Carotenoid biosynthesis in the primitive red alga Cyanidioschyzon merolae
Carotenoid biosynthesis in the primitive red alga Cyanidioschyzon merolae
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DOI：
10.1128/ec.00265-06
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发表时间：
2007-03-01
期刊：
影响因子：
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通讯作者：
Gantt, Elisabeth
中科院分区：
文献类型：
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作者：
Cunningham, Francis X., Jr.;Lee, Hansel;Gantt, Elisabeth
Cyanidioschyzonmerolae被认为是最原始的真核光合生物之一。为了深入了解真核植物类胡萝卜素生物合成途径的起源和进化，研究了真核植物类胡萝卜素的含量。确定了merolae，鉴定了编码这种单细胞红曲霉中类胡萝卜素生物合成酶的基因，并检测了两种特别感兴趣的候选途径酶，番茄红素环化酶和β-胡萝卜素羟化酶的活性。C. merolae可能含有在任何真核光合生物中发现的最简单的叶绿素和类胡萝卜素：叶绿素a、β-胡萝卜素和玉米黄质。具有ε环的类胡萝卜素（例如，叶黄素），发现在许多其他红藻和绿色藻类和陆地植物，没有检测到，和番茄红素环化酶的C。当在大肠杆菌中提供番茄红素作为底物时，merolae非常特异地仅产生β-环类胡萝卜素。来自几种细菌、蓝藻和陆地植物的番茄红素β-环环化酶也被证明是高保真酶，而来自几种植物的结构相关的ε-环环化酶被发现特异性较低，产生具有β-环和ε-环的产物。C. merolae缺乏编码在陆地植物中发现的两种类型的β-胡萝卜素羟化酶的基因的直向同源物，一种是非血红素二铁加氧酶，另一种是细胞色素P450。梭merolae叶绿体基因指定了一种多肽，类似于蓝细菌中常见的第三类β-胡萝卜素羟化酶的成员，但该基因在大肠杆菌中表达时不产生活性酶。杆菌对C.因此，merolde β-胡萝卜素羟化酶仍然是不确定的。
Cyanidioschyzon merolae is considered to be one of the most primitive of eukaryotic photosynthetic organisms. To obtain insights into the origin and evolution of the pathway of carotenoid biosynthesis in eukaryotic plants, the carotenoid content of C. merolae was ascertained, genes encoding enzymes of carotenoid biosynthesis in this unicellular red alga were identified, and the activities of two candidate pathway enzymes of particular interest, lycopene cyclase and beta-carotene hydroxylase, were examined. C. merolae contains perhaps the simplest assortment of chlorophylls and carotenoids found in any eukaryotic photosynthetic organism: chlorophyll a, beta-carotene, and zeaxanthin. Carotenoids with epsilon-rings (e.g., lutein), found in many other red algae and in green algae and land plants, were not detected, and the lycopene cyclase of C. merolae quite specifically produced only beta-ringed carotenoids when provided with lycopene as the substrate in Escherichia coli. Lycopene beta-ring cyclases from several bacteria, cyanobacteria, and land plants also proved to be high-fidelity enzymes, whereas the structurally related epsilon-ring cyclases from several plant species were found to be less specific, yielding products with beta-rings as well as epsilon-rings. C. merolae lacks orthologs of genes that encode the two types of beta-carotene hydroxylase found in land plants, one a nonheme diiron oxygenase and the other a cytochrome P450. A C. merolae chloroplast gene specifies a polypeptide similar to members of a third class of beta-carotene hydroxylases, common in cyanobacteria, but this gene did not produce an active enzyme when expressed in E. coli. The identity of the C. merolde beta-carotene hydroxylase therefore remains uncertain.