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From the * Center for Cancer Research, Department of Biology, Massachusetts Institute of Technology,
Cambridge, Massachusetts 02139; The herpes simplex virus (HSV) immediate early protein ICP47 inhibits the transporter associated with antigen processing (TAP)-dependent peptide translocation. As a consequence, empty
major histocompatibility complex (MHC) class I molecules are retained in the endoplasmic reticulum and recognition of HSV-infected cells by cytotoxic T lymphocytes is abolished. We
chemically synthesized full-length ICP47 (sICP47) and show that sICP47 inhibits TAP-dependent peptide translocation in human cells. Its biological activity is indistinguishable from that of
recombinant 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 conserved between ICP47 from HSV-1 and HSV-2. Through alanine scanning substitution we identified three segments within this region that are critical for
the ability to inhibit TAP function. The interaction of ICP47 with TAP is unlikely to mimic
precisely that of the transported peptides, as deduced from differential labeling of the TAP1 and
TAP2 subunits using sICP47 fragments with chemical cross-linkers.
Medical Research Council Virology Unit, Institute of Virology,
Glasgow G11 5JR, United Kingdom; and the § Institute of Biochemistry, Swiss Federal Institute of
Technology Zürich (ETHZ), CH-8092, Zürich, Switzerland
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