ABSENCE OF FUNCTIONAL RELEVANCE OF HUMAN TRANSPORTER ASSOCIATED WITH ANTIGEN-PROCESSING POLYMORPHISM FOR PEPTIDE SELECTION

The polymorphic TAP (TAP1 and TAP2) genes code for a heteromeric compl ex that translocates cytosolic peptides across the membrane of the end oplasmic reticulum where they associate with MHC class I molecules, In the rat, extensive TAP2 polymorphism modifies the spectrum of peptide s presented by MHC class I molecules on the cell surface, Although pol ymorphism of human TAP proteins is more limited, it has been proposed to be associated with susceptibility to autoimmune diseases, To analyz e the peptide selectivity and transport efficiency of human TAP allele s, we have generated the most frequent TAP1 and TAP2 alleles using sit e-directed mutagenesis. Alleles were cloned in the baculovirus express ion system and six TAP1/2 allelic combinations were overexpressed in S f9 insect cells, Microsomes containing TAP1/2 dimers were isolated, an d peptide binding assays were performed using random sequence peptide libraries of variable length (7-18 mer) and a 9-mer polyalanine peptid e substituted with various amino acids in positions 1, 2, 3, 7, and 9. All studied allelic combinations selected peptides with identical sub stitutions and length, Furthermore, transport assays showed similar ef ficiency and kinetics of peptide translocation by the different TAP al leles, These data suggest that the major human TAP alleles transport i dentical peptide sets and are therefore unlikely to contribute to pred isposition to autoimmune diseases.