Figure 1.

Molecular environment of tapasin (Tsn) within the peptide-loading complex (PLC). Structural organization of the PLC. The individual components of the PLC are shown according to their domain organization. Tsn, covalently linked to the oxidoreductase ERp57 through a disulfide bridge (yellow line), interacts via its transmembrane region with the heterodimeric ATP-binding cassette transporter TAP1/2, which shuttles antigenic peptides across the endoplasmic reticulum (ER) membrane in an ATP-dependent manner. The monoglucosylated (G) N-glycan of the MHC I is shown as white branched lines. This multivalent interaction network localizes recruited calreticulin-associated MHC I molecules directly at the peptide source, facilitating selection of high-affinity epitopes.