Water-Soluble Chlorophyll Protein (WSCP) Stably Binds Two or Four Chlorophylls
Water-Soluble Chlorophyll Protein (WSCP) Stably Binds Two or Four Chlorophylls
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DOI：
10.1021/acs.biochem.7b00075
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发表时间：
2017-03-28
期刊：
影响因子：
2.9
通讯作者：
Paulsen, Harald
中科院分区：
文献类型：
--
作者：
Palm, Daniel M.;Agostini, Alessandro;Paulsen, Harald
来自十字花科的 Ha 类水溶性叶绿素蛋白 (WSCP) 形成四聚体复合物，每个脱辅基蛋白含有一个叶绿素 (CM)，但不含类胡萝卜素。即使在 100 摄氏度和极端 pH 值下，复合物对于解离和蛋白质变性也非常稳定，并且 Chls 受到部分保护，免受光氧化。有几种假说可以解释 WSCP 的生物学作用，其中之一提出它们是植物衰老或病原体攻击时释放的 Chls 的清道夫。本文描述的 WSCP 的生化特性与该蛋白质作为高效且灵活的叶绿素清除剂的作用一致。在有限的叶绿素浓度下，重组 WSCP 脱辅基蛋白结合亚化学计量的叶绿素（每个四聚体两个叶绿素）形成复合物，该复合物与完全着色的复合物一样对热解离、变性和光损伤稳定。如果添加更多的CM，这些两个叶绿素复合物可以结合另外两个叶绿素以达到完全着色的状态。 WSCP Chls 免受光损伤的保护归因于脱辅基蛋白作为氧的扩散屏障，阻止其接触三重态激发的 Chls，从而形成单线态氧。相比之下，WSCP 对 Chls 的顺序结合表明了一种部分开放或至少灵活的结构，这就提出了 WSCP 如何在没有类胡萝卜素帮助的情况下光保护其 Chls 的问题。
Water-soluble chlorophyll proteins (WSCPs) of class Ha from Brassicaceae form tetrameric complexes containing one chlorophyll (CM) per apoprotein but no carotenoids. The complexes are remarkably stable toward dissociation and protein denaturation even at 100 degrees C and extreme pH values, and the Chls are partially protected against photooxidation. There are several hypotheses that explain the biological role of WSCPs, one of them proposing that they function as a scavenger of Chls set free upon plant senescence or pathogen attack. The biochemical properties of WSCP described in this paper are consistent with the protein acting as an efficient and flexible Chl scavenger. At limiting Chl concentrations, the recombinant WSCP apoprotein binds substoichiometric amounts of Chl (two Chls per tetramer) to form complexes that are as stable toward thermal dissociation, denaturation, and photodamage as the fully pigmented ones. If more CM is added, these two-Chl complexes can bind another two Chls to reach the fully pigmented state. The protection of WSCP Chls against photodamage has been attributed to the apoprotein serving as a diffusion barrier for oxygen, preventing its access to triplet excited Chls and, thus, the formation of singlet oxygen. By contrast, the sequential binding of Chls by WSCP suggests a partially open or at least flexible structure, raising the question of how WSCP photoprotects its Chls without the help of carotenoids.