Mass Spectrometry-based Footprinting Reveals Structural Dynamics of Loop E of the Chlorophyll-binding Protein CP43 during Photosystem II Assembly in the Cyanobacterium Synechocystis 6803
Mass Spectrometry-based Footprinting Reveals Structural Dynamics of Loop E of the Chlorophyll-binding Protein CP43 during Photosystem II Assembly in the Cyanobacterium Synechocystis 6803
复制标题
DOI：
10.1074/jbc.m113.467613
复制
发表时间：
2013-05-17
影响因子：
4.8
通讯作者：
Pakrasi, Himadri B.
中科院分区：
文献类型：
--
作者：
Liu, Haijun;Chen, Jiawei;Pakrasi, Himadri B.
PSII修复循环是产氧光合生物持续光合作用所必需的。在蓝藻和高等植物中，前体D1蛋白（pD 1）的蛋白水解暴露C-末端羧酸基团是导致Mn 4CaO 5簇（水氧化位点）协调的重要步骤。Psb 27似乎通过与CP 43密切相互作用而与含有pD 1和D1的PSII组装中间体相关联。在这里，我们报告说，CP 43和Psb 27之间的结合亲和力降低是由去除pD 1蛋白的C-末端延伸引发的。采用基于质谱的足迹法策略来探测CP 43蛋白上溶剂暴露的天冬氨酸和谷氨酸残基。通过比较HT 3 Delta ctpA Delta 27 PSII和HT 3 Delta ctpAPS II（两种遗传修饰的PSII组装复合物）之间的足迹程度，我们发现Psb 27在假对称D1-D2轴远端的环E侧结合CP 43。通过比较第二对PSII组装复合物，我们发现CP 43的环E由于去除了pD 1 C-末端延伸而经历了显著的构象重排，改变了Psb 27-CP 43结合界面。这种构象重排的意义进行了讨论的背景下招聘的PSII内腔外源蛋白和Mn 4CaO 5集群组装。除了CP 43的先前已知的功能作为核心PSII天线蛋白之一，这项工作表明，环E的CP 43起着重要的作用，在PSII生物发生过程中的水氧化中心（WOC）的功能组装。
The PSII repair cycle is required for sustainable photosynthesis in oxygenic photosynthetic organisms. In cyanobacteria and higher plants, proteolysis of the precursor D1 protein (pD1) to expose a C-terminal carboxylate group is an essential step leading to coordination of the Mn4CaO5 cluster, the site of water oxidation. Psb27 appears to associate with both pD1- and D1-containing PSII assembly intermediates by closely interacting with CP43. Here, we report that reduced binding affinity between CP43 and Psb27 is triggered by the removal of the C-terminal extension of the pD1 protein. A mass spectrometry-based footprinting strategy was adopted to probe solvent-exposed aspartic and glutamic acid residues on the CP43 protein. By comparing the extent of footprinting between HT3 Delta ctpA Delta 27PSII and HT3 Delta ctpAPSII, two genetically modified PSII assembly complexes, we found that Psb27 binds to CP43 on the side of Loop E distal to the pseudo-symmetrical D1-D2 axis. By comparing a second pair of PSII assembly complexes, we discovered that Loop E of CP43 undergoes a significant conformational rearrangement due to the removal of the pD1 C-terminal extension, altering the Psb27-CP43 binding interface. The significance of this conformational rearrangement is discussed in the context of recruitment of the PSII lumenal extrinsic proteins and Mn4CaO5 cluster assembly. In addition to CP43's previously known function as one of the core PSII antenna proteins, this work demonstrates that Loop E of CP43 plays an important role in the functional assembly of the Water Oxidizing Center (WOC) during PSII biogenesis.