Molecular cloning and expression pattern analysis of two novel disulfide isomerases in shrimp

Protein disulfide isomerase (PDI) catalyzes formation and isomerization of disulfide bridges and has chaperone activity. Currently, increasing evidence suggests the significance of PDI in immune and stress responses. To clarify the role of PDIs in the innate immunity of shrimp, two PDI genes were isolated and identified from Fenneropenaeus chinensis (fleshy prawn). FcPDI1 is 1878bp in length and encodes a protein of 383 amino acids. It has 18-amino acid signal peptide, 3 thioredoxin domains with 3 active sites of CGHC, and KEDL retention signal at its C-end. FcPDI1 is an atypical PDI. The open reading frame of FcPDI2 encodes a 497-amino acid protein and shows the classical domain organization a-b-b'-a'. Phylogenic analysis and multiple alignments show that FcPDI1 is similar to PDI that contains 3 thioredoxin domains from other species including invertebrates and vertebrates. FcPDI2, LvPDI, and insect PDIs are grouped into one cluster and are similar to PDIs having a-b-b'-a' domain organization. Tissue distribution shows that FcPDI1 and FcPDI2 were expressed in all detected tissues at the mRNA level. Changes in FcPDI1 and FcPDI2 expression at the mRNA level in hemocytes, hepatopancreas, gills, and ovaries upon Vibrio or white spot syndrome virus challenge were also analyzed. The results suggest that FcPDI1 and FcPDI2 might have roles in the innate immunity of shrimp. FcPDI1 was also successfully expressed in Escherichia coli and the recombinant FcPDI1 showed insulin reductase activity. Results show that FcPDI might play an important role in the innate immunity of shrimp.