A POINT MUTATION IN HLA-A-ASTERISK-0201 RESULTS IN FAILURE TO BIND THE TAP COMPLEX AND TO PRESENT VIRUS-DERIVED PEPTIDES TO CTL

Mutating the HLA-A0201 heavy chain from threonine to lysine at positi on 134 (T134K) results in a molecule that presents exogenous peptide, but cannot present endogenously derived antigen. This is reflected in diminished cell surface expression and altered intracellular trafficki ng of T134K. The failure of T134K to present endogenous antigen can be overcome by using an ER targeting sequence, suggesting that the antig en presentation defect is restricted to TAP-dependent peptide loading. The ability of T134K to load peptide in a TAP-dependent manner is dra matically reduced compared with HLA-A0201. By coimmunoprecipitation t here is no detectable association of the T134K molecule with the TAP c omplex. Thus, T134K selectively affects TAP association and peptide lo ading, suggesting a requirement for the direct interaction of MHC clas s I heavy chain and the TAP complex for efficient presentation of endo genous antigen.