Prevents cell to cell fusion by interacting with and directing the viral K2 protein on the host plasma membrane. The A56-K2 complex associates with components of the entry fusion complex (EFC) presumably to avoid superinfection and syncytium formation. Via its interaction with C3/VCP protein, protects the infected cell and probably also the extracellular enveloped virus from complement attack. Heterodimerizes with K2. The heterodimer A56/K2 interacts with components of the entry fusion complex A16 and G9. Interacts with K2 protein. Heterodimer with C3/VPC protein; disulfide-linked. Component of extracellular enveloped virus (EEV) but not intracellular mature virus (IMV). Component of the outermost membrane of EEV. Glycosylated; contains phosphate and sulfate-substituted glycans. O-glycosylation is required for hemagglutination and hemadsorption activities of infected cell membranes.