CHARACTERIZATION OF HEPARIN AND HEPARAN-SULFATE DOMAINS BINDING TO THE LONG SPLICE VARIANT OF PLATELET-DERIVED GROWTH-FACTOR-A CHAIN

Platelet-derived growth factors (PDGFs) are homo- or heterodimers of t wo related polypeptides, known as A and B chains, The A chain exists a s two splice variants due to the alternative usage of exons 6 (PDGF-A( L), longer) and 7 (PDGF-A(S), shorter). Exon 6 encodes an 18-amino aci d sequence rich in basic amino acid residues, which has been implicate d as a cell retention signal, Several lines of evidence indicate that the retention is due to binding of PDGF-A(L) to glycosaminoglycans, es pecially to heparan sulfate. We have analyzed the saccharide domains o f smooth muscle cell-derived heparan sulfate involved in this interact ion, Furthermore, we have employed selectively modified heparin oligos accharides to elucidate the dependence of the binding on different sul fate groups and on fragment length, The shortest PDGF-A(L) binding dom ain consists of 6-8 monosaccharide units. Studies using selectively de sulfated heparins and heparin fragments suggest that N-, 2-O-, and 6-O -sulfate groups all contribute to the interaction Structural compariso n of heparan sulfate oligosaccharides separated by affinity chromatogr aphy on immobilized PDGF-A(L) showed that the bound pool was enriched in -IdceA(2-OSO3)-GleNSO(3)(6-OSO3)- disaccharide units. Furthermore, analogous separation of a partially O-desulfated heparin decamer prepa ration, using a highly selective nitrocellulose filter-trapping system , yielded a PDGF-A(L)-bound fraction in which more than half of the di saccharide units had the structure -IdceA(2-OSO3)-GIcNSO(3)(6-OSO3)-. Our results suggest that the interaction between PDGF-A(L) and heparin /heparan sulfate is mediated via N-sulfated saccharide domains contain ing both 2-O- and 6-O-sulfate groups.