Identification of two homologous genes, chlAI and chlAII, that are differentially involved in isocyclic ring formation of chlorophyll a in the cyanobacterium Synechocystis sp PCC 6803
Identification of two homologous genes, chlAI and chlAII, that are differentially involved in isocyclic ring formation of chlorophyll a in the cyanobacterium Synechocystis sp PCC 6803
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DOI：
10.1074/jbc.m708954200
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发表时间：
2008-02-01
影响因子：
4.8
通讯作者：
Fujita, Yuichi
中科院分区：
文献类型：
--
作者：
Minamizaki, Kei;Mizoguchi, Tadashi;Fujita, Yuichi
等碳环（E-ring）是叶绿素的一种常见结构特征。E环由两个结构上不相关的Mg-原卟啉IX单甲酯（MPE）环化酶系统、氧依赖性（AcsF）和氧非依赖性（BchE）系统形成，其涉及分别将来自分子氧和水的氧原子并入MPE的C-131位置。哪种系统在能够在各种厌氧环境中茁壮成长的蓝藻中起作用仍然是一个悬而未决的问题。蓝细菌集胞藻PCC 6803具有两个acsF样基因sll 1214（chlA（I））和sll 1874（chlA（II）），以及三个bchE样基因slr 0905、sll 1242和slr 0309。分离出5个缺失这些基因之一的突变体。Delta chlA（I）突变体不能在有氧条件下生长，并异常积累一种色素，其荧光发射峰位于595 nm处，通过高效液相色谱-质谱分析鉴定为3，8-二乙烯基MPE。通过在限氧（微氧）条件下的培养来恢复Delta chlA（I）的生长缺陷。MPE积累也检测到三角洲chlA（II）生长在微氧条件下，但不是在任何的bchE突变体。表型与两个chlA基因的表达模式一致：chlA（II）在微氧条件下诱导，与chlA（I）的组成型表达相反。这些结果表明，在有氧条件下，ChlA（I）是唯一的MPE环化酶系统，诱导的ChlA（II）在微氧条件下与ChlA（I）一起工作。此外，在Delta chlA突变体中积累的3，8-二乙烯基MPE表明，在集胞藻PCC 6803中，8-乙烯基的还原发生在E-环形成之后。
The isocyclic ring (E-ring) is a common structural feature of chlorophylls. The E-ring is formed by two structurally unrelated Mg-protoporphyrin IX monomethylester (MPE) cyclase systems, oxygen-dependent (AcsF), and oxygen-independent (BchE) systems, which involve incorporation of an oxygen atom from molecular oxygen and water into the C-131 position of MPE, respectively. Which system operates in cyanobacteria that can thrive in a variety of anaerobic environments remains an open question. The cyanobacterium Synechocystis sp.PCC 6803 has two acsF-like genes, sll1214 (chlA(I)) and sll1874 (chlA(II)), and three bchE-like genes, slr0905, sll1242, and slr0309. Five mutants lacking one of these genes were isolated. The Delta chlA(I) mutant failed to grow under aerobic conditions with anomalous accumulation of a pigment with fluorescence emission peak at 595 nm, which was identified 3,8-divinyl MPE by high-performance liquid chromatography-mass spectrometry analysis. The growth defect of Delta chlA(I) was restored by the cultivation under oxygen-limited (micro-oxic) conditions. MPE accumulation was also detected in Delta chlA(II) grown under microoxic conditions, but not in any of the bchE mutants. The phenotype was consistent with the expression pattern of two chlA genes: chlA(II) was induced under micro-oxic conditions in contrast to the constitutive expression of chlA(I). These findings suggested that ChlA(I) is the sole MPE cyclase system under aerobic conditions and that the induced ChlA(II) operates together with ChlA(I) under micro-oxic conditions. In addition, the accumulation of 3,8-divinyl MPE in the Delta chlA mutants suggested that the reduction of 8-vinyl group occurs after the formation of E-ring in Synechocystis sp. PCC 6803.