THE ACTIVE-SITE OF ICP47, A HERPES-SIMPLEX VIRUS-ENCODED INHIBITOR OFTHE MAJOR HISTOCOMPATIBILITY COMPLEX (MHC)-ENCODED PEPTIDE TRANSPORTER ASSOCIATED WITH ANTIGEN-PROCESSING (TAP), MAPS TO THE NH2-TERMINAL-35 RESIDUES

The herpes simplex virus (HSV) immediate early protein ICP47 inhibits the transporter associated with antigen processing (TAP)-dependent pep tide translocation. As a consequence, empty major histocompatibility c omplex (MHC) class I molecules are retained in the endoplasmic reticul um and recognition of HSV-infected cells by cytotoxic T lymphocytes is abolished. We chemically synthesized full-length ICP47 (sICP47) and s how that sICP47 inhibits TAP-dependent peptide translocation in human cells. Its biological activity is indistinguishable from that of recom binant ICP47 (rICP47). By using synthetic peptides, we mapped the core sequence of ICP47 minimally required for TAP inhibition to residues 2 -35. This segment is located within the region of the molecule conserv ed between ICP47 from HSV-1 and HSV-2. Through alanine scanning substi tution we identified three segments within this region that are critic al for the ability to inhibit TAP function. The interaction of ICP47 w ith TAP is unlikely to mimic precisely that of the transported peptide s, as deduced from differential labeling of the TAP1 and TAP2 subunits using sICP47 fragments with chemical cross-linkers.