Synergistic substrate inhibition of ent-copalyl diphosphate synthase:: A potential feed-forward inhibition mechanism limiting gibberellin metabolism
Synergistic substrate inhibition of ent-copalyl diphosphate synthase:: A potential feed-forward inhibition mechanism limiting gibberellin metabolism
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DOI：
10.1104/pp.106.095208
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发表时间：
2007-05-01
期刊：
影响因子：
7.4
通讯作者：
Peters, Reuben J.
中科院分区：
文献类型：
--
作者：
Prisic, Sladjana;Peters, Reuben J.
赤霉素 (GA) 或赤霉酸是普遍存在的二萜类植物激素，是植物生长和发育的许多方面所需的，包括在无光情况下抑制光合色素的产生（即脱黄化）。 GA 生物合成的关键步骤是在质体中由对映柯巴基二磷酸合酶 (CPS) 催化，其底物 (E,E,E,)-香叶基香叶基二磷酸 (GGPP) 也是类胡萝卜素和叶绿素叶绿醇侧链的直接前体。因此，在脱黄化过程中，GA 的产生受到抑制，而通过其共同的 GGPP 前体流向这些光合色素的通量则显着增加。这是如何实现的尚不清楚，因为尚未报道 CPS 活动的调节机制。我们在此对来自拟南芥 (Arabidopsis thaliana; rAtCPS) 的重组假成熟 CPS 进行动力学分析，证明 Mg2+ 和 GGPP 对 CPS 活性发挥协同底物抑制作用。这些结果表明 GA 代谢可能受到 CPS 前馈抑制的限制。特别是 Mg 21 的影响，因为光诱导质体 Mg 21 水平增加，其范围与此处观察到的影响 rAtCPS 活性的范围相似。值得注意的是，这种效应在 GA 特异性 AtCPS 中最为明显，因为树脂酸生物合成酶松香二烯合酶的相应活性对 [Mg2+] 的敏感性要低 100 倍。此外，Mg2+ 以变构方式激活参与叶绿素生产的植物胆色素原合酶。因此，Mg2+可能在脱黄化过程中调节质体代谢通量方面具有广泛的作用。最后，观察到的 CPS 协同底物/前馈抑制似乎也提供了直接调节激素生物合成中酶活性的新例子。
Gibberellins (GAs) or gibberellic acids are ubiquitous diterpenoid phytohormones required for many aspects of plant growth and development, including repression of photosynthetic pigment production (i.e. deetiolation) in the absence of light. The committed step in GA biosynthesis is catalyzed in plastids by ent-copalyl diphosphate synthase (CPS), whose substrate, (E,E,E,)-geranylgeranyl diphosphate (GGPP), is also a direct precursor of carotenoids and the phytol side chain of chlorophyll. Accordingly, during deetiolation, GA production is repressed, whereas flux toward these photosynthetic pigments through their common GGPP precursor is dramatically increased. How this is accomplished has been unclear because no mechanism for regulation of CPS activity has been reported. We present here kinetic analysis of recombinant pseudomature CPS from Arabidopsis (Arabidopsis thaliana; rAtCPS) demonstrating that Mg2+ and GGPP exert synergistic substrate inhibition effects on CPS activity. These results suggest that GA metabolism may be limited by feed-forward inhibition of CPS; in particular, the effect of Mg 21 because light induces increases in plastid Mg 21 levels over a similar range as that observed here to affect rAtCPS activity. Notably, this effect is most pronounced in the GA-specific AtCPS because the corresponding activity of the resin acid biosynthetic enzyme abietadiene synthase is 100-fold less sensitive to [Mg2+]. Furthermore, Mg2+ allosterically activates the plant porphobilinogen synthase involved in chlorophyll production. Hence, Mg2+ may have a broad role in regulating plastidial metabolic flux during deetiolation. Finally, the observed synergistic substrate/feed-forward inhibition of CPS also seems to provide a novel example of direct regulation of enzymatic activity in hormone biosynthesis.