PDIA3(Protein disulfide isomerase family A, member 3), also called GRP58, Erp57 or ER60, is an isomerase enzyme, mapped on 15q15.3. The PDIA3 protein has protein disulfide isomerase activity. PDIA3 is also part of the major histocompatibility complex (MHC) class I peptide-loading complex, which is essential for formation of the final antigen conformation and export from the endoplasmic reticulum to the cell surface. Koivunen et al. showed that PDIA3 could not substitute for the beta subunit of PDI. When coexpressed with alpha prolyl 4-hydroxylase, PDIA3 did not form prolyl 4-hydroxylase tetramers, nor did it have prolyl 4-hydroxylase activity. Hirano et al. expressed human PDIA3 and found that the protein had a thiol-dependent reductase activity. They showed that the expression level of PDIA3 is increased after oncogenic transformation of normal rat kidney cells and NIH 3T3 cells.