Leibniz-Institute of Plant Biochemistry, Halle, Germany.
Phytochemistry. 2009 Oct-Nov;70(15-16):1696-707. doi: 10.1016/j.phytochem.2009.07.006. Epub 2009 Aug 6.
Benzylisoquinoline alkaloids (BIAs) are a group of nitrogen-containing plant secondary metabolites comprised of an estimated 2500 identified structures. In BIA metabolism, (S)-reticuline is a key branch-point intermediate that can be directed into several alkaloid subtypes with different structural skeleton configurations. The morphinan alkaloids are one subclass of BIAs produced in only a few plant species, most notably and abundantly in the opium poppy (Papaver somniferum). Comparative transcriptome analysis of opium poppy and several other Papaver species that do not accumulate morphinan alkaloids showed that known genes encoding BIA biosynthetic enzymes are expressed at higher levels in P. somniferum. Three unknown cDNAs that are co-ordinately expressed with several BIA biosynthetic genes were identified as enzymes in the pathway. One of these enzymes, salutaridine reductase (SalR), which is specific for the production of morphinan alkaloids, was isolated and heterologously overexpressed in its active form not only from P. somniferum, but also from Papaver species that do not produce morphinan alkaloids. SalR is a member of a class of short chain dehydrogenase/reductases (SDRs) that are active as monomers and possess an extended amino acid sequence compared with classical SDRs. Homology modelling and substrate docking revealed the substrate binding site for SalR. The amino acids residues conferring salutaridine binding were compared to several members of the SDR family from different plant species, which non-specifically reduce (-)-menthone to (+)-neomenthol. Previously, it was shown that some of these proteins are involved in plant defence. The recruitment of specific monomeric SDRs from monomeric SDRs involved in plant defence is discussed.
苯并异喹啉生物碱（BIAs）是一组含氮的植物次生代谢产物，据估计有 2500 种已被鉴定的结构。在 BIA 代谢中，（S）-黎藤碱是一个关键的分支点中间产物，可以定向形成几种具有不同结构骨架构型的生物碱亚型。吗啡烷生物碱是 BIAs 的一个子类，仅在少数几种植物物种中产生，最显著和丰富的是在罂粟（Papaver somniferum）中。对罂粟和其他几种不积累吗啡烷生物碱的 Papaver 物种的比较转录组分析表明，编码 BIA 生物合成酶的已知基因在 P. somniferum 中的表达水平更高。鉴定出三个与几个 BIA 生物合成基因协调表达的未知 cDNA，它们是该途径中的酶。这些酶中的一种，即吗啡烷生物碱特异性的 Salutaridine 还原酶（SalR），不仅从 P. somniferum ，而且从不产生吗啡烷生物碱的 Papaver 物种中分离出来，并以其活性形式异源过表达。SalR 是短链脱氢酶/还原酶（SDRs）的一个成员，作为单体发挥作用，与经典 SDRs 相比具有扩展的氨基酸序列。同源建模和底物对接揭示了 SalR 的底物结合位点。SalR 结合 Salutaridine 的氨基酸残基与来自不同植物物种的 SDR 家族的几个成员进行了比较，这些成员非特异性地将（-）-薄荷酮还原为（+）-新薄荷醇。此前，已经表明其中一些蛋白质参与植物防御。讨论了从参与植物防御的单体 SDR 中招募特定的单体 SDR。
