Reconstitution of active recombinant Shiga toxin (Stx)1 from recombinant Stx1-A and Stx1-B subunits independently produced by E. coli clones

Hetero-Pathogenic O181:H4 EAHEC Strain of Sequence Type ST678 Associated with Hemolytic-Uremic Syndrome in Schoolchildren in Russia

BACKGROUND

In the last decade, the importance of hetero-pathogenic enteroaggregative Shiga-toxin-producing E. coli for public health has increased. Recently, we described the genetic background of the EAHEC O181:H4 strain of ST678 carrying the stx2 gene in prophage and five plasmids, including the plasmid-carrying aggR and aaiC genes. Here, we present the morphological and enzymatic characteristics of this strain, as well as susceptibility to antimicrobials, biofilm formation, etc. Methods: Bacterial morphology was studied using an electron microscope. Susceptibility to antimicrobials was determined using the microdilution method. Cytotoxicity was estimated in Vero cells. Virulence was studied on mice.

RESULTS

The morphological and enzymatic properties of the hetero-pathogenic EAHEC strain were typical for E. coli; electron microscopy revealed the specific flagella. The strain was susceptible to most antibiotics and disinfectants but resistant to ampicillin and ciprofloxacin and showed a high degree of biofilm formation. Cytotoxicity towards Vero cells was estimated as 80%.

CONCLUSIONS

The emergence of a new O181:H4 EAHEC strain poses a potential threat to humans because of the virulence potential that must be taken into account in the epidemiological analysis of outbreaks and sporadic cases of foodborne infections associated with hemolytic-uremic syndrome.

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.

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

The entire stx1 region from Escherichia coli O157:H7, containing two open reading frames (stx1a and stx1b), was cloned into pET-32a with a single promoter. This region was transformed into E. coli TransB (DE3), which is a trxB and gor mutation strain. After expression in the E. coli periplasm in a completely soluble form, the rStx1 was purified and verified by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), ELISA, and Western blot analysis. Our rStx1 have Vero cell median cytotoxic dose (CD50 ) and median lethal dose (LD50 ) values of approximately 30 ng and 1.5 µg, respectively. The final yield of the purified rStx1 ranged from 2 to 3 mg/L by one-step nickel affinity gel column chromatography. This method is an easy approach to the large-scale preparation of Stx1 at a reasonable cost.

Improved production of holotoxin Stx2 with biological activities by using a single-promoter vector and an auto-induction expression system

The entire stx2 region from Escherichia coli O157:H7, containing two open reading frames (stx2a and stx2b), was cloned into pET-32a with a single promoter, and transformed into E. coli BL21 (DE3) pLysS. We used two methods of IPTG induction using LB medium and auto-induction using ZYM-5052 medium to express recombinant Shiga toxin 2 (rStx2). rStx2 was expressed in the E. coli periplasm in a completely soluble, biologically active form. The final yield of purified rStx2 from each liter of culture in LB medium and ZYM-5052 medium was approximately 2.3mg and 3.5mg, respectively. The highest amount of rStx2 accounted for 27.8% of total bacteria protein in ZYM-5052 medium. rStx2A and rStx2B isolated from rStx2 by electroelution were, respectively, identified by N-terminal protein sequencing. Signal peptides with the sequence MKCILFKWVLCLLLGFSSVSYS and MKKMFMAVLFALASVNAMA were identified at the N terminus of rStx2A and rStx2B, respectively. Our rStx2 possessed Vero cell CD(50) value about 500pg and LD(50) value approximately 6ng. rStx2 can be substitute for natural toxin Stx2, which can be used for animal models, drug screening, vaccine research, and so on.