Team:UST Beijing/Experiments


Experimental Design

Ginseng products offer a unique opportunity to meet the atherosclerosis challenge. Herbs containing ginsenosides include: Ginseng, Western Ginseng, Notoginseng, Jiaogulan etc. Common herb preparation and oral administration practice results in poor absorption profile thus limits its efficacy and cost-effectiveness. Since the ginseno-sterols are responsible for their main pharmacological effects, how to achieve effective concentration of sterol in the human body become critical.
Our long-term goal is to improve the health-promoting effects of ginsenosides. We believe that sterols (triterpenes)in the ginsenosides are responsible for their main benefits. Therefore in the past projects we engineered synthetic squalene cyclase for in situ production of ginseng-sterols in human cells and produced synthetic β-glucosidase in E.coli for removal of sugar from ginsenosides. In the current strategy, in the wake of “No release” policy of the iGEM community, we are able to by-pass synthetic biology methods to achieve our goal by applying in vitro chemical reactions.

In the past, two approaches have been tried to achieve this:

(1) Synthesize ginseno-sterols in situ. Pro: no need to plant ginseng and harvest, continuous supply of ginseno-sterols; Con: interference with host physiology, lack of control in production.
(2) Produce beta-glucosides in the host gut micro-organism. Pro: convenient to hydrolyze ginsenosides in the gut; Con: interference with gut physiology and probiotics.

In the current third approach, we use chemical reaction to hydrolyze the conjugated sugars, to satisfy “No-release” policy if iGEM safety requirement.

A synthetic beta-glucosidase gene is introduced into E.coli, which is cultured along with PNPG as illustrated below. The enzyme (structure as illustrated) will produce a yellow color product which is secreted to the medium, and measured by spectrometry.
Experiment assignment:

We set three different concentrations of PNPG in 2.5%, 5%, 10% and chose ten different germs (including germ 1 without plasmids) to examine their OD (optional density) by spectrometer once hour.
Specific experimental scheme:
Plate E.coli (empty, without Beta glycosidase plasmid) and transformed E.coli on solid medium and culture overnight to obtain a single clone of bacteria and repeat the experiment for three times.(temperature:37℃)
Pick a single clone bacteria into 2ml liquid LB medium and culture overnight.(temperature:37℃)
Isolate E.coli(BL21) from 2 ml LB culture and grow E.coli(BL21) in M9 culture for four to six hours.(temperature:37℃)Repeat it for several times.
Use PNPG to verify whether E.coli is transformed by beta-glucosidase expressing plasmid. Put samples(including untransformed E.coli as negative control) at three different concentrations 5,10,20% in a 96-well plate by micropipet.
Use spectrophotometer to measure OD405nm and OD620nm value every 2 hours hour for 12 hours to test whether the plasmid in E. coli was expressed. The color is getting yellow visibly.

Time-dependent production of hydrolzyed color product by beta-glucosidase under different culture conditions. (The blue line: OD405nm, red line: OD620nm, green line: logistic model simulation.)

Use chemical methods to hydrolyze ginsenoside:

Chemical hydrolysis of ginsenosides have been well studied and widely reported in the past. Methods include hydrochloric acid, sodium hydroxide, lactic acid, acidic amino acids, acetic acid, etc. The published methods could generate partial hydrolyzed ginsenosides. However, strong acid hydrolyzation results in modification of sterol side chains, as examplified in the following reaction:

In the current approach, we applied a combination of water, butanol, and acetic acid in a proprietary ratio to the ginsenoside substrate mixture to perform the hydrolysis:

Experimental procedure:

①use different hydrolysis system to hydrolyze ginsenosides.
②Separate hydrolyzed ginsenosides by standarded TLC system.
③utilize Double Gene report Test system built in Laboratory to test the bioactivity of hydrolyzed ginsenosides.

Cellular assay of Ginsenoside hydrolysate biological activity:


Through the chart, we can see that the hydrolyzed ginsenosides has better LXR tranactivation ability compared to the unhydrolyzed. Meanwhile, the effect of hydrolyzed ginsenosides is relatively closed to a positive control sample. To conclude, we demonstrate that our "natural RE-lease" approach is working.