Molecular Cloning, Expression and Characterization of Plasmid Encoding Rhomboid 4 (ROM4) of Tachyzoite of Toxoplasma gondii RH Strain

The objective of this study was to clone, express and characterize the gene encoding rhomboid 4 (ROM4) proteins, a vital gene in surface adhesion and host cell invasion process of tachyzoite of T. gondii in an appropriate expression vector and eukaryotic cell for production of recombinant protein.
Toxoplasma RNA was isolated from tachyzoites (RH strain) and complementary DNA was synthesized. Oligonucleotide primer pair was designed based on Toxoplasma ROM4 gene sequence with XhoI and EcoRI restriction sites at 5´ end of forward and reverse primers, respectively. ROM4 gene was amplified by PCR, cloned into pTG19-T vector and the recombinant plasmid was sequenced. The gene was subcloned into pcDNA3 plasmid and expressed in CHO cells as eukaryotic cell. SDS-PAGE and western blotting were performed for protein determination and verification.
Cloning of ROM4 gene in pTG19-T vector was confirmed by colony-PCR and enzymatic digestion. The results of enzymatic digestion and gene sequencing confirmed successful cloning and subcloning procedures. The nucleotide sequence of the cloned ROM4 gene showed 99% homology compared to the corresponding sequences of original gene. SDS-PAGE and western blotting analyses of the purified protein revealed a single band having expected size of 65 kDa.
This eukaryotic expression system is an appropriate system for high-level recombinant protein production of ROM4 gene from T. gondii tachyzoites used as antigenic component for serological assay and vaccine development.