Peptide Translocation by Variants of the Transporter Associated with Antigen Processing

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Major histocompatibility complex (MHC) class I molecules associate with peptides that are delivered from the cytosol to the lumen of the endoplasmic reticulum by the transporter associated with antigen processing (TAP).Liver microsomes of SHR and Lewis rats, which express different alleles of TAP (cimb and cima, respectively), accumulate different sets of peptides. Use of MHC congenic rats assigned this difference to the MHC, independent of the class I products expressed. Both the cima and cimb TAP complexes translocate peptides with a hydrophobic carboxyl terminus, but translocation of peptides with a carboxyl-terminal His, Lys, or Arg residue is unique to cima. Thus, the specificity of the TAP peptide translocator restricts the peptides available for antigen presentation.

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