4.3 Nucleocapsid protein (N)
The N protein is highly conserved and most abundant protein in coronavirus which is actively involved in viral propagation (McBride et al., 2014) and is a potential additional target for the development of SARS and MERS vaccines. It is highly antigenic and induced specific humoral and cellular immune responses in convalescent-phase SARS patients (Leung et al., 2004) and C57BL/6 mice (Kim et al., 2004). However, in contrast, it has been reported that it does not elicit VN antibodies to block virus binding the ACE2 receptor and prevent viral infection (Liu et al., 2006; Zheng et al., 2009). Also, in hamsters N protein immunization did not induce VN antibodies and provided no protection against SARS-CoV (Buchholz et al., 2004). These conflicting results suggest that N protein is not a reliable candidate for vaccine development for SARS-CoV but has a good diagnostic value because of its high immunogenicity (Zhang et al., 2020).