Herpesvirus Entry Mediator and Cytomegalovirus ORF UL144 bind a common region of B and T Lymphocyte Attenuator

Abstract

Herpesvirus entry mediator (HVEM) interacts with the TNF ligands LIGHT and Lymphotoxin, and with the immunoglobulin (Ig) domains of B and T lymphocyte attenuator (BTLA) and herpes simplex virus‐1 glycoprotein D (gD), demonstrating complex ligand interactions. The crystal structures of mouse BTLA and of human BTLA bound to human HVEM show that BTLA folds as an I‐set Ig domain, and that BTLA binds HVEM similar to gD. BTLA also binds the Cytomegalovirus (CMV) mimic of HVEM, ORF UL144, with lower affinity but causing greater T cell inhibition. We sought to determine how BTLA interacts with both HVEM and ORF UL144 and to clarify how BTLA may interact with multiple ligands to induce different activities. Here we show by single point mutation of human BTLA that key solvent exposed residues clustered at one face of the molecule are critical for binding both human HVEM and ORF UL144. In addition, a monoclonal antibody to human BTLA that blocks binding to human HVEM recognizes one of the residues in this region. Furthermore, we show that ORF UL144 from rhesus monkey CMV also binds human BTLA. The requirement of the same residues for BTLA binding to its ligands indicates a conserved binding mode between mammalian and viral proteins, providing insight to how BTLA is activated by diverse ligands. This research is supported by a fellowship from the Diabetes & Immune Disease Natioinal Research Institute.