Molecular cloning, expression, and immunolocalization of protein disulfide isomerase in excretory-secretory products from Clonorchis sinensis

Protein disulfide isomerase (PDI) is an essential catalyst of the endoplasmic reticulum with folding and chaperone activities in different biological systems. Here, PDI of Clonorchis sinensis (CsPDI) was isolated from the cDNA library of adult C. sinensis. The open reading frame contains 1,317 bp encoding 438 amino acids and shares 53 %, 49 %, and 43 % identity with PDI from Bos taurus, Homo sapiens, and Schistosoma mansoni, respectively. Two catalytic thioredoxin motifs CxxC were found in this sequence, which were characteristic domains of thioredoxin superfamily. The CsPDI protein was expressed and purified from Escherichia coli BL21 (DE3). According to western blotting analysis, the recombinant CsPDI could be recognized by anti-CsPDI rat serum, anti-excretory/secretory products rat serum, and serum of rat infected with C. sinensis, respectively. Quantitative real-time polymerase chain reaction showed that transcription level of CsPDI in the metacercaria stage was six and four times higher than that in the adult worm and egg stage, respectively. Immunolocalization analysis showed CsPDI could be detected in the intestine, vitellarium, and intrauterine eggs of adult worm, as well as in the cyst wall and vitellarium of metacercaria. In addition, the strong fluorescence signal was observed both on the wall of bile duct and in the lumen of liver tissue of C. sinensis-infected cat. Those results demonstrated that CsPDI was a component of C. sinensis excretory-secretory products. The present study will enhance our understanding of biological functions of CsPDI and pave the way for further studies on host-parasite interaction during C. sinensis infection.