Abstract：
To convert ginsenosides Rb1, Rb2, Rb3, and Rc into Rd by a single enzyme, a putative β-glycosidase (Pxbgl) from the xylan-degrading bacterium Petroclostridium xylanilyticum was identified and used. The kcat/Km value of Pxbgl for Rb3 was 18.18 ± 0.07 mM-1/s, which was significantly higher than those of Pxbgl for other ginsenosides. Pxbgl converted almost all Rb3 to Rd with a productivity of 5884 μM/h, which was 346-fold higher than that of only β-xylosidase from Thermoascus aurantiacus. The productivity of Rd from the Panax ginseng root and Panax notoginseng leaf was 146 and 995 μM/h, respectively. Mutants N293 K and I447L from site-directed mutagenesis based on bioinformatics analysis showed an increase in specific activity of 29 and 7% toward Rb3, respectively. This is the first report of a β-glycosidase that can simultaneously remove four different glycosyls at the C-20 position of natural PPD-type ginsenosides and produce Rd as the sole product from P. notoginseng leaf extracts with the highest productivity.
摘要：
通过单一酶将人参皂苷Rb1，Rb2，Rb3和Rc转化为Rd，鉴定并使用了一种来自木聚糖降解细菌的推定的β-糖苷酶（Pxbgl）。Pxbgl对Rb3的kcat/Km值为18.18±0.07mM-1/s,显著高于其他人参皂苷的Pxbgl。Pxbgl以5884μM/h的生产率将几乎所有Rb3转化为Rd，比仅来自热曲菌的β-木糖苷酶高346倍。人参根和三七叶的Rd生产率分别为146和995μM/h，分别。基于生物信息学分析的定点诱变的突变体N293K和I447L分别显示出对Rb3的比活性增加29％和7％。这是关于β-糖苷酶的首次报道，该酶可以同时去除天然PPD型人参皂苷的C-20位置的四种不同糖基，并以最高的生产率从三七叶提取物中产生Rd作为唯一的产物。
