Characterization of the Herpesvirus saimiri Orf51 protein

Herpesvirus saimiri (HVS) is a gamma(2)-herpesvirus sharing genomic colinearity and a high degree of functional homology with HHV-8. To begin exploring the correlates of HVS infectivity and neutralization, we designed and implemented a new reporter assay. Using this assay, we could demonstrate that HVS neutralizing antibodies are present at high levels in naturally infected squirrel monkeys and are strongly induced after pathogenic, experimental infection of common marmosets. Further, we demonstrated that viral entry is influenced by cellular glycosaminoglycans and that, similar to HHV-8, soluble heparin is capable of blocking infectivity. We next cloned and characterized the positional homologue of HHV-8 K8.1, HVS Orf51. N-glycosidase F treatment indicates that like K8.1, Orf51 is a glycoprotein. Found in the viral particle, it localizes to the endoplasmic reticulum of expressing cells. Like K8.1, Orf51 could bind to agarose-conjugated heparin, implicating this molecule in viral attachment to cells. These studies provide the groundwork for additional experiments into the role that this protein may be playing in viral pathogenicity, persistence, and cell tropism.