Shanghai Key Laboratory of Bio-Energy Crops, Research Center for Natural Products, School of Life Sciences, Shanghai University, 333 Nanchen Road, Shanghai, 200444, China.
State Key Laboratory of Biocatalysis and Enzyme Engineering, Hubei Collaborative Innovation Center for Green Transformation of Bio-resources, Hubei Key Laboratory of Industrial Biotechnology, School of Life Sciences, Hubei University, 368 Youyi Road, Wuhan, 430062, China.
Plant J. 2022 Feb;109(4):940-951. doi: 10.1111/tpj.15604. Epub 2021 Dec 7.
Diosgenin is an important compound in the pharmaceutical industry and it is biosynthesized in several eudicot and monocot species, herein represented by fenugreek (a eudicot), and Dioscorea zingiberensis (a monocot). Formation of diosgenin can be achieved by the early C22,16-oxidations of cholesterol followed by a late C26-oxidation. This study reveals that, in both fenugreek and D. zingiberensis, the early C22,16-oxygenase(s) shows strict 22R-stereospecificity for hydroxylation of the substrates. Evidence against the recently proposed intermediacy of 16S,22S-dihydroxycholesterol in diosgenin biosynthesis was also found. Moreover, in contrast to the eudicot fenugreek, which utilizes a single multifunctional cytochrome P450 (TfCYP90B50) to perform the early C22,16-oxidations, the monocot D. zingiberensis has evolved two separate cytochrome P450 enzymes, with DzCYP90B71 being specific for the 22R-oxidation and DzCYP90G6 for the C16-oxidation. We suggest that the DzCYP90B71/DzCYP90G6 pair represent more broadly conserved catalysts for diosgenin biosynthesis in monocots.
薯蓣皂素是制药行业的重要化合物，它在几种双子叶植物和单子叶植物中生物合成，在此以葫芦巴（双子叶植物）和盾叶薯蓣（单子叶植物）为例。薯蓣皂素的形成可以通过胆固醇的早期 C22,16-氧化反应，随后进行晚期 C26-氧化反应来实现。本研究表明，在葫芦巴和盾叶薯蓣中，早期 C22,16-加氧酶（s）对底物的羟基化具有严格的 22R-立体特异性。也发现了反对最近提出的薯蓣皂素生物合成中 16S,22S-二羟基胆固醇中间体的证据。此外，与利用单一多功能细胞色素 P450（TfCYP90B50）进行早期 C22,16-氧化反应的双子叶植物葫芦巴不同，单子叶植物盾叶薯蓣已经进化出两种独立的细胞色素 P450 酶，DzCYP90B71 特异性地进行 22R-氧化反应，DzCYP90G6 进行 C16-氧化反应。我们认为，DzCYP90B71/DzCYP90G6 对代表了单子叶植物薯蓣皂素生物合成中更为广泛保守的催化剂。
