Molecular cloning and characterization of a novel serpin gene of Clonorchis sinensis, highly expressed in the stage of metacercaria.

The serpins are a superfamily of proteins (350-500 amino acids in size) that fold into a conserved structure. From about 3,475 unigenes of Clonorchis sinensis metacercaria, a novel gene-encoding serpin was identified and characterized. The opening reading frame is 1,149 bp encoding 382 amino acids. The deduced amino acid sequence shows high identity to previously reported serpins from C. sinensis and other helminthic parasites. A typical serpin signature was found by motif search. The recombinant C. sinensis serpin protein (rCsproSERPIN) was produced and purified. Semiquantitative analysis revealed that the transcripts of this serpin gene in metacercaria were much higher than that in adult worms and that the corresponding band of serpin protein in the crude soluble antigen of metacercaria probed by rat anti-CsproSERPIN serum was also much clearer compared with that of adult, suggesting that it plays an important role in the stage of C. sinensis metacercaria. Although we are not much clear about the detailed function of this serpin protein, the study that proteinase initiates metacercaria excystment gives a clue that it may participate in the encystment of cercaria.