Mediates thiol-dependent retention in the early secretory pathway, forming mixed disulfides with substrate proteins through its conserved CRFS motif (PubMed:11847130, PubMed:14517240). Inhibits the calcium channel activity of ITPR1 (PubMed:15652484). May have a role in the control of oxidative protein folding in the endoplasmic reticulum (PubMed:11847130, PubMed:14517240, PubMed:29858230). Required to retain ERO1A and ERO1B in the endoplasmic reticulum (PubMed:11847130, PubMed:29858230).
