Over-expression of proteins using a modified pBAD24 vector in E. coli expression system

Enhancing Enzyme Activity and Thermostability of Bacillus amyloliquefaciens Chitosanase BaCsn46A Through Saturation Mutagenesis at Ser196

Chitosanase plays an important role in chitooligosaccharides (COS) production. We found that the chitosanase (BaCsn46A) of Bacillus amyloliquefacien was a good candidate for chitosan hydrolysis of COS. In order to further improve the enzyme properties of BaCsn46A, the S196 located near the active center was found to be a critical site impacts on enzyme properties by sequence alignment analysis. Herein, saturation mutation was carried out to study role of 196 site on BaCsn46A catalytic function. Compared with WT, the specific enzyme activity of S196A increased by 118.79%, and the thermostability of S196A was much higher than WT. In addition, we found that the enzyme activity of S196P was 2.41% of that of WT, indicating that the type of amino acid in 196 site could significant affect the catalytic activity and thermostability of BaCsn46A. After molecular docking analysis we found that the increase in hydrogen bonds and decrease in unfavorable bonds interacting with the substrate were the main reason for the change of enzyme properties which is valuable for future studies on Bacillus species chitosanase.

Efficient secretory production of CotA-laccase and its application in the decolorization and detoxification of industrial textile wastewater

Fungal laccases are typically unstable at high pH and temperature conditions, which limit their application in the decolorization of textile wastewater. By contrast, the highly stable bacterial laccases can function within a wider pH range and at high temperatures, thus have significant potential in treatment for textile wastewater. In our previous work, a thermo-alkali-stable CotA-laccase gene was cloned from Bacillus pumilus W3 and overexpressed in Escherichia coli. In this study, the robust CotA-laccase achieved efficient secretory expression in Bacillus subtilis WB600 by screening a suitable signal peptide. A maximum CotA-laccase yield of 373.1 U/mL was obtained at optimum culture conditions in a 3-L fermentor. Furthermore, the decolorization and detoxification of textile industry effluent by the purified recombinant CotA-laccase in the presence and absence of redox mediators were investigated. Among the potential mediators that enhanced effluent decolorization, acetosyringone (ACS) was the most effective. The toxicity of the CotA-laccase-ACS-treated effluent was greatly reduced compared with that of the crude effluent. To the best of our knowledge, this study is the first to report on the heterologous expression of CotA-laccase in B. subtilis. The recombinant strain B. subtilis WB600-5 has a great potential in the industrial production of this bacterial enzyme, and the CotA-laccase-ACS system is a promising candidate for the biological treatment of industrial textile effluents.

Cloning and expression of thermo-alkali-stable laccase of Bacillus licheniformis in Pichia pastoris and its characterization

A thermo-alkali-stable laccase gene from Bacillus licheniformis was cloned and expressed in Pichia pastoris. The recombinant laccase was secreted into the culture medium with a maximum activity of 227.9 U/L. The purified laccase is a monomeric glycoprotein, and its molecular weight was estimated to be 65 kDa on SDS-PAGE after deglycosylation. Optimal enzyme activity was observed at pH 6.2 and 70°C with syringaldazine as substrate. The recombinant laccase was highly stable in the pH range 7-9 after 10 days at 30°C. The enzyme displayed remarkable thermostability at 50-70°C, with a half-life of inactivation at 70°C of 6.9 h. It also exhibited high tolerance to NaCl and organic solvents like the native spore laccase. The purified laccase could rapidly decolorize reactive blue 19, reactive black 5 and indigo carmine in the presence of acetosyringone. More than 93% of the tested dyes were decolorized in 4 h at pH 9.0.

Tuning different expression parameters to achieve soluble recombinant proteins in E. coli: advantages of high-throughput screening

Proteins are the main reagents for structural, biomedical, and biotechnological studies; however, some important challenges remain concerning protein solubility and stability. Numerous strategies have been developed, with some success, to mitigate these challenges, but a universal strategy is still elusive. Currently, researchers face a plethora of alternatives for the expression of the target protein, which generates a great diversity of conditions to be evaluated. Among these, different promoter strength, diverse expression host and constructs, or special culture conditions have an important role in protein solubility. With the arrival of automated high-throughput screening (HTS) systems, the evaluation of hundreds of different conditions within reasonable cost and time limits is possible. This technology increases the chances to obtain the target protein in a pure, soluble, and stable state. This review focuses on some of the most commonly used strategies for the expression of recombinant proteins in the enterobacterium Escherichia coli, including the use of HTS for the production of soluble proteins.

