A synthetic glycan and the most abundant disaccharide repeat unit of glycosaminoglycans heparin and heparan sulfate (HS) components of proteoglycans. HS, in close proximity to cell surfaces or extracellular matrix proteins, plays essential physiological roles binding to hundreds of proteins. HS may play a role in SARS-CoV-2 infection and virus binding to ACE2. Heparin is mainly found in mast cell secretory granules.