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.
Rui Fan,Jingjing Dong,Xiaoxiao Li,Ying Chen,Zhengyu Jin,Yuxiang Bai
Reuteran is a functional homopolysaccharide comprising major (α1 → 4) and interspersed (α1 → 6) linkages whose properties and functions are directly associated with the structure. In order to enrich the structural variety and application prospects of reuteran, a GtfB-type 4,6-α-glucanotransferase from Limosilactobacillus mucosae L24-B (LmGtfB), which can synthesize reuteran with high-content linear (α1 → 6) linkages, was screened. LmGtfB exhibited 4,6-α-glucanotransferase activity against starch or dextrin and can synthesize both linear and branching (α1 → 6) linkages, which offered advantages in terms of source and cost. The as-produced reuteran had the highest content of linear (α1 → 6) linkages (19% in the methylation result) among the reuterans synthesized by other GtfB-type 4,6-α-glucanotransferases. A purification method was established and applied to the extraction of the core structure of the LmGtfB products. 1H NMR and enzymatic hydrolysis revealed that the core structure contains 46.24% (α1 → 6) linkages and alternating (α1 → 4)/(α1 → 6) linkages, which was formed by enzymatic transfer of maltose.
Yueyang Zhang,Yue Jiang,Yina Jia,Xiaoyu Pan,Tianrun Zhao,Kaiyue Wang,He Yan,Zhiqing Ma
Background Omphalia lapidescens is a saprophytic and parasitic fungus belonging to the Polypora genus of Tricholomataceae . It has repellent, insecticidal, anti-inflammatory and immunomodulatory effects. Result This study found that the extract of O. lapidescens had significant anti-TMV activity, and the main active component was homopolysaccharide LW-1 by Bioassay-guided fractionation. LW-1 is a glucan with β-(1,3) glucoside bond as the main chain and β-(1,6) glucoside bond as the branch chain, with molecular weight in the range of 172,916–338,827 Da. The protective and inactive efficacies of LW-1(100 mg/L) against TMV were 78.10% and 48.20%, but had no direct effect on the morphology of TMV particles. The results of mechanism of action showed that LW-1 induced the increase of the activity of defense enzymes such as POD, SOD and PAL in Nicotiana glutinosa . The overexpression of resistance genes such as NPR1, PR1 and PR5 , and the increase of SA content. Further transcriptome sequencing showed that LW-1 activated MAPK signaling pathway, plant-pathogen interaction pathway and glucosinolide metabolic pathway in Arabidopsis thaliana . Besides, LW-1 induced crops resistance against plant pathogenic fungi. Conclusion Taken together, the anti-TMV mechanism of LW-1 was to activate MAPK signaling pathway, inducing overexpression of resistance genes, activating plant immune system, and improving the synthesis and accumulation of plant defencins such as glucosinolide. LW-1-induced plant disease resistance has the advantages of broad spectrum and long duration, which has the potential to be developed as a new antiviral agent or plant immune resistance inducer.
危险品化学品经营许可证（带存储）