Envelope protein that binds to heparan sulfate on the cell surface and might provide virion attachment to target cell. Component of the mature virion (MV) membrane. Becomes membrane associated presumably during virus maturation. The mature virion is located in the cytoplasm of infected cells and is probably released by cell lysis (By similarity). Expressed in the late phase of the viral replicative cycle. Does not contain disulfide bonds. Immunodominant protein. Belongs to the chordopoxvirinae protein H3 family.