Post-translational modifications of coronavirus proteins: roles and function

Fung, To Sing; Liu, Ding Xiang

Apart from the structural and nonstructural proteins, coronavirus genome also encodes various accessory proteins, most of which share no homology to any known proteins. These accessory proteins are dispensable for viral replication in cell culture. In fact, when the coding sequences of accessory proteins were deleted by reverse genetics, the resulting recombinant viruses still replicated similarly to wild-type virus. [159] However, some of the coronavirus accessory proteins are incorporated in mature virions, while others have been implicated in the modulation of host immune response and in vivo pathogenesis [159] . Only a few coronavirus accessory proteins are known to be modified by PTMs ( Figure 6 & Table 1 ). Apart from the S protein, some Betacoronaviruses also encode the HE protein, which forms homodimers and constitutes a second type of shorter projections on the virion surface [10] . Similar to S protein, the HE protein of MHV was also found to be modified by N-linked glycosylation, which was inhibited by tunicamycin but not monensin [160] . The HE protein of BCoV was also shown to be glycosylated when expressed using a human adenovirus vector [161] . The importance of N-linked glycosylation for the function of coronavirus HE protein has not been fully characterized.