Institute of Biology, Dept. of Biochemistry of Plant Secondary Metabolism (190b), University of Hohenheim, Garbenstraße 30, 70593 Stuttgart, Germany.
Molecules. 2020 Apr 22;25(8):1935. doi: 10.3390/molecules25081935.
The characterization of plant enzymes by expression in prokaryotic and eukaryotic (yeast and plants) heterologous hosts has widely been used in recent decades to elucidate metabolic pathways in plant secondary metabolism. Yeast and plant systems provide the cellular environment of a eukaryotic cell and the subcellular compartmentalization necessary to facilitate enzyme function. The expression of candidate genes in these cell systems and the identification of the resulting products guide the way for the identification of enzymes with new functions. However, in many cases, the detected compounds are not the direct enzyme products but are caused by unspecific subsequent reactions. Even if the mechanisms for these unspecific reactions are in many cases widely reported, there is a lack of overview of potential reactions that may occur to provide a guideline for researchers working on the characterization of new enzymes. Here, an across-the-board summary of rearrangement reactions of sesquiterpenes in metabolic pathway engineering is presented. The different kinds of unspecific reactions as well as their chemical and cellular background are explained and strategies how to spot and how to avoid these unspecific reactions are given. Also, a systematic approach of classification of unspecific reactions is introduced. It is hoped that this mini-review will stimulate a discussion on how to systematically classify unspecific reactions in metabolic engineering and to expand this approach to other classes of plant secondary metabolites.
近几十年来，通过在原核和真核（酵母和植物）异源宿主中表达来对植物酶进行表征，已广泛用于阐明植物次生代谢中的代谢途径。酵母和植物系统提供了真核细胞的细胞环境和必要的亚细胞区室化，以促进酶的功能。在这些细胞系统中表达候选基因并鉴定产生的产物，为鉴定具有新功能的酶指明了方向。然而，在许多情况下，检测到的化合物不是直接的酶产物，而是由非特异性后续反应引起的。即使这些非特异性反应的机制在许多情况下都有广泛的报道，但缺乏可能发生的潜在反应的概述，为从事新酶表征的研究人员提供了指导。本文全面总结了代谢途径工程中倍半萜的重排反应。解释了不同类型的非特异性反应及其化学和细胞背景，并给出了如何发现和避免这些非特异性反应的策略。此外，还介绍了一种非特异性反应的系统分类方法。希望这篇综述能够激发关于如何在代谢工程中系统地分类非特异性反应以及将这种方法扩展到其他类别的植物次生代谢物的讨论。
