Post-translational modifications of coronavirus proteins: roles and function

Fung, To Sing; Liu, Ding Xiang

Similar to O-linked glycosylation of MHV, N-linked glycosylation of SARS-CoV M protein is not essential for viral replication, as recombinant SARS-CoV with glycosylation-deficient M protein had normal virion morphology and retained its infectivity in cell culture [110] . However, unlike O-linked glycosylation that conferred IFN antagonism to the MHV M protein, the IFN-antagonizing activity of SARS-CoV M protein was independent of N-linked glycosylation and might be mediated through its first TM domain [111] . N protein N protein (43-50 kDa) is the protein constituent of the helical nucleocapsid, which binds the RNA genome in a beads-on-a-string fashion. The N protein contains two major domains ( Figure 5) , an N-terminal domain and a C-terminal domain [112, 113] . While both domains contribute to the binding of viral RNA genome, C-terminal domain is also important for N protein dimerization [114, 115] . Linking these two major domains is a serine argininerich motif that may play an important role in the multimerization of N protein [116] . At last, domain 3 at the C-terminus is shown to be critical for interaction between coronavirus N and M protein [117] . N protein is mainly modified by phosphorylation, which usually occurs in clusters in the N-terminal domain, serine arginine-rich or domain 3 [118, 119] . Moreover, proteolytic cleavage, SUMOylation and ADP-ribosylation have also been observed in coronavirus N protein ( Figure 5 & Table 1 ) [120] [121] [122] .