Elongation factor-1 (EF-1) plays a primary role in protein synthesis, e.g., in the regulation of cell growth, aging, motility, embryogenesis, and signal transduction. The authors identified a clone CsIH23 by immunoscreening a Clonorchis sinensis cDNA library. The cDNA of CsIH23 was found to have a putative open reading frame containing 461 amino acids with a predicted molecular mass of 50.5 kDa. Its polypeptide sequence was highly homologous with EF-1alpha of parasites and vertebrate animals. CsIH23 polypeptide contained three GTP/GDP-binding sites, one ribosome-binding domain, one actin-binding domain, one tRNA-binding domain, and two glyceryl-phosphoryl-ethanolamine attachment sites. Based on these primary and secondary structural similarities, it was concluded that CsIH23 cDNA encodes C. sinensis EF-1alpha (CsEF-1alpha). In a molecular phylogenic tree, CsEF-1alpha clustered with the EF-1alpha of helminthic parasites. Subsequently, CsEF-1alpha recombinant protein was bacterially overexpressed and purified by Ni-NTA affinity column chromatography. Immunoblotting using CsEF-1alpha recombinant protein produced positive signals for all serum samples tested from clonorchiasis, opisthorchiasis viverinii, and paragonimiasis westermani patients and normal healthy controls. These findings suggest that recombinant CsEF-1alpha is of limited usefulness as serodiagnostic antigen for clonorchiasis.

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