The S protein of coronaviruses (~1255 amino acids) is a highly N-glycosylated type I transmembrane protein, from 180 to 200 kDa, that plays a major role in viral entry [18]. It insures a double function in viral entry by binding the cellular receptor before conformational changes and proceeding to the fusion of the viral envelope with the membranes of the target cells. S protein has a long N-terminal domain, a short C-terminal domain and assembles into homotrimers on the surface of the viral particle [19]. S protein has a decisive role in cellular tropism and for pathogenicity [20].