Protein recognition domains in heparan sulfate

Sammanfattning: Heparan sulfate (HS) is a sulfated glycosaminoglycan (GAG) implicated in various physiological and pathological processes such as cell proliferation, viral infection and inhibition of blood coagulation. These effects are due to interactions of HS with proteins. The first aim of the current work was to characterize HS domains recognizing the long splice variant of platelet-derived growth factor A chain (PDGF-AL) and the gC protein, the principal attachment-mediating coat protein of herpes simplex virus type 1 (HSV-1). The second aim was to study the biological regulation of the growth factor binding HS domains using human aorta as a model tissue. The third aim was to study the structural and functional aspects of heparin/HS-analogs generated by modification of the capsular polysaccharide of E. coli K5.The PDGF-AL binding HS domain is shown to comprise an N-sulfated octasaccharide sequence, entailing essential 2-O- sulfated iduronic acid (IdoA) and 6-O-sulfated glucosamine (GlcN) residues. The gC binding domain showed similar preferences for 0-sulfation, but clearly required a longer, deca/dodecasaccharide, HS domain. In both cases, the O-sulfate groups appear to be preferentially localized adjacent to each other in -IdoA(2-OSO3)-GlcNSO3(6-OSO3)- disaccharide units.Analysis of human aorta HS from subjects of various ages revealed that the binding of HS to PDGF isoforms was significantly higher in old individuals, due to age-dependent upregulation of -IdoA(2-OSO3)-GlcNSO3(6-OSO3)- disaccharide units. These findings represent a novel recognition of structural and functional regulation of a human macromolecule.Chemical N- and 0-sulfation of the E. coli K5 polysaccharide is shown to yield structures interacting with antithrombin in a fashion similar to heparin. The semisynthetic saccharide structures contained 3-0-sulfated GlcN residues, critical for the anticoagulant activity of heparin, and prolonged coagulation time in in vitro assays. These results suggest that bacterial polysaccharides can be exploited in production of pharmacologically active heparin analogs.