSF, 1QP2 and 1GXI) subunits were solved by NMR. The PsaC subunit of PS I is a small (9.3 kDa) protein that harbors binding sites for two [4Fe-4S] clusters F(A) and F(B), which are the terminal electron acceptors in PS I. Comparison of the PsaC structure in solution with that in the X-ray structure of PS I reveals significant differences between them which are summarized and evaluated here. Changes in the magnetic properties of [4Fe-4S] centers F(A) and F(B) are related to changes in the protein structure of PsaC, and they are further influenced by the presence of PsaD. Based on experimental evidence, three assembly stages are analyzed: PsaC(free), PsaC(only), PsaC(PS I). Unbound, recombinant PsaD, studied by NMR, has only a few elements of secondary structure and no stable three-dimensional structure in solution. When PsaD is bound in PS I, it has a well-defined three-dimensional structure. For PsaE the three-dimensional structure is very similar in solution and in the PS I-bound form, with the exception of two loop regions. We suggest that the changes in the structures of PsaC and PsaD are caused by the sequential formation of multiple networks of contacts between the polypeptides of the stromal ridge and between those polypeptides and the PsaA/PsaB core polypeptides. The three-dimensional structure of the C(2)-symmetric F(X)-binding loops on PsaA and PsaB were also analyzed and found to be significantly different from the binding sites of other proteins that contain interpolypeptide [4Fe-4S] clusters. The aim of this work is to relate contact information to structural changes in the proteins and to propose a model for the assembly of the stromal ridge of PS I based on this analysis.
嗜热栖热放线菌光系统I（PS I）的X射线结构最近已在2.5埃分辨率下解析出来（蛋白质数据库条目1JB0）。它为构成PS I“基质脊”的基质亚基PsaC、PsaD和PsaE提供了一个结构模型。在另一组研究中，通过核磁共振解析了未结合的重组PsaC（蛋白质数据库条目1K0T）和PsaE（蛋白质数据库条目1PSF、1QP2和1GXI）亚基的三维溶液结构。PS I的PsaC亚基是一种小蛋白（9.3 kDa），含有两个[4Fe-4S]簇F(A)和F(B)的结合位点，这两个簇是PS I中的末端电子受体。将溶液中PsaC的结构与PS I的X射线结构中的结构进行比较，发现它们之间存在显著差异，本文对此进行了总结和评估。[4Fe-4S]中心F(A)和F(B)的磁性变化与PsaC的蛋白质结构变化有关，并且它们还受到PsaD存在的进一步影响。基于实验证据，分析了三个组装阶段：PsaC（游离）、PsaC（仅）、PsaC（PS I）。通过核磁共振研究的未结合重组PsaD在溶液中只有少数二级结构元件，没有稳定的三维结构。当PsaD结合在PS I中时，它具有明确的三维结构。对于PsaE，除了两个环区域外，其三维结构在溶液中和与PS I结合的形式中非常相似。我们认为，PsaC和PsaD结构的变化是由基质脊的多肽之间以及这些多肽与PsaA/PsaB核心多肽之间依次形成多个接触网络引起的。还分析了PsaA和PsaB上C(2)对称的F(X)结合环的三维结构，发现其与其他含有多肽间[4Fe-4S]簇的蛋白质的结合位点有显著差异。这项工作的目的是将接触信息与蛋白质的结构变化联系起来，并基于此分析提出一个PS I基质脊组装的模型。
