Part:BBa_K2856001

Bifunctional glutamate-cysteine ligase/glutathione synthase (gshF)

The BBa_K2856001 harbors a coding sequence of bi-functional glutamate--cysteine ligase/glutathione synthase (gshF) derived from S.agalactiae. Codon-optimization has been made for Lactococcus Lactis. gshFp catalyzes the conversion of Cys, Glu and Gly to GSH.

Usage and Biology

Bifunctional glutamate--cysteine ligase/glutathione synthase (gshF) is an enzyme involved and responded to synthetic reaction of GSH. In this reaction, one Cysteine and one Glutamate are converted to one γ-GC, then one γ-GC and one Glycine are converted to one GSH (Figure 1). The Lactococcus Lactis NZ9000 has inability to synthesis GSH. In our project, we construct a plasmid harboring gshF in order to produce GSH in Lactococcus Lactis NZ9000.

Construction and validation of plasmid pNZ-gshF

Gene gshF was amplified from genomic DNA of S. agalactiae and cut with restriction enzyme Hind III and NcoI, and ligased with plasmid pNZ8148 cut with the same enzyme. Then the ligation product was transferred to E.coli and spread on plates containing 10 mg/L chloramphenicol. Colonies on the plates were randomly picked and inoculated in 1ml LB medium for 3 hours at 37℃, 200 rpm. 1 μl culture were added to the PCR system as template. As shown in Figure. 2, all the picked colonies had gene gshF, illustrating that the plasmid pNZ-gshF was successfully constructed.

Figure. 2 Validation of plasmid pNZ-gshF. M represented marker. 1, 2 and 3 represented three randomly picked colonies.

Protein Analysis

After transferring the plasmid pNZ-gshF to L. lactis NZ9000, SDS-PAGE was performed to detect the protein expression level of gshF gene. The cells were washed twice with 0.1 M PBS after centrifugation. Crude protein was extracted through cell breaking using ultrasonication and centrifugation. Then the supernatant of the samples were used to analysis the protein expression. As shown in Figure. 3, expected bands of the GshF protein were observed on the gel in the lane of recombinant L. lactis containing pNZ-gshF induced with different nisin concentration while no GshF protein existed in L. lactis NZ9000.

Figure. 3 SDS PAGE validation of gene gshF expression in L. lactis. M represented marker. WT represented L. lactis NZ9000. 1-3 represented L. lactis/pNZ-gshF induced with 100, 50 and 20 ng/ml nisin.