Glycosylation plays a significant role in the life cycle of many viruses: from providing a receptor
to assisting in the folding of viral proteins, as well as shielding these proteins from the host’s
immune system.
In the case of influenza A viruses, their surface glycoproteins haemagglutinin (HA) and
neuraminidase bind to glycans expressing sialic acid (Sia). In general, human IAVs prefer a2-
6 linked Sia, however, there are reports that H3N2 viruses are more selective in their HA
receptor preference: H3N2 viruses have evolved a preference for bi-antennary glycans
containing extended poly-LacNAc chains terminating in a2-6 linked Sia. This shift in receptor
preference has led to challenges propagating and characterising modern H3N2 viruses in the
laboratory. Here we demonstrate that targeting specific enzymes involved in glycosylation
pathways can produce extended glycan receptors in HEK cells, demonstrating the potential of
this approach to be applied to other cell lines.
Glycans have also been reported to act as secondary receptors enhancing infection of
the novel respiratory virus SARS-CoV-2. Multiple studies have highlighted the potential for
heparan sulfate (HS) to enhance SARS-CoV-2 cell entry. The mechanism by which SARS-
CoV-2 Spike binds to HS is poorly understood despite HS having been demonstrated to
enhance SARS-CoV-2 infection in vitro. We confirm that SARS-CoV-2 may utilize HS as a
potential secondary receptor and that both the receptor binding domain and N-terminal domain
of the Spike protein are likely to contribute to HS binding.
Finally, SARS-CoV-2 Spike itself is heavily glycosylated, however, there is variance
among the glycosylation profiles published to date, which provides increasing evidence that
the expression system used influences the glycosylation present on the Spike protein. We
have assessed the effect of using different expression systems to express SARS-CoV-2 spike
and find significant differences between glycosylation profiles depending on the expression
system used.