CHARACTERISTICS OF ATP-DEPENDENT PEPTIDE-TRANSPORT IN ISOLATED MICROSOMES

This report examines the transport properties and specificity of ATP-d ependent peptide transport by the murine transporter for Ag presentati on (TAP) complex in isolated microsome preparations from H-2(d) haplot ype mice. The murine TAP complex has a K-m of 661 nM and a maximum vel ocity of 2.9 fmol/min .mu g microsome protein for a modified peptide c orresponding to a defined MHC class I binding epitope from influenza n ucleoprotein recognized by CD8(+) CTL in association with the K-d mole cule. This high K-m value for peptide transport suggests that the rate and efficiency of peptide transport of the TAP complex are influenced by the concentration of processed peptides derived from self and fore ign proteins in the cell cytoplasm. Furthermore, these findings imply that competition among peptides for TAP-dependent transport is unlikel y to be an important factor in determining the immunodominance of cert ain peptide epitopes within a foreign protein recognized by CD8(+) T l ymphocytes. We also examined the specificity of TAP transport for pept ides containing bona fide murine MHC class I binding epitopes and prov ide evidence that certain flanking residues can affect the efficiency of peptide epitope transport by the TAP complex.