Recent studies have revealed a correlation between amino acid sequences around
glycosylation sites in proteoglycans and the ability of cells to initiate and process
glycosaminoglycan chains. Initiation depends on Ser—Gly/Ala dipeptides that have one or
more acidic amino acids in close proximity. The formation of heparan sulfate chains
depends on a nearby cluster of acidic residues, hydrophobic amino acids, and the close
spacing of glycosylation sites.