Post-translational modifications of coronavirus proteins: roles and function

Fung, To Sing; Liu, Ding Xiang

Phosphorylation of coronavirus N protein was first described in ip60K cells infected with MHV-JHM, where a protein kinase associated with purified virions was shown to transfer the γ-phosphate of ATP to serine residues to the MHV N protein [118] . A later study showed that the MHV-JHM N protein was synthesized initially in a nonphosphorylated 57-kDa form detected exclusively in the cytosol, while the subsequent phosphorylated 60-kDa form was associated with the cellular membrane fraction and mature virion [123] . Similarly, 32 P-orthophosphate labeling showed that the phosphorylation level of IBV N protein was significantly higher in the virion than in the infected cell lysates [124] . In sharp contrast, only the phosphatase insensitive nonphosphorylated form of N protein was detected in extracellular virions of BCoV-infected cells, suggesting that dephosphorylation of BCoV N protein may facilitate its specific assembly [125] . Therefore, the phosphorylation status of N protein may differentially regulate coronavirus assembly for different viruses in question.