PDIA4, also known as ERP72, is an endoplasmic reticulum luminal protein that is both a stress protein and a member of the protein disulfide isomerase family of proteins. It is involved in the catalysis of protein- S-S-bond rearrangement. PDIA3 and PDIA4 act as proteases, protein disulfide isomerases, phospholipases or a combination of these.