Post-translational modifications of coronavirus proteins: roles and function

Fung, To Sing; Liu, Ding Xiang

Based on sequence prediction, SARS-CoV E protein contains two potential N-linked glycosylation sites on N48 and N66, whereas IBV E contains one potential site on N5. Although topological study demonstrated that IBV E protein spanned the membrane once with a luminal N-terminus and a cytoplasmic C-terminus, the glycosylation site on N5 was not functional [79, 80] . On the other hand, SARS-CoV E protein in transfected cells seemed to adopt two distinct membrane topologies [80] . In one form, both the N-and C-termini were exposed to the cytoplasmic side and the protein was not modified by glycosylation. In an alternative minor form, SARS-CoV E protein was shown to be glycosylated on N66, with the C-terminus exposed to the luminal side [80] . A later study using transfected SARS-CoV E protein with an N-terminal Myc-tag confirmed that SARS-CoV E protein was glycosylated co-translationally [83] . Although the two putative TM domains were required for its interaction with the SARS-CoV M protein, the hydrophilic region (60-76) flanking the N66 glycosylation site was dispensable as shown by co-immunoprecipitation experiment [83] . The glycosylation of SARS-CoV E protein during actual infection and its biological function remain to be further investigated.