Essential for the initial attachment to heparan sulfate moieties of the host cell surface proteoglycans (By similarity). Plays also a role in host immune evasion by inhibiting the host complement cascade activation. Interacts with host complement component C3; this interaction inhibits host immune response by disregulating complement cascade. The three heparin-binding domains (HDB1, HDB2 and HDB3) mediate virus attachment through specific arrangements of basic residues. Belongs to the herpesviridae glycoprotein C family.