Herpes viral proteins blocking the transporter associated with antigen processing TAP--from genes to function and structure.

In adaptation to the immune system, viruses have developed manifold mechanisms to evade the immune response, causing lifelong persistence in the host. Several members of the herpesvirus family are known to interfere with antigen presentation via MHC class I molecules. Here we compare the mechanistic and structural aspects of two unrelated herpesviral proteins, both of which have selected the transporter associated with antigen processing (TAP) as target for immune evasion. However, ICP47 (IE12) encoded by the herpes simplex virus and US6 from human cytomegalovirus utilize entirely different strategies to block TAP function. Detailed knowledge of the function and structure of these viral factors will help to understand TAP function and to design novel immune suppressors or vectors for gene transfer.