Many proteins are studded with sugars called glycans. SARS-CoV-2 uses a sugar-coated spike protein to enter human cells. The glycans on blood cells define your ABO blood group.

In our new review we discuss the "promiscuous" enzymes that build glycans: https://portlandpress.com/biochemsoctrans/article/doi/10.1042/BST20190651/225299/Promiscuity-and-specificity-of-eukaryotic">https://portlandpress.com/biochemso... 1/5

A promiscuous enzyme can make different glycans with the same sugar building blocks, creating variability in the types of sugars attached to proteins.

Many viruses, including SARS-CoV-2, use such variable glycans as shields against our immune system. https://www.sciencedirect.com/science/article/pii/S0092867420302622">https://www.sciencedirect.com/science/a... 2/5

A variable, sugar-shielded protein presents a moving target for immune-system antibodies, complicating the process of vaccine development. #34e00995726b">https://www.forbes.com/sites/jvchamary/2020/05/04/coronavirus-vaccine-sugar-shield/ #34e00995726b">https://www.forbes.com/sites/jvc... 3/5

Luckily, the glycan shield on the SARS-CoV-2 spike protein doesn& #39;t seem to be as dense as that of other coronaviruses. The non-variable exposed parts of the protein are promising targets for developing vaccines. 4/5
https://science.sciencemag.org/content/early/2020/05/01/science.abb9983">https://science.sciencemag.org/content/e...

An independent, interesting observation: a region of chromosome 9 is associated with differing susceptibility to Covid-19. This region contains genes that encode ABO blood group enzymes. This result is still preliminary, and needs to be followed up. 5/5 https://www.medrxiv.org/content/10.1101/2020.05.31.20114991v1.full.pdf">https://www.medrxiv.org/content/1...

Here& #39;s a great thread on how important glycans are for proper functioning of the SARS-CoV-2 spike protein: https://twitter.com/RommieAmaro/status/1271487699216551941">https://twitter.com/RommieAma...