Roy J. Carver Department of Biochemistry, Biophysics and Molecular Biology, Iowa State University, Ames, IA 50011, U.S.A.
Biochem J. 2019 Sep 24;476(18):2607-2621. doi: 10.1042/BCJ20190479.
All land plants contain at least one class II diterpene cyclase (DTC), which utilize an acid-base catalytic mechanism, for the requisite production of -copalyl diphosphate (-CPP) in gibberellin A (GA) phytohormone biosynthesis. These -CPP synthases (CPSs) are hypothesized to be derived from ancient bacterial origins and, in turn, to have given rise to the frequently observed additional DTCs utilized in more specialized plant metabolism. However, such gene duplication and neo-functionalization has occurred repeatedly, reducing the utility of phylogenetic analyses. Support for evolutionary scenarios can be found in more specific conservation of key enzymatic features. While DTCs generally utilize a DxDD motif as the catalytic acid, the identity of the catalytic base seems to vary depending, at least in part, on product outcome. The CPS from has been found to utilize a histidine-asparagine dyad to ligate a water molecule that serves as the catalytic base, with alanine substitution leading to the production of 8β-hydroxy--CPP. Here this dyad and effect of Ala substitution is shown to be specifically conserved in plant CPSs involved in GA biosynthesis, providing insight into plant DTC evolution and assisting functional assignment. Even more strikingly, while GA biosynthesis arose independently in plant-associated bacteria and fungi, the catalytic base dyad also is specifically found in the relevant bacterial, but not fungal, CPSs. This suggests functional conservation of CPSs from bacteria to plants, presumably reflecting an early role for derived diterpenoids in both plant development and plant-microbe interactions, eventually leading to GA, and a speculative evolutionary scenario is presented.
所有陆地植物至少含有一种 II 类二萜环化酶 (DTC)，用于在赤霉素 A (GA) 植物激素生物合成中产生必需的 -贝壳杉烯二磷酸 (-CPP)。这些 -CPP 合酶 (CPS) 据推测来自古老的细菌起源，并由此产生了在更专门的植物代谢中经常观察到的额外 DTC。然而，这种基因复制和新功能化已经反复发生，降低了系统发育分析的实用性。对进化情景的支持可以在更特定的关键酶特征保守性中找到。虽然 DTC 通常使用 DxDD 基序作为催化酸，但催化碱的身份似乎因产物而异，至少部分如此。已经发现来自 的 CPS 利用组氨酸-天冬酰胺二联体来连接水分子作为催化碱，用丙氨酸取代导致 8β-羟基--CPP 的产生。在这里，这个二联体和 Ala 取代的作用被证明在参与 GA 生物合成的植物 CPS 中是特异性保守的，这为植物 DTC 进化提供了深入了解，并有助于功能分配。更引人注目的是，虽然 GA 生物合成在与植物相关的细菌和真菌中独立出现，但催化碱二联体也特异性地存在于相关的细菌中，但不存在于真菌中。这表明从细菌到植物的 CPS 功能保守，可能反映了衍生二萜类化合物在植物发育和植物-微生物相互作用中的早期作用，最终导致 GA，并提出了一个推测的进化情景。
