Flagellin FljB composes flagellar antigen (H:1,2) of S. Typhimurium. This kind of antigen increases immunogenicity of any conjugated antigen upon administration. Thus, it is supposed to have an enormous potentiality for vaccine development against bacterial infections and cancer diseases. fljB gene (1515 nucleotides) coding for mature FljB was amplified by PCR from genomic DNA of S. Typhimurium and inserted into pET32a(+) for expression in E. coli BL21. The protein FljB was well expressed under the fusion form with Trx, Stag at N terminal and hexahistidine at C terminal, thus the recombinant protein was abbreviated to TrxFljB. Study on the impact of temperature on the gene expression showed that TrxFljB was synthesized at lower level at 37 o C comparing to the levels at 22 o C and 25 o C. 13% of the protein synthesized at 37 o C was inclusion body. Lower temperatures used during induction phase increased the solubility of the recombinant protein. About 97% of TrxFljB synthesized at 25 o C was soluble. IPTG concentration had a strong effect on the growth of freshly transformed cells but did not affect on the growth of stored and re-cultivated cells. The increase of IPTG concentration resulted in the decrease of the growth of freshly transformed cells and the TrxFljB productivity. However, 0.05 mM IPTG concentration was found to gain the full TrxFljB expression. TrxFljB productivity declined during storage of cells at 4 o C and re-cultivation. At optimal condition, volumetric productivity of TrxFljB was about 300 mg/ l broth.
Exotic gene expression in P. pastoris is dependent on multistep processes involving regulation at the level of transcription, protein translation, and posttranslational modifications. In order to further improve the
Glycoside Hydrolase family 5 (GH5) members share a broad range of enzymatic activities on oligosaccharides, polysaccharides and glycoconjugates from a wide range of species. The subfamily 4 (GH5-4) is enriched in some broad-specificity endo-β-1,4-endoglucanases (EG). From metagenomic DNA data of bacteria in Vietnam goats' rumen, a gene GL0361920 coding for endoglucanase GH5-4 was mined and selected for expression in Escherichia coli. Firstly, the codons of the gene were optimized and the codon optimized gene (eg3) was artificially synthesized and inserted into pET21a(+) at NdeI-XhoI positions for expression in E. coli. The results of the gene expression in five E. coli strains analyzed by SDS-PAGE showed that the recombinant endoglucanase (EG3) coded by eg3 was the best expressed in BL21, Origami strains, was not expressed in JM109 strain and expressed at very little amount in C43 and Rosetta strains. Among LB, TB, LB, SB, TBD media, the recombinant BL21 strain grew best at TB medium and produced total EG3 higher than the other media. The inducer IPTG gave a negative effect on the growth of the cells but the increase concentration of IPTG from 0.05 mM to 0.9 mM did not increase the negative impact on the cell mass and produced EG3 was nearly the same at the different IPTG concentrations. At 25 oC, in the TB medium containing 0.1 mM IPTG, the recombinant E. coli BL21 strain harboring pET21-eg3 produced about half of endoglucanase EG3 in a soluble form exhibiting activity hydrolyzing CMC substrate. At the OD600=10, soluble EG3 accumulated in the recombinant E. coli BL21 strain had the activity of 0.22 ± 0.006 U/ml.
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