Structural basis and potential role of heparin/heparan sulfate binding to the angiogenesis inhibitor endostatin

Abstract

Furthermore, a substantial proportion (10-50%) of heparan sulfate chains obtained from various tissues showed a distinct binding to endostatin, indicating its potential to interact with extracellular and/or membrane-bound proteoglycans. Angiogenesis induced by basic fibroblast growth factor-2 (FGF-2), but not by vascular endothelial growth factor (VEGF), in a chick chorioallantoic membrane assay could be inhibited by endostatin in a dose-dependent manner. The mutational block of heparin binding decreased endostatin inhibition to low levels but elimination of zinc binding had no effect.

Heparan sulfate proteoglycans: heavy hitters in the angiogenesis arena

“…Mutation of either the zinc-binding site, which originally was thought to be necessary for endostatin's function, or the heparinbinding regions was ineffective (39). In another study, mouse recombinant endostatin inhibited FGF2-mediated, but not VEGF-mediated, angiogenesis in a chorioallantoic membrane assay (40). Although mutation of the zinc-binding region had no effect, the mutational block of heparin-binding sites decreased endostatin activity.…”

Structure and Function of Collagen‐Derived Endostatin Inhibitors of Angiogenesis

“…The efficient binding of endostatin-XVIII to heparin (K d = 0.3 µM) requires a dodecasaccharide structure modified by 2-0 and 6-0 sulfation, suggesting that a simultaneous occupation of the primary and secondary binding sites is essential for a strong interaction (29). Furthermore, the substantial binding in a similar fashion of a large fraction of heparan sulfate from various tissues suggests that cell membrane-bound proteoglycans can In endostatin-XVIII are shown the zinc ligands, basic residues involved in heparin binding, and three solvent-exposed hydrophobic residues.…”

“…There is no compelling evidence for a competitive binding to one of the major receptors for pro-angiogenic factors, such as FGF-2 and VEGF. The binding of endostatin-XVIII to heparin/heparan sulfate suggested the involvement of cell membrane-bound proteoglycans and a relative large binding epitope (29). A possible mechanism might involve competition for heparan sulfate coreceptors required for the mitogenic activity of FGF-2, or a coreceptor role of heparan sulfate for endostatin binding to a specific receptor.…”

“…It remains unclear, however, why mutation of the surface-exposed F162 and F165 of endostatin (Fig. 3B) also abolished binding to cells, because these residues have no role in heparin binding (29).…”

“…The major effect was a reduced capillary sprouting that in most studies was evaluated by a nonquantitative scoring of vessel branching. Mutations of endostatin indicated that heparin, but not zinc binding, is essential for the inhibitory activity (29,37 ). A comparative analysis of NC1/endostatin of both collagen types showed a variable pattern for both FGF-2 and VEGF stimulation (21) and thus far did not allow the determination of whether oligovalency and/or proteolytic activation are critical parameters for inhibition.…”