Identification of a protein disulfide isomerase of Neospora caninum in excretory–secretory products and its IgA binding and enzymatic activities

A protein disulfide isomerase of Neospora caninum (NcPDI) with a molecular weight of 50 kDa was identified in tachyzoite lysate and excretory–secretory (ES) products. The IgA antibody in 58.0% of the individual cattle tear samples recognized the NcPDI, which suggests that the PDI-specific antibody may be involved in defense against parasites. In addition, PDI-specific inhibitors and NcPDI antiserum showed inhibitory effects on the growth of N. caninum tachyzoites. Furthermore, the purified recombinant NcPDI demonstrated biological activities in vitro by catalysis and refolding of reduced RNase A and assisted in the recovery of native lysozyme. These findings indicate that NcPDI possesses PDI-specific enzymatic activity and could be a putative target for chemotherapy for neosporosis.