An Approach for Separation and Complete Structural Sequencing of Heparin/Heparan Sulfate-like Oligosaccharides

As members of the glycosaminoglycan (GAG) family, heparin and heparan sulfate (HS) are responsible for mediation of a wide range of essential biological actions, most of which are mediated by specific patterns of modifications of regions of these polysaccharides. To fully understand the regulation of HS modification and the biological function of HS through its interactions with protein ligands, it is essential to know the specific HS sequences present. However, the sequencing of mixtures of HS oligosaccharides presents major challenges due to the lability of the sulfate modifications, as well as difficulties in separating isomeric HS chains. Here, we apply a sequential chemical derivatization strategy involving permethylation, desulfation, and trideuteroperacetylation to label original sulfation sites with stable and hydrophobic trideuteroacetyl groups. The derivatization chemistry differentiates between all possible heparin/HS sequences solely by glycosidic bond cleavages, without the need to generate cross-ring cleavages. This derivatization strategy combined with LC-MS/MS analysis has been used to separate and sequence five synthetic HS-like oligosaccharides of sizes up to dodecasaccharide, as well as a highly sulfated Arixtra-like heptamer. This strategy offers a unique capability for the sequencing of microgram quantities of HS oligosaccharide mixtures by LC-MS/MS.