a College of Biotechnology and Pharmaceutical Engineering , Nanjing Tech University , Nanjing , China.
Bioengineered. 2019 Dec;10(1):142-149. doi: 10.1080/21655979.2019.1607710.
Quercetin-4'-O-glucoside is one of the major quercetin derivatives in the mature red onion bulb. It has an adjuvant effect on allergies, asthma, arthritis, and cancer. The present study aimed to use uridine diphosphate glycosyltransferase 88A1 (UGT88A1) from Arabidopsis thaliana to achieve the enzymatic synthesis of quercetin-4'-O-glucoside from quercetin. The results showed that UGT88A1 was most active at pH 9.0. The optimum temperature of UGT88A1 for synthesizing quercetin-4'-O-glucoside was 45°C, which was a little lower than that for synthesizing quercetin-3-O-glucoside (50°C). One mutant, V18R, of UGT88A1 was obtained by site-directed mutation and showed a greater affinity (K 0.20 mM) and twice the enzyme activity (552.3 mU/mg) towards quercetin compared with the wild-type enzyme (0.36 mM and 227.6 mU/mg, respectively). The possible reason could be attributed to the distance change between the 18th amino-acid residue of UGT88A1 and the substrate quercetin, as deduced by molecular simulation.
槲皮素-4'-O-葡萄糖苷是成熟红洋葱鳞茎中主要的槲皮素衍生物之一。它对过敏、哮喘、关节炎和癌症具有辅助作用。本研究旨在利用拟南芥尿苷二磷酸糖基转移酶 88A1（UGT88A1）从槲皮素实现槲皮素-4'-O-葡萄糖苷的酶促合成。结果表明，UGT88A1 在 pH9.0 时最活跃。UGT88A1 合成槲皮素-4'-O-葡萄糖苷的最适温度为 45°C，略低于合成槲皮素-3-O-葡萄糖苷（50°C）的温度。通过定点突变获得了 UGT88A1 的一个突变体 V18R，与野生型酶相比，该突变体对槲皮素的亲和力（K 0.20 mM）提高了一倍，酶活性提高了两倍（分别为 552.3 mU/mg 和 227.6 mU/mg）。可能的原因可以归因于分子模拟推断的 UGT88A1 的第 18 个氨基酸残基与底物槲皮素之间的距离变化。
