Structural protein that makes short spikes at the surface of the virus. Contains receptor binding and receptor-destroying activities. Mediates de-O-acetylation of N-acetyl-9-O-acetylneuraminic acid, which is probably the receptor determinant recognized by the virus on the surface of erythrocytes and susceptible cells. This receptor-destroying activity is important for virus release as it probably helps preventing self-aggregation and ensures the efficient spread of the progeny virus from cell to cell. May serve as a secondary viral attachment protein for initiating infection, the spike protein being the major one. Seems to be a 'luxury' protein that is not absolutely necessary for virus infection in culture. However, its presence in the virus may alter its pathogenicity. May become a target for both the humoral and the cellular branches of the immune system. H2O + N-acetyl-9-O-acetylneuraminate = acetate + H(+) + N-acetylneuraminate H2O + N-acetyl-4-O-acetylneuraminate = acetate + H(+) + N-acetylneuraminate In infected cells becomes incorporated into the envelope of virions during virus assembly at the endoplasmic reticulum and cis Golgi. However, some may escape incorporation into virions and subsequently migrate to the cell surface (By similarity). N-glycosylated. Belongs to the influenza type C/coronaviruses hemagglutinin-esterase family.