Vulnerabilities in coronavirus glycan shields despite extensive glycosylation

Yasunori Watanabe; Zachary T. Berndsen; Jayna Raghwani; Gemma E. Seabright; Joel D. Allen; Jason S. McLellan; Ian A. Wilson; Thomas A. Bowden; Andrew B. Ward; Max Crispin

Whether the restricted glycan shielding observed on coronaviruses is linked to the zoonosis of the pathogens is unknown. However, it is tempting to speculate, for example, that MERS has not evolved a dense shield since it would not offer as much of a protective advantage against camel nanobodies (also known as single-domain antibodies) which could more easily penetrate it. Investigation of the host immune response to viruses in their natural reservoirs may offer a route to understanding why coronavirus glycosylation does not reach the density of other viruses such as HIV-1. Additionally, it may be that functional constraints, such as maintaining flexibility of the receptor binding domains, limit the accretion of glycans on . CC-BY 4.0 International license author/funder. It is made available under a The copyright holder for this preprint (which was not peer-reviewed) is the . https://doi.org/10.1101/2020.02.20.957472 doi: bioRxiv preprint coronavirus spikes, which would render it incapable of performing its primary functions, including receptor binding and membrane fusion. This phenomenon has been observed on other viral glycoproteins, including influenza HAs, where there is a limit to the accumulation of glycosylation sites that can be incorporated in vivo 64, 65 , compared to in vitro 66 , with H3N2 and H1N1 HAs replacing existing PNGs rather than continually adding them upon the glycoprotein 26, 65 .