THE ACTIVE DOMAIN OF THE HERPES-SIMPLEX VIRUS PROTEIN ICP47 - A POTENT INHIBITOR OF THE TRANSPORTER ASSOCIATED WITH ANTIGEN-PROCESSING (TAP)

The herpes simplex virus type 1 (HSV-1) protein ICP47 binds specifical ly to the transporter associated with antigen processing (TAP), thereb y blocking peptide-binding and translocation by TAP and subsequent loa ding of peptides onto MHC class I molecules in the endoplasmic reticul um. in consequence, HSV-infected cells are masked for immune recogniti on by cytotoxic T-lymphocytes. To investigate the molecular details of this, so far, unique transporter-inhibitor interaction, the active do main and critical amino acid residues were identified by using short o verlapping fragments and systematic deletions of the viral inhibitor. A fragment of 32 amino acid residues, ICP47(3-34), was found to be the minimal region harboring an activity to inhibit peptide-binding to TA P comparable to the action of the full-length protein and therefore re presenting the active domain. Further N or C-terminal truncations caus e an abrupt loss in activity. Within the identified active domain, var ious mutants and chimeras of ICP47 derived from HSV-1 and HSV-2 helped to identify amino acid residues critical for TAP inhibition. On the b asis of these results, therapeutic drugs could be designed that are ap plicable in treatment of allograft rejection or in novel vaccination s trategies against HSV, restoring the ability of the immune system to r ecognize HSV-infected cells. (C) 1997 Academic Press Limited.