Selective and ATP-dependent translocation of peptides by the MHC-encoded transporter.

Major histocompatibility complex (MHC) class I molecules present peptides derived from nuclear and cytosolic proteins to CD8+ T cells. These peptides are translocated into the lumen of the endoplasmic reticulum (ER) to associate with class I molecules. Two MHC-encoded putative transporter proteins, TAP1 and TAP2, are required for efficient assembly of class I molecules and presentation of endogenous peptides. Expression of TAP1 and TAP2 in a mutant cell line resulted in the delivery of an 11-amino acid oligomer model peptide to the ER. Peptide translocation depended on the sequence of the peptide, was adenosine triphosphate (ATP)-dependent, required ATP hydrolysis, and was inhibited in a concentration-dependent manner.