Post-translational modifications of coronavirus proteins: roles and function

Fung, To Sing; Liu, Ding Xiang

All the three cysteine residues (C40, C43 and C44) in SARS-CoV E protein are also modified by palmitoylation [82] , which may regulate its subcellular trafficking and association with lipid rafts. In fact, when the homologous cysteine residues in the E protein of MHV-A59 (C40, C44 and C47) were doubly or triply mutated to alanine, its ability to induce VLP formation was significantly reduced [84, 85] . Moreover, MHV E protein carrying triple mutations (C40A/C44A/C47A) was prone to degradation, and the corresponding recombinant MHV had significantly reduced yield compared with wild-type [85] . While wild-type MHV E protein mobilized co-expressed M protein into detergent-soluble secreted forms, in cells expressing the triple C-to-A MHV E protein, the co-expressed M protein accumulated into detergent-insoluble complexes that were not secreted [84] . Therefore, palmitoylation of MHV E protein contributes to its stability and biological activity during assembly of mature virions. On the other hand, palmitoylation of SARS-CoV E protein is not required for its association with N protein and VLP production, and thus possibly dispensable for SARS-CoV assembly [86] .