Analysis of the herpesvirus chemokine-binding glycoprotein G residues essential for chemokine binding and biological activity.

Viral chemokine-binding protein (vCKBP) are expressed by large DNA viruses, such as herpesviruses and poxviruses. vCKBP can bind chemokines with high affinity and efficiently neutralize their ability to induce cell migration. Recently, herpesvirus glycoprotein G (gG) was identified as a member of the vCKBP-4 subfamily. The structural domains of gG important for binding to chemokines and biological activity, however, are unknown. Here, we used equine herpesvirus type 1 (EHV-1) as a model to determine residues in EHV-1 gG that are involved in the processes of chemokine binding and interaction with target cells. First, comprehensive analysis of glycosylation of EHV-1 gG revealed that N-glycosylation is not required for binding of gG to chemokines but is essential for biological activity of the protein. Second, the epitope responsible for the binding to chemokines was localized to 40 amino acids in the hypervariable region (amino acids 301-340) of the protein. Third, hybrid molecules, designed as loss- and gain-of-function gG proteins, were engineered. In these hybrid glycoproteins the hypervariable regions of EHV-1 gG, a vCKBP, and the closely related EHV-4 gG, which does not display any chemokine binding capabilities, were exchanged. gG variants containing the EHV-1 hypervariable region were able to bind chemokines and were biologically active, whereas hybrid gGs containing the corresponding region of EHV-4 gG were not. Taking these results together, this report is the first to provide insight into the functional residues of an alphaherpesviral vCKBP.