Filter-entrapment enrichment pull-down assay for glycosaminoglycan structural characterization and protein interaction.

Heparins are the most pharmaceutically important polysaccharides. These heparin-based anticoagulant/antithrombotic agents include unfractionated heparins, low molecular weight heparins (LMWHs) and ultralow molecular weight heparins (ULMWHs). Heparins exhibit their pharmacological and biological activities through interaction with heparin-binding proteins. The prototypical heparin-binding protein is antithrombin III (AT), responsible for heparin's anticoagulant/antithrombotic activity. This study describes a filter-trapping method to isolate the chains in enoxaparin, a LMWH, which bind to AT. We demonstrate this method using the ULMWH, fondaparinux, which consists of a single well defined AT binding site. The interacting chains of enoxaparin are then characterized by activity assays, top-down liquid chromatography-mass spectrometry, and capillary zone electrophoresis mass spectrometry. This filter-trapping assay is an improvement over affinity chromatography for isolating heparin chains interacting with heparin binding proteins.