Endoplasmic reticulum resident protein 44 (TXNDC4) is is a 406 amino acid protein that contains one thioredoxin domain. TXNDC4 mediates thiol-dependent retention in the early secretory pathway and forms mixed disulfides with substrate proteins through its conserved CRFS motif.It can inhibit the calcium channel activity of ITPR1.It may have a role in the control of oxidative protein folding in the endoplasmic reticulum.