Activation of the Chloroplast Monogalactosyldiacylglycerol Synthase MGD1 by Phosphatidic Acid and Phosphatidylglycerol
Activation of the Chloroplast Monogalactosyldiacylglycerol Synthase MGD1 by Phosphatidic Acid and Phosphatidylglycerol
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DOI：
10.1074/jbc.m109.071928
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发表时间：
2010-02-26
影响因子：
4.8
通讯作者：
Block, Maryse A.
中科院分区：
文献类型：
--
作者：
Dubots, Emmanuelle;Audry, Magali;Block, Maryse A.
叶绿体膜的主要特征之一是它们富含半乳糖甘油脂、单半乳糖基二酰基甘油（MGDG）和双半乳糖基二酰基甘油（DGDG），而磷脂很少被代表，主要是磷脂酰甘油（PG）。所有这些脂质都在叶绿体被膜中合成，但半乳糖脂的合成也部分依赖于位于非质体膜中的磷脂合成。MGDG合成以前被证明是叶绿体发育所必需的。在这份报告中，我们分析了MGDG合成的调节磷脂酸（PA），这是一个一般的前体在所有的甘油酯的合成，也是一个信号分子在植物中。我们证明，在生理条件下，MGDG合成是不活跃的MGDG合成酶时，提供其底物，即甘油二酯和UDP-半乳糖。相反，PA在供应时激活酶。这在叶匀浆、叶绿体被膜以及重组MGDG合酶MGD 1中显示。PG也可以激活酶，但PA和PG对MGD 1活性的影响的比较表明，PA和PG通过不同的机制进行，这是进一步区分点突变的重组MGD 1的酶分析。PA和PG激活MGD 1被认为是植物磷脂和半乳糖脂合成的重要耦合机制。
One of the major characteristics of chloroplast membranes is their enrichment in galactoglycerolipids, monogalactosyldiacylglycerol (MGDG), and digalactosyldiacylglycerol (DGDG), whereas phospholipids are poorly represented, mainly as phosphatidylglycerol (PG). All these lipids are synthesized in the chloroplast envelope, but galactolipid synthesis is also partially dependent on phospholipid synthesis localized in non-plastidial membranes. MGDG synthesis was previously shown essential for chloroplast development. In this report, we analyze the regulation of MGDG synthesis by phosphatidic acid (PA), which is a general precursor in the synthesis of all glycerolipids and is also a signaling molecule in plants. We demonstrate that under physiological conditions, MGDG synthesis is not active when the MGDG synthase enzyme is supplied with its substrates only, i.e. diacylglycerol and UDP-gal. In contrast, PA activates the enzyme when supplied. This is shown in leaf homogenates, in the chloroplast envelope, as well as on the recombinant MGDG synthase, MGD1. PG can also activate the enzyme, but comparison of PA and PG effects on MGD1 activity indicates that PA and PG proceed through different mechanisms, which are further differentiated by enzymatic analysis of point-mutated recombinant MGD1s. Activation of MGD1 by PA and PG is proposed as an important mechanism coupling phospholipid and galactolipid syntheses in plants.