Post-translational modifications of coronavirus proteins: roles and function

Fung, To Sing; Liu, Ding Xiang

Distinct from the O-link glycosylation observed in the M protein of MHV, BCoV and HCoV-OC43, the M protein of Alphacoronavirus TGEV [105] and PEDV [106] , as well as Gammacoronavirus IBV [91] and turkey enteric coronavirus [107] are all modified by N-linked glycosylation, which is sensitive to endo H and can be inhibited by tunicamycin. The N-linked glycosylation sites were mapped to N3 and N6 of IBV (unpublished data from this group). Within the Betacoronavirus genus, M protein of coronaviruses in other lineages is also N-linked glycosylated. For example, SARS-CoV M protein contains a single N-glycosylation site at N4 [108, 109] . When transiently transfected as a C-terminally FLAG-tagged protein, SARS-CoV M protein was found to obtain highmannose N-glycans that were modified into complex N-glycans in the Golgi [29] . However, in a later study using SARS-CoV infected cells and purified SARS-CoV virions, glycosylated M protein was shown to remain endo H sensitive, suggesting that trimming and maturation of N-linked glycans were inhibited during actual SARS-CoV infection [109] .