The Optimization of Soluble PTEN Expression in Escherichia coli

The DNA polymerase of bacteriophage YerA41 replicates its T-modified DNA in a primer-independent manner

Yersinia phage YerA41 is morphologically similar to jumbo bacteriophages. The isolated genomic material of YerA41 could not be digested by restriction enzymes, and used as a template by conventional DNA polymerases. Nucleoside analysis of the YerA41 genomic material, carried out to find out whether this was due to modified nucleotides, revealed the presence of a ca 1 kDa substitution of thymidine with apparent oligosaccharide character. We identified and purified the phage DNA polymerase (DNAP) that could replicate the YerA41 genomic DNA even without added primers. Cryo-electron microscopy (EM) was used to characterize structural details of the phage particle. The storage capacity of the 131 nm diameter head was calculated to accommodate a significantly longer genome than that of the 145 577 bp genomic DNA of YerA41 determined here. Indeed, cryo-EM revealed, in contrast to the 25 Å in other phages, spacings of 33-36 Å between shells of the genomic material inside YerA41 heads suggesting that the heavily substituted thymidine increases significantly the spacing of the DNA packaged inside the capsid. In conclusion, YerA41 appears to be an unconventional phage that packages thymidine-modified genomic DNA into its capsids along with its own DNAP that has the ability to replicate the genome.

Expression and purification of biologically active recombinant rabbit monocyte chemoattractant protein1 in Escherichia coli

Monocyte chemoattractant protein 1 (MCP1) with recruiting monocytes is an important factor at the beginning of inflammatory disorders such as atherosclerosis which seems its blocking preclude this process and help improvement of related diseases. To perform clinical research in this field, MCP1 protein is required but firstly, animal studies should be done. As the rabbit is a suitable model for many inflammatory disorders, and Escherichia coli BL21(DE3) (BL21) cell is a high-efficiency host for protein expression, we decided to produce recombinant rabbit MCP1 (rRMCP1) in BL21/pET28a system. After codon usage, a construct containing RMCP1 sequence was synthesized, cloned into the pET28a plasmid, and overexpressed in BL21 cells. Followed that, with changing expression condition such as cell concentration before the induction, time period, temperature, shaking rate and inducer concentration (IPTG), rRMCP1 expression was optimized, and purified by Ni-NTA. The biological activity of the expressed protein was verified using monocyte migration assay. Using this expression system, nearly 28 mg/mL rRMCP1 was produced at 26°C/180 rpm for 24 h in LB broth medium with 1 mM IPTG. Therefore, we were succeeded to express the intermediate level of rRMCP1 with this method. This amount of protein is sufficient for biological researches in the laboratory.

Screening through the PLICable promoter toolbox enhances protein production in Escherichia coli

Escherichia coli is a common host for recombinant protein production in which production titers are highly dependent on the employed expression system. Promoters are thereby a key element to control gene expression levels. In this study, a novel PLICable promoter toolbox was developed which enables in a single cloning step and after a screening experiment to identify out of ten IPTG-inducible promoters (T7, A3, lpp, tac, pac, Sp6, lac, npr, trc and syn) the most suitable one for high level protein production. The target gene is cloned under the control of different promoters in a single and efficient cloning step using the ligase-free cloning method PLICing (phosphorothioate-based ligase-independent gene cloning). The promoter toolbox was firstly validated using three well producible proteins (a cellulase from a metagenome library, a phytase from Yersinia mollaretii and an alcohol dehydrogenase from Pseudomonas putida) and then applied to two enzymes (3D1 DNA polymerase and glutamate dehydrogenase mutant) which are poorly produced in E. coli. By applying our PLICable pET-promoter toolbox, the authors were able to increase production by two-fold for 3D1 DNA polymerase (lac promoter) and 29-fold for glutamate dehydrogenase mutant H52Y (trc promoter).