Mass spectrometry analysis of newly emerging coronavirus HCoV-19 spike S protein and human ACE2 reveals camouflaging glycans and unique post-translational modifications

The pneumonia-causing COVID-19 pandemia has prompt worldwide efforts to understand its biological and clinical traits of newly identified HCoV-19 virus. In this study, post-translational modification (PTM) of recombinant HCoV-19 S and hACE2 were characterized by LC-MSMS. We revealed that both proteins were highly decorated with specific proportions of N-glycan subtypes. Out of 21 possible glycosites in HCoV-19 S protein, 20 were confirmed completely occupied by N-glycans, with oligomannose glycans being the most abundant type. All 7 possible glycosylation sites in hACE2 were completely occupied mainly by complex type N-glycans. However, we showed that glycosylation did not directly contribute to the binding affinity between SARS-CoV spike protein and hACE2. Additionally, we also identified multiple sites methylated in both proteins, and multiple prolines in hACE2 were converted to hydroxylproline. Refined structural models were built by adding N-glycan and PTMs to recently published cryo-EM structure of the HCoV-19 S and hACE2 generated with glycosylation sites in the vicinity of binding surface. The PTM and glycan maps of both HCoV-19 S and hACE2 provide additional structural details to study mechanisms underlying host attachment, immune response mediated by S protein and hACE2, as well as knowledge to develop remedies and vaccines desperately needed nowadays.