Two Unrelated 8-Vinyl Reductases Ensure Production of Mature Chlorophylls in Acaryochloris marina.
Two Unrelated 8-Vinyl Reductases Ensure Production of Mature Chlorophylls in Acaryochloris marina.
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DOI：
10.1128/jb.00925-15
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发表时间：
2016-05
影响因子：
3.2
通讯作者：
Canniffe DP
中科院分区：
文献类型：
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作者：
Chen GE;Hitchcock A;Jackson PJ;Chaudhuri RR;Dickman MJ;Hunter CN;Canniffe DP
蓝藻Acaryoloris marina的主要光色素是叶绿素d，其直接生物合成前体叶绿素a也存在于细胞中。在生物合成过程中，这些色素与大多数供氧光养生物利用的叶绿素一起，在分子的C-8位携带乙基，经历了乙烯基团的还原。已知存在两类与叶绿素生物合成无关的8-乙烯基还原酶，即BCIA和BciB。Acaryoloris marina的基因组包含开放阅读框架(ORF)，编码的蛋白质与BCIA或BciB具有很高的序列相似性，尽管它们分别被注释为参与转录控制(NmrA)和产甲烷(FrB)的基因。将这些基因导入聚球藻产生8-乙烯基叶绿素a的ΔBciB菌株。菌株PCC6803，两者都能恢复色素的合成，在C-8位带有乙基，表明它们具有8-乙烯基还原酶的活性。我们建议将nmrA和frhB分别重新命名为BCIA和BciB；对无叶绿藻的转录本和蛋白质组学分析表明，BCIA和BciB在细胞中都有表达，并且它们的编码蛋白存在于细胞中，这可能是为了确保所有合成的叶绿素色素都在C-8位带有乙基。讨论了在该菌株中存在两种8-乙烯基还原酶的可能原因，这种酶是蓝藻所特有的。重要性利用叶绿素d进行光合作用的蓝藻是被研究得最好的光营养生物。在迄今测序的蓝藻中，它的基因组是独一无二的，它的基因组包含编码两种无关酶的ORF，这两种酶催化前体分子的C-8乙烯基还原为乙基。携带还原的C-8基团对含有叶绿素d的生物体可能特别重要。植物基因组也包含这两个基因的同源基因；因此，叶绿体的细菌祖先可能也包含BCIA和BCIB。
The major photopigment of the cyanobacterium Acaryochloris marina is chlorophyll d, while its direct biosynthetic precursor, chlorophyll a, is also present in the cell. These pigments, along with the majority of chlorophylls utilized by oxygenic phototrophs, carry an ethyl group at the C-8 position of the molecule, having undergone reduction of a vinyl group during biosynthesis. Two unrelated classes of 8-vinyl reductase involved in the biosynthesis of chlorophylls are known to exist, BciA and BciB. The genome of Acaryochloris marina contains open reading frames (ORFs) encoding proteins displaying high sequence similarity to BciA or BciB, although they are annotated as genes involved in transcriptional control (nmrA) and methanogenesis (frhB), respectively. These genes were introduced into an 8-vinyl chlorophyll a-producing ΔbciB strain of Synechocystis sp. strain PCC 6803, and both were shown to restore synthesis of the pigment with an ethyl group at C-8, demonstrating their activities as 8-vinyl reductases. We propose that nmrA and frhB be reassigned as bciA and bciB, respectively; transcript and proteomic analysis of Acaryochloris marina reveal that both bciA and bciB are expressed and their encoded proteins are present in the cell, possibly in order to ensure that all synthesized chlorophyll pigment carries an ethyl group at C-8. Potential reasons for the presence of two 8-vinyl reductases in this strain, which is unique for cyanobacteria, are discussed. IMPORTANCE The cyanobacterium Acaryochloris marina is the best-studied phototrophic organism that uses chlorophyll d for photosynthesis. Unique among cyanobacteria sequenced to date, its genome contains ORFs encoding two unrelated enzymes that catalyze the reduction of the C-8 vinyl group of a precursor molecule to an ethyl group. Carrying a reduced C-8 group may be of particular importance to organisms containing chlorophyll d. Plant genomes also contain orthologs of both of these genes; thus, the bacterial progenitor of the chloroplast may also have contained both bciA and bciB.