Before revision:  mostly positively charged patches on the spike, and thereby mask the basic residues of the receptor binding domain and the basic S1/S2 site , which is unique specific to SAR-CoV-2 and is important for furin-mediated spike cleavage and the subsequent formation of its post-fusion conformation . Experiments corroborated the simulation results by showing that heparin binds the basic S1/S2 site of spike, inhibiting cleavage by furin.
After revision:  mostly positively charged patches on the spike, and thereby mask the basic residues of the receptor binding domain and the basic S1/S2 site . Experiments corroborated the simulation results by showing that heparin binds the basic S1/S2 site of spike, inhibiting cleavage by furin.