Investigating viral glycosylation pathways for drug and vaccine development

Glycosylation is the most common protein co- and post-translational modification. It has crucial functions for glycoprotein folding, structure, trafficking, localisation and stability. Glycosylation is not only critical for eukaryotic cell function but vital for many enveloped viruses which have evolved to exploit the host cell glycosylation pathway in order to fold their proteins correctly and coat many of their surface proteins with glycans that can contribute to viral pathogenesis. Vaccines often focus on the viral fusion glycoproteins that protrude from the virion envelope as they are among the most immunogenic biomolecules and can elicit a humoral immune response. A robust vaccine antigen needs to mimic viral glycosylation to produce an appropriate and strong B-cell response, as many neutralising antibodies incorporate glycans as part of their binding epitopes, and other epitopes are shielded by sugars and inducing antibodies against those would lead to a less relevant antibody response. The current COVID-19 pandemic has highlighted the urgent need for vaccines and antiviral drugs. The principal topic of my DPhil centres on addressing these needs for viral infection. Chapter 4 focuses on the site-specific glycosylation occupancy, and N- and O-glycan structures attached to virion derived SARS-CoV-2 spike glycoproteins. This glycan signature was compared to a stabilised prefusion trimeric spike, to a monomeric subunit of spike (S1) and to an antigen of a non-stabilised vaccine candidate, revealing subunit shedding of the S1 glycoprotein for the vaccine candidate. Whether or not monomeric S1 shedding has an effect on the vaccine antibody response or could be implicated in the observed rare side effects, remains to be investigated but evidence from other studies implicates this occurrence as detrimental in animal models. The COVID-19 pandemic highlighted again the lack of broad-spectrum antivirals available to patients before thorough investigation of an emergent virus, such as its genome or target host ...