Mass Spectrometry Analysis of Newly Emerging Coronavirus HCoV-19 Spike Protein and Human ACE2 Reveals Camouflaging Glycans and Unique Post-Translational Modifications

The coronavirus disease 2019(COVID-19)pandemic has led to worldwide efforts to understand the biological traits of the newly identified human coronavirus(HCoV-19)virus.In this mass spectrometry(MS)-based study,we reveal that out of 21 possible glycosites in the HCoV-19 spike protein(S protein),20 are completely occupied by N-glycans,predominantly of the oligomannose type.All seven glycosylation sites in human angiotensin I converting enzyme 2(hACE2)were found to be completely occupied,mainly by complex N-glycans.However,glycosylation did not directly contribute to the binding affinity between HCoV-19 S protein and hACE2.Additional post-translational modification(PTM)was identified,including multiple methylated sites in both proteins and multiple sites with hydroxylproline in hACE2.Refined structural models of HCoV-19 S protein and hACE2 were built by adding N-glycan and PTMs to recently published cryogenic electron microscopy structures.The PTM and glycan maps of HCoV-19 S protein and hACE2 provide additional structural details for studying the mechanisms underlying host attachment and the immune response of HCoV-19,as well as knowledge for developing desperately needed remedies and vaccines.