A novel prokaryotic vector for identification and selection of recombinants: direct use of the vector for expression studies in E. coli

Background

The selection of bacterial recombinants that harbour a desired insert, has been a key factor in molecular cloning and a series of screening procedures need to be performed for selection of clones carrying the genes of interest. The conventional cloning techniques are reported to have problems such as screening high number of colonies, generation of false positives, setting up of control ligation mix with vector alone etc.

Results

We describe the development of a novel dual cloning/expression vector, which enables to screen the recombinants directly and expression of the gene of interest. The vector contains Green fluorescence protein (GFP) as the reporter gene and is constructed in such a way that the E. coli cells upon transformation with this vector does not show any fluorescence, but readily fluoresce upon insertion of a foreign gene of interest. The same construct could be easily used for screening of the clones and expression studies by mere switching to specific hosts.

Conclusions

This is the first vector reported that takes the property of colour or fluorescence to be achieved only upon cloning while all the other vectors available commercially show loss of colour or loss of fluorescence upon cloning. As the fluorescence of GFP depends on the solubility of the protein, the intensity of the fluorescence would also indicate the extent of solubility of the expressed target protein.

Enhanced fluorescent properties of an OmpT site deleted mutant of green fluorescent protein

BACKGROUND

The green fluorescent protein has revolutionized many areas of cell biology and biotechnology since it is widely used in determining gene expression and for localization of protein expression. Expression of recombinant GFP in E. coli K12 host from pBAD24M-GFP construct upon arabinose induction was significantly lower than that seen in E. coli B cells with higher expression at 30 degrees C as compared to 37 degrees C in E. coli K12 hosts. Since OmpT levels are higher at 37 degrees C than at 30 degrees C, it prompted us to modify the OmpT proteolytic sites of GFP and examine such an effect on GFP expression and fluorescence. Upon modification of one of the two putative OmpT cleavage sites of GFP, we observed several folds enhanced fluorescence of GFP as compared to unmodified GFPuv (Wild Type-WT). The western blot studies of the WT and the SDM II GFP mutant using anti-GFP antibody showed prominent degradation of GFP with negligible degradation in case of SDM II GFP mutant while no such degradation of GFP was seen for both the clones when expressed in BL21 cells. The SDM II GFP mutant also showed enhanced GFP fluorescence in other E. coli K12 OmpT hosts like E. coli JM109 and LE 392 in comparison to WT GFPuv. Inclusion of an OmpT inhibitor, like zinc with WT GFP lysate expressed from an E. coli K12 host was found to reduce degradation of GFP fluorescence by two fold.

RESULTS

We describe the construction of two GFP variants with modified putative OmpT proteolytic sites by site directed mutagenesis (SDM). Such modified genes upon arabinose induction exhibited varied degrees of GFP fluorescence. While the mutation of K79G/R80A (SDM I) resulted in dramatic loss of fluorescence activity, the modification of K214A/R215A (SDM II) resulted in four fold enhanced fluorescence of GFP.

CONCLUSIONS

This is the first report on effect of OmpT protease site modification on GFP fluorescence. The wild type and the GFP variants showed similar growth profile in bioreactor studies with similar amounts of recombinant GFP expressed in the soluble fraction of the cell. Our observations on higher levels of fluorescence of SDM II GFP mutant over native GFPuv in an OmpT+ host like DH5alpha, JM109 and LE392 at 37 degrees C reiterates the role played by host OmpT in determining differences in fluorescent property of the expressed GFP. Both the WT GFP and the SDM II GFP plasmids in E. coli BL21 cells showed similar expression levels and similar GFP fluorescent activity at 37 degrees C. This result substantiates our hypothesis that OmpT protease could be a possible factor responsible for reducing the expression of GFP at 37 degrees C for WT GFP clone in K12 hosts like DH5alpha, JM109, LE 392 since the levels of GFP expression of SDM II clone in such cells at 37 degrees C is higher than that seen with WT GFP clone at the same temperature.

Construction of a novel zero background prokaryotic expression vector: potential advantages

A novel DNA sequence, derived from the antisense strand of the DNA gyrase inhibitor protein, CcdB, was toxic to E. coli. This protein (approximately 6 kDa) decreased the growth rate of E. coli K12 by three orders of magnitude upon induction. The expressed toxic protein in E. coli K12 was soluble while it was insoluble in induced E. coli BL21. A high efficiency prokaryotic cloning/expression vector was constructed using this toxic gene sequence and gave zero background with approximately 100% cloning efficiency requiring no dephosphorylation. The toxic gene product also affected the survival of a ccdB resistant cell line, thus indicating a different mechanism of toxicity, other than DNA gyrase inhibition, as compared to the ccdB toxicity.