The N-terminal Proline Hinge Motif Controls the Structure of Bovine Herpesvirus 1-encoded Inhibitor of the Transporter Associated with Antigen Processing Required for its Immunomodulatory Function

Due to unique features, proline residues may control protein structure and function. Here, we investigated the role of 52PPQ54 residues, indicated by the recently established experimental 3D structure of bovine herpesvirus 1-encoded UL49.5 protein as forming a characteristic proline hinge motif in its N-terminal domain. UL49.5 acts as a potent inhibitor of the transporter associated with antigen processing (TAP), which alters the antiviral immune response. Mechanisms employed by UL49.5 to affect TAP remain unde-termined on a molecular level. We found that mutations in the 52PPQ54 region had a vast impact on its immunomodulatory function, increasing cell surface MHC class I expression, TAP levels, and peptide transport efficiency. This inhibitory effect was specific for UL49.5 activity towards TAP but not towards the viral glycoprotein M. To get an insight into the impact of proline hinge modifications on structure and dynamics, we performed all-atom and coarse-grained molecular dynamics studies on the native pro-tein and PPQ mutants. The results demonstrated that the proline hinge sequence with its highly rigid con-formation served as an anchor into the membrane. This anchor was responsible for the structural and dynamical behavior of the whole protein, constraining the mobility of the C-terminus, increasing the mobil-ity of the transmembrane region, and controlling the accessibility of the C-terminal residues to the cyto-plasmic environment. Those features appear crucial for TAP binding and inhibition. Our findings significantly advance the structural understanding of the UL49.5 protein and its functional regions and support the importance of proline motifs for the protein structure.(c) 2023 The Author(s). Published by Elsevier Ltd. This is an open access article under the CC BY license (http://creativecom-mons.org/licenses/by/4.0/).

Automated summary

Proline residues, in particular the 52PPQ54 residues, play a crucial role in controlling the structure and function of proteins, especially in the N-terminal domain of the UL49.5 protein encoded by bovine herpesvirus 1. The proline hinge motif serves as an anchor into the membrane and is responsible for the structural and dynamic behavior of the protein, affecting its interaction with TAP and inhibition of its activity.