IMPORTANCE OF SPECIFIC AMINO-ACIDS IN PROTEIN-BINDING SITES FOR HEPARIN AND HEPARAN-SULFATE

Heparin and heparan sulfate bind a variety of proteins and peptides to regulate many biological activities. Past studies have examined a lim ited number of established heparin binding sites and have focused on b asic amino acids when modeling binding site structural motifs. This st udy examines the prevalence of individual amino acids in peptides bind ing to heparin or heparan sulfate. A 7-mer random peptide library was synthesized using the 20 common amino acids. This ir-mer library was a ffinity separated using both heparin and heparan sulfate-Sepharose. Bo und peptide populations were eluted with a salt step gradient (pH 7) a nd analysed for amino acid composition. Peptides released from heparin -Sepharose by 0.3 M NaCl were enriched in arginine, lysine, glycine an d serine; and depleted in methionine and phenylalanine. In contrast, p eptides released from heparan sulfate-Sepharose were enriched in argin ine, glycine, serine, and proline (at 0.15 M NaCl). These peptides wer e depleted in histidine, isoleucine, methionine (not detectable) and p henylalanine. In the heparin binding sites of proteins, which have bee n published, the enriched amino acids were arginine, lysine and tyrosi ne. Depleted amino acids include aspartic acid, glutamic acid, glutami ne, alanine, glycine, phenylalanine, serine, threonine and valine. Thi s study demonstrates that heparin and heparan sulfate bind different p opulations of peptide sequences. The differences in amino acid composi tion indicate that the positive charge density and spacing requirement s differ for peptides binding these two glycosaminoglycans.