High-level Expression of Tetanus Toxin Fragment C in Escherichia coli

Fragment C is the C-terminal domain of the heavy chain of tetanus toxin that can promote the immune response against the lethal dose of this toxin. Therefore, this portion can be considered as a candidate vaccine against tetanus infection, which occurs by Clostridium tetani. The present study aimed to compare the expression of tetanus toxin fragment C in Escherichia coli BL21 (DE3) pLysS cells having a high tolerance to toxins between two different expression vectors, namely pET22b and pET28a, using the sodium dodecyl sulfate polyacrylamide gel electrophoresis and western blot analyses. After DNA extraction from Harvard CN49205 strain of C. tetani, the gene of interest was amplified using polymerase chain reaction, and then sequenced and cloned into the expression vectors of pET22b and pET28a, transformed into competent BL21 (DE3) pLysS cells, and finally expressed using an optimized protocol. The cells were induced with isopropyl β-D-1-thiogalactopyranoside (IPTG) at four different incubation temperatures (i.e., 37, 33, 30, and 25 °C) and three different incubation times (i.e., 1, 2, and 3 h). Although the SDS-PAGE and western blot analyses confirmed the expression of the recombinant fragment C (r-fragment C) ligated into both of the expression vectors, pET28a showed a higher r-fragment C expression level than the other vector (38.66 mg/L versus 32.33 mg/L, P<0.05). An optimal expression condition was acquired 3 h after 1 mM IPTG induction at 25 °C. The results demonstrated that E. coli BL21 (DE3) pLysS as an expression host in combination with pET-28a as an expression vector was a more compatible expression system to express the fragment C of tetanus toxin, compared to E. coli BL21 (DE3) pLysS/pET-22b expression system. Overall, these results may represent an opportunity to improve the expression system for the production of tetanus toxin vaccine using recombinant protein strategy.

Rapid assessment of tetanus vaccine-induced immunity in Bangladesh and the Gambia

We have developed recombinant fragment C based rapid point of care dipstick devices to assess tetanus immunization status using plasma or whole blood. The devices demonstrated specificity of 0.90 and sensitivity of 0.90 (whole blood)/0.94 (plasma) at field sites in Bangladesh and The Gambia when compared to a commercial ELISA with the immune cut-off titer set as ≥0.1IU/mL.

Utility of recombinant fragment C for assessment of anti-tetanus antibodies in plasma

Anti-tetanus antibodies in biological samples are typically detected using an enzyme-linked immunosorbent assay based on toxoided tetanus neurotoxin as antigen. We demonstrate that recombinantly produced fragment C of the toxin heavy chain is an effective alternative antigen for assessment of tetanus-immune status in plasma samples.

Production and characterization of recombinant light chain and carboxyterminal heavy chain fragments of tetanus toxin

BACKGROUND

Light chain (LC) and heavy chain carboxyterminal subdomain (HCC) fragments are the most important parts of tetanus neurotoxin (TeNT) which play key roles in toxicity and binding of TeNT, respectively. In the present study, these two fragments were cloned and expressed in a prokaryotic system and their identity was confirmed using anti-TeNT specific polyclonal and monoclonal antibodies.

METHODS

LC and HCC gene segments were amplified from Clostridium tetani genomic DNA by PCR, cloned into pET28b(+) cloning vector and transformed in Escherichia coli (E. coli) BL21(DE3) expression host. Recombinant proteins were then purified through His-tag using Nickel-based chromatography and characterized by SDS-PAGE, Western blotting and ELISA techniques.

RESULTS

Recombinant light chain and HCC fragments were successfully cloned and expressed in (E. coli) BL21 (DE3). Optimization of the induction protocol resulted in production of high levels of HCC (~35% of total bacterial protein) and to lesser extends of LC (~5%). Reactivity of the His-tag purified proteins with specific polyclonal and monoclonal antibodies confirmed their renatured structure and identity.

CONCLUSION

Our results indicate successful cloning and production of recombinant LC and HCC fragments of TeNT. These two recombinant proteins are potentially useful tools for screening and monitoring of anti-TeNT antibody response and vaccine production.