Mutational analysis of three bchH paralogs in (bacterio-)chlorophyll biosynthesis in Chlorobaculum tepidum
Mutational analysis of three bchH paralogs in (bacterio-)chlorophyll biosynthesis in Chlorobaculum tepidum
复制标题
DOI：
10.1007/s11120-009-9460-0
复制
发表时间：
2009-07-01
影响因子：
3.7
通讯作者：
Bryant, Donald A.
中科院分区：
文献类型：
--
作者：
Chew, Aline Gomez Maqueo;Frigaard, Niels-Ulrik;Bryant, Donald A.
(细菌)叶绿素生物合成的第一步是镁-螯合酶将镁离子插入原卟啉IX。在所有已知的(B)Chl合成菌中，镁螯合酶由三个基因编码，这三个基因与红杆菌的bchH、bchd和bchI同源。所有测序的绿色硫磺细菌(Chlorobi)的基因组都编码多个bchH类似物，而在苔绿杆菌基因组中有三个bchH类似物，分别表示为CT1295(BCHT)、CT1955(BCHS)和CT1957(BchH)。CBA。构建了缺少一个或两个这些并列基因的替匹姆突变体，并对其进行了鉴定。所有缺乏其中一个BchH同源物的突变体以及分别只能产生BchH或BchS的BchS BCHT和bchH BCHT双突变体都是有效的。然而，构建只有BCHT具有功能的bchH BCHS双重突变体的尝试一直没有成功。这一结果表明，BCHT本身不能支持细胞存活所需的最低(B)Chl合成要求。不同突变株的色素组成差异较大。BCHS突变体的Bchl-c含量仅为野生型的10%，并且该突变体分泌大量原卟啉IX到生长培养基中。突变菌株BchL-c产量的差异与三个BchH同系物在Bchl-c生物合成途径的最终产物调节和/或底物通道中起作用的假设一致。
The first committed step in the biosynthesis of (bacterio-)chlorophyll is the insertion of Mg2+ into protoporphyrin IX by Mg-chelatase. In all known (B)Chl-synthesizing organisms, Mg-chelatase is encoded by three genes that are homologous to bchH, bchD, and bchI of Rhodobacter spp. The genomes of all sequenced strains of green sulfur bacteria (Chlorobi) encode multiple bchH paralogs, and in the genome of Chlorobaculum tepidum, there are three bchH paralogs, denoted CT1295 (bchT), CT1955 (bchS), and CT1957 (bchH). Cba. tepidum mutants lacking one or two of these paralogs were constructed and characterized. All of the mutants lacking only one of these BchH homologs, as well as bchS bchT and bchH bchT double mutants, which can only produce BchH or BchS, respectively, were viable. However, attempts to construct a bchH bchS double mutant, in which only BchT was functional, were consistently unsuccessful. This result suggested that BchT alone is unable to support the minimal (B)Chl synthesis requirements of cells required for viability. The pigment compositions of the various mutant strains varied significantly. The BChl c content of the bchS mutant was only similar to 10% of that of the wild type, and this mutant excreted large amounts of protoporphyrin IX into the growth medium. The observed differences in BChl c production of the mutant strains were consistent with the hypothesis that the three BchH homologs function in end product regulation and/or substrate channeling of intermediates in the BChl c biosynthetic pathway.