Hemaglutinin-esterase dimer (HE) have been located on the surface of the viral. The HE protein may be involved in virus entry, is not required for replication, but appears to be important for infection of the natural host-cell. State-of-the-art cryo-EM experiments have revealed the full structure of the Spike (S) protein in the close and open (prefusion) states. Such glycoprotein is made of three identical chains with 1273 amino acids each and it is composed by two well-defined protein domain regions: S1 and S2 subunits which are associated to cell recognition and the fusion of viral and  cellular membrane respectively. The latter process occurs through different protein conformational changes that remain still uncharacterized.