Involved in the association of MHC class I with transporter associated with antigen processing (TAP) and in the assembly of MHC class I with peptide (peptide loading). Heterodimer with PDIA3; disulfide-linked. Obligatory mediator for the interaction between newly assembled MHC class I molecules, calreticulin, PDIA3 and TAP. Up to 4 MHC class I/tapasin complexes bind to 1 TAP (PubMed:19119025, PubMed:21263072, PubMed:26611325). Interacts with HLA-G-B2M complex; this interaction is required for loading of high affinity peptides. Neutrophils, mostly in fully differentiated cells. The N-terminus is required for efficient association with MHC class I molecule and for a stable interaction between MHC I and calreticulin. Binding to TAP is mediated by the C-terminal region. The 2 alleles of TAPBP; TAPBP*01 (Tapasin*01) (shown here) and TAPBP*02 (Tapasin*02); are in linkage disequilibria with the HLA-DRB1 locus in a Japanese population. The disease is caused by variants affecting the gene represented in this entry. Due to a partial intron retention. Probable cloning artifact. TAPBP mutation db