Institute of Medicinal Plant Development, Chinese Academy of Medical Sciences & Peking Union Medical College, Beijing 100193, China.
Guilin GFS Monk Fruit Corp., Guilin 541006, China.
Molecules. 2019 Feb 11;24(3):627. doi: 10.3390/molecules24030627.
Mogrosides, the main bioactive compounds isolated from the fruits of , are a group of cucurbitane-type triterpenoid glycosides that exhibit a wide range of notable biological activities and are commercially available worldwide as natural sweeteners. However, the extraction cost is high due to their relatively low contents in plants. Therefore, molecular breeding needs to be achieved when conventional plant breeding can hardly improve the quality so far. In this study, the levels of 21 active mogrosides and two precursors in 15 varieties were determined by HPLC-MS/MS and GC-MS, respectively. The results showed that the variations in mogroside V content may be caused by the accumulation of cucurbitadienol. Furthermore, a total of four wild-type cucurbitadienol synthase protein variants (50R573L, 50C573L, 50R573Q, and 50C573Q) based on two missense mutation single nucleotide polymorphism (SNP) sites were discovered. An in vitro enzyme reaction analysis indicated that 50R573L had the highest activity, with a specific activity of 10.24 nmol min mg. In addition, a site-directed mutant, namely, 50K573L, showed a 33% enhancement of catalytic efficiency compared to wild-type 50R573L. Our findings identify a novel cucurbitadienol synthase allele correlates with high catalytic efficiency. These results are valuable for the molecular breeding of luohanguo.
罗汉果中的主要生物活性化合物——甜苷，是一组葫芦烷型三萜糖苷，具有广泛的显著生物活性，作为天然甜味剂在全球范围内商业上可获得。然而，由于其在植物中的含量相对较低，提取成本很高。因此，到目前为止，常规植物育种很难提高品质，需要通过分子育种来实现。在这项研究中，通过 HPLC-MS/MS 和 GC-MS 分别测定了 15 个品种中 21 种活性甜苷和两种前体的含量。结果表明，甜苷 V 含量的变化可能是由于葫芦二烯醇的积累造成的。此外，还发现了总共四种基于两个错义突变单核苷酸多态性（SNP）位点的野生型葫芦二烯醇合酶蛋白变异体（50R573L、50C573L、50R573Q 和 50C573Q）。体外酶反应分析表明，50R573L 具有最高的活性，比活为 10.24 nmol min mg。此外，与野生型 50R573L 相比，定点突变体 50K573L 的催化效率提高了 33%。我们的研究结果确定了一个与高催化效率相关的新型葫芦二烯醇合酶等位基因。这些结果对于罗汉果的分子育种具有重要意义。
