Specific N-glycosites have been identified, that are important for glycoprotein secretion and viral particle formation in some viruses, including Zika virus, hepatitis viruses B and C (HBV and HCV), HSV-2 and HIV-1 (Fournillier et al. 2001; Falkowska et al. 2007; Helle et al. 2010; Ito et al. 2010; Wang et al. 2013; Luo et al. 2015; Mossenta et al. 2017). A few N-glycosites on influenza A virus neuraminidase have been shown to affect protein activity and viral particle release (Wu et al. 2017). Also, it is well documented that N-linked glycosylation of alphaherpesvirus envelope proteins is required for trafficking to the cell surface and viral particle egress (Norrild and Pedersen 1982; Montalvo et al. 1985; Luo et al. 2015; Suenaga et al. 2015). In particular, complex-type N-glycans are required for robust egress (Serafini-Cessi, Dall’Olio, Scannavini, Campadelli-Fiume et al. 1983). In varicella zoster virus the role of potential O-glycosylation sites has also been addressed by site-directed mutagenesis. Several glycosites were found to affect cell surface expression of the protein. However, such an approach is too laborious for analysis of all potential O-glycosylation sites, given the lack of conserved sequence motifs for O-glycosylation (Suenaga et al. 2015). As a more targeted approach, site-directed mutagenesis of some of the O-glycosites on Hendra virus glycoprotein G, identified via an O-glycoproteomic approach, affected the incorporation of glycoprotein F into pseudotyped virions. This suggests that the O-glycans might be required for protein–protein interaction (Stone et al. 2016). Similarly, in HIV gp120 O-glycosylation of a conserved threonine that is crucial for the association with gp41 has recently been shown to enhance infectivity and incorporation of gp120 into virions, though the virus maintains normal functionality in the absence of the O-glycan (Termini et al. 2017).