Genetic and antigenic characterization of recombinant nucleocapsid proteins derived from canine coronavirus and canine respiratory coronavirus in China

Lu, Shuai; Chen, Yingzhu; Qin, Kun; Zhou, Jianfang; Lou, Yongliang; Tan, Wenjie

Coronavirus harbors the largest genome among the known RNA viruses, about 27-31 kb, mainly encoding for the structural proteins spike (S), envelope (E), membrane (M), and nucleocapsid (N), and several other open reading frames (ORFs) encoding non-structural proteins. As reported, the glycosylated S protein mediates attachment of the coronavirus to cellular receptors and fusion with the cell membrane (Belouzard et al., 2012) . The N protein is a phosphorylated protein, and is the most abundant. It interacts with viral RNA and makes up the core structure of viral particles (Li et al., 2005) . It has been revealed that a high level of IgG antibodies against the N protein of SARS-CoV can persist for a long time after the onset of symptoms, and thus may be a marker for highly sensitive serological diagnosis (Tan et al., 2004) . As the N protein is an unglycosylated protein, it can be easily expressed in bacteria and isolated with high purity. Therefore, antibodies against N protein appear to be ideal candidates as diagnostic markers.