Protein disulfide isomerase that catalyzes the formation, isomerization, and reduction or oxidation of disulfide bonds in client proteins and functions as a protein folding chaperone (PubMed:11825568, PubMed:16193070, PubMed:27897272, PubMed:36104323, PubMed:7487104). Core component of the major histocompatibility complex class I (MHC I) peptide loading complex where it functions as an essential folding chaperone for TAPBP. Through TAPBP, assists the dynamic assembly of the MHC I complex with high affinity antigens in the endoplasmic reticulum.

Therefore, plays a crucial role in the presentation of antigens to cytotoxic T cells in adaptive immunity (PubMed:35948544, PubMed:36104323)

Part of the major histocompatibility complex class I (MHC I) peptide loading complex composed of TAP1, TAP2, B2M, MHC heavy chain, TAPBP, PDIA3, and CALR (PubMed:19119025, PubMed:35948544, PubMed:36104323). Interacts with ERP27 and CANX (PubMed:16905107, PubMed:16940051). Interacts with SERPINA2 and with the S and Z variants of SERPINA1 (PubMed:23826168).

Interacts with ATP2A2 (By similarity)

Detected in the flagellum and head region of spermatozoa (at protein level) (PubMed:20400973). Expressed in liver, stomach and colon (at protein level). Expressed in gastric parietal cells and chief cells (at protein level) (PubMed:24188822)