A simple method for expression and purification of Shiga toxin 1 (Stx1) with biological activities by using a single-promoter vector and native signal peptide

Synthesis of biologically active Shiga toxins in cell-free systems

Shiga toxins (Stx) produced by pathogenic bacteria can cause mild to severe diseases in humans. Thus, the analysis of such toxins is of utmost importance. As an AB5 toxin, Stx consist of a catalytic A-subunit acting as a ribosome-inactivating protein (RIP) and a B-pentamer binding domain. In this study we synthesized the subunits and holotoxins from Stx and Stx2a using different cell-free systems, namely an E. coli- and CHO-based cell-free protein synthesis (CFPS) system. The functional activity of the protein toxins was analyzed in two ways. First, activity of the A-subunits was assessed using an in vitro protein inhibition assay. StxA produced in an E. coli cell-free system showed significant RIP activity at concentrations of 0.02 nM, whereas toxins synthesized in a CHO cell-free system revealed significant activity at concentrations of 0.2 nM. Cell-free synthesized StxA2a was compared to StxA2a expressed in E. coli cells. Cell-based StxA2a had to be added at concentrations of 20 to 200 nM to yield a significant RIP activity. Furthermore, holotoxin analysis on cultured HeLa cells using an O-propargyl-puromycin assay showed significant protein translation reduction at concentrations of 10 nM and 5 nM for cell-free synthesized toxins derived from E. coli and CHO systems, respectively. Overall, these results show that Stx can be synthesized using different cell-free systems while remaining functionally active. In addition, we were able to use CFPS to assess the activity of different Stx variants which can further be used for RIPs in general.

Preparation of chitosan nanoparticle containing recombinant CD44v antigen and evaluation of its immunization capacity against breast cancer in BALB/c mice

OBJECTIVE(S)

Breast tumors show heterogeneity containing cancer stem cells as a small subpopulation of a tumor mass. CD44 as a cancer stem cells antigen is abnormally expressed by carcinomas of epithelial origin. Also, overexpression of CD44 variable isoforms (CD44v) is associated with malignancy in breast cancer. In the present research, our objective was to evaluate the immunogenicity of prepared nanoparticles containing a novel recombinant CD44v (rCD44v) protein in the mouse model.

MATERIALS AND METHODS

CD44 gene was expressed in E. coli BL21 DE3 using the pET28a-CD44 vector. The expressed rCD44v protein was purified, encapsulated into the chitosan nanoparticles, and administered to BALB/c mice. ELISA was used to evaluate the immunoglobulin levels of immunized animals. For challenge experiment, 2 × 10⁶ 4T1-CD44 tumor cells were injected subcutaneously in mice, and tumor size, necrosis, and metastases were measured. Finally, cell proliferation assay, cytokines assay, and neutralization assay of the mouse anti-rCD44v on the human breast cancer cell line were examined.

RESULTS

The measured size of chitosan-rCD44v nanoparticles was 146.5 nm. Recombinant CD44v encapsulated by chitosan nanoparticles increases immunological responses via the adjuvant nature of chitosan nanoparticles. In the immunized mice, IgG and IgA titers were significantly increased. Tumor growth in injection and nano-injection test groups compared with the mice control groups displayed a significant reduction (P < 0.05). A high amount of splenocytes secreting IFNγ and IL-17 was seen in immunized mice with rCD44v (P < 0.05). Furthermore, a smaller size of lung metastases compared to the control mice groups was detected.

CONCLUSION

The encapsulated rCD44v within the chitosan nanoparticles induced a significant immune response in mice and can establish significant protection against breast cancer. Therefore, it can be considered a vaccine candidate for breast cancer therapeutic modalities.

Inconsistent PCR detection of Shiga toxin-producing Escherichia coli: Insights from whole genome sequence analyses

