TAP-binding protein (TAPBP)

TAP-binding protein, widely known as tapasin, is a 48-kDa transmembrane glycoprotein residing in the endoplasmic reticulum (ER) that serves as an essential chaperone for major histocompatibility complex (MHC) class I molecules. It acts as a central scaffold within the peptide-loading complex (PLC), physically bridging nascent MHC-I heterodimers with the transporter associated with antigen processing (TAP) to facilitate the acquisition of peptides from the cytosolic pool. Beyond its structural bridging role, tapasin functions as a peptide editor, catalyzing the exchange of suboptimal, low-affinity peptides for those with higher affinity, thereby ensuring the stability and immunogenicity of MHC-I complexes presented on the cell surface for CD8+ T cell surveillance. Downregulation or loss of tapasin expression is a common immune evasion strategy observed in several malignancies, including colorectal and lung cancers, and is frequently correlated with poor clinical prognosis. While no direct small-molecule inhibitors or agonists are currently FDA-approved, therapeutic approaches under investigation include utilizing interferon-gamma to restore tapasin levels and employing soluble tapasin-related proteins to enhance tumor antigen presentation.

Other names

TapasinTPSNTPNNGS17TAPATAP-associated proteinNGS-17TAP-associated glycoprotein

Functions as a peptide editor and molecular bridge within the peptide-loading complex to facilitate the selection and loading of high-affinity antigenic peptides onto major histocompatibility complex (MHC) class I molecules for immune presentation.