Team:UESTC Life/Results and Discussion

From 2013.igem.org

Latest revision as of 18:09, 25 September 2013

TCP Biodegradation achieved

Growth of E.coli strain MC1061 transformed DhaA+P2A+HheC and DhaA gene in LB medium with inducer and 5mM TCP respectively, as the substrate was monitored in batch culture. The concentration of the products were confirmed using GC column(AC5). Growth resulted in disappearance of the substrate and simultaneous formation of biomass, 2,3-DCP, epichlorohydrin, chloropropanol, and glycerin. The result was screened by GC analysis. Above the degradation of TCP and the intermediate product 2,3-DCP indicate that multistep biodegradation are working. (Fig.1 and Fig.2). And cultivating in medium with 2,3-DCP, the concentration of epichlorohydrin can be detected(Fig.2). It means HheC degrade 2,3-DCP to epichlorohydrin. The degradation followed the desired path, TCP will be degraded to glycerol finally. The deficiency of our project is chloropropanol and glycerin couldn’t be detected by the columns. In the future, new columns and new methods will be used.

Fig.1. E.coli MC1061 carried DhaA+P2A+HheC gene incubated in LB medium with TCP(5mM) at 30℃. The concentration of TCP and it mediate product 2,3-DCP were measured by GC. 2,3-DCP was degraded at the same time.

Fig.2. E.coli MC1061 carried DhaA incubated in LB medium with TCP(5mM) at 30℃. The concentration of TCP and its mediate product 2,3-DCP were measured by GC. 2,3-DCP couldn’t be degraded.

Fig.3. E.coli MC1061 carried DhaA+P2A+HheC gene incubated in LB medium with 2,3-DCP(5mM) at 30℃. The concentration of 2,3-DCP and its mediate product epichlorohydrin were measured by GC.

γ-HCH Biodegradation and F2A cleaving achieved

Growth of E.coli strain MC1061 transformed LinA+F2A+LinB and LinA gene in LB medium with inducer and 5Mm γ-HCH respectively, as the substrate was monitored in batch culture. The result was screened by GC analysis(Fig.4). Growth resulted in disappearance of the substrate and simultaneous formation of biomass and γ-PCCH et. But the available column is limited that the intermediate product can’t be detected. Through SDS-PAGE analysis, F2A could cleave LinA and LinB(Fig.5). LinB would degrade the intermediate product ofγ-HCH.

Fig.4. E.coli MC1061 carried LinA and LinA+F2A+LinB gene incubated in LB medium withγ-HCH(5mM) at 30℃. The concentration ofγ-HCH were measured by GC.

FIG.5. SDS-PAGE analysis. Supernatant and sediment collected after breaking cell. Lane1 and lane2 are blank control; in the lane3 and lane5 LinA and LinB are solved in the buffer.; in the lane 7 and lane8, F2A peptide sequence has cleaved LinA and LinB, both of them are solved. The most of protein, LinA+F2A+LinB, is in the sediment as an inclusion body.

P2A being an excellent linker in chimeric protein

As for P2A peptide sequence, it didn’t cleave the DhaA and HheC, and the chimeric protein was linked by P2A peptide. (FIG.6).

DhaA+P2A+HheC gene were expressed in E.coli strain MC1061. Separating supernatant and sediment of the broken cell liquid and used colorimetric method to detect the activity with TCP and 1,3-DCP.(FIG.7). DhaA+P2A+HheC in supernatant has activity of DhaA and HheC, while in sediment, it doesn’t have this ability.

Only if four single HheC compose as a tetramer can it catalyze dehalogenation. Measuring the activity of HheC in chimeric protein, DhaA+P2A+HheC is an ideal way to detect the effect of P2A peptide. The purified enzyme, HheC and DhaA+P2A+HheC chimeric protein was isolated by AKTA FPLC. Using 1,3-DCP as substrate, HheC specific activity was 6.72(U/mg) and the fusion protein specific activity is 5.28(U/mg). It indicates that the 2A peptide is an excellent linker to compose the two enzymes function together.

FIG.6 lane7 and lane8 are blank control; lane1 and lane3 are DhaA and HheC. In the lane5 and lane6, HheC and DhaA bands can’t be found, a part of DhaA+P2A+HheC are solved, P2A peptide sequence can’t cleave DhaA and HheC. In the sediment, there are also inclusion protein.

FIG.7 the reaction in buffer(50MmTris-SO3,PH=8.0), after breaking the cell. Blank control was the cell transformed empty vector. incubating at 30℃. Colorimetric method is a way of detecting the concentration of Cl-(refer to protocol). The solved chimeric protein DhaA+P2A+HheC could degrade 1,3-DCP and TCP. The inclusion protein doesn’t have any activity.

Polycistronic co-expression system constructed

In polycistronic co-expression system, the quantity of HheC was less than DhaA and LinB is less than LinA(FIG.9). Because the gene is further from promoter, the expression is less. That is why we want to utilize 2A peptide in prokaryotic system.

FIG.9 (a) In the lane5 and lane6, LinA and LinB are expressed, according to the bands, the quantity of LinB is less than LinA. (b) In the lane1 and lane2, there are both bands of DhaA and HheC, the quantity of DhaA is more than HheC.