Faculty of Agriculture, Shizuoka University, 836 Ohya, Suruga-ku, Shizuoka, 422-8529, Japan; The United Graduate School of Agricultural Science, Gifu University, 1-1, Yanagido, Gifu-shi, 501-1193, Japan.
Faculty of Agriculture, Shizuoka University, 836 Ohya, Suruga-ku, Shizuoka, 422-8529, Japan.
Phytochemistry. 2023 Nov;215:113850. doi: 10.1016/j.phytochem.2023.113850. Epub 2023 Sep 1.
Diarylheptanoids are secondary metabolites of plants that comprise a C-C-C scaffold. They can be broadly classified into linear-type and cyclic-type diarylheptanoids based on their chemical structures. Actinorhizal trees, such as Casuarina, Alnus, and Myrica, which form nodule symbiosis with actinomycetes Frankia, produce cyclic diarylheptanoids (CDHs); in Alnus sieboldiana Matsum. in particular, we have reported that the addition of CDHs leads to an increase in the number of nodules. However, the information available on the biosynthesis of CDHs is scarce. A greater number of plants CDHs (including those isolated from actinorhizal trees) with a saturated heptane chain have been isolated compared with linear, non-cyclic diarylheptanoids. To identify the genes involved in the synthesis of these compounds, genes with significant sequence similarity to existing plant double-bond reductases were screened in A. sieboldiana. This report describes the isolation and characterization of two A. sieboldiana double-bond reductases (AsDBR1 and AsDBR2) that catalyze the NADPH-dependent reduction of bisdemethoxycurcumin and curcumin. The optimum pH for the two enzymes was 5.0. The apparent K values for bisdemethoxycurcumin and NADPH were 4.24 and 3.53 μM in the case of AsDBR1, and 2.55 and 2.13 μM for AsDBR2. The k value was 9.4-fold higher for AsDBR1 vs. AsDBR2 when using the bisdemethoxycurcumin substrate. Interestingly, the two AsDBRs failed to reduce the phenylpropanoid monomer.
二芳基庚烷类化合物是植物的次生代谢产物，其包含 C-C-C 支架。根据其化学结构，它们可以广泛分为线性型和环状型二芳基庚烷类化合物。与放线菌弗兰克氏菌形成根瘤共生的结瘤固氮树木，如 Casuarina、Alnus 和 Myrica 等，会产生环状二芳基庚烷类化合物（CDHs）；特别是在 Alnus sieboldiana Matsum. 中，我们已经报道过添加 CDHs 会导致根瘤数量增加。然而，有关 CDHs 生物合成的信息却很少。与线性、非环状二芳基庚烷类化合物相比，已经分离出更多具有饱和庚烷链的植物 CDHs（包括从结瘤固氮树木中分离出的化合物）。为了鉴定参与这些化合物合成的基因，在 A. sieboldiana 中筛选了与现有植物双键还原酶具有显著序列相似性的基因。本报告描述了两种 A. sieboldiana 双键还原酶（AsDBR1 和 AsDBR2）的分离和特性，它们催化 NADPH 依赖性还原双甲氧基姜黄素和姜黄素。两种酶的最适 pH 值均为 5.0。对于 AsDBR1，双甲氧基姜黄素和 NADPH 的表观 K 值分别为 4.24 和 3.53 μM，而对于 AsDBR2，则分别为 2.55 和 2.13 μM。当使用双甲氧基姜黄素作为底物时，AsDBR1 的 k 值比 AsDBR2 高 9.4 倍。有趣的是，两种 AsDBRs 都无法还原苯丙烷单体。
