PRISEs (progesterone 5β-reductase and/or iridoid synthase-like 1,4-enone reductases) are involved in cardenolide and iridoid biosynthesis. We here investigated a PRISE (rAtSt5βR) from Arabidopsis thaliana, a plant producing neither cardenolides nor iridoids. The structure of rAtSt5βR was elucidated with X-ray crystallography and compared to the known structures of PRISEs from Catharanthus roseus (rCrISY) and Digitalis lanata (rDlP5βR). The three enzymes show a high degree of sequence and structure conservation in the active site. Amino acids previously considered to allow discrimination between progesterone 5β-reductase and iridoid synthase were interchanged among rAtSt5βR, rCrISY and rDlP5βR applying site-directed mutagenesis. Structural homologous substitutions had different effects, and changes in progesterone 5β-reductase and iridoid synthase activity were not correlated in all cases. Our results help to explain fortuitous emergence of metabolic pathways and product accumulation. The fact that PRISEs are found ubiquitously in spermatophytes insinuates that PRISEs might have a more general function in plant metabolism such as, for example, the detoxification of reactive carbonyl species.

中文翻译：

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PRISEs（孕酮 5β-还原酶和/或环烯醚萜合酶样 1,4-烯酮还原酶）：催化和底物混杂允许实现植物代谢中的多种途径

PRISEs（孕酮 5β-还原酶和/或环烯醚萜合酶样 1,4-烯酮还原酶）参与了cardenolide 和环烯醚萜的生物合成。我们在这里调查了来自拟南芥的奖品 (rAtSt5βR)，拟南芥是一种既不产生强心内酯也不产生环烯醚萜的植物。rAtSt5βR 的结构通过 X 射线晶体学进行了阐明，并与长春花 (rCrISY) 和洋地黄 (rDlP5βR) 中 PRISE 的已知结构进行了比较。这三种酶在活性位点表现出高度的序列和结构保守性。以前被认为允许区分孕酮 5β-还原酶和环烯醚萜合酶的氨基酸在 rAtSt5βR、rCrISY 和 rDlP5βR 之间互换，应用定点诱变。结构同源取代有不同的效果，并且孕酮 5β-还原酶和环烯醚萜合酶活性的变化并非在所有情况下都相关。我们的结果有助于解释代谢途径和产物积累的偶然出现。PRISEs 在精子植物中无处不在的事实暗示 PRISEs 可能在植物代谢中具有更普遍的功能，例如，活性羰基物质的解毒。