Expression and single-step purification of GRA8 antigen of toxoplasma gondii in Escherichia coli

ABSTRACT

Diagnosis of Toxoplasma gondii [T.gondii] infection is of great medical importance especially for pregnant women and immunosuppressed patients. Numerous studies have shown that the recombinant production of several tToxoplasma antigens, including dense granule antigens [GRAs] has a great potential as diagnostic reagents. Previous studies reported expression of amino terminal GRA8 protein in fusion with large tags. In the present study, we produced truncated GRA8 [GRA8], excluded from the signal peptide and C-terminal transmembrane domain, with a short fusion tag in Escherichia coli. [E.coli]. GRA8 was purified using an optimized single-step Iimmobilized Mmetal ion Aaffinity Cchromatography [IMAC]. The purity and yield of GRA8 was highest at pH= 9.25. At this pH, 13.6 mg of GRA8 was obtained with the purity of 97.97%. Immunogenicity of the protein was evaluated in Western blot analysis showing the serum sample from a rabbit immunized with GRA8 recognized a single antigen of T. gondii tachyzoite at the expected molecular weight of native GRA8. To diagnosis acute tToxoplasma infection in pregnant women, an indirect immunoglobulin M [IgM] enzyme-linked immunosorbent assay [ELISA] was developed using GRA8 resulting in a test specificity and sensitivity of 97.1% and 60.6%, respectively. These results demonstrated that immunogenic GRA8 can be produced in fusion with a short tag and purified near to homogeneity using an optimized IMAC. GRA8-IgM-ELISA was useful for detection of acute toxoplasma infection