Shiga toxin-producing Escherichia coli (STEC) have been linked to food-borne disease outbreaks. As PCR is routinely used to screen foods for STEC, it is important that factors leading to inconsistent detection of STEC by PCR are understood. This study used whole genome sequencing (WGS) to investigate causes of inconsistent PCR detection of stx1, stx2, and serogroup-specific genes. Fifty strains isolated from Alberta feedlot cattle from three different studies were selected with inconsistent or consistent detection of stx and serogroup by PCR. All isolates were initially classified as STEC by PCR. Sequencing was performed using Illumina MiSeq® with sample library by Nextera XT. Virtual PCRs were performed using Geneious and bacteriophage content was determined using PHASTER. Sequencing coverage ranged from 47 to 102x, averaging 74x, with sequences deposited in the NCBI database. Eleven strains were confirmed by WGS as STEC having complete stxA and stxB subunits. However, truncated stx fragments occurred in twenty-two other isolates, some having multiple stx fragments in the genome. Isolates with complete stx by WGS had consistent stx1 and stx2 detection by PCR, although one also having a stx2 fragment had inconsistent stx2 PCR. For all STEC and 18/39 non-STEC, serogroups determined by PCR agreed with those determined by WGS. An additional three WGS serotypes were inconclusive and two isolates were Citrobacter spp. Results demonstrate that stx fragments associated with stx-carrying bacteriophages in the E. coli genome may contribute to inconsistent detection of stx1 and stx2 by PCR. Fourteen isolates had integrated stx bacteriophage but lacked complete or fragmentary stx possibly due to partial bacteriophage excision after sub-cultivation or other unclear mechanisms. The majority of STEC isolates (7/11) did not have identifiable bacteriophage DNA in the contig(s) where stx was located, likely increasing the stability of stx in the bacterial genome and its detection by PCR.

Strategies for Optimizing the Production of Proteins and Peptides with Multiple Disulfide Bonds

Bacteria can produce recombinant proteins quickly and cost effectively. However, their physiological properties limit their use for the production of proteins in their native form, especially polypeptides that are subjected to major post-translational modifications. Proteins that rely on disulfide bridges for their stability are difficult to produce in Escherichia coli. The bacterium offers the least costly, simplest, and fastest method for protein production. However, it is difficult to produce proteins with a very large size. Saccharomyces cerevisiae and Pichia pastoris are the most commonly used yeast species for protein production. At a low expense, yeasts can offer high protein yields, generate proteins with a molecular weight greater than 50 kDa, extract signal sequences, and glycosylate proteins. Both eukaryotic and prokaryotic species maintain reducing conditions in the cytoplasm. Hence, the formation of disulfide bonds is inhibited. These bonds are formed in eukaryotic cells during the export cycle, under the oxidizing conditions of the endoplasmic reticulum. Bacteria do not have an advanced subcellular space, but in the oxidizing periplasm, they exhibit both export systems and enzymatic activities directed at the formation and quality of disulfide bonds. Here, we discuss current techniques used to target eukaryotic and prokaryotic species for the generation of correctly folded proteins with disulfide bonds.

A quantitative single-cell assay for retrograde membrane traffic enables rapid detection of defects in cellular organization

Retrograde membrane trafficking from plasma membrane to Golgi and endoplasmic reticulum typifies one of the key sorting steps emerging from the early endosome that affects cell surface and intracellular protein dynamics underlying cell function. While some cell surface proteins and lipids are known to sort retrograde, there are few effective methods to quantitatively measure the extent or kinetics of these events. Here we took advantage of the well-known retrograde trafficking of cholera toxin and newly defined split fluorescent protein technology to develop a quantitative, sensitive, and effectively real-time single-cell flow cytometry assay for retrograde membrane transport. The approach can be applied in high throughput to elucidate the underlying biology of membrane traffic and how endosomes adapt to the physiologic needs of different cell types and cell states.

Oral immunization of mice with Lactococcus lactis expressing Shiga toxin truncate confers enhanced protection against Shiga toxins of Escherichia coli O157:H7 and Shigella dysenteriae

Regardless of the communal impact of Shiga toxins, till today neither a specific treatment nor licensed vaccine is available. Lactococcus lactis (L. lactis), generally regarded as safe organism, is well known to provide a valuable approach regarding the oral delivery of vaccines. This study was undertaken to evaluate the protective efficacy of Stx2a1 expressed in nisin-inducible L. lactis, against Shiga toxins (Stx1, Stx2) in mouse model. Oral immunization of BALB/c mice with LL-Stx2a1 elicited significant serum antibody titer with elevated fecal and serum IgA, along with minimized intestinal and kidney damage resulting in survival of immunized animals at 84% and 100% when challenged with 10 × LD₅₀ of Escherichia coli O157 and Shigella dysenteriae toxins, respectively. HeLa cells incubated with immune sera and toxin mixture revealed high neutralizing capacity with 90% cell survivability against both the toxins. Mice immunized passively with both toxins and antibody mixture survived the observation period of 15 days, and the controls administered with sham sera and toxins were succumbed to death within 3 days. Our results revealed protective efficacy and toxin neutralization ability of LL-Stx2a1, proposing it as an oral vaccine candidate against Shiga toxicity mediated by E. coli O157 and S. dysenteriae.

