Post-translational modifications of coronavirus proteins: roles and function

Fung, To Sing; Liu, Ding Xiang

However, it should be noted that not all of the putative glycosylation sites are functional. In fact, among the 23 putative glycosylation sites in the SARS-CoV S protein, only 12 sites were actually glycosylated, as determined by mass spectrometry following peptide:N-glycosidase F (PNGase F) digestion [45] . Recently, we have used in solution deglycosylation combined with mass spectrometry to determine the N-linked glycosylation sites in the IBV S protein [46] . As deglycosylation was carried out in the H 2 O 18 environment, incorporation of O 18 to Asp resulted in a mass increment of 2.98 Da, leading to a more robust identification of glycosylated sites by mass spectrometry. Among the 29 predicted N-linked glycosylation sites, only eight sites were confirmed using this method. Therefore, majority of the predicted N-linked glycosylation sites on coronavirus S protein may not be modified, possibly due to the massive amount of S protein produced during infection and the limited capacities of the cellular glycosylation enzymes. Some sites may be preferentially modified due to their relatively better spatial availability, while some inefficiently and/or partially glycosylated sites may not reach the detection limit for mass spectrometry [46] . Thus, the predicted glycosylation sites are not fully utilized in coronavirus S protein. Preferential glycosylation on certain future science group www.futuremedicine.com critical sites, such as those located within or near the RBD, may be of particular importance in the functionality of S protein.