Domain structures of chlorophyllide a oxygenase of green plants and Prochlorothrix hollandica in relation to catalytic functions
Domain structures of chlorophyllide a oxygenase of green plants and Prochlorothrix hollandica in relation to catalytic functions
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DOI：
10.1007/s00425-003-1181-6
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发表时间：
2004-04-01
期刊：
影响因子：
4.3
通讯作者：
Tanaka, A
中科院分区：
文献类型：
--
作者：
Nagata, N;Satoh, S;Tanaka, A
叶绿素B是一种存在于原绿藻和绿藻中的光合天线色素。在绿藻中，它的生物合成调节光合天线的大小。叶绿素B是由叶绿素a通过叶绿素a加氧酶（CAO）在两步氧化反应中合成的。在这项研究中，我们首先确定了一个Prochlorothrix hollandica的prochlorophyte CAO基因的整个序列，比较它与那些从绿藻，我们研究了基因产物的催化活性。Southern杂交分析表明，CAO基因在荷兰黑杨基因组中以一个拷贝存在。荷兰矮牵牛CAO基因（PhCAO）编码367个氨基酸，远小于拟南芥（537个氨基酸）和水稻（542个氨基酸）CAO基因。尽管PhCAO的尺寸很小，但它仍催化叶绿素B的形成。通过比较这些序列，我们将陆生植物序列分为四个部分：预测为转运肽的N-末端序列、陆生植物中特有的连续保守序列（A-结构域，134个氨基酸）、较不保守的序列（B-结构域，30个氨基酸）和绿藻和原绿藻中共有的C-末端保守序列（C-结构域，337至344个氨基酸）。我们证明了C-结构域是足够的催化活性，通过转化蓝细菌集胞藻6803与C-结构域从A。thaliana.在本文中，A-结构域的作用进行了讨论，在陆地植物中捕光叶绿素a/b-蛋白复合物的形成。
Chlorophyll b is a photosynthetic antenna pigment found in prochlorophytes and chlorophytes. In chlorophytes, its biosynthesis regulates the photosynthetic antenna size. Chlorophyll b is synthesized from chlorophyll a in a two-step oxygenation reaction by chlorophyllide a oxygenase (CAO). In this study, we first identified the entire sequence of a prochlorophyte CAO gene from Prochlorothrix hollandica to compare it with those from chlorophytes, and we examined the catalytic activity of the gene product. Southern blot analysis showed that the CAO gene is presented in one copy in the P. hollandica genome. The P. hollandica CAO gene (PhCAO) has a coding capacity for 367 amino acids, which is much smaller than that of Arabidopsis thaliana (537 amino acids) and Oryza sativa (542 amino acids) CAO genes. In spite of the small size, PhCAO catalyzed the formation of chlorophyll b. By comparing these sequences, we classified the land-plant sequences into four parts: the N-terminal sequence predicted to be a transit peptide, the successive conserved sequence unique in land plants (A-domain, 134 amino acids), a less-conserved sequence (B-domain, 30 amino acids) and the C-terminal conserved sequence common in chlorophytes and prochlorophytes (C-domain, 337 to 344 amino acids). We demonstrated that the C-domain is sufficient for catalytic activity by transforming the cyanobacterium Synechocystis sp. PCC6803 with the C-domain from A. thaliana. In this paper, the role of the A-domain is discussed in relation to the formation of light-harvesting chlorophyll a/b-protein complexes in land plants.