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The SARS‐CoV‐2 Spike Glycoprotein Directly Binds Exogeneous Sialic Acids:  A NMR View

The interaction of the SARS CoV2 spike glycoprotein with two sialic acid-containing trisaccharides (a2,3 and a2,6 sialyl N-Acetyllactosamine) has been demonstrated by NMR. The NMR-based distinction between the signals of those sialic acids in the glycans covalently attached to the spike protein and those belonging to the exogenous a2,3 and a2,6 sialyl N-Acetyllactosamine ligands has been achieved by synthesizing uniformly 13C-labelled trisaccharides at the sialic acid and galactose moieties. STD-1H,13C-HSQC NMR experiments elegantly demonstrate the direct interaction of the sialic acid residues of both trisaccharides with additional participation of the galactose moieties, especially for the a2,3-linked analogue. Additional experiments with the spike protein in the presence of a specific antibody for the N-terminal domain and with the isolated receptor binding and N-terminal domains of the spike protein unambiguously show that the sialic acid binding site is located at the N-terminal domain.