The antigenic peptide transporter (TAP) plays a crucial role in the antigen presentation pathway by transporting antigenic peptides into the endoplasmic reticulum for loading onto MHC class I molecules. Certain alphaherpesviruses encode immunomodulatory proteins that inhibit TAP function, allowing viral evasion from host immune responses. Despite their significance, the structural basis of these TAP inhibitors remains poorly understood.

In our project, we analyze key structural elements of TAP inhibitors encoded by cowpox herpesvirus (CPXV), an infectious zoonotic virus belonging to the Poxviridae family. For experimental reasons, the sequence of the CPXV virus was divided into three peptides, each comprising various fragments of the whole virus. These peptides were analyzed with multidimensional NMR spectroscopy in DPC micelles, which were used as a model of the cell membrane. Based on the acquired NMR data, it was possible to reconstruct the 3D structure of CPVX in the cell membrane using Molecular Dynamics (MD) simulations. Based on available structural data, the CPXV freezes TAP in a specific, non-functional state. In particular, the bound CPVX stabilizes the antigen in its outward-facing conformation, which prevents TAP from rotating back to its inward-facing state to pick up peptides. As a result, the CPXV protein acts as a physical plug, completely obstructing the peptide channel.

Our results will provide insights into viral immune evasion strategies and be applicable for developing and designing novel antiviral treatments against CPXV infections.