Identification of sequences in the human peptide transporter subunit TAP1 required for transporter associated with antigen processing (TAP) function

The heterodimeric peptide transporter associated with antigen processing (T AP) consisting of the subunits TAP1 and TAP2 mediates the transport of cyto solic peptides into the lumen of the endoplasmic reticulum (ER), in order t o accurately define domains required for peptide transporter function, a mo lecular approach based on the construction of a panel of human TAP1 mutants and their expression in TAP1(-/-) cells was employed, The characteristics and biological activity of the various TAP1 mutants were determined, and co mpared to that of wild-type TAP1 and TAP1(-/-) control cells, All mutant TA P1 proteins were localized in the ER and were capable of forming complexes with the TAPP subunit, However, the TAP1 mutants analyzed transported pepti des with different efficiencies and displayed a heterogeneous MHC class I s urface expression pattern which was directly associated with their suscepti bility to cytotoxic T lymphocyte-mediated lysis, Based on this study, the T AP1 mutants can be divided into three categories: those expressing a simila r phenotype compared to TAP1(-/-) or wild-type TAP1 cells respectively, and those representing an intermediate phenotype in terms of peptide transport rate, MHC class I surface expression and immune recognition. Thus, the res ults provide evidence that specific regions in the TAP1 subunit are crucial for the proper processing and presentation of cytosolic antigens to MHC cl ass I-restricted T cells, whereas others may play a minor role in this proc ess.