TAPassociated

TAP-associated refers to proteins and complexes that physically or functionally associate with the Transporter associated with Antigen Processing (TAP) in the endoplasmic reticulum. The best-characterized TAP-associated network forms the peptide-loading complex (PLC), which includes Tapasin (the TAPBP gene product), ERp57 (encoded by PDIA3), and calreticulin. These components with TAP help ensure efficient delivery and proper loading of peptides onto major histocompatibility complex class I (MHC I) molecules, a crucial step for presenting endogenous peptides to CD8+ T cells.

In the antigen processing pathway, cytosolic protein degradation by the proteasome generates peptide fragments that are transported into the ER by TAP. The TAP-associated PLC then captures these peptides, promotes the binding of high-affinity peptides to nascent MHC I molecules, and stabilizes the complex until it is ready to travel to the cell surface. This quality control mechanism helps shape the repertoire of peptides displayed on MHC I and enhances immune surveillance against infected or malignant cells.

Genetically, components of the TAP system include TAP1, TAP2, and TAPBP (Tapasin). Defects in these genes can reduce surface MHC I expression and impair CD8+ T cell responses, contributing to immunodeficiency disorders such as Bare Lymphocyte Syndrome Type I. Beyond immunodeficiency, TAP-associated pathways are relevant to cancer immunology and infectious disease, where altered antigen presentation can influence immune recognition and evasion.