Preparation of a novel monoclonal antibody against caprine interleukin-17A and its applications in immunofluorescence and immunohistochemistry assays

BACKGROUND

Interleukin-17 (IL-17), the characteristic cytokine secreted by T helper 17 lymphocytes (Th17 cells), plays a pivotal role in host defense and many inflammatory or autoimmune diseases. The aim of this study was to obtain purified protein caprine IL-17A (cIL-17A) as an antigen for preparing an IL-17A-specific monoclonal antibody (mAb).

RESULTS

The coding sequence (CDS) region of cIL-17A was cloned from the peripheral blood mononuclear cells (PBMCs) of dairy goats and then inserted into the expression vector PET 32a and transformed into competent TransB (DE3) cells. Recombinant fusion protein obtained under optimized conditions was used to immunize BALB/c mice for preparing monoclonal antibodies. Finally, the supernatants of two hybridoma cell lines showing positive reaction with the recombinant fusion protein and negative reaction with fusion tags of PET 32a were collected for western blot, immunofluorescence (IF) and immunohistochemistry (IHC) analysis. Our results showed that the maximum amount of soluble protein could be obtained directly in the supernatant when the recombinant expression cells were induced by isopropyl-β-d-thiogalactoside (IPTG) at a concentration of 0.3 mmol/L at 16 °C for 42 h. Western blot analysis showed that the mAb H8 could recognize the eukaryotically expressed cIL-17A in the supernatant of transfected HEK293T cells. Immunofluorescence and immunohistochemistry assays showed that mAb H8 could strongly recognize both the eukaryotically expressed and natural cIL-17A.

CONCLUSIONS

The monoclonal antibody mAb H8 prepared in this study may be a potential tool for the detection of cIL-17A and beneficial for investigating the pathogenesis of various IL-17-associated diseases.

Biochemical Characterization of In vitro Reconstituted Biologically Active Recombinant Shiga Toxin

Background:

Shiga toxins comprise a family of related proteins produced by bacteria Shigella dysenteriae and some strains of Escherichia coli that cause severe clinical manifestations. Severe Shiga toxin intoxication results in Haemolytic-Uremic Syndrome (HUS), up to 50% of HUS patients manifest some degree of renal failure and ~10% of such cases develop permanent renal failure or death. </P><P> Objective: In present research work production of biologically active rStx from non-toxic rStxA and rStxB subunits were established that can be used in many biomedical applications.

Methods:

Purification of Shiga toxin from bacteria is a multistep time consuming process resulting in low yield. To overcome this problem, the rStxA and rStxB protein were separately cloned and expressed in E. coli host and purified through affinity chromatography. GST pull-down assay was performed for interaction study between rStxA and pentameric rStxB. The affinity between A and B subunits of reconstituted recombinant Shiga toxin (AB5) was determined by SPR. The biological activity of the toxin was confirmed in Vero cells and mouse lethality assay.

Results:

The yield of GST-StxA and His6X-StxB obtained after affinity chromatography was estimated to 2 and 5 mg/l, respectively. Samples analyzed in pull down assay revealed two bands of ~58 kDa (rStxA) and ~7.7 kDa (rStxB) on SDS-PAGE. Affinity was confirmed through SPR with KD of 0.85 pM. This rStx produced from 1:5 molar ratio found to be cytotoxic in Vero cell line and resulted lethality in mouse.

Conclusions:

Large scale production of rStx using the method can facilitate screening and evaluation of small molecule inhibitors for therapeutics development.

Intracellular drug delivery: Potential usefulness of engineered Shiga toxin subunit B for targeted cancer therapy

A treasure trove of intracellular cancer drug targets remains hidden behind cell membranes. However, engineered pathogen-derived toxins such as Shiga toxins can deliver small or macromolecular drugs to specific intracellular organelles. After binding to ganglioglobotriaosylceramide (Gb3, CD77), the non-toxic subunit B (StxB) of the Shiga-holotoxin is endocytosed and delivers its payload by a unique retrograde trafficking pathway via the endoplasmic reticulum to the cytosol. This review provides an overview of biomedical applications of StxB-based drug delivery systems in targeted cancer diagnosis and therapy. Biotechnological production of the Stx-material is discussed from the perspective of developing efficacious and safe therapeutics.