Tsukatani Yusuke, Harada Jiro, Nomata Jiro, Yamamoto Haruki, Fujita Yuichi, Mizoguchi Tadashi, Tamiaki Hitoshi
1] Graduate School of Life Sciences, Ritsumeikan University, Shiga 525-8577, Japan [2] PRESTO, Japan Science and Technology Agency, Saitama 332-0012, Japan [3] Earth-Life Science Institute, Tokyo Institute of Technology, Tokyo 152-8550, Japan.
Department of Medical Biochemistry, Kurume University School of Medicine, Fukuoka 830-0011, Japan.
Sci Rep. 2015 May 15;5:9741. doi: 10.1038/srep09741.
In previous studies we have demonstrated that chlorophyllide a oxidoreductases (CORs) from bacteriochlorophyll (BChl) a-producing Rhodobacter species and BChl b-producing Blastochloris viridis show distinct substrate recognition and different catalytic hydrogenation reactions, and that these two types of CORs therefore cause committed steps for BChls a and b biosynthesis. In this study, COR genes from B. viridis were incorporated and overexpressed in a series of Rhodobacter sphaeroides mutants. We found that the following two factors are essential in making R. sphaeroides produce BChl b: the loss of functions of both intrinsic COR and 8-vinyl reductase (BciA) in the host R. sphaeroides strain; and expression of the BchYZ catalytic components of COR from B. viridis, not the complete set of COR (BchXYZ), in the host strain. In addition, we incorporated bchYZ of B. viridis into the R. sphaeroides mutant lacking BchJ and BciA, resulting in the strain accumulating both BChl a and BChl b. This is the first example of an anoxygenic photosynthetic bacterium producing BChls a and b together. The results suggest that BchJ enhances activity of the intrinsic COR. The physiological significance of BchJ in pigment biosynthetic pathways will be discussed.
在之前的研究中，我们已经证明，来自产细菌叶绿素（BChl）a的红杆菌属物种和产BChl b的绿色绿球藻的叶绿素酸a氧化还原酶（CORs）表现出不同的底物识别和不同的催化氢化反应，因此这两种类型的CORs导致了BChls a和b生物合成的关键步骤。在本研究中，将来自绿色绿球藻的COR基因导入一系列球形红杆菌突变体中并使其过表达。我们发现，使球形红杆菌产生BChl b有两个关键因素：宿主球形红杆菌菌株中内在COR和8-乙烯基还原酶（BciA）的功能丧失；以及在宿主菌株中表达来自绿色绿球藻的COR的BchYZ催化组分，而不是完整的COR（BchXYZ）。此外，我们将绿色绿球藻的bchYZ导入缺乏BchJ和BciA的球形红杆菌突变体中，导致该菌株同时积累BChl a和BChl b。这是第一例不产氧光合细菌同时产生BChls a和b的例子。结果表明，BchJ增强了内在COR的活性。将讨论BchJ在色素生物合成途径中的生理意义。
