Uncovering the Relationship between Sulphation Patterns and Conformation of Iduronic Acid in Heparan Sulphate

Abstract

The L-iduronic acid (IdoA) residue is a critically important structural component in heparan sulphate polysaccharide for the biological functions. The pyranose ring of IdoA is present in 1C4-chair, 2SO-skew boat, and less frequently, in 4C1-chair conformations. Here, we analyzed the conformation of IdoA residue in eight hexasaccharides by NMR. The data demonstrate a correlation between the conformation of IdoA and sulphations in the surrounding saccharide residues. For the 2-O-sulpho IdoA residue, a high degree of sulphation on neighboring residues drives ring dynamics towards the 2SO-skew boat conformer. In contrast, the nonsulphated IdoA residue is pushed towards the 1C4-chair conformer when the neighboring residues are highly sulphated. Our data suggest that the conformation of IdoA is regulated by the sulphation pattern of nearby saccharides that is genetically controlled by the heparan sulphate biosynthetic pathway.

Synthesis of 3-O-Sulfated Oligosaccharides to Understand the Relationship between Structures and Functions of Heparan Sulfate

“…In the present study, the impact of 3- O -sulfation on the conformation of neighboring IdoA2S residues was investigated. The conformational analysis was completed by NMR through measuring the three bond proton proton coupling constants ( 3 J H-H ) 30 . The 3- O -sulfation increases the population of 2 S O conformer of the IdoA2S residue in hexasaccharides (compound 1 to 3 , Table 1 and Fig 1A), compared to that of the IdoA2S residue in a hexasaccharide without the GlcNS3S6S residue (compound 7* ).…”

“…The X-ray crystal structure and NMR solution structure of the complex of AT and fondaparinux demonstrate that the IdoA2S residue is present in 2 S O conformation in the complex 32–33 . We reported that an IdoA-containing 6-mer, where the IdoA2S residue was substituted with an IdoA residue displaying 2 S O conformation, exhibited anti-FXa activity 30 (Table 2). However, a GlcA2S-containing 6-mer, where the IdoA2S residue was substituted with a GlcA2S residue displaying 4 C 1 conformation, did not display anti-FXa activity 8 (Table 2).…”

“… a The calculated values (presented in parentheses) were obtained using Amber 14 with GLYCAM06 parameters 46 . b The conversion of the measured values of coupling constant to population of different conformers was described in a previous publication 30 . c The residual sum of squares (RSS) was used to determine how well the calculated population ratios fit the experimental data. d The population of conformation of comp 7* was reported in a paper published previously 30 . e The position of 3- O -sulfated glucosamine (GlcNS3S or GlcNS3S6S) is bolded and underlined. …”

“… b The conversion of the measured values of coupling constant to population of different conformers was described in a previous publication 30 . …”

“…The -GlcNS3S6S-IdoA2S- disaccharide units are presented in bold face and underlined. b The binding constants for comp 8* and comp 11* were determined by affinity coelectrophoresis as reported in a previous publication 17 . c Comp 4 did not bind to AT nor display anti-FXa activity, due to the fact that it does not contain 6- O -sulfo groups at the GlcNS residues at the nonreducing end 29 . d The IdoA-containing 6-mer was reported in a previous publication 30 . IdoA also displays both 1 C 4 and 2 S O conformations.…”