Our collaborators Alex Guseman and Angela Gronenborn proposed that lectins in the Oscillatoria agardhii agglutinin (OAA) family could bind SARS-CoV-2 S protein and inhibit infection. Using S pseudotyped lentivirus, Chandra showed that one OAA lectin, BOA, could potently inhibit infection (2 nM EC50). This was confirmed in collaboration with the Duprex lab and David Martinez in the Baric lab using real SARS-CoV-2, including important variants of concern, as well as the original SARS-CoV 2003.
In addition, Alex wondered whether specific glycans bound BOA. Making mutations N234A and N165A in S, Chandra showed that N234A rendered pseudoviruses noninfectious, suggesting this residue is required for viral entry. Interestingly, N165A rendered pseudoviruses moderately resistant to BOA (10 nM EC50). Thus, it is likely that BOA interacts with multiple S glycans.
Alex used SEC chromatography, DLS aggregation assays, and fluorescence binding experiments to show that BOA binds spike at nM concentrations and rapidly forms soluble aggregates. He suggested a mechanism whereby these lectins can interact with multiple spikes at once (on one or multiple virions) and prevent them from undergoing the requisite dynamics needed to bind the ACE-2 receptor to facilitate membrane fusion. Alex tested this hypothesis using mutations in BOA where he reduced its valency from four glycan binding sites to one. In doing so, BOA could no longer interact with multiple spikes, and thus no inhibitory activity was observed.
Check out the preprint in bioRxiv!
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