Identification of an 8-vinyl reductase involved in bacteriochlorophyll biosynthesis in Rhodobacter sphaeroides and evidence for the existence of a third distinct class of the enzyme
Identification of an 8-vinyl reductase involved in bacteriochlorophyll biosynthesis in Rhodobacter sphaeroides and evidence for the existence of a third distinct class of the enzyme
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DOI：
10.1042/bj20121723
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发表时间：
2013-03-01
影响因子：
4.1
通讯作者：
Hunter, C. Neil
中科院分区：
文献类型：
--
作者：
Canniffe, Daniel P.;Jackson, Philip J.;Hunter, C. Neil
紫色光合细菌球形红细菌利用细菌叶绿素a进行光捕获和光化学。该色素的合成包括在C8-乙烯基还原酶催化下将C8位的乙烯基还原为乙基。这种酶的活性形式尚未在R. sphaeroides，但它的基因组包含两个候选ORF（开放阅读框），类似于报道的在密切相关的荚膜红细菌（bchJ），以及在植物和绿色硫细菌（rsp_3070）中编码C8-乙烯基还原酶。为了确定哪个基因编码活性酶，构建了两个基因的敲除突变体。令人惊讶的是，其中一个或两个基因被删除的突变体仍然保留了合成C8-乙基细菌叶绿素的能力。这些基因随后在不能合成C8-乙基叶绿素a的蓝藻突变体中表达。R. sphaeroides rsp_3070能够恢复突变体中WT（野生型）C8-乙基叶绿素a的合成，而bchJ不能。本研究结果表明，Rsp_3070是一种功能性的C8-乙烯基还原酶。Sphaeroides利用至少两种酶来催化该反应，表明存在第三类，而BchJ作为C8-乙烯基还原酶的活性仍然没有直接证据。
The purple phototrophic bacterium Rhodobacter sphaeroides utilises bacteriochlorophyll a for light harvesting and photochemistry. The synthesis of this photopigment includes the reduction of a vinyl group at the C8 position to an ethyl group, catalysed by a C8-vinyl reductase. An active form of this enzyme has not been identified in R. sphaeroides, but its genome contains two candidate ORFs (open reading frames) similar to those reported to encode C8-vinyl reductases in the closely related Rhodobacter capsulatus (bchJ), and in plants and green sulfur bacteria (rsp_3070). To determine which gene encodes the active enzyme, knock-out mutants in both genes were constructed. Surprisingly, mutants in which one or both genes were deleted still retained the ability to synthesize C8-ethyl bacteriochlorophyll. These genes were subsequently expressed in a cyanobacterial mutant that cannot synthesize C8-ethyl chlorophyll a. R. sphaeroides rsp_3070 was able to restore synthesis of the WT (wild-type) C8-ethyl chlorophyll a in the mutant, whereas bchJ did not. The results of the present study demonstrate that Rsp_3070 is a functional C8-vinyl reductase and that R. sphaeroides utilises at least two enzymes to catalyse this reaction, indicating the existence of a third class, while there remains no direct evidence for the activity of BchJ as a C8-vinyl reductase.