Difference between revisions of "Part:BBa K4225022"

Revision as of 13:48, 11 October 2022

pelB-rDAO

This is a composite part that consists of rDAO that is tagged with N-terminal pelB translocation tag (BBa_J32015). To study this composite part, we added promoter, 6xHis tag and terminator to create a new composite part, BBa_K4225007.

Contribution: HKUST 2022: Improvement of an Existing Part - Gold Medal Requirement

Characterization of pelB-rDAO with Ninhydrin and Histamine Assay

Summary

We use ninhydrin and histamine to measure the activity of rDAO to decrease the concentration of histamine. From the experiment, we would expect a decrease of ninhydrin absorbance using pelB-rDAO compared to the negative control.

Experiment

pelB-rDAO (BBa K4225007) constructs are tested with 600 ppm of histamine alongside Pc-rDAO (BBa K4225021) as a positive control and pSB1C3 as a negative control. Constructs are inoculated in 5mL LB with chloramphenicol (CHL LB) for 16 hours. The constructs are then back diluted to 1.0 OD600. These steps are done to equalize the amount of cells for each culture. They are then added to 600 ppm of histamine and incubate for 1 hour. Before and after incubation for 1 hr, the samples are spun down. Afterwards, the supernatants are taken, mixed with ninhydrin and heated at 80oC for 20 min. Finally, the samples are placed in an ice box for 3 minutes and absorbance is measured at 570 nm.

Results and Discussion

Statistically significant decrease (p<0.01, p<0.03 and p<0.01) of absorbances can be seen with pelB-rDAO from 0 to 1 hr, 1 to 2 hr and 0 to 2 hr respectively. On the other hand, no statistically significant decrease can be seen for the rDAO construct for every hour, and only a statistically decrease (p<0.03) can be seen for 0 to 2 hr result. Moreover, for our -ve construct, no significant decrease or increase can be seen. Thus, the evaporation of histamine and the effect of bacterial culture towards the result of our experiment could be ignored. Therefore, we can state that the decrease of absorbance, which is related to the concentration of diamine, in pelB-rDAO and rDAO construct is due to the rDAO enzyme. Knowing that the function of rDAO is to catalyze the conversion of diamine to H2O2, then this result indirectly proves that H2O2 is also produced due to the rDAO enzyme.

The decrease of the percentage of absorbance for pelB-rDAO construct are: -17.8% for 0 hr to 1 hr, -6.59% for 1 to 2 hr, and -23.2% for 0 hr to 2 hr, while for rDAO construct are: -6.59% for 0 hr to 1 hr, -7.19% for 1 hr to 2 hr and -10.8% for 0 hr to 2 hr. Comparing just the time point with the statistically significant result, which is 0 to 2 hr, then the pelB-rDAO construct has a larger decrease of percentage of absorbance compared to the rDAO construct ( -23.2% v/s -10.8%). This demonstrates that there is a higher activity of rDAO in the bacteria with pelB-rDAO compared to the latter, proving that the pelB tag functions like we hypothesised. For more information on the effect on pelB on rDAO in our DH5α chassis, refer to our wiki page.

Sequence and Features