Water-soluble chlorophyll-binding proteins (WSCPs) from Brassicaceae constitute a small family of non-photosynthetic proteins that may provide a useful benchmark and model system for studying molecular aspects of chlorophyll-protein interactions such as the tuning of absorption and emission spectra, and binding selectivity. WSCP apo-proteins are readily expressed by recombinant DNA techniques and can be assembled in vitro with natural and synthetic chlorophyll derivatives. The complexes with native chlorophylls are exceptionally stable toward thermal dissociation and protein denaturation due to hydrophobic interactions with the chlorophyll’s phytyl chains that stabilize the core of the WSCP tetrameric complexes. However, assembly requires the use of detergents or water-in-oil emulsions to introduce the hydrophobic pigments into the water-soluble apo-proteins. Here, we explore the direct assembly of recombinant WSCPs with the water-soluble phytyl-free chlorophyll analogue chlorophyllide a in aqueous solutions. We show that the complexes formed by mixing chlorophyllide and WSCP apo-proteins are exclusively tetrameric, and while they lack the extreme thermostability of the respective chlorophyll complexes, they are still thermostable up to around 60°C. Their absorption and CD spectra are very similar to the chlorophyll complexes albeit slight peak shifts and broadening of the bands indicate variations in pigment and protein conformations, and less rigid structures. Simplifying the assembly process of WSCPs opens new possibilities for their use in modelling natural chlorophyll-protein complexes, and as templates for designing novel artificial protein-pigment complexes.

中文翻译：

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在水溶液中直接组装具有 II 型水溶性叶绿素蛋白的稳定叶绿素复合物

来自十字花科的水溶性叶绿素结合蛋白 (WSCP)构成了一个小家族的非光合蛋白，可为研究叶绿素-蛋白质相互作用的分子方面（例如吸收和发射光谱的调节）提供有用的基准和模型系统，以及结合选择性。WSCP 载脂蛋白很容易通过重组 DNA 技术表达，并可在体外组装与天然和合成的叶绿素衍生物。由于与稳定 WSCP 四聚体复合物核心的叶绿素植基链的疏水相互作用，天然叶绿素的复合物对热解离和蛋白质变性非常稳定。然而，组装需要使用去污剂或油包水乳液将疏水性色素引入水溶性脱辅基蛋白。在这里，我们探索了重组 WSCPs 与水溶性无植基叶绿素类似物叶绿素a的直接组装。在水溶液中。我们表明，通过混合叶绿素和 WSCP 载脂蛋白形成的复合物完全是四聚体，虽然它们缺乏各自叶绿素复合物的极端热稳定性，但它们在高达 60°C 左右仍然是热稳定的。它们的吸收光谱和 CD 光谱与叶绿素复合物非常相似，尽管有轻微的峰位移和谱带变宽表明色素和蛋白质构象的变化以及刚性结构的减少。简化 WSCP 的组装过程为它们用于模拟天然叶绿素-蛋白质复合物以及作为设计新型人工蛋白质-色素复合物的模板开辟了新的可能性。