Identification of TAP2 protein variants resistant to inhibition by the HSV1 ICP47 protein

Herpes Simplex Virus 1 evades the host immune system by expressing a protein, ICP47, that binds to and inhibits the heterodimeric Transporter Associated with Antigen Processing (TAP). We screened a library of 1786 variants in TAP2, one of the components of the TAP heterodimer, and identified 39 variants that were resistant to inhibition by ICP47. Of these 39 variants, five were individually tested, and three (T257I, S274H, and T244R) were confirmed to be significantly resistant to inhibition by ICP47. This resistance to inhibition did not extend to the Epstein Barr Virus BNLF2a protein, another viral factor known to inhibit antigen presentation by targeting TAP. These three residues localize close to the binding site of ICP47, on the 3D structure of TAP, but only Ser274 is spatially close to the antigenic peptide binding site of TAP. These results functionally resolve the TAP2 residues required for peptide binding from those required for ICP47 binding and identify TAP2 residues whose targeting with small molecule inhibitors could effectively prevent Herpes virus downregulation of antigen processing.