Abstract:

Using homologous sequence alignment and molecular phylogenetic tree analysis, two flavonoid synthase genes are successfully cloned from the Glycyrrhiza inflata: Gur.gene26505 and Gur.gene26116. Gur.gene26505 is characterized as a flavonoid synthase Ⅱ, catalyzing liquiritigenin to specifically synthesize 7,4'-dihydroxyflavone, while Gur.gene26116 is a flavanone 2-hydroxylase that catalyzes liquiritigenin to synthesize three products including 7,4'-dihydroxyflavone. The reason for the specificity of 7,4'-dihydroxyflavone catalyzed by flavonoid synthase Ⅱ (Gur.gene26505) was further explored through protein structure prediction, molecular docking, and molecular dynamics simulations. Due to the unique rigid structure β-sheet near the active pocket of Gur.gene26505, the large sterically hindered phenylalanine residue is turned over to the lower part of the hydroxylation center, which eliminates the resistance of the hydroxylated product 2-hydroxyliquiritigenin to enter the dehydration center, occurring dehydration at C₂-C₃ positions and generating 7,4'-dihydroxyflavone. Finally, the optimal cell catalysis process for the specific synthesis of 7,4'-dihydroxyflavone is established through gene overexpression, optimization of reaction conditions and enhancement of bacterial growth, and the conversion rate of liquiritigenin reaches 76.67%.

Key words: licorice flavonoid synthase Ⅱ, liquiritigenin, 7,4'-dihydroxyflavone, specific transformation, biocatalysis

摘要：

利用同源序列比对和分子进化树分析从胀果甘草转录组数据库中挖掘并成功克隆到2个黄酮合酶基因：Gur.gene26505和Gur.gene26116。经表征Gur.gene26505为黄酮合酶Ⅱ，具有催化甘草素特异性合成7,4′-二羟基黄酮的特性，而Gur.gene26116为黄烷酮2位羟化酶，可催化甘草素生成包括7,4′-二羟基黄酮在内的三种产物。进一步通过蛋白质结构预测、分子对接和分子动力学模拟探究了黄酮合酶Ⅱ(Gur.gene26505)催化合成7,4′-二羟基黄酮特异性的原因。由于Gur.gene26505活性口袋附近特有的刚性结构β片层使大位阻苯丙氨酸残基翻转至羟化中心下方，消除了羟化产物2-羟基甘草素进入脱水中心的阻力进而发生C₂-C₃位的脱水反应特异性生成7,4′-二羟基黄酮。最后通过基因过表达、反应条件优化和强化菌体生长建立了7,4′-二羟基黄酮特异性合成的最佳细胞催化工艺，使甘草素转化率达到了76.67%。

关键词: 甘草黄酮合酶Ⅱ, 甘草素, 7,4′-二羟基黄酮, 特异性转化, 生物催化