Difference between revisions of "Part:BBa K2973019"

Revision as of 01:28, 16 October 2019

TEM-optimized beta-lactamase / J23119

Beta-lactamase is an enzyme found widely in the procaryots, and confers resistance to ampicillin. This composite part comprises of the TEM-optimized beta-lactamase CDS (BBa_I757010), regulated by the 119 constitutive Anderson Family Promoter (BBa_J23119) and a universal RBS (BBa_B0034). Transcription is terminated by double terminator (BBa_B0015). This allows for enhanced protein expression in E. coli cells.

Thessaly 2019 Characterization

Thessaly 2019 sought to characterize the coding sequence of TEM-optimized beta-lactamase (Part:BBa_I757010) under the regulation of the constituve Anderson Family promoters Part:BBa_J23100, Part:BBa_J23105, Part:BBa_J23106, Part:BBa_J23119. Beta-lactamase is an enzyme that hydrolyses beta-lactams (e.g. ampicillin) and is naturally found in prokaryotic cells. A colorimetric assay has been developed using nitrocefin as a substrate which after hydrolysis from beta-lactamase changes the reaction color, from yellow (380nm) to red (490nm).

To achieve that, the coding sequence was assembled with each promoter, a universal RBS (Part:BBa_B0034) and a double terminator(Part:BBa_B0015). The parts were cloned in pSB1C3 and pSB1K3 and transformed into E. coli DH5a competent cells.

In the photo below you can see the results of the primer addition using overhang PCR:

For protein expression, the plasmids were transformed into E. coli BL21 (DE3) competent cells.

For the beta-lactamase assay, we set up the following experimental design:

1. Grow BL21 (DE3) pre-culture overnight in 5ml LB (~16h) at a shaken incubator, 37 degrees C / 210rpm

2. The following morning, measure the OD600 of overnight cultures

3. Dilute all cultures to OD600¬ = 0.05 in M9 minimal medium

4. Grow cells 37 degrees C /210 RPM until OD600=0.4-0.6 (~2h)

5. Dilute all cells to the same OD600 (e.g. 0.4)

6. Load 160 of culture in a 96-well plate (do triplicates). Add 40 ul 0.5 uM nitrocefin for a final concentration of 100nM

7. Measure the absorbance at 490nm (for nitrocefin hydrolysis) and 600nm (for cell growth) every 30 seconds for 2 hours in a microplate reader. Shake between readings. Because plateau was reached within the first 30 minutes of the reaction, only those are depicted in the graph.

To ensure that the absorbance shown corresponds only to enzymatic activity by beta-lactamase, we included 3 controls in the experiment. The first control has M9 medium only (no cells) and nitrocefin, the second has empty BL21 (DE3) cells (no plasmid) and nitrocefin, while the third has BL21 (DE3) cells containing the plasmid but not the part (empty plasmid). To obtain comparable results, we normalized all values by dividing OD490 by OD600.

The results are shown in the graph below

The maximum expression of beta-lactamase was observed under control of the J23119 (brown line) which is the wild type promoter of the Anderson family. The expression is reduced with the J23100 and J23106 (yellow and purple line respectively), while the lowest expression levels were observed with the J23105 promoter (blue line). These results are in accordance with those from previous teams that measured fluorescence and the same pattern is observed. The controls conditions (pSB1C3 and BL21, or light purple and light blue respectively) confirm that the absorbance measured derives from beta-lactamase activity only, both quantitatively and visually.

Below you can see the 96-well plate of the assay:

Note that the picture was taken after the plate-reader assay was completed and all conditions had reached a plateau, except the controls.

Sequence and Features